Add a dimmer and change screen brightness on android like twilight app

Question

I want to add a dimmer to device screen and filters the flux of light like the twilight app
The result look like this:

I'm looking for the APIs, example code or documents to achieve it. At the moment, I just know how to change the brightness programmatically on android.
Is there any suggestion?

Answer 1

To achieve this result you need to create a window, using the type TYPE_SYSTEM_ALERT and show it on top of all other apps. To do so you need the permission SYSTEM_ALERT_WINDOW:

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

Then create a new layout with the desired background color:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#FF4081"
    android:orientation="vertical">
</LinearLayout>

And a Service:

public class DrawOverAppsService extends Service {

    public static final String TAG = "DrawOverAppsService";

    private View mOverlayView;

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate() {
        super.onCreate();

        Log.d(TAG, "onCreate");

        WindowManager.LayoutParams params = new WindowManager.LayoutParams(
                WindowManager.LayoutParams.MATCH_PARENT,
                WindowManager.LayoutParams.MATCH_PARENT,
                WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY,
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE |
                        WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL |
                        WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN |
                        WindowManager.LayoutParams.FLAG_DIM_BEHIND,
                PixelFormat.TRANSLUCENT);

        // An alpha value to apply to this entire window.
        // An alpha of 1.0 means fully opaque and 0.0 means fully transparent
        params.alpha = 0.1F;

        // When FLAG_DIM_BEHIND is set, this is the amount of dimming to apply.
        // Range is from 1.0 for completely opaque to 0.0 for no dim.
        params.dimAmount = 0.8F;

        WindowManager wm = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
        LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        mOverlayView = inflater.inflate(R.layout.overlay_view, null);

        wm.addView(mOverlayView, params);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();

        Log.d(TAG, "onDestroy");

        WindowManager wm = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
        wm.removeView(mOverlayView);
    }
}

To display the overlay start the service with:

Intent intent = new Intent(this, DrawOverAppsService.class);
startService(intent);

And stop the overlay with:

Intent intent = new Intent(this, DrawOverAppsService.class);
stopService(intent);