I have a picture (jpg) that I want to display on the screen. Additionally the picture should be covered partially by a transparent effect. The transparent cover should be dynamic. So e.g. each day more of the picture is shown. Here a picture to show what I mean: 
I have the picture without the gray cover and want to add this cover but in different steps.
Can someone give me a hint how to do that.
You can do this simply with widgets:
FrameLayout is the general mechanism for overlaying a view on top of another:
<?xml version="1.0" encoding="utf-8"?> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="wrap_content" android:layout_height="wrap_content"> <ImageView android:id="@+id/image" android:layout_width="wrap_content" android:layout_height="wrap_content" android:src="@drawable/my_image"/> <View android:id="@+id/overlay" android:layout_width="fill_parent" android:layout_height="fill_parent"/> </FrameLayout> Then in your Java code you can dynamically set the transparency of your overlay:
View overlay = (View) findViewById(R.id.overlay); int opacity = 200; // from 0 to 255 overlay.setBackgroundColor(opacity * 0x1000000); // black with a variable alpha FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(FrameLayout.LayoutParams.FILL_PARENT, 100); params.gravity = Gravity.BOTTOM; overlay.setLayoutParams(params); overlay.invalidate(); // update the view You can do something like this where the canvas is coming from an onDraw() request:
Paint paint = new Paint(); Rect r = new Rect(); paint.setColor(0x80808080); // translucent gray r.right = iDisplayWidth-1; r.left = 0; r.top = iDisplayHeight/2; r.bottom = iDisplayHeight-1; canvas.drawRect(r, paint); // fill with gray