mirror of
https://github.com/glfw/glfw.git
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1288 lines
51 KiB
TeX
1288 lines
51 KiB
TeX
%-------------------------------------------------------------------------
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% GLFW Users Guide
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% API Version: 2.7
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%-------------------------------------------------------------------------
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% Document class
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\documentclass[a4paper,11pt,oneside]{report}
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% Document title and API version
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\newcommand{\glfwdoctype}[1][0]{Users Guide}
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\newcommand{\glfwapiver}[1][0]{2.7}
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% Common document settings and macros
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\input{glfwdoc.sty}
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% PDF specific document settings
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\hypersetup{pdftitle={GLFW Users Guide}}
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\hypersetup{pdfauthor={Marcus Geelnard}}
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\hypersetup{pdfkeywords={GLFW,OpenGL,guide,manual}}
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%-------------------------------------------------------------------------
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% Document body
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%-------------------------------------------------------------------------
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\begin{document}
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\pagestyle{plain}
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% Title page
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\glfwmaketitle
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% Summary, trademarks and table of contents
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\pagenumbering{roman}
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\setcounter{page}{1}
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%-------------------------------------------------------------------------
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% Summary and Trademarks
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%-------------------------------------------------------------------------
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\chapter*{Summary}
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This document is a users guide for the \GLFW\ API that gives a practical
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introduction to using \GLFW . For a more detailed description of the
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\GLFW\ API you should refer to the \textit{GLFW Reference Manual}.
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\vspace{10cm}
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\large
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Trademarks
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\small
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OpenGL and IRIX are registered trademarks of Silicon Graphics, Inc.\linebreak
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Microsoft and Windows are registered trademarks of Microsoft Corporation.\linebreak
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Mac OS is a registered trademark of Apple Computer, Inc.\linebreak
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Linux is a registered trademark of Linus Torvalds.\linebreak
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FreeBSD is a registered trademark of Wind River Systems, Inc.\linebreak
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Solaris is a trademark of Sun Microsystems, Inc.\linebreak
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UNIX is a registered trademark of The Open Group.\linebreak
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X Window System is a trademark of The Open Group.\linebreak
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POSIX is a trademark of IEEE.\linebreak
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Truevision, TARGA and TGA are registered trademarks of Truevision, Inc.\linebreak
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IBM is a registered trademark of IBM Corporation.\linebreak
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All other trademarks mentioned in this document are the property of their respective owners.
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\normalsize
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%-------------------------------------------------------------------------
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% Table of contents
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%-------------------------------------------------------------------------
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\tableofcontents
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\pagebreak
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% Document chapters starts here...
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\pagenumbering{arabic}
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\setcounter{page}{1}
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\pagestyle{fancy}
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%-------------------------------------------------------------------------
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% Introduction
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%-------------------------------------------------------------------------
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\chapter{Introduction}
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\thispagestyle{fancy}
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\GLFW\ is a portable API (Application Program Interface) that handles
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operating system specific tasks related to \OpenGL\ programming. While
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\OpenGL\ in general is portable, easy to use and often results in tidy and
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compact code, the operating system specific mechanisms that are required
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to set up and manage an \OpenGL\ window are quite the opposite. \GLFW\ tries
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to remedy this by providing the following functionality:
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\begin{itemize}
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\item Opening and managing an \OpenGL\ window.
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\item Keyboard, mouse and joystick input.
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\item A high precision timer.
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\item Support for querying and using \OpenGL\ extensions.
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\end{itemize}
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\vspace{18pt}
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All this functionality is implemented as a set of easy-to-use functions,
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which makes it possible to write an \OpenGL\ application framework in just a
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few lines of code. The \GLFW\ API is completely operating system and
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platform independent, which makes it very simple to port \GLFW\ based \OpenGL\
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applications to a variety of platforms.
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Currently supported platforms are:
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\begin{itemize}
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\item Microsoft Windows\textsuperscript{\textregistered} 95/98/ME/NT/2000/XP/.NET Server.
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\item Unix\textsuperscript{\textregistered} or Unix<69>-like systems running the
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X Window System\texttrademark, e.g. Linux\textsuperscript{\textregistered},
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IRIX\textsuperscript{\textregistered}, FreeBSD\textsuperscript{\textregistered},
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Solaris\texttrademark, QNX\textsuperscript{\textregistered} and
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Mac OS\textsuperscript{\textregistered} X.
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\item Mac OS\textsuperscript{\textregistered} X (Carbon)\footnote{Support for joysticks missing at the time of writing.}
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\end{itemize}
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%-------------------------------------------------------------------------
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% Getting Started
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%-------------------------------------------------------------------------
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\chapter{Getting Started}
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\thispagestyle{fancy}
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In this chapter you will learn how to write a simple \OpenGL\ application
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using \GLFW . We start by initializing \GLFW , then we open a window and
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read some user keyboard input.
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%-------------------------------------------------------------------------
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\section{Initializing GLFW}
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Before using any of the \GLFW\ functions, it is necessary to call
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\textbf{glfwInit}. It initializes internal working variables that are used
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by other \GLFW\ functions. The C syntax is:
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\begin{lstlisting}
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int glfwInit( void )
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\end{lstlisting}
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\textbf{glfwInit} returns GL\_TRUE if initialization succeeded, or
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GL\_FALSE if it failed.
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When your application is done using \GLFW , typically at the very end of
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the program, you should call \textbf{glfwTerminate}, which makes a clean
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up and places \GLFW\ in a non-initialized state (i.e. it is necessary to
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call \textbf{glfwInit} again before using any \GLFW\ functions). The C
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syntax is:
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\begin{lstlisting}
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void glfwTerminate( void )
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\end{lstlisting}
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Among other things, \textbf{glfwTerminate} closes the \OpenGL\ window
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unless it was closed manually.
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%-------------------------------------------------------------------------
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\section{Opening An OpenGL Window}
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Opening an \OpenGL\ window is done with the function
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\textbf{glfwOpenWindow}. The function takes nine arguments, which are used
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to describe the following properties of the window to open:
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\begin{itemize}
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\item Window dimensions (width and height) in pixels.
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\item Color and alpha buffer depth.
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\item Depth buffer (Z-buffer) depth.
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\item Stencil buffer depth.
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\item Fullscreen or windowed mode.
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\end{itemize}
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The C language syntax for \textbf{glfwOpenWindow} is:
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\begin{lstlisting}
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int glfwOpenWindow( int width, int height,
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int redbits, int greenbits, int bluebits,
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int alphabits, int depthbits, int stencilbits,
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int mode )
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\end{lstlisting}
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\textbf{glfwOpenWindow} returns GL\_TRUE if the window was opened
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correctly, or GL\_FALSE if \GLFW\ failed to open the window.
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\GLFW\ tries to open a window that best matches the requested parameters.
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Some parameters may be omitted by setting them to zero, which will result
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in \GLFW\ either using a default value, or the related functionality to be
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disabled. For instance, if \textit{width} and \textit{height} are both
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zero, \GLFW\ will use a window resolution of 640x480. If
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\textit{depthbits} is zero, the opened window may not have a depth buffer.
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The \textit{mode} argument is used to specify if the window is to be a
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s.c. fullscreen window, or a regular window.
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If \textit{mode} is GLFW\_FULLSCREEN, the window will cover the entire
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screen and no window borders will be visible. If possible, the video mode
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will be changed to the mode that closest matches the \textit{width},
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\textit{height}, \textit{redbits}, \textit{greenbits}, \textit{bluebits}
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and \textit{alphabits} arguments. Furthermore, the mouse pointer will be
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hidden, and screensavers are prohibited. This is usually the best mode for
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games and demos.
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If \textit{mode} is GLFW\_WINDOW, the window will be opened as a normal
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window on the desktop. The mouse pointer will not be hidden, and
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screensavers are allowed to be activated.
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To close the window, you can either use \textbf{glfwTerminate}, as
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described earlier, or you can use the more explicit approach by calling
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\textbf{glfwCloseWindow}, which has the C syntax:
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\begin{lstlisting}
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void glfwCloseWindow( void )
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\end{lstlisting}
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%-------------------------------------------------------------------------
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\section{Using Keyboard Input}
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\GLFW\ provides several means for receiving user input, which will be
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discussed in more detail in chapter \ref{par:inputhandling}. One of the
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simplest ways of checking for keyboard input is to use the function
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\textbf{glfwGetKey}:
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\begin{lstlisting}
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int glfwGetKey( int key )
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\end{lstlisting}
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It queries the current status of individual keyboard keys. The argument
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\textit{key} specifies which key to check, and it can be either an
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uppercase printable ISO 8859-1 (Latin 1) character (e.g. `A', `3' or `.'),
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or a special key identifier (see the \textit{GLFW Reference Manual} for a
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list of special key identifiers). \textbf{glfwGetKey} returns GLFW\_PRESS
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(or 1) if the key is currently held down, or GLFW\_RELEASE (or 0) if the
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key is not being held down. For example:
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\begin{lstlisting}
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A_pressed = glfwGetKey( 'A' );
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esc_pressed = glfwGetKey( GLFW_KEY_ESC );
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\end{lstlisting}
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In order for \textbf{glfwGetKey} to have any effect, you need to poll for
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input events on a regular basis. This can be done in one of two ways:
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\begin{enumerate}
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\item Implicitly by calling \textbf{glfwSwapBuffers} often.
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\item Explicitly by calling \textbf{glfwPollEvents} often.
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\end{enumerate}
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In general you do not have to care about this, since you will normally
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call \textbf{glfwSwapBuffers} to swap front and back rendering buffers
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every animation frame anyway. If, however, this is not the case, you
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should call \textbf{glfwPollEvents} in the order of 10-100 times per
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second in order for \GLFW\ to maintain an up to date input state.
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%-------------------------------------------------------------------------
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\section{Putting It Together: A Minimal GLFW Application}
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Now that you know how to initialize \GLFW , open a window and poll for
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keyboard input, let us exemplify this with a simple \OpenGL\ program. In
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the following example some error-checking has been omitted for the sake of
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brevity:
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\begin{lstlisting}
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#include <GL/glfw.h>
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int main( void )
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{
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int running = GL_TRUE;
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// Initialize GLFW
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glfwInit();
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// Open an OpenGL window
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if( !glfwOpenWindow( 300,300, 0,0,0,0,0,0, GLFW_WINDOW ) )
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{
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glfwTerminate();
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return 0;
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}
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// Main loop
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while( running )
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{
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// OpenGL rendering goes here...
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glClear( GL_COLOR_BUFFER_BIT );
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// Swap front and back rendering buffers
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glfwSwapBuffers();
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// Check if ESC key was pressed or window was closed
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running = !glfwGetKey( GLFW_KEY_ESC ) &&
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glfwGetWindowParam( GLFW_OPENED );
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}
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// Close window and terminate GLFW
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glfwTerminate();
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// Exit program
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return 0;
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}
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\end{lstlisting}
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The program opens a 300x300 window and runs in a loop until the escape key
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is pressed, or the window was closed. All the \OpenGL\ ``rendering'' that
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is done in this example is to clear the window.
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%-------------------------------------------------------------------------
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% Window Operations
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%-------------------------------------------------------------------------
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\chapter{Window Operations}
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\thispagestyle{fancy}
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In this chapter, you will learn more about window related \GLFW\
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functionality, including: setting and getting window properties, buffer
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swap control and video mode querying.
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%-------------------------------------------------------------------------
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\section{Setting Window Properties}
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In the previous chapter the \textbf{glfwOpenWindow} function was
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described, which specifies the sizes of the color, alpha, depth and
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stencil buffers. It is also possible to request an accumulator buffer,
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auxiliary buffers and stereo rendering by using the
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\textbf{glfwOpenWindowHint} function:
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\begin{lstlisting}
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void glfwOpenWindowHint( int target, int hint )
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\end{lstlisting}
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The \textit{target} argument can be one of the constants listed in table~
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\ref{tab:winhints}, and \textit{hint} is the value to assign to the
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specified target.
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%-------------------------------------------------------------------------
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\begin{table}[p]
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\begin{center}
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\begin{tabular}{|l|l|p{7.0cm}|} \hline \raggedright
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\textbf{Name} & \textbf{Default} & \textbf{Description} \\ \hline
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GLFW\_REFRESH\_RATE & 0 & Vertical monitor refresh rate in Hz (only used for fullscreen windows). Zero means system default.\\ \hline
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GLFW\_ACCUM\_RED\_BITS & 0 & Number of bits for the red channel of the accumulator buffer.\\ \hline
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GLFW\_ACCUM\_GREEN\_BITS & 0 & Number of bits for the green channel of the accumulator buffer.\\ \hline
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GLFW\_ACCUM\_BLUE\_BITS & 0 & Number of bits for the blue channel of the accumulator buffer.\\ \hline
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GLFW\_ACCUM\_ALPHA\_BITS & 0 & Number of bits for the alpha channel of the accumulator buffer.\\ \hline
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GLFW\_AUX\_BUFFERS & 0 & Number of auxiliary buffers.\\ \hline
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GLFW\_STEREO & GL\_FALSE & Specify if stereo rendering should be supported (can be GL\_TRUE or GL\_FALSE).\\ \hline
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GLFW\_WINDOW\_NO\_RESIZE & GL\_FALSE & Specify whether the window can be resized (not used for fullscreen windows).\\ \hline
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GLFW\_FSAA\_SAMPLES & 0 & Number of samples to use for the multisampling buffer. Zero disables multisampling.\\ \hline
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GLFW\_OPENGL\_VERSION\_MAJOR & 0 & Major number of the desired OpenGL version.
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The default requests the highest OpenGL version equal to or lower than 2.1.\\ \hline
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GLFW\_OPENGL\_VERSION\_MINOR & 0 & Minor number of the desired OpenGL version.
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The default requests the highest OpenGL version equal to or lower than 2.1.\\ \hline
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GLFW\_OPENGL\_FORWARD\_COMPAT & GL\_FALSE & Specify whether the OpenGL context should be forward compatible (i.e. disallow legacy functionality).
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This hint is ignored for OpenGL version 2.1 and below.\\ \hline
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\end{tabular}
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\end{center}
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\caption{Targets for \textbf{glfwOpenWindowHint}}
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\label{tab:winhints}
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\end{table}
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%-------------------------------------------------------------------------
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For a hint to have any effect, the \textbf{glfwOpenWindowHint} function
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must be called before opening the window with the \textbf{glfwOpenWindow}
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function.
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To request an accumulator buffer, set the GLFW\_ACCUM\_x\_BITS targets to
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values greater than zero (usually eight or sixteen bits per component).
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To request auxiliary buffers, set the GLFW\_AUX\_BUFFERS target to a value
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greater than zero. To request a stereo rendering capable window, set the
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GLFW\_STEREO target to GL\_TRUE.
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If you want to enable fullscreen antialiasing, set the GLFW\_FSAA\_SAMPLES
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target to a value greater than zero. If the windowing system is unable to
|
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fulfil the request, \GLFW\ will degrade gracefully and disable FSAA if necessary.
|
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The GLFW\_REFRESH\_RATE target should be used with caution, since it may
|
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result in suboptimal operation, or even a blank or damaged screen.
|
||
|
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If you want to create a context with OpenGL version 3.0 or above you have to
|
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set the GLFW\_OPENGL\_VERSION\_MAJOR and GLFW\_OPENGL\_VERSION\_MINOR hints
|
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accordingly. If you don't do this, the highest OpenGL version available for a
|
||
context is 2.1 or lower.
|
||
|
||
Besides the parameters that are given with the \textbf{glfwOpenWindow} and
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\textbf{glfwOpenWindowHint} functions, a few more properties of a window
|
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can be changed after the window has been opened, namely the window title,
|
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window size, and window position.
|
||
|
||
To change the window title of an open window, use the
|
||
\textbf{glfwSetWindowTitle} function:
|
||
|
||
\begin{lstlisting}
|
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void glfwSetWindowTitle( const char *title )
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\end{lstlisting}
|
||
|
||
\textit{title} is a null terminated ISO~8859-1 (8-bit Latin~1) string that
|
||
will be used as the window title. It will also be used as the application
|
||
name (for instance in the application list when using \texttt{ALT+TAB}
|
||
under Windows, or as the icon name when the window is iconified under
|
||
the X Window System). The default window name is ``GLFW Window'', which
|
||
will be used unless \textbf{glfwSetWindowTitle} is called after the window
|
||
has been opened.
|
||
|
||
To change the size of a window, call \textbf{glfwSetWindowSize}:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSetWindowSize( int width, int height )
|
||
\end{lstlisting}
|
||
|
||
Where \textit{width} and \textit{height} are the new dimensions of the
|
||
window.
|
||
|
||
To change the position of a window, call \textbf{glfwSetWindowPos}:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSetWindowPos( int x, int y )
|
||
\end{lstlisting}
|
||
|
||
Where \textit{x} and \textit{y} are the new desktop coordinates of the
|
||
window. This function does not have any effect when in fullscreen mode.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Getting Window Properties}
|
||
When opening a window, the opened window will not necessarily have the
|
||
requested properties, so you should always check the parameters that your
|
||
application relies on (e.g. number of stencil bits) using
|
||
\textbf{glfwGetWindowParam}, which has the C syntax:
|
||
|
||
\begin{lstlisting}
|
||
int glfwGetWindowParam( int param )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{param} can be one of the tokens listed in table
|
||
\ref{tab:winparams}, and the return value is an integer holding the
|
||
requested value.
|
||
|
||
%-------------------------------------------------------------------------
|
||
\begin{table}[p]
|
||
\begin{center}
|
||
\begin{tabular}{|l|p{9.5cm}|} \hline \raggedright
|
||
\textbf{Name} & \textbf{Description} \\ \hline
|
||
GLFW\_OPENED & GL\_TRUE if window is opened, else GL\_FALSE.\\ \hline
|
||
GLFW\_ACTIVE & GL\_TRUE if window has focus, else GL\_FALSE.\\ \hline
|
||
GLFW\_ICONIFIED & GL\_TRUE if window is iconified, else GL\_FALSE.\\ \hline
|
||
GLFW\_ACCELERATED & GL\_TRUE if window is hardware accelerated, else GL\_FALSE.\\ \hline
|
||
GLFW\_RED\_BITS & Number of bits for the red color component.\\ \hline
|
||
GLFW\_GREEN\_BITS & Number of bits for the green color component.\\ \hline
|
||
GLFW\_BLUE\_BITS & Number of bits for the blue color component.\\ \hline
|
||
GLFW\_ALPHA\_BITS & Number of bits for the alpha buffer.\\ \hline
|
||
GLFW\_DEPTH\_BITS & Number of bits for the depth buffer.\\ \hline
|
||
GLFW\_STENCIL\_BITS & Number of bits for the stencil buffer.\\ \hline
|
||
GLFW\_REFRESH\_RATE & Vertical monitor refresh rate in Hz. Zero indicates an unknown or a default refresh rate.\\ \hline
|
||
GLFW\_ACCUM\_RED\_BITS & Number of bits for the red channel of the accumulator buffer.\\ \hline
|
||
GLFW\_ACCUM\_GREEN\_BITS & Number of bits for the green channel of the accumulator buffer.\\ \hline
|
||
GLFW\_ACCUM\_BLUE\_BITS & Number of bits for the blue channel of the accumulator buffer.\\ \hline
|
||
GLFW\_ACCUM\_ALPHA\_BITS & Number of bits for the alpha channel of the accumulator buffer.\\ \hline
|
||
GLFW\_AUX\_BUFFERS & Number of auxiliary buffers.\\ \hline
|
||
GLFW\_STEREO & GL\_TRUE if stereo rendering is supported, else GL\_FALSE.\\ \hline
|
||
GLFW\_WINDOW\_NO\_RESIZE & GL\_TRUE if the window cannot be resized, else GL\_FALSE.\\ \hline
|
||
GLFW\_FSAA\_SAMPLES & Number of multisampling buffer samples. Zero indicated multisampling is disabled.\\ \hline
|
||
GLFW\_OPENGL\_VERSION\_MAJOR & Major number of the desired OpenGL version.\\ \hline
|
||
GLFW\_OPENGL\_VERSION\_MINOR & Minor number of the desired OpenGL version.\\ \hline
|
||
GLFW\_OPENGL\_FORWARD\_COMPAT & GL\_TRUE if the OpenGL context is forward compatible (i.e. disallows legacy functionality), else GL\_FALSE.
|
||
This is always GL\_FALSE for OpenGL version 2.1 and below.\\ \hline
|
||
\end{tabular}
|
||
\end{center}
|
||
\caption{Window parameters for \textbf{glfwGetWindowParam}}
|
||
\label{tab:winparams}
|
||
\end{table}
|
||
%-------------------------------------------------------------------------
|
||
|
||
Another useful function is \textbf{glfwSetWindowSizeCallback}, which
|
||
specifies a user function that will be called every time the window size
|
||
has changed. The C syntax is:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSetWindowSizeCallback( GLFWwindowsizefun cbfun )
|
||
\end{lstlisting}
|
||
|
||
The user function \textit{fun} should be of the type:
|
||
|
||
\begin{lstlisting}
|
||
void GLFWCALL fun( int width, int height )
|
||
\end{lstlisting}
|
||
|
||
The first argument passed to the user function is the width of the window,
|
||
and the second argument is the height of the window. Here is an example
|
||
of how to use a window size callback function:
|
||
|
||
\begin{lstlisting}
|
||
int WinWidth, WinHeight;
|
||
|
||
void GLFWCALL WindowResize( int width, int height )
|
||
{
|
||
WinWidth = width;
|
||
WinHeight = height;
|
||
}
|
||
|
||
int main( void )
|
||
{
|
||
...
|
||
glfwSetWindowSizeCallback( WindowResize );
|
||
...
|
||
}
|
||
\end{lstlisting}
|
||
|
||
Using a callback function for getting the window size is mostly useful for
|
||
windowed applications, since the window size may be changed at any time by
|
||
the user. It can also be used to determine the actual fullscreen
|
||
resolution.
|
||
|
||
An alternative to using a callback function for getting the window size,
|
||
is to use the function \textbf{glfwGetWindowSize}:
|
||
|
||
\begin{lstlisting}
|
||
void glfwGetWindowSize( int *width, int *height )
|
||
\end{lstlisting}
|
||
|
||
The \textit{width} and \textit{height} arguments are filled out with the
|
||
current window dimensions.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Buffer Swapping}
|
||
\GLFW\ windows are always double buffered. That means that you have two
|
||
rendering buffers; a front buffer and a back buffer. The front buffer is
|
||
the buffer that is being displayed, and the back buffer is not displayed.
|
||
\OpenGL\ lets you select which of these two buffers you want to render to
|
||
(with the \textbf{glDrawBuffer} command), but the default (and preferred)
|
||
rendering buffer is the back buffer. This way you will avoid flickering
|
||
and artifacts caused by graphics being only partly drawn at the same time
|
||
as the video raster beam is displaying the graphics on the monitor.
|
||
|
||
When an entire frame has been rendered to the back buffer, it is time to
|
||
swap the back and the front buffers in order to display the rendered
|
||
frame, and begin rendering a new frame. This is done with the command
|
||
\textbf{glfwSwapBuffers}. The C syntax is:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSwapBuffers( void )
|
||
\end{lstlisting}
|
||
|
||
Besides swapping the front and back rendering buffers,
|
||
\textbf{glfwSwapBuffers} also calls \textbf{glfwPollEvents}\footnote{This
|
||
behavior can be disabled by calling \textbf{glfwDisable} with the argument
|
||
GLFW\_AUTO\_POLL\_EVENTS.}. This is to ensure frequent polling of events,
|
||
such as keyboard and mouse input, and window reshaping events.
|
||
|
||
Sometimes it can be useful to select when the buffer swap will occur. With
|
||
the function \textbf{glfwSwapInterval} it is possible to select the
|
||
minimum number of vertical retraces the video raster line should do before
|
||
swapping the buffers:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSwapInterval( int interval )
|
||
\end{lstlisting}
|
||
|
||
If \textit{interval} is zero, the swap will take place immediately when
|
||
\textbf{glfwSwapBuffers} is called, without waiting for a vertical retrace
|
||
(also known as ``vsync off''). Otherwise at least \textit{interval}
|
||
retraces will pass between each buffer swap (also known as ``vsync on'').
|
||
Using a swap interval of zero can be useful for benchmarking purposes,
|
||
when it is not desirable to measure the time it takes to wait for the
|
||
vertical retrace. However, a swap interval of 1 generally gives better
|
||
visual quality.
|
||
|
||
It should be noted that not all \OpenGL\ implementations and hardware
|
||
support this function, in which case \textbf{glfwSwapInterval} will have
|
||
no effect. Sometimes it is only possible to affect the swap interval
|
||
through driver settings (e.g. the display settings under Windows, or as an
|
||
environment variable setting under Unix).
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Querying Video Modes}
|
||
Although \GLFW\ generally does a good job at selecting a suitable video
|
||
mode for you when you open a fullscreen window, it is sometimes useful to
|
||
know exactly which modes are available on a certain system. For example,
|
||
you may want to present the user with a list of video modes to select
|
||
from. To get a list of available video modes, you can use the function
|
||
\textbf{glfwGetVideoModes}:
|
||
|
||
\begin{lstlisting}
|
||
int glfwGetVideoModes( GLFWvidmode *list, int maxcount )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{list} is a vector of GLFWvidmode structures, and
|
||
\textit{maxcount} is the maximum number of video modes that your vector
|
||
can hold. \textbf{glfwGetVideoModes} will return the actual number of
|
||
video modes detected on the system.
|
||
|
||
The GLFWvidmode structure looks like this:
|
||
|
||
\begin{lstlisting}
|
||
typedef struct {
|
||
int Width, Height; // Video resolution
|
||
int RedBits; // Red bits per pixel
|
||
int GreenBits; // Green bits per pixel
|
||
int BlueBits; // Blue bits per pixel
|
||
} GLFWvidmode;
|
||
\end{lstlisting}
|
||
|
||
Here is an example of retrieving all available video modes:
|
||
|
||
\begin{lstlisting}
|
||
int nummodes;
|
||
GLFWvidmode list[ 200 ];
|
||
nummodes = glfwGetVideoModes( list, 200 );
|
||
\end{lstlisting}
|
||
|
||
The returned list is sorted, first by color depth ($RedBits + GreenBits +
|
||
BlueBits$), and then by resolution ($Width\times Height$), with the
|
||
lowest resolution, fewest bits per pixel mode first.
|
||
|
||
To get the desktop video mode, use the function
|
||
\textbf{glfwGetDesktopMode}:
|
||
|
||
\begin{lstlisting}
|
||
void glfwGetDesktopMode( GLFWvidmode *mode )
|
||
\end{lstlisting}
|
||
|
||
The function returns the resolution and color depth of the user desktop in
|
||
the mode structure. Note that the user desktop mode is independent of the
|
||
current video mode if a \GLFW\ fullscreen window has been opened.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
% Input Handling
|
||
%-------------------------------------------------------------------------
|
||
\chapter{Input Handling}
|
||
\label{par:inputhandling}
|
||
\thispagestyle{fancy}
|
||
In this chapter you will learn how to use keyboard, mouse and joystick
|
||
input, using either polling or callback functions.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Event Polling}
|
||
The first thing to know about input handling in \GLFW\ is that all
|
||
keyboard and mouse input is collected by checking for input events. This
|
||
has do be done manually by calling either \textbf{glfwPollEvents} or
|
||
\textbf{glfwSwapBuffers} (which implicitly calls \textbf{glfwPollEvents}
|
||
for you). Normally this does not have to be a concern, since
|
||
\textbf{glfwSwapBuffers} is called every frame, which should be often
|
||
enough (about 10-100 times per second for a normal \OpenGL\ application).
|
||
One exception is when rendering is paused, and then the program waits for
|
||
input to begin animation again. In this case \textbf{glfwPollEvents} has
|
||
to be called repeatedly until any new input events arrive.
|
||
|
||
If it is not desirable that \textbf{glfwPollEvents is} called implicitly
|
||
from \textbf{glfwSwapBuffers}, call \textbf{glfwDisable} with the argument
|
||
GLFW\_AUTO\_POLL\_EVENTS.
|
||
|
||
Note that event polling is not needed for joystick input, since all
|
||
relevant joystick state is gathered every time a joystick function is
|
||
called.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Keyboard Input}
|
||
\GLFW\ gives three options for getting keyboard input:
|
||
|
||
\begin{itemize}
|
||
\item Manually polling the state of individual keys.
|
||
\item Automatically receive new key state for any key, using a callback
|
||
function.
|
||
\item Automatically receive characters, using a callback function.
|
||
\end{itemize}
|
||
|
||
Depending on what the keyboard input will be used for, either of the
|
||
methods may be more suitable. The main difference between the two last
|
||
options is that while characters are affected by modifier keys (such as
|
||
shift), key state is independent of any modifier keys. Also, special keys
|
||
(such as function keys, cursor keys and modifier keys) are not reported to
|
||
the character callback function.
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Key state}
|
||
To check if a key is held down or not at any given moment, use the
|
||
function \textbf{glfwGetKey}:
|
||
|
||
\begin{lstlisting}
|
||
int glfwGetKey( int key )
|
||
\end{lstlisting}
|
||
|
||
It queries the current status of individual keyboard keys. The argument
|
||
\textit{key} specifies which key to check, and it can be either an
|
||
uppercase ISO~8859-1 character, or a special key identifier.
|
||
\textbf{glfwGetKey} returns GLFW\_PRESS (or 1) if the key is currently
|
||
held down, or GLFW\_RELEASE (or 0) if the key is not being held down.
|
||
|
||
In most situations, it may be useful to know if a key has been pressed and
|
||
released between two calls to \textbf{glfwGetKey} (especially if the
|
||
animation is fairly slow, which may allow the user to press and release a
|
||
key between two calls to \textbf{glfwGetKey}). This can be accomplished by
|
||
enabling sticky keys, which is done by calling \textbf{glfwEnable} with
|
||
the argument GLFW\_STICKY\_KEYS, as in the following example:
|
||
|
||
\begin{lstlisting}
|
||
glfwEnable( GLFW_STICKY_KEYS );
|
||
\end{lstlisting}
|
||
|
||
When sticky keys are enabled, a key will not be released until it is
|
||
checked with \textbf{glfwGetKey}. To disable sticky keys, call
|
||
\textbf{glfwDisable} witht the argument GLFW\_STICKY\_KEYS. Then all keys
|
||
that are not currently held down will be released, and future key releases
|
||
will take place immediately when the user releases the key, without
|
||
waiting for \textbf{glfwGetKey} to check the key. By default sticky keys
|
||
are disabled.
|
||
|
||
Sticky keys are often very useful and should be used in most cases where
|
||
\textbf{glfwGetKey} is used. There is however a danger involved with
|
||
enabling sticky keys, and that is that keys that are pressed by the user
|
||
but are not checked with \textbf{glfwGetKey}, may remain ``pressed'' for a
|
||
very long time. A typical situation where this may be dangerous is in a
|
||
program that consists of two or more sections (e.g. a menu section and a
|
||
game section). If the first section enables sticky keys but does not check
|
||
for keys which the second section checks for, there is a potential of
|
||
recording many key presses in the first section that will be detected in
|
||
the second section. To avoid this problem, always disable sticky keys
|
||
before leaving a section of a program.
|
||
|
||
An alternative to using \textbf{glfwGetKey} is to register a keyboard
|
||
input callback function with \textbf{glfwSetKeyCallback}:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSetKeyCallback( GLFWkeyfun cbfun )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{fun} is a pointer to a callback function. The
|
||
callback function shall take two integer arguments. The first is the key
|
||
identifier, and the second is the new key state, which can be GLFW\_PRESS
|
||
or GLFW\_RELEASE. To unregister a callback function, call
|
||
\textbf{glfwSetKeyCallback} with \textit{fun} = NULL.
|
||
|
||
A callback function can be useful in some situations. For instance it can
|
||
replace multiple \textbf{glfwGetKey} calls with a switch/case statement.
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Character input}
|
||
If the keyboard is to be used as a text input device (e.g. in a user
|
||
dialog) rather than as a set of independent buttons, a character callback
|
||
function is more suitable. To register a character callback function, use
|
||
\textbf{glfwSetCharCallback}:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSetCharCallback( GLFWcharfun cbfun )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{fun} is a pointer to a callback function. The
|
||
callback function shall take two integer arguments. The first is a Unicode
|
||
character code, and the second is GLFW\_PRESS if the key that generated
|
||
the character was pressed, or GLFW\_RELEASE if it was released. To
|
||
unregister a callback function, call \textbf{glfwSetCharCallback} with
|
||
\textit{fun} = NULL.
|
||
|
||
The Unicode character set is an international standard for encoding
|
||
characters. It is much more comprehensive than seven or eight bit
|
||
character sets (e.g. US-ASCII and Latin~1), and includes characters for
|
||
most written languages in the world. It should be noted that Unicode
|
||
character codes 0 to 255 are the same as for ISO~8859-1 (Latin~1), so as
|
||
long as a proper range check is performed on the Unicode character code,
|
||
it can be used just as an eight bit Latin~1 character code (which can be
|
||
useful if full Unicode support is not possible).
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Key repeat}
|
||
By default, \GLFW\ does not report key repeats when a key is held down.
|
||
To activate key repeat, call \textbf{glfwEnable} with the argument
|
||
GLFW\_KEY\_REPEAT:
|
||
|
||
\begin{lstlisting}
|
||
glfwEnable( GLFW_KEY_REPEAT );
|
||
\end{lstlisting}
|
||
|
||
This will let a registered key or character callback function receive key
|
||
repeat events when a key is held down.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Special system keys}
|
||
On most systems there are some special system keys that are normally not
|
||
intercepted by an application. For instance, under Windows it is possible
|
||
to switch programs by pressing \texttt{ALT+TAB}, which brings up a list of
|
||
running programs to select from. In certain situations it can be desirable
|
||
to prevent such special system keys from interfering with the program.
|
||
With \GLFW\ it is possible to do by calling \textbf{glfwDisable} with the
|
||
argument GLFW\_SYSTEM\_KEYS:
|
||
|
||
\begin{lstlisting}
|
||
glfwDisable( GLFW_SYSTEM_KEYS );
|
||
\end{lstlisting}
|
||
|
||
By doing so, most system keys will have no effect and will not interfere
|
||
with your program. System keys can be re-enabled by calling
|
||
\textbf{glfwEnable} with the argument GLFW\_SYSTEM\_KEYS. By default,
|
||
system keys are enabled.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Mouse Input}
|
||
Just like for keyboard input, mouse input can be realized with either
|
||
polling or callback functions.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Mouse position}
|
||
To read the mouse position, you can use the function
|
||
\textbf{glfwGetMousePos}:
|
||
|
||
\begin{lstlisting}
|
||
void glfwGetMousePos( int *x, int *y )
|
||
\end{lstlisting}
|
||
|
||
The arguments \textit{x} and \textit{y} point to integer variables that
|
||
will be updated with the current absolute mouse position. An alternative
|
||
is to use a callback function instead, which can be set with
|
||
\textbf{glfwSetMousePosCallback}:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSetMousePosCallback( GLFWmouseposfun cbfun )
|
||
\end{lstlisting}
|
||
|
||
The function that \textit{fun} points to will be called every time the
|
||
mouse position changes. The first argument to the callback function is
|
||
the mouse x position, and the second argument is the mouse y position.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Mouse buttons}
|
||
To query the state of a mouse button, call \textbf{glfwGetMouseButton}:
|
||
|
||
\begin{lstlisting}
|
||
int glfwGetMouseButton( int button )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{button} can be one of the following mouse button
|
||
identifiers: GLFW\_MOUSE\_BUTTON\_LEFT, GLFW\_MOUSE\_BUTTON\_RIGHT or
|
||
GLFW\_MOUSE\_BUTTON\_MIDDLE. \textbf{glfwGetMouseButton} will return
|
||
GLFW\_PRESS (which is a non-zero value) if the corresponding mouse
|
||
button is held down, otherwise it will return GLFW\_RELEASE (which is
|
||
equal to zero).
|
||
|
||
Just as it is possible to make keys ``sticky'', it is also possible to
|
||
make mouse buttons appear as held down until the button is checked for
|
||
with \textbf{glfwGetMouseButton}. To enable sticky mouse buttons, call
|
||
\textbf{glfwEnable} with the argument GLFW\_STICKY\_MOUSE\_BUTTONS.
|
||
|
||
When sticky mouse buttons are enabled, a mouse button will not be released
|
||
until it is checked with \textbf{glfwGetMouseButton}. To disable sticky
|
||
mouse buttons, call \textbf{glfwDisable} with the argument
|
||
GLFW\_STICKY\_MOUSE\_BUTTONS. Then all mouse buttons that are not
|
||
currently held down will be released, and future mouse button releases
|
||
will take place immediately when the user releases the mouse button,
|
||
without waiting for \textbf{glfwGetMouseButton} to check for the mouse
|
||
button. By default sticky mouse buttons are disabled.
|
||
|
||
There is also a callback function for mouse button activities, which can
|
||
be set with \textbf{glfwSetMouseButtonCallback}:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSetMouseButtonCallback( GLFWmousebuttonfun fun )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{fun} specifies a function that will be called
|
||
whenever a mouse button is pressed or released, or NULL to unregister a
|
||
callback function. The first argument to the callback function is a mouse
|
||
button identifier, and the second is either GLFW\_PRESS or GLFW\_RELEASE,
|
||
depending on the new state of the corresponding mouse button.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Mouse wheel}
|
||
Some mice have a mouse wheel, which can be thought of as a third mouse
|
||
axis. To get the position of the mouse wheel, call
|
||
\textbf{glfwGetMouseWheel}:
|
||
|
||
\begin{lstlisting}
|
||
int glfwGetMouseWheel( void )
|
||
\end{lstlisting}
|
||
|
||
The function returns an integer that represents the position of the mouse
|
||
wheel. When the user turns the wheel, the wheel position will increase or
|
||
decrease.
|
||
|
||
It is also possible to register a callback function for mouse wheel events
|
||
with the \textbf{glfwSetMouseWheelCallback} function:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSetMouseWheelCallback( GLFWmousewheelfun fun )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{fun} specifies a function that will be called
|
||
whenever the mouse wheel is moved, or NULL to unregister a callback
|
||
function. The argument to the callback function is the position of the
|
||
mouse wheel.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Hiding the mouse cursor}
|
||
It is possible to hide the mouse cursor with the function call:
|
||
|
||
\begin{lstlisting}
|
||
glfwDisable( GLFW_MOUSE_CURSOR );
|
||
\end{lstlisting}
|
||
|
||
Hiding the mouse cursor has three effects:
|
||
|
||
\begin{enumerate}
|
||
\item The cursor becomes invisible.
|
||
\item The cursor is guaranteed to be confined to the window.
|
||
\item Mouse coordinates are not limited to the window size.
|
||
\end{enumerate}
|
||
|
||
To show the mouse cursor again, call \textbf{glfwEnable} with the
|
||
argument GLFW\_MOUSE\_CURSOR:
|
||
|
||
\begin{lstlisting}
|
||
glfwEnable( GLFW_MOUSE_CURSOR );
|
||
\end{lstlisting}
|
||
|
||
By default the mouse cursor is hidden if a window is opened in fullscreen
|
||
mode, otherwise it is not hidden.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Joystick Input}
|
||
\GLFW\ has support for up to sixteen joysticks, and an infinite\footnote{%
|
||
There are of course actual limitations posed by the underlying hardware,
|
||
drivers and operation system.} number of axes and buttons per joystick.
|
||
Unlike keyboard and mouse input, joystick input does not need an opened
|
||
window, and \textbf{glfwPollEvents} or \textbf{glfwSwapBuffers} does not
|
||
have to be called in order for joystick state to be updated.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Joystick capabilities}
|
||
First, it is often necessary to determine if a joystick is connected, and
|
||
what its capabilities are. To get this information the function
|
||
\textbf{glfwGetJoystickParam} can be used:
|
||
|
||
\begin{lstlisting}
|
||
int glfwGetJoystickParam( int joy, int param )
|
||
\end{lstlisting}
|
||
|
||
The \textit{joy} argument specifies which joystick to retrieve the
|
||
parameter from, and it should be GLFW\_JOYSTICK\_\textit{n}, where
|
||
\textit{n} is in the range 1 to 16. The \textit{param} argument specifies
|
||
which parameter to retrieve. To determine if a joystick is connected,
|
||
\textit{param} should be GLFW\_PRESENT, which will cause the function to
|
||
return GL\_TRUE if the joystick is connected, or GL\_FALSE if it is not.
|
||
To determine the number of axes or buttons that are supported by the
|
||
joystick, \textit{param} should be GLFW\_AXES or GLFW\_BUTTONS,
|
||
respectively.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Joystick position}
|
||
To get the current axis positions of the joystick, the
|
||
\textbf{glfwGetJoystickPos} is used:
|
||
|
||
\begin{lstlisting}
|
||
int glfwGetJoystickPos( int joy, float *pos, int numaxes )
|
||
\end{lstlisting}
|
||
|
||
As with \textbf{glfwGetJoystickParam}, the \textit{joy} argument
|
||
specifies which joystick to retrieve information from. The
|
||
\textit{numaxes} argument specifies how many axes to return, and the
|
||
\textit{pos} argument specifies an array in which all the axis positions
|
||
are stored. The function returns the actual number of axes that were
|
||
returned, which could be less than \textit{numaxes} if the joystick does
|
||
not support all the requested axes, or if the joystick is not connected.
|
||
|
||
For instance, to get the position of the first two axes (the X and Y axes)
|
||
of joystick 1, the following code can be used:
|
||
|
||
\begin{lstlisting}
|
||
float position[ 2 ];
|
||
|
||
glfwGetJoystickPos( GLFW_JOYSTICK_1, position, 2 );
|
||
\end{lstlisting}
|
||
|
||
After this call, the first element of the \textit{position} array will
|
||
hold the X axis position of the joystick, and the second element will hold
|
||
the Y axis position. In this example we do not use the information about
|
||
how many axes were really returned.
|
||
|
||
The position of an axis can be in the range -1.0 to 1.0, where positive
|
||
values represent right, forward or up directions, while negative values
|
||
represent left, back or down directions. If a requested axis is not
|
||
supported by the joystick, the corresponding array element will be set
|
||
to zero. The same goes for the situation when the joystick is not
|
||
connected (all axes are treated as unsupported).
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Joystick buttons}
|
||
A function similar to the \textbf{glfwGetJoystickPos} function is
|
||
available for querying the state of joystick buttons, namely the
|
||
\textbf{glfwGetJoystickButtons} function:
|
||
|
||
\begin{lstlisting}
|
||
int glfwGetJoystickButtons( int joy, unsigned char *buttons,
|
||
int numbuttons )
|
||
\end{lstlisting}
|
||
|
||
The function works just like the \textbf{glfwGetJoystickAxis} function,
|
||
except that it returns the state of joystick buttons instead of axis
|
||
positions. Each button in the array specified by the \textit{buttons}
|
||
argument can be either GLFW\_PRESS or GLFW\_RELEASE, telling if the
|
||
corresponding button is currently held down or not. Unsupported buttons
|
||
will have the value GLFW\_RELEASE.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
% Timing
|
||
%-------------------------------------------------------------------------
|
||
\chapter{Timing}
|
||
\thispagestyle{fancy}
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{High Resolution Timer}
|
||
In most applications, it is useful to know exactly how much time has
|
||
passed between point $A$ and point $B$ in a program. A typical situation
|
||
is in a game, where you need to know how much time has passed between two
|
||
rendered frames in order to calculate the correct movement and physics
|
||
etc. Another example is when you want to benchmark a certain piece of
|
||
code.
|
||
|
||
\GLFW\ provides a high-resolution timer, which reports a double precision
|
||
floating point value representing the number of seconds that have passed
|
||
since \textbf{glfwInit} was called. The timer is accessed with the
|
||
function \textbf{glfwGetTime}:
|
||
|
||
\begin{lstlisting}
|
||
double glfwGetTime( void )
|
||
\end{lstlisting}
|
||
|
||
The precision of the timer depends on which computer and operating
|
||
system you are running, but it is almost guaranteed to be better than
|
||
$10~ms$, and in most cases it is much better than $1~ms$ (on a modern PC
|
||
you can get resolutions in the order of $1~ns$).
|
||
|
||
It is possible to set the value of the high precision timer using the
|
||
\textbf{glfwSetTime} function:
|
||
|
||
\begin{lstlisting}
|
||
void glfwSetTime( double time )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{time} is the time, in seconds, that the timer should
|
||
be set to.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
% OpenGL Extension Support
|
||
%-------------------------------------------------------------------------
|
||
\chapter{OpenGL Extension Support}
|
||
\thispagestyle{fancy}
|
||
One of the benefits of \OpenGL\ is that it is extensible. Independent
|
||
hardware vendors (IHVs) may include functionality in their \OpenGL\
|
||
implementations that exceed that of the \OpenGL\ standard.
|
||
|
||
An extension is defined by:
|
||
|
||
\begin{enumerate}
|
||
\item An extension name (e.g. GL\_ARB\_multitexture).
|
||
\item New OpenGL tokens (e.g. GL\_TEXTURE1\_ARB).
|
||
\item New OpenGL functions (e.g. \textbf{glActiveTextureARB}).
|
||
\end{enumerate}
|
||
|
||
A list of official extensions, together with their definitions, can be
|
||
found at the \textit{OpenGL Extension Registry}
|
||
(\url{http://oss.sgi.com/projects/ogl-sample/registry/}).
|
||
|
||
To use a certain extension, the following steps must be performed:
|
||
|
||
\begin{enumerate}
|
||
\item A compile time check for the support of the extension.
|
||
\item A run time check for the support of the extension.
|
||
\item Fetch function pointers for the extended \OpenGL\ functions (done at
|
||
run time).
|
||
\end{enumerate}
|
||
|
||
How this is done using \GLFW\ is described in the following sections.
|
||
Please note that this chapter covers some advanced topics, and is quite
|
||
specific to the C programming language.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Compile Time Check}
|
||
The compile time check is necessary to perform in order to know if the
|
||
compiler include files have defined the necessary tokens. It is very easy
|
||
to do. The include file \texttt{GL/gl.h} will define a constant with the
|
||
same name as the extension, if all the extension tokens are defined. Here
|
||
is an example of how to check for the extension GL\_ARB\_multitexture:
|
||
|
||
\begin{lstlisting}
|
||
#ifdef GL_ARB_multitexture
|
||
// Extension is supported by the include files
|
||
#else
|
||
// Extension is not supported by the include files
|
||
// Update your <GL/gl.h> file!
|
||
#endif
|
||
\end{lstlisting}
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Runtime Check}
|
||
Even if the compiler include files have defined all the necessary tokens,
|
||
the target system may not support the extension (perhaps it has a
|
||
different graphic card with a different \OpenGL\ implementation, or it has
|
||
an older driver). That is why it is necessary to do a run time check for
|
||
the extension support as well. This is done with the \GLFW\ function
|
||
\textbf{glfwExtensionSupported}, which has the C syntax:
|
||
|
||
\begin{lstlisting}
|
||
int glfwExtensionSupported( const char *extension )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{extension} is a null terminated ISO~8859-1 string
|
||
with the extension name. \textbf{glfwExtensionSupported} returns GL\_TRUE
|
||
if the extension is supported, otherwise it returns GL\_FALSE.
|
||
|
||
Let us extend the previous example of checking for support of the
|
||
extension GL\_ARB\_multitexture. This time we add a run time check, and a
|
||
variable which we set to GL\_TRUE if the extension is supported, or
|
||
GL\_FALSE if it is not supported.
|
||
|
||
\begin{lstlisting}
|
||
int multitexture_supported;
|
||
|
||
#ifdef GL_ARB_multitexture
|
||
// Check if extension is supported at run time
|
||
multitexture_supported =
|
||
glfwExtensionSupported( "GL_ARB_multitexture" );
|
||
#else
|
||
// Extension is not supported by the include files
|
||
// Update your <GL/gl.h> file!
|
||
multitexture_supported = GL_FALSE;
|
||
#endif
|
||
\end{lstlisting}
|
||
|
||
Now it is easy to check for the extension within the program, simply do:
|
||
|
||
\begin{lstlisting}
|
||
if( multitexture_supported )
|
||
{
|
||
// Use multi texturing
|
||
}
|
||
else
|
||
{
|
||
// Use some other solution (or fail)
|
||
}
|
||
\end{lstlisting}
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\section{Fetching Function Pointers}
|
||
Some extensions (not all) require the use of new \OpenGL\ functions, which
|
||
are not necessarily defined by your link libraries. Thus it is necessary
|
||
to get the function pointers dynamically at run time. This is done with
|
||
the \GLFW\ function \textbf{glfwGetProcAddress}:
|
||
|
||
\begin{lstlisting}
|
||
void * glfwGetProcAddress( const char *procname )
|
||
\end{lstlisting}
|
||
|
||
The argument \textit{procname} is a null terminated ISO~8859-1 string
|
||
holding the name of the \OpenGL\ function. \textbf{glfwGetProcAddress}
|
||
returns the address to the function if the function is available,
|
||
otherwise NULL is returned.
|
||
|
||
Obviously, fetching the function pointer is trivial. For instance, if we
|
||
want to obtain the pointer to \textbf{glActiveTextureARB}, we simply call:
|
||
|
||
\begin{lstlisting}
|
||
glActiveTextureARB = glfwGetProcAddress( "glActiveTextureARB" );
|
||
\end{lstlisting}
|
||
|
||
However, there are many possible naming and type definition conflicts
|
||
involved with such an operation, which may result in compiler warnings or
|
||
errors. My proposed solution is the following:
|
||
|
||
\begin{itemize}
|
||
\item Do not use the function name for the variable name. Use something
|
||
similar (perhaps with a prefix or suffix), and then use
|
||
\texttt{\#define} to map the function name to your variable.
|
||
\item The standard type definition naming convention for function pointers
|
||
is \texttt{PFN\textit{xxxx}PROC}, where \texttt{\textit{xxxx}} is
|
||
the uppercase version of the function name (e.g.
|
||
\texttt{PFNGLACTIVETEXTUREARBPROC}). Either make sure that a
|
||
compatible \texttt{gl.h} and/or \texttt{glext.h} file is used by
|
||
your compiler and rely on it to do the type definitions for you, or
|
||
use a custom type definition naming convention (e.g.
|
||
\texttt{\textit{xxxx}\_T} or something) and do the type definitions
|
||
yourself.
|
||
\end{itemize}
|
||
|
||
Here is an example of how to do it (here we use our own function pointer
|
||
type defintion):
|
||
|
||
\begin{lstlisting}
|
||
// Type definition of the function pointer
|
||
typedef void (APIENTRY * GLACTIVETEXTUREARB_T) (GLenum texture);
|
||
|
||
// Function pointer
|
||
GLACTIVETEXTUREARB_T _ActiveTextureARB;
|
||
#define glActiveTextureARB _ActiveTextureARB
|
||
|
||
// Extension availability flag
|
||
int multitexture_supported;
|
||
|
||
#ifdef GL_ARB_multitexture
|
||
// Check if extension is supported at run time
|
||
if( glfwExtensionSupported( "GL_ARB_multitexture" ) )
|
||
{
|
||
// Get the function pointer
|
||
glActiveTextureARB = (GLACTIVETEXTUREARB_T)
|
||
glfwGetProcAddress( "glActiveTextureARB" );
|
||
|
||
multitexture_supported = GL_TRUE;
|
||
}
|
||
else
|
||
{
|
||
multitexture_supported = GL_FALSE;
|
||
}
|
||
#else
|
||
// Extension is not supported by the include files
|
||
multitexture_supported = GL_FALSE;
|
||
#endif
|
||
\end{lstlisting}
|
||
|
||
Please note that the code example is not 100\% complete. First of all,
|
||
the GL\_ARB\_multitexture extension defines many more functions than the
|
||
single function that the code example defines. Secondly, checking if an
|
||
extension is supported using \textbf{glfwExtensionSupported} is not enough
|
||
to ensure that the corresponding functions will be valid. You also need to
|
||
check if the function pointers returned by \textbf{glfwGetProcAddress} are
|
||
non-NULL values.
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
\subsection{Function pointer type definitions}
|
||
To make a function pointer type definition, you need to know the function
|
||
prototype. This can often be found in the extension definitions (e.g. at
|
||
the \textit{OpenGL Extension Registry}). All the functions that are
|
||
defined for an extension are listed with their C prototype definitions
|
||
under the section \textit{New Procedures and Functions} in the extension
|
||
definition.
|
||
|
||
For instance, if we look at the definition of the
|
||
GL\_ARB\_texture\_compression extension, we find a list of new functions.
|
||
One of the functions looks like this:
|
||
|
||
\begin{lstlisting}
|
||
void GetCompressedTexImageARB(enum target, int lod, void *img);
|
||
\end{lstlisting}
|
||
|
||
Like in most official \OpenGL\ documentation, all the \texttt{GL} and
|
||
\texttt{gl} prefixes have been left out. In other words, the real function
|
||
prototype would look like this:
|
||
|
||
\begin{lstlisting}
|
||
void glGetCompressedTexImageARB(GLenum target, GLint lod, void *img);
|
||
\end{lstlisting}
|
||
|
||
All we have to do to turn this prototype definition into a function
|
||
pointer type definition, is to replace the function name with
|
||
\texttt{(APIENTRY * \textit{xxxx}\_T)}, where \textit{xxxx} is the
|
||
uppercase version of the name (according to the proposed naming
|
||
convention). The keyword \texttt{APIENTRY} is needed to be compatible
|
||
between different platforms. The \GLFW\ include file \texttt{GL/glfw.h}
|
||
always makes sure that \texttt{APIENTRY} is properly defined, regardless
|
||
of which platform the program is compiled on.
|
||
|
||
In other words, for the function \textbf{glGetCompressedTexImageARB} we
|
||
get:
|
||
|
||
\begin{lstlisting}
|
||
typedef void (APIENTRY * GLGETCOMPRESSEDTEXIMAGEARB_T)
|
||
(GLenum target, GLint level, void *img);
|
||
\end{lstlisting}
|
||
|
||
|
||
|
||
%-------------------------------------------------------------------------
|
||
% Index
|
||
%-------------------------------------------------------------------------
|
||
% ...
|
||
|
||
\end{document}
|