[Mesa-dev] glGetString(GL_EXTENSIONS) omits mapbuffer extension

Ian Romanick idr at freedesktop.org
Fri Feb 24 23:24:47 PST 2012

You can call GetProcAddress on ANYTHING and it won't return NULL.  It will even return a pointer for glHamSandwich. You must check the extension string.

On Feb 24, 2012, at 6:13 PM, Simon Que <sque at chromium.org> wrote:

> Previously posted at mesa-users.
> TL;DR: GL_EXTENSIONS string does not contain "GL_OES_mapbuffer", but
> the mapbuffer extension functions are still available through
> eglGetProcAddress().
> I am using Mesa GLESv2 with Linaro's glmark2 benchmark.  The benchmark
> uses the functions "glMapBufferOES" and "glUnmapBufferOES" from the
> "GL_OES_mapbuffer" extension, as seen in this function:
> http://git.linaro.org/gitweb?p=people/afrantzis/glmark2.git;a=blob;f=src/canvas-x11-egl.cpp;h=f69e6f40a32832c5cb12eafc94afc8d5d320887e;hb=HEAD#l256
> What this function does:
> 1. Call glGetString(GL_EXTENSIONS), to get a string containing all the
> extensions.
> 2. Checks for "GL_OES_mapbuffer" in the extension list string from Step #1.
> 3. If "GL_OES_mapbuffer" is found in Step #2, it proceeds to get the
> functions gl[Map|UnMap]BufferOES.
> 4. If it is not found, the function takes no action, and the benchmark
> later fails because it was not given the map/unmap functions.
> However, I was able to get the map/unmap functions by bypassing the
> check in Step #2 and calling eglGetProcAddress() regardless of whether
> the string contained the mapbuffer extension.  And then the benchmark
> runs successfully, meaning that the mapbuffer extension actually does
> exist, it is just not being exported in by glGetString(GL_EXTENSIONS).
> For reference, I am building Mesa with the following configuration:
> ./configure --prefix=/usr --build=x86_64-pc-linux-gnu
> --host=i686-pc-linux-gnu --mandir=/usr/share/man
> --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc
> --localstatedir=/var/lib --disable-option-checking --with-driver=dri
> --disable-glut --without-demos --enable-xcb --enable-egl
> --enable-gles1 --enable-gles2 --enable-shared-glapi --enable-gallium
> --disable-debug --enable-glx-tls --disable-glw --disable-motif
> --enable-asm --with-dri-drivers=,i915,i965
> --with-gallium-drivers=,swrast,i915 --with-egl-platforms=drm
> The only GL_OES extensions contained in the GL_EXTENSIONS string are:
> GL_OES_read_format
> GL_OES_EGL_image
> Thanks,
> Simon
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