This is a simple example of doing graphics without X11 on the pi4. it is a simplied version of the well known triangle[_rpi4].c with some additional improvements for robustness.

The raspberry Pi 4, at the moment of writing this, has a limited KMS driver, and a buggy "fake" kms driver. This is because the GPU is different from the previous ones. Instead of using the vc libraries, you will need to use the DRM/GBM.

What do I need?

You need a GCC compiler, GDM, EGL, and GLES libraries. The GCC compiler is already included in the Raspbian image. To install the other libraries, simply run:

sudo apt-get install libegl1-mesa-dev libgbm-dev libgles2-mesa-dev

You will also need to connect your Raspberry Pi to a screen. The boot config from /boot/config.txt that I have used for my tests, if it helps in any way:

dtoverlay=vc4-fkms-v3d
max_framebuffers=2
hdmi_force_hotplug=1
hdmi_group=2
hdmi_mode=81

How do I try it?

Copy or download the triangle_rpi4.c file onto your Raspberry Pi. Using any terminal, write the following commands to compile the source file:

gcc -o triangle_rpi4 triangle_rpi4.c -ldrm -lgbm -lEGL -lGLESv2 -I/usr/include/libdrm -I/usr/include/GLES2

To run the executable, type the following:

./triangle_rpi4

You should see the following output:

/dev/dri/card0 not supporting DRM, trying card1, resolution: 3840x2160
Initialized EGL version: 1.4
GL Viewport size: 3840x2160

The program will briefly show the following full screen:

Failed to get EGL version! Error:

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.

I get "Error! The glViewport/glGetIntegerv are not working! EGL might be faulty!" What should I do?

Same as above.

How do I change the pixelbuffer resolution?

Find pbufferAttribs and change EGL_WIDTH and EGL_HEIGHT.

I get "undefined reference" on some gl functions!

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

How do I change the buffer sample size or the depth buffer size or the stencil size?

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

Can I use glBegin() and glEnd()?

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.

Do whatever you want.

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