How to update off screen bitmap in a surfaceview thread
- by DKDiveDude
I have a Surfaceview thread and an off canvas texture bitmap that is being generated (changed), first row (line), every frame and then copied one position (line) down on regular surfaceview bitmap to make a scrolling effect, and I then continue to draw other things on top of that. Well that is what I really want, however I can't get it to work even though I am creating a separate canvas for off screen bitmap. It is just not scrolling at all.
I other words I have a memory bitmap, same size as Surfaceview canvas, which I need to scroll (shift) down one line every frame, and then replace top line with new random texture, and then draw that on regular Surfaceview canvas.
Here is what I thought would work;
My surfaceChanged where I specify bitmap and canvasses and start thread:
@Override
public void surfaceCreated(SurfaceHolder holder) {
intSurfaceWidth = mSurfaceView.getWidth();
intSurfaceHeight = mSurfaceView.getHeight();
memBitmap = Bitmap.createBitmap(intSurfaceWidth, intSurfaceHeight,
Bitmap.Config.ARGB_8888);
memCanvas = new Canvas(memCanvas);
myThread = new MyThread(holder, this);
myThread.setRunning(true);
blnPause = false;
myThread.start();
}
My thread, only showing essential middle running part:
@Override
public void run() {
while (running) {
c = null;
try {
// Lock canvas for drawing
c = myHolder.lockCanvas(null);
synchronized (mSurfaceHolder) {
// First draw off screen bitmap to off screen canvas one line down
memCanvas.drawBitmap(memBitmap, 0, 1, null);
// Create random one line(row) texture bitmap
memTexture = Bitmap.createBitmap(imgTexture, 0, rnd.nextInt(intTextureImageHeight), intSurfaceWidth, 1);
// Now add this texture bitmap to top of off screen canvas and hopefully bitmap
memCanvas.drawBitmap(textureBitmap,
intSurfaceWidth, 0, null);
// Draw above updated off screen bitmap to regular canvas, at least I thought it would update (save changes) shifting down and add the texture line to off screen bitmap the off screen canvas was pointing to.
c.drawBitmap(memBitmap, 0, 0, null);
// Other drawing to canvas comes here
} finally {
// do this in a finally so that if an exception is thrown
// during the above, we don't leave the Surface in an
// inconsistent state
if (c != null) {
myHolder.unlockCanvasAndPost(c);
}
}
}
}
For my game Tunnel Run.
Right now I have a working solution where I instead have an array of bitmaps, size of surface height, that I populate with my random texture and then shift down in a loop for each frame. I get 50 frames per second, but I think I can do better by instead scrolling bitmap.
