Draw an Android canvas on top of all applications?

Question

I suspect this isn\'t possible, given the nature of Android, but is there a way to create a view of sorts (perhaps using a Canvas object?) that is shown on top of all applicatio

Answer 1

Here is what I think may work:

You will need the following values:

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

Store them in a preference after using 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 which extends the view and is used to draw the 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();
  }
}

Next write a service which is supposed to handle the changes in these values and apply them to the windows.

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

//Declare views for applying the values that are stored in Prefs private static Layer view; ... 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 values previously stored in preferences,

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 for setting the retrieved 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 wherever 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);

Don't forget to declare your service in the Manifest xml file

I might have missed a thing or two as I did this on the fly, but I think this should do it.