I can't believe no one has answered this yet! A rare occurrence on SO!

1

The question doesn't quite make sense to me. But I'll give it a stab.If you're asking about direct drawing to a canvas (polygons, shading, text etc...) vs. loading a bitmap and blitting it onto the canvas that would depend on the complexity of your drawing. As the drawing gets more complex the CPU time required will increase accordingly.However, blitting a bitmap onto a canvas will always be a constant time which is proportional to the size of the bitmap.

2

Without knowing what "something" is how can I show you how to do it?You should be able to figure out #2 from the answer for #3.

3

Assumptions:

• bmp1 is larger than bmp2.

• You want them both overlaid from the top left corner.

      private Bitmap overlay(Bitmap bmp1, Bitmap bmp2) {        Bitmap bmOverlay = Bitmap.createBitmap(bmp1.getWidth(), bmp1.getHeight(), bmp1.getConfig());        Canvas canvas = new Canvas(bmOverlay);        canvas.drawBitmap(bmp1, new Matrix(), null);        canvas.drawBitmap(bmp2, new Matrix(), null);        return bmOverlay;    }

You can do something like this:

public void putOverlay(Bitmap bitmap, Bitmap overlay) {    Canvas canvas = new Canvas(bitmap);    Paint paint = new Paint(Paint.FILTER_BITMAP_FLAG);    canvas.drawBitmap(overlay, 0, 0, paint);} 

The idea is very simple: Once you associate a bitmap with a canvas, you can call any of the canvas' methods to draw over the bitmap.

This will work for bitmaps that have transparency. A bitmap will have transparency, if it has an alpha channel. Look at Bitmap.Config. You'd probably want to use ARGB_8888.

Important: Look at this Android sample for the different ways you can perform drawing. It will help you a lot.

Performance wise (memory-wise, to be exact), Bitmaps are the best objects to use, since they simply wrap a native bitmap. An ImageView is a subclass of View, and a BitmapDrawable holds a Bitmap inside, but it holds many other things as well. But this is an over-simplification. You can suggest a performance-specific scenario for a precise answer.

public static Bitmap overlayBitmapToCenter(Bitmap bitmap1, Bitmap bitmap2) {    int bitmap1Width = bitmap1.getWidth();    int bitmap1Height = bitmap1.getHeight();    int bitmap2Width = bitmap2.getWidth();    int bitmap2Height = bitmap2.getHeight();    float marginLeft = (float) (bitmap1Width * 0.5 - bitmap2Width * 0.5);    float marginTop = (float) (bitmap1Height * 0.5 - bitmap2Height * 0.5);    Bitmap overlayBitmap = Bitmap.createBitmap(bitmap1Width, bitmap1Height, bitmap1.getConfig());    Canvas canvas = new Canvas(overlayBitmap);    canvas.drawBitmap(bitmap1, new Matrix(), null);    canvas.drawBitmap(bitmap2, marginLeft, marginTop, null);    return overlayBitmap;}