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Epoxy is a library for handling OpenGL function pointer management for
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you.
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It hides the complexity of dlopen(), dlsym(), glXGetProcAddress(),
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eglGetProcAddress(), etc. from the app developer, with very little
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knowledge needed on their part. Just read your GL specs and write
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code using undecorated function names like glCompileShader().
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Don't forget to check for your extensions or versions being present
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before you use them, just like before! We'll tell you what you forgot
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to check for instead of just segfaulting, though.
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Why does this library exist?
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----------------------------
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OpenGL on Linux (and other platforms) made some ABI decisions back in
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the days when symbol versioning and dlsym() weren't as widely
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available, that resulted in window-systems-specific APIs that looked
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kind of like dlsym. They allowed you to build an app that required
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OpenGL 1.2, but could optionally use features of OpenGL 1.4 if the
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implementation made those available through the glXGetProcAddress()
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(or other similarly-named) mechanism.
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The downside is that the fixed OpenGL 1.2 ABI means that application
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developers have to GetProcAddress() out every modern GL entrypoint
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they want to use and stash that function pointer somewhere. Sometimes
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this is done in a pretty way (like libGLEW), sometimes it is done in
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an ad-hoc way (like most applications I've seen), but it's never done
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as well as we think it could be done.
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Additionally, the proliferation of OpenGL ABIs (desktop GL, GLESv1,
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GLESv2) and window systems (GLX, AGL, WGL, all versus EGL) means that
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an individual developer needs to know more and more about how to load
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their classes symbols.
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Switching your code to using epoxy
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----------------------------------
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It should be as easy as replacing:
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#include <GL/gl.h>
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#include <GL/glx.h>
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#include <GL/glext.h>
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with:
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#include <epoxy/gl.h>
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#include <epoxy/glx.h>
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Additionally, some new helpers become available, so you don't have to
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write them:
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int epoxy_gl_version() returns the GL version:
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12 for GL 1.2
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20 for GL 2.0
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44 for GL 4.4
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bool epoxy_has_gl_extension() returns whether a GL extension is
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available ("GL_ARB_texture_buffer_object", for example).
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Note that this is not terribly fast, so keep it out of your hot paths,
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ok?
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