README.md
1[](https://travis-ci.org/anholt/libepoxy)
2[](https://ci.appveyor.com/project/ebassi/libepoxy/branch/master)
3
4Epoxy is a library for handling OpenGL function pointer management for
5you.
6
7It hides the complexity of `dlopen()`, `dlsym()`, `glXGetProcAddress()`,
8`eglGetProcAddress()`, etc. from the app developer, with very little
9knowledge needed on their part. They get to read GL specs and write
10code using undecorated function names like `glCompileShader()`.
11
12Don't forget to check for your extensions or versions being present
13before you use them, just like before! We'll tell you what you forgot
14to check for instead of just segfaulting, though.
15
16Features
17--------
18
19 * Automatically initializes as new GL functions are used.
20 * GL 4.6 core and compatibility context support.
21 * GLES 1/2/3 context support.
22 * Knows about function aliases so (e.g.) `glBufferData()` can be
23 used with `GL_ARB_vertex_buffer_object` implementations, along
24 with GL 1.5+ implementations.
25 * EGL, GLX, and WGL support.
26 * Can be mixed with non-epoxy GL usage.
27
28Building
29--------
30
31```sh
32mkdir _build && cd _build
33meson
34ninja
35sudo ninja install
36```
37
38Dependencies for Debian:
39
40 * meson
41 * libegl1-mesa-dev
42
43Dependencies for macOS (using MacPorts):
44
45 * pkgconfig
46 * meson
47
48The test suite has additional dependencies depending on the platform.
49(X11, EGL, a running X Server).
50
51Switching your code to using epoxy
52----------------------------------
53
54It should be as easy as replacing:
55
56```cpp
57#include <GL/gl.h>
58#include <GL/glx.h>
59#include <GL/glext.h>
60```
61
62with:
63
64```cpp
65#include <epoxy/gl.h>
66#include <epoxy/glx.h>
67```
68
69As long as epoxy's headers appear first, you should be ready to go.
70Additionally, some new helpers become available, so you don't have to
71write them:
72
73`int epoxy_gl_version()` returns the GL version:
74
75 * 12 for GL 1.2
76 * 20 for GL 2.0
77 * 44 for GL 4.4
78
79`bool epoxy_has_gl_extension()` returns whether a GL extension is
80available (`GL_ARB_texture_buffer_object`, for example).
81
82Note that this is not terribly fast, so keep it out of your hot paths,
83ok?
84
85Why not use libGLEW?
86--------------------
87
88GLEW has several issues:
89
90 * Doesn't know about aliases of functions (There are 5 providers of
91 `glPointParameterfv()`, for example, and you don't want to have to
92 choose which one to call when they're all the same).
93 * Doesn't support OpenGL ES.
94 * Has a hard-to-maintain parser of extension specification text
95 instead of using the old .spec file or the new .xml.
96 * Has significant startup time overhead when `glewInit()`
97 autodetects the world.
98 * User-visible multithreading support choice for win32.
99
100The motivation for this project came out of previous use of libGLEW in
101[piglit](http://piglit.freedesktop.org/). Other GL dispatch code
102generation projects had similar failures. Ideally, piglit wants to be
103able to build a single binary for a test that can run on whatever
104context or window system it chooses, not based on link time choices.
105
106We had to solve some of GLEW's problems for piglit and solving them
107meant replacing every single piece of GLEW, so we built
108piglit-dispatch from scratch. And since we wanted to reuse it in
109other GL-related projects, this is the result.
110
111Known issues when running on Windows
112------------------------------------
113
114The automatic per-context symbol resolution for win32 requires that
115epoxy knows when `wglMakeCurrent()` is called, because `wglGetProcAddress()`
116returns values depend on the context's device and pixel format. If
117`wglMakeCurrent()` is called from outside of epoxy (in a way that might
118change the device or pixel format), then epoxy needs to be notified of
119the change using the `epoxy_handle_external_wglMakeCurrent()` function.
120
121The win32 `wglMakeCurrent()` variants are slower than they should be,
122because they should be caching the resolved dispatch tables instead of
123resetting an entire thread-local dispatch table every time.
124
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