[CyberShadow]

Same, I've added a .#screenshots derivation. High up-front effort but almost zero maintenance afterwards.

Bonus: since you're generating screenshots programmatically anyway, you can generate a pair of each with your app's light/dark theme, and swap them in/out depending on prefers-color-scheme: dark. <picture> elements work in GitHub READMEs, too: https://github.com/CyberShadow/CyDo#readme

[neobrain]

+1 for this approach. For a mobile app, I made Nix spawn an ephemeral Android emulator instance for generating up-to-date screenshots, requiring no prior setup and leaving no lingering data around after running. Setting it up wasn't that high-effort in my case either; coming up with the idea was the hard part, the Nix code was one-shot by your favorite LLM.

Granted manually updating the screenshots isn't the most laborious task in the world, but the "upload-apk + take-screenshot + transfer-back-to-PC + edit" process is usually barely annoying enough that you end up almost never doing it otherwise (similar to the OP's experience in the closing paragraph).

[Landing7610]

That sounds so cool! Is the repo available anywhere?

[neobrain]

Nothing public yet, but this is the Nix output for taking the screenshot, to be executed via `nix run .#screenshot`:

        outputs.apps.x86_64.screenshot = {
          type = "app";
          program = toString (pkgs.writeShellScript "screenshot-script" ''
            set -euo pipefail

            EMU_SDK="${androidEmulatorComposition.androidsdk}/libexec/android-sdk"
            ADB="$EMU_SDK/platform-tools/adb"
            EMULATOR="$EMU_SDK/emulator/emulator"
            APK="${self.packages.${system}.debug}/myapp-debug.apk"

            SRC_DIR="$(${pkgs.git}/bin/git rev-parse --show-toplevel)"
            AVD_HOME="$(mktemp -d)"
            trap 'kill "$EMU_PID" 2>/dev/null; wait "$EMU_PID" 2>/dev/null; rm -rf "$AVD_HOME"' EXIT

            # Create AVD
            AVD_DIR="$AVD_HOME/screenshot.avd"
            mkdir -p "$AVD_DIR"
            cat > "$AVD_HOME/screenshot.ini" <<EOF
            avd.ini.encoding=UTF-8
            path=$AVD_DIR
            target=android-${platformVersion}
            EOF
            cat > "$AVD_DIR/config.ini" <<EOF
            AvdId=screenshot
            PlayStore.enabled=false
            abi.type=x86_64
            avd.ini.encoding=UTF-8
            hw.cpu.arch=x86_64
            hw.gpu.enabled=yes
            hw.gpu.mode=swiftshader_indirect
            hw.lcd.density=420
            hw.lcd.height=2400
            hw.lcd.width=1080
            hw.ramSize=2048
            image.sysdir.1=system-images/android-${platformVersion}/google_apis/x86_64/
            skin.dynamic=yes
            tag.display=Google APIs
            tag.id=google_apis
            disk.dataPartition.size=2G
            EOF

            echo "==> Starting emulator..."
            ANDROID_AVD_HOME="$AVD_HOME" ANDROID_HOME="$EMU_SDK" \
              "$EMULATOR" -avd screenshot -no-window -no-audio -no-boot-anim \
              -gpu swiftshader_indirect -no-snapshot 2>&1 &
            EMU_PID=$!

            echo "==> Waiting for boot..."
            for i in $(seq 1 90); do
              BOOT=$("$ADB" shell getprop sys.boot_completed 2>/dev/null | tr -d '\r') || true
              if [ "$BOOT" = "1" ]; then
                echo "    Booted after ~$((i * 2))s"
                break
              fi
              sleep 2
            done
            if [ "$BOOT" != "1" ]; then
              echo "ERROR: Emulator failed to boot" >&2
              exit 1
            fi

            # Enable dark mode
            "$ADB" shell cmd uimode night yes

            # Install and launch
            echo "==> Installing APK..."
            "$ADB" install -r "$APK"
            "$ADB" shell pm grant com.me.myapp android.permission.WRITE_SECURE_SETTINGS
            "$ADB" shell am start -n com.me.myapp/.MainActivity
            sleep 3

            # Navigate to settings screen by tapping "Notification Filters" button
            # This uses uiautomator to find the button by text for robustness
            "$ADB" shell uiautomator dump /sdcard/ui.xml
            BOUNDS=$("$ADB" shell cat /sdcard/ui.xml \
              | ${pkgs.gnugrep}/bin/grep -oP 'text="Notification Filters"[^>]*bounds="\K[^"]+' \
              || true)
            if [ -z "$BOUNDS" ]; then
              echo "ERROR: Could not find Notification Filters button" >&2
              exit 1
            fi
            # Parse bounds "[x1,y1][x2,y2]" to compute center tap coordinates
            X1=$(echo "$BOUNDS" | ${pkgs.gnused}/bin/sed 's/\[\([0-9]*\),\([0-9]*\)\]\[\([0-9]*\),\([0-9]*\)\]/\1/')
            Y1=$(echo "$BOUNDS" | ${pkgs.gnused}/bin/sed 's/\[\([0-9]*\),\([0-9]*\)\]\[\([0-9]*\),\([0-9]*\)\]/\2/')
            X2=$(echo "$BOUNDS" | ${pkgs.gnused}/bin/sed 's/\[\([0-9]*\),\([0-9]*\)\]\[\([0-9]*\),\([0-9]*\)\]/\3/')
            Y2=$(echo "$BOUNDS" | ${pkgs.gnused}/bin/sed 's/\[\([0-9]*\),\([0-9]*\)\]\[\([0-9]*\),\([0-9]*\)\]/\4/')
            TAP_X=$(( (X1 + X2) / 2 ))
            TAP_Y=$(( (Y1 + Y2) / 2 ))
            "$ADB" shell input tap "$TAP_X" "$TAP_Y"
            sleep 2

            # Capture and process screenshot
            echo "==> Capturing screenshot..."
            "$ADB" shell screencap -p /sdcard/screenshot.png
            "$ADB" pull /sdcard/screenshot.png "$AVD_HOME/raw.png"

            # Crop to content: remove status bar (top 128px) and empty space below
            # Per-App Overrides, then resize with high-quality Lanczos filter
            ${pkgs.imagemagick}/bin/magick "$AVD_HOME/raw.png" \
              -crop 1080x1100+0+128 +repage \
              -filter Lanczos -resize 540x \
              "$SRC_DIR/fastlane/metadata/android/en-US/images/phoneScreenshots/settings.png"

            echo "==> Screenshot saved to fastlane/metadata/android/en-US/images/phoneScreenshots/settings.png"
          '');
        };

[9dev]

The <picture> in README trick works like magic. Thank you! I'm going to steal it.