GBM ES2 Demo

• Example OpenGL ES2 demo using GBM and DRM (KMS) modesetting
• This shows how ChromeOS renders GLES2 contents on the screen.
• It uses OpenGL ES2/3 without X11 dependency, so it fits pretty good with the embedded devices world.

Build

• If you are on Ubuntu, first make sure you have the dependencies installed

> sudo apt-get install libgles2-mesa-dev libgbm-dev

> mkdir build; cd build
> cmake ../
> make

Run

• I have successfully ran it on Ubuntu, ChromeOS and Yocto.

Ubuntu

• Go to tty1 with Ctrl + Alt + F1
• Kill gdm or lightdm because they are DRM master now. This demo has to be DRM master.

> sudo service lightdm stop

• Run the demo

> gbm_es2_demo
or
> gbm_es2_demo -M # mmap test

Yocto

• The easiest way to build embedded linux image is to use Yocto.
• I make Yocto recipes to make standalone emebeded OpenGL ES2 demo image.
• Check Yocto GBM ES2 Demo
• Enjoy building Linux image from the scratch.

Demo detail

gbm_es2_demo

• Show how to glue DRM, GBM and EGL
• Show how to swap buffer and vsync
• Show how to implement GLES2 app

gbm_es2_demo -M

• Same to gbm_es2_demo except for updating cube surface using dma_buf mmap
• It's very nice demo to show how Chromium zero-copy texture upload works. Chromium doesn't use glTexImage2D to update texture thank to new dma_buf mmap API. For more Chromium detail, check the chrome issue
• After Linux kernel v4.6, you can use following code. (currently only Intel Architecture supports it)
• Tiago Vignatti made this change in kernel.

  void* data = mmap(dma_buf_fd)
  update contents on |data|
  munmap(data)

Code style

• The style complying with Chromium’s style guide
• Before submitting a patch, always run clang-format

> clang-format-5.0 -i `find . -name "*.cpp" -o -name "*.h"`

Reference

• overview by jbarnes
• My mesa-demo
• My ChromeOS dma-test demo
• greatest drm tutorial by dvdhrm
• kmscube by robclark