/*! @page quick Getting started @tableofcontents This guide takes you through writing a simple application using GLFW 3. The application will create a window and OpenGL context, render a rotating triangle and exit when the user closes the window or presses Escape. This guide will introduce a few of the most commonly used functions, but there are many more. This guide assumes no experience with earlier versions of GLFW. If you have used GLFW 2 in the past, read the @ref moving guide, as some functions behave differently in GLFW 3. @section quick_steps Step by step @subsection quick_include Including the GLFW header In the source files of your application where you use OpenGL or GLFW, you need to include the GLFW 3 header file. @code #include @endcode This defines all the constants, types and function prototypes of the GLFW API. It also includes the OpenGL header, and defines all the constants and types necessary for it to work on your platform. For example, under Windows you are normally required to include `windows.h` before including `GL/gl.h`. This would make your source file tied to Windows and pollute your code's namespace with the whole Win32 API. Instead, the GLFW header takes care of this for you, not by including `windows.h`, but rather by itself duplicating only the necessary parts of it. It does this only where needed, so if `windows.h` _is_ included, the GLFW header does not try to redefine those symbols. In other words: - Do _not_ include the OpenGL headers yourself, as GLFW does this for you - Do _not_ include `windows.h` or other platform-specific headers unless you plan on using those APIs directly - If you _do_ need to include such headers, do it _before_ including the GLFW one and it will detect this Starting with version 3.0, the GLU header `glu.h` is no longer included by default. If you wish to include it, define `GLFW_INCLUDE_GLU` before the inclusion of the GLFW header. @code #define GLFW_INCLUDE_GLU #include @endcode @subsection quick_init_term Initializing and terminating GLFW Before you can use most GLFW functions, the library must be initialized. On successful initialization, non-zero is returned. If an error occurred, zero is returned. @code if (!glfwInit()) exit(EXIT_FAILURE); @endcode When you are done using GLFW, typically just before the application exits, you need to terminate GLFW. @code glfwTerminate(); @endcode This destroys any remaining windows and releases any other resources allocated by GLFW. After this call, you must initialize GLFW again before using any GLFW functions that require it. @subsection quick_capture_error Setting an error callback Most events are reported through callbacks, whether it's a key being pressed, a GLFW window being moved, or an error occurring. Callbacks are simply C functions (or C++ static methods) that are called by GLFW with arguments describing the event. In case a GLFW function fails, an error is reported to the GLFW error callback. You can receive these reports with an error callback. This function must have the signature below. This simple error callback just prints the error description to `stderr`. @code void error_callback(int error, const char* description) { fputs(description, stderr); } @endcode Callback functions must be set, so GLFW knows to call them. The function to set the error callback is one of the few GLFW functions that may be called before initialization, which lets you be notified of errors both during and after initialization. @code glfwSetErrorCallback(error_callback); @endcode @subsection quick_create_window Creating a window and context The window and its OpenGL context are created with a single call, which returns a handle to the created combined window and context object. For example, this creates a 640 by 480 windowed mode window with an OpenGL context: @code GLFWwindow* window = glfwCreateWindow(640, 480, "My Title", NULL, NULL); @endcode If window or context creation fails, `NULL` will be returned, so it is necessary to check the return value. @code if (!window) { glfwTerminate(); exit(EXIT_FAILURE); } @endcode The window handle is passed to all window related functions and is provided to along to all window related callbacks, so they can tell which window received the event. When a window is no longer needed, destroy it. @code glfwDestroyWindow(window); @endcode Once this function is called, no more events will be delivered for that window and its handle becomes invalid. @subsection quick_context_current Making the OpenGL context current Before you can use the OpenGL API, it must have a current OpenGL context. You make a window's context current. @code glfwMakeContextCurrent(window); @endcode The context will then remain as current until you make another context current or until the window owning the current context is destroyed. @subsection quick_window_close Checking the window close flag Each window has a flag indicating whether the window should be closed. When the user attempts to close the window, either by pressing the close widget in the title bar or using a key combination like Alt+F4, this flag is set to 1. Note that __the window isn't actually closed__, so you are expected to monitor this flag and either destroy the window or give some kind of feedback to the user. @code while (!glfwWindowShouldClose(window)) { // Keep running } @endcode You can be notified when user is attempting to close the window by setting a close callback with @ref glfwSetWindowCloseCallback. The callback will be called immediately after the close flag has been set. You can also set it yourself with @ref glfwSetWindowShouldClose. This can be useful if you want to interpret other kinds of input as closing the window, like for example pressing the escape key. @subsection quick_key_input Receiving input events Each window has a large number of callbacks that can be set to receive all the various kinds of events. To receive key press and release events, create a key callback function. @code static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods) { if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) glfwSetWindowShouldClose(window, GL_TRUE); } @endcode The key callback, like other window related callbacks, are set per-window. @code glfwSetKeyCallback(window, key_callback); @endcode In order for event callbacks to be called when events occur, you need to process events as described below. @subsection quick_render Rendering with OpenGL Once you have a current OpenGL context, you can use OpenGL normally. In this tutorial, a multi-colored rotating triangle will be rendered. The framebuffer size needs to be retrieved for `glViewport`. @code int width, height; glfwGetFramebufferSize(window, &width, &height); glViewport(0, 0, width, height); @endcode You can also set a framebuffer size callback using @ref glfwSetFramebufferSizeCallback and call `glViewport` from there. @subsection quick_timer Reading the timer To create smooth animation, a time source is needed. GLFW provides a timer that returns the number of seconds since initialization. The time source used is the most accurate on each platform and generally has micro- or nanosecond resolution. @code double time = glfwGetTime(); @endcode @subsection quick_swap_buffers Swapping buffers GLFW windows by default use double buffering. That means that each window has two rendering buffers; a front buffer and a back buffer. The front buffer is the one being displayed and the back buffer the one you render to. When the entire frame has been rendered, the buffers need to be swapped with one another, so the back buffer becomes the front buffer and vice versa. @code glfwSwapBuffers(window); @endcode The swap interval indicates how many frames to wait until swapping the buffers, commonly known as _vsync_. By default, the swap interval is zero, meaning buffer swapping will occur immediately. On fast machines, many of those frames will never be seen, as the screen is still only updated typically 60-75 times per second, so this wastes a lot of CPU and GPU cycles. Also, because the buffers will be swapped in the middle the screen update, leading to [screen tearing](https://en.wikipedia.org/wiki/Screen_tearing). For these reasons, applications will typically want to set the swap interval to one. It can be set to higher values, but this is usually not recommended, because of the input latency it leads to. @code glfwSwapInterval(1); @endcode This function acts on the current context and will fail unless a context is current. @subsection quick_process_events Processing events GLFW needs to communicate regularly with the window system both in order to receive events and to show that the application hasn't locked up. Event processing must be done regularly while you have visible windows and is normally done each frame after buffer swapping. There are two methods for processing pending events; polling and waiting. This example will use event polling, which processes only those events that have already been received and then returns immediately. @code glfwPollEvents(); @endcode This is the best choice when rendering continually, like most games do. If instead you only need to update your rendering once you have received new input, @ref glfwWaitEvents is a better choice. It waits until at least one event has been received, putting the thread to sleep in the meantime, and then processes all received events. This saves a great deal of CPU cycles and is useful for, for example, many kinds of editing tools. @section quick_example Putting it together Now that you know how to initialize GLFW, create a window and poll for keyboard input, it's possible to create a simple program. @snippet simple.c code This program creates a 640 by 480 windowed mode window and starts a loop that clears the screen, renders a triangle and processes events until the user either presses Escape or closes the window. This program uses only a few of the many functions GLFW provides. There are guides for each of the areas covered by GLFW. Each guide will introduce all the functions for that category. - @ref intro - @ref window - @ref context - @ref monitor - @ref input @section quick_build Compiling and linking the program The complete program above can be found in the source distribution as `examples/simple.c` and is compiled along with all other examples when you build GLFW. That is, if you have compiled GLFW then you have already built this as `simple.exe` on Windows, `simple` on Linux or `simple.app` on OS X. This tutorial ends here. Once you have written a program that uses GLFW, you will need to compile and link it. How to do that depends on the development environment you are using and is best explained by the documentation for that environment. To learn about the details that are specific to GLFW, see @ref build. */