Draw an Android canvas on top of all apps?

Question

I suspect this is not possible given the nature of Android, but is there a way to create a representation of types (perhaps using a Canvas object?) That appears on top of all applications?

My intention for this project is not malicious. I created some simple Color Filter software for Windows, which simply adds a window on top of all the windows, which is filled with a user-selected color and has low opacity. This adds a touch of light to the screen, which helps users with Scoptopic Sensitivity Syndrome use their computer for extended periods of time. I would like to make a version of this software for Android. For instance:

The image on the left is the original, and on the right is what I'm trying to achieve.

Is there any way to do this with Android? I understand that the application must run as a system service so that it does not stop unexpectedly, but as far as I know, there is no way to draw on the screen on top of other applications as a whole. If possible, can you suggest which APIs to learn?

Answer 1

Here is what I think might work:

You will need the following values:

Red, Green, Blue, Alpha and Contrast (r, g, b, a, c)

Save them in preference after using the sliders:

private SharedPreferences pref; //In onCreate.. this.pref = getSharedPreferences("pref", 0); //Method to save the values in Preferences private void save() { SharedPreferences.Editor localEditor = this.pref.edit(); localEditor.putInt("a", this.a); localEditor.putInt("r", this.r); localEditor.putInt("g", this.g); localEditor.putInt("b", this.b); localEditor.putInt("c", this.c); localEditor.commit(); } 

Define a layer class that extends the view and is used to draw applied values ​​on the canvas.

 import android.view.View; import android.graphics.Canvas; import android.content.Context; public class Layer extends View { private int a; private int b; private int g; private int r; public Layer(Context context){ super(context) } protected void onDraw(Canvas canvas){ super.onDraw(canvas); canvas.drawARGB(this.a, this.r, this.g, this.b); } public void setColor(int a, int r, int g, int b){ this.a = a; this.r = r; this.g = g; this.b = b; invalidate(); } } 

Then write a service that should handle changes to these values ​​and apply them to windows.

 public class ScreenAdjustService extends Service { //Handle everything here } 

// Declare views for applying values ​​that are stored in Prefs private static view of the layer; ... public static int r; public static int b; public static int g; public static int a; public static int c;

In the onCreate method

Get the values ​​previously saved in the settings,

 SharedPreferences localSharedPreferences = getSharedPreferences("pref", 0); a = localSharedPreferences.getInt("a", 0); r = localSharedPreferences.getInt("r", 0); g = localSharedPreferences.getInt("g", 0); b = localSharedPreferences.getInt("b", 0); c = localSharedPreferences.getInt("c", 0); 

set views to set the resulting values,

 view = new Layer(this); redView = new Layer(this); ... 

Add these views to the window.

 //Pass the necessary values for localLayoutParams WindowManager.LayoutParams localLayoutParams = new WindowManager.LayoutParams(...); WindowManager localWindowManager = (WindowManager)getSystemService("window"); localWindowManager.addView(view, localLayoutParams); localWindowManager.addView(redView, localLayoutParams); localWindowManager.addView(greenView, localLayoutParams); 

Write reusable methods

 public static void setAlpha(int alpha){ //Handle all conditions view.setColor(alpha, 0, 0, 0); } public static void setContrast(int contrast){ //Handle all conditions view.setColor(c, 100, 100, 100); } public static void setRGB(int r, int g, int b){ //Handle all conditions redView.setColor(r, 255, 0, 0); greenView.setColor(g, 0, 255, 0); blueView.setColor(b, 0, 0, 255); } 

Call these methods where necessary using the service class.

 ScreenAdjustService.setRGB(MyActivity.this.r, MyActivity.this.g, MyActivity.this.b); ScreenAdjustService.setAlpha(MyActivity.this.a); ScreenAdjustService.setContrast(MyActivity.this.c); 

Remember to declare your service in the manifest XML file

 <service android:name=".ScreenAdjustService " /> 

Maybe I missed something because I did it on the fly, but I think it should do it.