How to use OpenGL via SDL2?

Question

I am looking for a "Hello World" type example that makes use of OpenGL-ES2 via SDL2. So far I could gather:

• SDL2 that ships with Raspbian does not support OpenGL-ES2 out of the box
• SDL-2.0.3 manually compiled from source should support OpenGL-ES2 in theory

However even with a manually compiled SDL-2.0.3 I can't get OpenGL-ES2 to work, the displays goes black, so something is working, but even a simple glClearColor()/glClear() doesn't have any effect. The same code via EGL or run via OpenGL on a desktop computer however works as expected.

Source code is available at: https://github.com/Grumbel/rpi-opengl

Answer 1

The problem turned out to not be in the code, but in the library path. A simple -L/opt/vc/lib/ added to the compile command line fixed it. Without that the compiler would pick:

/usr/lib/arm-linux-gnueabihf/libGLESv2.so.2

While the right one would be (use ldd to check):

/opt/vc/lib/libGLESv2.so

Answer 2

On my RPI the file /opt/vc/lib/libGLESv2.so does not exist. And libGLESv2.so gives me a blank screen.

Found that linking to this file works: /opt/vc/lib/libbrcmGLESv2.so.

In order to compile a small program with both SDL2 and GLES I needed this command line:

g++ -o gltest gltest.cpp -L/opt/vc/lib `sdl2-config --libs` -lbrcmGLESv2