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Documentation work.

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Fixes #416.
This commit is contained in:
Camilla Berglund 2015-01-10 23:05:20 +01:00
parent 1591caa0e5
commit 500f5ebf04
1 changed files with 57 additions and 36 deletions
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docs/context.dox
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@ -86,26 +86,26 @@ Before you can make OpenGL or OpenGL ES calls, you need to have a current
context of the correct type. A context can only be current for a single thread
at a time, and a thread can only have a single context current at a time.
A context is made current with @ref glfwMakeContextCurrent.
The context of a window is made current with @ref glfwMakeContextCurrent.
@code
glfwMakeContextCurrent(window);
@endcode
The current context is returned by @ref glfwGetCurrentContext.
The window of the current context is returned by @ref glfwGetCurrentContext.
@code
GLFWwindow* window = glfwGetCurrentContext();
@endcode
The following GLFW functions require a context to be current:
The following GLFW functions require a context to be current. Calling any these
functions without a current context will generate a @ref GLFW_NO_CURRENT_CONTEXT
error.
- @ref glfwSwapInterval
- @ref glfwExtensionSupported
- @ref glfwGetProcAddress
Calling any these functions without a current context will generate a @ref
GLFW_NO_CURRENT_CONTEXT error.
@section context_swap Buffer swapping
@ -136,14 +136,15 @@ their specifications, can be found at the
[OpenGL ES Registry](https://www.khronos.org/registry/gles/).
@subsection context_glext_auto Using an extension loader library
@subsection context_glext_auto Loading extension with a loader library
This is the easiest and best way to load extensions and newer versions of the
OpenGL or OpenGL ES API. One such library is
[glad](https://github.com/Dav1dde/glad) and there are several others. They will
take care of all the details of declaring and loading everything you need.
An extension loader library is the easiest and best way to access both OpenGL and
OpenGL ES extensions and modern versions of the core OpenGL or OpenGL ES APIs.
They will take care of all the details of declaring and loading everything you
need. One such library is [glad](https://github.com/Dav1dde/glad) and there are
several others.
The following example will use glad, but other extension loader libraries work
The following example will use glad but all extension loader libraries work
similarly.
First you need to generate the source files using the glad Python script. This
@ -153,24 +154,26 @@ API versions and extension sets can be generated. The generated files are
written to the `output` directory.
@code{.sh}
python main.py --no-loader --out-path output
python main.py --generator c --no-loader --out-path output
@endcode
The `--no-loader` option is added because GLFW already provides a function for
loading OpenGL and OpenGL ES function pointers and glad can call this instead of
having to implement its own.
having to implement its own. There are several other command-line options as
well. See the glad documentation for details.
Add the generated `output/src/glad.c`, `output/include/glad/glad.h` and
`output/include/KHR/khrplatform.h` files to your build. Then you need to
include the glad header file, which will replace the OpenGL header of your
development environment.
development environment. By including the glad header before the GLFW header,
it suppresses the development environment's OpenGL or OpenGL ES header.
@code
#include <glad/glad.h>
#include <GLFW/glfw3.h>
@endcode
Finally you need to initialize glad once you have a matching current context.
Finally you need to initialize glad once you have a suitable current context.
@code
window = glfwCreateWindow(640, 480, "My Window", NULL, NULL);
@ -185,8 +188,8 @@ gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);
@endcode
Once glad has been loaded, you have access to all OpenGL core and extension
functions supported by the context you created and you are ready to start
rendering.
functions supported by both the context you created and the glad loader you
generated and you are ready to start rendering.
You can specify a minimum required OpenGL or OpenGL ES version with
[context hints](@ref window_hints_ctx). If your needs are more complex, you can
@ -215,36 +218,50 @@ if (GLAD_GL_ARB_debug_output)
@subsection context_glext_manual Loading extensions manually
__Do not use this technique__ unless it is absolutely necessary. An
[extension loader library](@ref context_glext_auto) will save you a ton of
tedious, repetitive, error prone work.
To use a certain extension, you must first check whether the context supports
that extension and then, if it introduces new functions, retrieve the pointers
to those functions. GLFW provides @ref glfwExtensionSupported and @ref
glfwGetProcAddress for manual loading of extensions and new API functions.
@note It is recommended that you use an existing extension loader library, as
described above, instead of loading manually.
This section will demonstrate manual loading of OpenGL extensions. The loading
of OpenGL ES extensions is identical except for the name of the extension header.
@subsubsection context_glext_header The glext.h header
The `glext.h` header is a continually updated file that defines the interfaces
for all OpenGL extensions. The latest version of this can always be found at
the [OpenGL Registry](http://www.opengl.org/registry/). It it strongly
recommended that you use your own copy, as the one shipped with your development
environment may be several years out of date and may not include the extensions
you wish to use.
The `glext.h` extension header is a continually updated file that defines the
interfaces for all OpenGL extensions. The latest version of this can always be
found at the [OpenGL Registry](http://www.opengl.org/registry/). There are also
extension headers for the various versions of OpenGL ES at the
[OpenGL ES Registry](https://www.khronos.org/registry/gles/). It it strongly
recommended that you use your own copy of the extension header, as the one
included in your development environment may be several years out of date and
may not include the extensions you wish to use.
The header defines function pointer types for all functions of all extensions it
supports. These have names like `PFNGLGETDEBUGMESSAGELOGARB` (for
supports. These have names like `PFNGLGETDEBUGMESSAGELOGARBPROC` (for
`glGetDebugMessageLogARB`), i.e. the name is made uppercase and `PFN` (pointer
to function) and `PROC` (procedure) are added to the ends.
To include the extension header, define [GLFW_INCLUDE_GLEXT](@ref build_macros)
before including the GLFW header.
@code
#define GLFW_INCLUDE_GLEXT
#include <GLFW/glfw3.h>
@endcode
@subsubsection context_glext_string Checking for extensions
A given machine may not actually support the extension (it may have older
drivers or a graphics card that lacks the necessary hardware features), so it
is necessary to check whether the context supports the extension. This is done
with @ref glfwExtensionSupported.
is necessary to check at run-time whether the context supports the extension.
This is done with @ref glfwExtensionSupported.
@code
if (glfwExtensionSupported("GL_ARB_debug_output"))
@ -266,7 +283,7 @@ your operating system, making it necessary to fetch them at run time. You can
retrieve pointers to these functions with @ref glfwGetProcAddress.
@code
PFNGLGETDEBUGMESSAGELOGARB pfnGetDebugMessageLog = glfwGetProcAddress("glGetDebugMessageLogARB");
PFNGLGETDEBUGMESSAGELOGARBPROC pfnGetDebugMessageLog = glfwGetProcAddress("glGetDebugMessageLogARB");
@endcode
In general, you should avoid giving the function pointer variables the (exact)
@ -277,32 +294,36 @@ Now that all the pieces have been introduced, here is what they might look like
when used together.
@code
#include "glext.h"
#define GLFW_INCLUDE_GLEXT
#include <GLFW/glfw3.h>
#define glGetDebugMessageLogARB pfnGetDebugMessageLog
PFNGLGETDEBUGMESSAGELOGARB pfnGetDebugMessageLog;
PFNGLGETDEBUGMESSAGELOGARBPROC pfnGetDebugMessageLog;
// Flag indicating whether the extension is supported
int has_debug_output = 0;
int has_ARB_debug_output = 0;
void load_extensions(void)
{
if (glfwExtensionSupported("GL_ARB_debug_output"))
{
pfnGetDebugMessageLog = (PFNGLGETDEBUGMESSAGELOGARB) glfwGetProcAddress("glGetDebugMessageLogARB");
pfnGetDebugMessageLog = (PFNGLGETDEBUGMESSAGELOGARBPROC) glfwGetProcAddress("glGetDebugMessageLogARB");
if (pfnGetDebugMessageLog)
{
// Both the extension name and the function pointer are present
has_debug_output = 1;
has_ARB_debug_output = 1;
}
}
}
void some_function(void)
{
if (has_ARB_debug_output)
{
// Now the extension function can be called as usual
glGetDebugMessageLogARB(...);
}
}
@endcode
*/