Add support for rotating output, on RPi 7" touch screen

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Author: troglobit

Dockerfile

@@ -37,6 +37,7 @@ RUN apk add --no-cache \
  xf86-video-modesetting \
  xf86-input-libinput \
  xdpyinfo \
+ xrandr \
  xinit
 
 WORKDIR /app

README.md

@@ -140,12 +140,32 @@ docker run --rm -it \
  /app/start.sh -d 30 0 2 6
 ```
 
+**With display rotation (e.g., RPi 7" touchscreen):**
+
+```bash
+# Rotate display 180 degrees
+docker run --rm -it \
+ --privileged \
+ -v /dev/fb0:/dev/fb0 \
+ -v /dev/tty1:/dev/tty1 \
+ -e DISPLAY_ROTATE=inverted \
+ ghcr.io/kernelkit/demo:latest
+```
+
 #### Using docker-compose
 
 ```bash
 docker compose up
 ```
 
+#### Environment Variables
+
+- **`DISPLAY_ROTATE`** - Rotate the display (values: `normal`, `left`, `right`, `inverted`)
+ - `normal` - 0° (default)
+ - `left` - 90° counter-clockwise
+ - `right` - 90° clockwise
+ - `inverted` - 180° upside down
+
 **Notes:**
 - The container automatically detects if X11 is available via `xdpyinfo`
 - With X11: Uses the host's X server

start.sh

@@ -30,6 +30,13 @@ else
  XPID=$!
  sleep 2
 
+ # Apply display rotation if requested
+ if [ -n "$DISPLAY_ROTATE" ]; then
+ echo "Applying display rotation: $DISPLAY_ROTATE"
+ OUTPUT=$(DISPLAY=:0 xrandr | grep " connected" | head -1 | cut -d' ' -f1)
+ DISPLAY=:0 xrandr --output "$OUTPUT" --rotate "$DISPLAY_ROTATE"
+ fi
+
  # Run demo in background so we can handle signals
  DISPLAY=:0 ./demo "$@" &
  DEMOPID=$!