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124 lines
4.0 KiB
124 lines
4.0 KiB
[](https://travis-ci.org/anholt/libepoxy)
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[](https://ci.appveyor.com/project/ebassi/libepoxy/branch/master)
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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. They get to read 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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Features
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--------
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* Automatically initializes as new GL functions are used.
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* GL 4.5 core and compatibility context support.
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* GLES 1/2/3 context support.
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* Knows about function aliases so (e.g.) `glBufferData()` can be
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used with `GL_ARB_vertex_buffer_object` implementations, along
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with GL 1.5+ implementations.
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* EGL, GLX, and WGL support.
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* Can be mixed with non-epoxy GL usage.
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Building
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--------
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```sh
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mkdir _build && cd _build
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meson
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ninja
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sudo ninja install
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```
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Dependencies for Debian:
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* meson
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* libegl1-mesa-dev
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Dependencies for macOS (using MacPorts):
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* pkgconfig
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* meson
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The test suite has additional dependencies depending on the platform.
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(X11, EGL, a running X Server).
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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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```cpp
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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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```
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with:
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```cpp
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#include <epoxy/gl.h>
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#include <epoxy/glx.h>
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```
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As long as epoxy's headers appear first, you should be ready to go.
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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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Why not use libGLEW?
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--------------------
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GLEW has several issues:
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* Doesn't know about aliases of functions (There are 5 providers of
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`glPointParameterfv()`, for example, and you don't want to have to
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choose which one to call when they're all the same).
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* Doesn't support OpenGL ES.
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* Doesn't support EGL.
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* Has a hard-to-maintain parser of extension specification text
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instead of using the old .spec file or the new .xml.
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* Has significant startup time overhead when `glewInit()`
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autodetects the world.
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* User-visible multithreading support choice for win32.
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The motivation for this project came out of previous use of libGLEW in
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[piglit](http://piglit.freedesktop.org/). Other GL dispatch code
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generation projects had similar failures. Ideally, piglit wants to be
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able to build a single binary for a test that can run on whatever
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context or window system it chooses, not based on link time choices.
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We had to solve some of GLEW's problems for piglit and solving them
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meant replacing every single piece of GLEW, so we built
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piglit-dispatch from scratch. And since we wanted to reuse it in
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other GL-related projects, this is the result.
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Known issues when running on Windows
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------------------------------------
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The automatic per-context symbol resolution for win32 requires that
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epoxy knows when `wglMakeCurrent()` is called, because `wglGetProcAddress()`
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returns values depend on the context's device and pixel format. If
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`wglMakeCurrent()` is called from outside of epoxy (in a way that might
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change the device or pixel format), then epoxy needs to be notified of
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the change using the `epoxy_handle_external_wglMakeCurrent()` function.
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The win32 `wglMakeCurrent()` variants are slower than they should be,
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because they should be caching the resolved dispatch tables instead of
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resetting an entire thread-local dispatch table every time.
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