SDL2, RPi CM4, Multiple Displays [no X]

Hi there!

I’m using SDL2 2.0.16 on a RPi 4 (CM4) in a buildroot (not RaspberryPi OS) with and my app is using OpenGLES and kmsdrm (without X), and SDL_GetNumVideoDisplays(); always returns 1, where the CM4 has 2 HDMI ports.

HDMI0 shows my app and that works great, but HDMI1 always shows the linux console FB.

Is there a way I can use the second port, either in an extended mode or by a second process?

I’m probably doing something basically wrong, I’m very much a SDL and GL novice and working of a modified version of the Dear ImGui SDL2 backend.

Any help or pointers would be appreciated.