[osg-users] OSG and OpenGL ES 2.0

Robert Osfield robert.osfield at gmail.com
Mon Apr 18 02:16:42 PDT 2011


Hi Ankur,

On Sat, Apr 16, 2011 at 10:40 AM, Ankur Gandhi <ank.gandhi at tcs.com> wrote:
> You are right. both are quire different. I ported OSG over OpenGL ES 2.0 and everything is behaving in different way. I guess I almost need to rewrite my OpenGL application. Also i think i need to go through ShaderGen to understand how well the OpenGL application gets converted to GLSL language.

The big difference with GLES2 is that there is no fixed function
pipeline so you have to provide shaders yourself.  This situtation is
the same for the GL 3.x and beyond profiles where backwards
compatability is dropped, so it's in't really a case of GL vs GLES2,
rather it's GL1/GLES1 fixed function vs GL3/GL4/GLES2 shader based,
with GL2 sitting on the fence - doing both fixed function and shaders.

You can also used shaders entirely with GL2, and even your the CMake
to build only the shader backends, and not implement the fixed
function state, so replicate much of what it takes to program GLES2
entirely on a machine with only GL2 available.  This approach also
allows you to build final applications that will more easily port
between desktop and GLES2 targets.

Robert.



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