which library should OpenGL ES clients link to?

[Jerome Glisse]

2010/11/10 Kristian Høgsberg <krh at bitplanet.net>:
> On Wed, Nov 10, 2010 at 12:37 AM, Chia-I Wu <olvaffe at gmail.com> wrote:
>> Hi list,
>>
>> I am curious which library should, say, gears links to when it is
>> ported to OpenGL ES 2.0.  libGL.so or libGLESv2.so?  I'd like to say
>> libGLESv2, but cairo links to libGL and there is going to be a
>> conflict: both libraries export _glapi_tls_Dispatch for current
>> dispatch table.  It is not possible to tell which _glapi_tls_Dispatch
>> eglMakeCurrent will update and which one glDrawArrays will use.
>
> Yup, that is a problem.  Ideally cairo-gl should support GL and GLES2,
> maybe even dlopen libGL.so or libGLESv2.so at runtime so we could
> support both in one cairo build.  As it is now, it's just hardcoded
> full GL support.  cairo-gl isn't a core dependency for wayland though,
> just for the demo clients.  Qt, for example, lets you select GL, GLES1
> or GLES2 at compile time, which is then used for the entire stack.
>
> Cairo gl uses glew for looking up extensions, but I think it would
> make sense to just use a cairo-specific function table that would hold
> the required core functions as well as the extension functions needed
> by cairo.  That way you can specify the GL dialect at runtime and
> cairo-gl will open the right .so and lookup the necessary extension
> functions for that dialect.
>
> For the demo clients, it may be nice to move the cairo dependency out
> of the toytoolkit, but even then, the toy toolkit still has to use
> libGL, since otherwise it won't work with cairo-gl.
>
> Kristian

Side question to this how to pick which GPU to use at runtime ? (i
haven't looked at how EGL create it's context and how we pick which
driver to use inside EGL but i guess there is some mecanism and i
think we should worry about this early as this is an important feature
for multi-GPU support).

Cheers,
Jerome