Fix AppImage runtime and Docker multi-arch builds

- AppImage: Download and prepend proper AppImage runtime instead of
  creating raw squashfs files, fixing "Exec format error"
- Docker: Build both platforms in single job to create proper
  multi-arch manifest instead of overwriting tags
- Add wget dependency for AppImage runtime download

Signed-off-by: Joachim Wiberg <[email protected]>

Author: troglobit

.github/workflows/build.yml

@@ -32,14 +32,14 @@ jobs:
               -v $PWD:/workspace -w /workspace \
               ubuntu:22.04 /bin/bash -c '
                 apt-get update && \
-                apt-get install -y xxd libsdl2-dev libsdl2-ttf-dev \
+                apt-get install -y xxd wget libsdl2-dev libsdl2-ttf-dev \
                   libsdl2-image-dev libsdl2-mixer-dev build-essential squashfs-tools && \
                 make clean && make && \
                 ./utils/build-appimage.sh aarch64
               '
           else
             sudo apt-get update
-            sudo apt-get install -y libsdl2-dev libsdl2-ttf-dev \
+            sudo apt-get install -y wget libsdl2-dev libsdl2-ttf-dev \
               libsdl2-image-dev libsdl2-mixer-dev squashfs-tools
             make clean && make
             ./utils/build-appimage.sh x86_64
@@ -56,9 +56,6 @@ jobs:
     permissions:
       contents: read
       packages: write
-    strategy:
-      matrix:
-        platform: [linux/amd64, linux/arm64]
 
     steps:
       - uses: actions/checkout@v4
@@ -89,7 +86,7 @@ jobs:
         uses: docker/build-push-action@v5
         with:
           context: .
-          platforms: ${{ matrix.platform }}
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}

utils/build-appimage.sh

@@ -42,12 +42,21 @@ EOF
 
 chmod +x AppDir/AppRun
 
-# Create AppImage using mksquashfs
+# Download AppImage runtime for the target architecture
+RUNTIME_URL="https://github.com/AppImage/AppImageKit/releases/download/continuous/runtime-${ARCH}"
+echo "Downloading AppImage runtime for ${ARCH}..."
+wget -q -O runtime "${RUNTIME_URL}"
+
+# Create squashfs filesystem
+echo "Creating squashfs filesystem..."
+mksquashfs AppDir filesystem.squashfs -root-owned -noappend
+
+# Combine runtime + squashfs to create proper AppImage
 echo "Creating ${APPIMAGE_NAME}..."
-mksquashfs AppDir "${APPIMAGE_NAME}" -root-owned -noappend
+cat runtime filesystem.squashfs > "${APPIMAGE_NAME}"
 chmod +x "${APPIMAGE_NAME}"
 
 # Cleanup
-rm -rf AppDir
+rm -rf AppDir runtime filesystem.squashfs
 
 echo "AppImage created: ${APPIMAGE_NAME}"