Question

I just started writing a live wallpaper.

What I would like to do is to set the background to a bitmap from my resources. And I will draw my animations on top of this.

What is the most efficient way to do this? Is there a way to set the background to a bitmap in a live wallpaper? Do I just need to draw the bitmap into the canvas each time before I draw my animations (which seems like it might be hideously inefficient)?

thanks,

Jay

Answer 1

This is what I found.

From the eclipse graphic documentation:

Note: On each pass you retrieve the Canvas from the SurfaceHolder, the previous state of the Canvas will be retained. In order to properly animate your graphics, you must re-paint the entire surface. For example, you can clear the previous state of the Canvas by filling in a color with drawColor() or setting a background image with drawBitmap(). Otherwise, you will see traces of the drawings you previously performed

So the code I used is as follows:

in onCreate()
mBitmapBase = BitmapFactory.decodeResource(getResources(), R.drawable.bidBackground);

in onSurfaceChanged()
// size the background bitmap so it draws efficiently
mBitmapBackground = Bitmap.createScaledBitmap(mBitmapBackground, xMax, yMax, true);

and in Run()
try
{
canvas = sHolder.lockCanvas();
if (canvas != null)
canvas.drawBitmap(mBitmapBackground, 0, 0, null);

As far as I can tell this is as efficient as it can get. Although if anybody can correct me on this I would love to hear it.