rpi-opengl-without-x | Raspberry Pi OpenGL ES 2 without an X server

Your EGL might be faulty! Make sure you are using the libraries provided by Raspbian and not the ones installed through apt-get or other package managers. Use the ones in the /opt/vc/lib folder. If that does not work, try reinstalling your Raspberry Pi OS. Find pbufferAttribs and change EGL_WIDTH and EGL_HEIGHT. Some GL functions may not come from GLES library. You may need to get GL1 library by executing sudo apt-get install libgl1-mesa-dev and then simply add: -lGL flag to the linker, so you get: gcc -o triangle triangle.o -lbrcmEGL -lbrcmGLESv2 -lGL -L/opt/vc/lib. Find configAttribs at the top of the triangle.c file and modify the attributes you need. All config attributes are located here https://www.khronos.org/registry/EGL/sdk/docs/man/html/eglChooseConfig.xhtml. You should not, but you can. However, it seems that OpenGL ES does not like that and nothing will be rendered. For this you will need to link the GL library as well. Simply, add -lGL to the gcc command.