null-dev / tt

egui port to Car Thing (and maybe an alternative Car Thing UI?)

tt

This project contains a port of egui to the Spotify Car Thing although in the future I also plan for it to contain a custom Car Thing UI.

Technical information

• Display/Touchscreen:
  • It's actually a portrait touchscreen
    • Seems like no way to rotate in hardware:
      • /sys/class/graphics/fb0/rotate doesn't seem to work
      • /sys/class/graphics/fb0/osd_reverse only flips/mirrors it (so it doesn't help either)
  • echo 1 > /sys/class/graphics/fb0/osd_clear can be used to clear the display
• A branch of winit with KMS/DRM is used:
  • The KMS/DRM portion of the branch is not actually being used because the Car Thing doesn't support KMS/DRM.
    • The Car Thing supports FBDev instead (but I don't actually use that either, I use EGL directly)
  • Instead, it is being used because it supports libinput.
  • Other changes:
    • needed to config a custom calibration matrix in libinput to rotate the touchscreen
    • libinput Touch::Frame event is ignored (in the original implementation it was mapped to TouchEnd which doesn't make sense, that's not what it means)
    • xkb_compose is disabled, it caused runtime errors and we don't need it on the Car Thing anyways cause it doesn't have a keyboard
• I have forked egui:
  • egui_glow rendering backend is used
    • OpenGL shader had to be modified to rotate everything (cause the touchscreen is rotated)
    • Calls to glViewport and glScissor has to be modified to be rotated as well
    • Custom rendering is still broken, I'm not sure how to fix that as I don't think there is a way to tell OpenGL to rotate everything rendered by custom renderers.
      • Maybe have custom renderers render to an intermediate buffer and then rotate that when copying it to the output framebuffer?
• I have forked glutin:
  • A modification of the Android backend is used because it is similar to the graphical config of the Car Thing
  • KMS/DRM support is NOT used because again, the Car Thing is more similar to Android in that respect
• buildroot.sh builds and deploys the program using my Car Thing buildroot
  • You will probably have to modify it so it uses the correct paths and adb