gl3w: Simple OpenGL core profile loading

Introduction

This is a modified gl3w generator, used to create a minimal amalgamated OpenGL loader header file. It is specifically created for use within Dear ImGui project.

gl3w is the easiest way to get your hands on the functionality offered by the OpenGL core profile specification.

Its main part is a simple gl3w_gen.py Python script that downloads the Khronos supported glcorearb.h header and generates gl3w.h and gl3w.c from it. Those files can then be added and linked (statically or dynamically) into your project.

Requirements

gl3w_gen.py requires Python version 2.7 or newer. It is also compatible with Python 3.x.

Building

imgui_impl_opengl3_loader.h is generated by executing:

Windows:

python ./gl3w_gen.py --output ../imgui/backends/imgui_impl_opengl3_loader.h --ref ../imgui/backends/imgui_impl_opengl3.cpp ./extra_symbols.txt

Linux, OSX and other Unix-based:

./gl3w_gen.py --output ../imgui/backends/imgui_impl_opengl3_loader.h --ref ../imgui/backends/imgui_impl_opengl3.cpp ./extra_symbols.txt

Not specifying --ref parameter will skip file scan and generate a loader including all available OpenGL APIs.

Example

Here is a simple example of using gl3w with glut. Note that GL/gl3w.h must be included before any other OpenGL related headers:

#include <stdio.h>
#include <GL/gl3w.h>
#include <GL/glut.h>

// ...

int main(int argc, char **argv)
{
        glutInit(&argc, argv);
        glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);
        glutInitWindowSize(width, height);
        glutCreateWindow("cookie");

        glutReshapeFunc(reshape);
        glutDisplayFunc(display);
        glutKeyboardFunc(keyboard);
        glutSpecialFunc(special);
        glutMouseFunc(mouse);
        glutMotionFunc(motion);

        if (imgl3wInit()) {
                fprintf(stderr, "failed to initialize OpenGL\n");
                return -1;
        }
        if (!imgl3wIsSupported(3, 2)) {
                fprintf(stderr, "OpenGL 3.2 not supported\n");
                return -1;
        }
        printf("OpenGL %s, GLSL %s\n", glGetString(GL_VERSION),
               glGetString(GL_SHADING_LANGUAGE_VERSION));

        // ...

        glutMainLoop();
        return 0;
}

API Reference

The gl3w API consists of just three functions:

int imgl3wInit(void)

Initializes the library. Should be called once after an OpenGL context has been created. Returns 0 when gl3w was initialized successfully, non-zero if there was an error.

int imgl3wIsSupported(int major, int minor)

Returns 1 when OpenGL core profile version major.minor is available and 0 otherwise.

GL3WglProc imgl3wGetProcAddress(const char *proc)

Returns the address of an OpenGL extension function. Generally, you won't need to use it since gl3w loads all functions defined in the OpenGL core profile on initialization. It allows you to load OpenGL extensions outside of the core profile.

Options

The generator script optionally takes the arguments:

--ext to include the GL Extensions in output header.

--root=outputdir to set the location for the output to something else than current working directory.

License

gl3w is in the public domain. See the file UNLICENSE for more information.

Credits

Slavomir Kaslev <slavomir.kaslev@gmail.com>

Initial implementation

Kelvin McDowell

Mac OS X support

Sjors Gielen

Mac OS X support

Travis Gesslein

Patches regarding glcorearb.h

Arthur Tombs

Port to Python 3

Daniel Cousens [https://github.com/dcousens]

Code contributions

Copyright

OpenGL is a registered trademark of SGI.