Better frame rate drawing bitmaps in a Canvas?

Question

I'm shooting for an animation in a live wallpaper. Here's the code. It pretty much follows the CubeWallpaper demo:

    void drawFrame() {
        final SurfaceHolder holder = getSurfaceHolder();
    final BufferedInputStream buf;
    final Bitmap bitmap, rbitmap;

        Canvas c = null;
        try {
            c = holder.lockCanvas();
            if (c != null) {
        try {
        buf = new 
            BufferedInputStream(assets.
                    open(folder+"/"
                         +imageList[ilen++])
                    );
        bitmap = BitmapFactory.
            decodeStream(buf);
        rbitmap = Bitmap.createBitmap
            (bitmap,
             0,0,imageWidth,imageHeight,
             transMatrix,false);
        c.drawBitmap(rbitmap,
                 paddingX,
                 paddingY,
                 null);
        if ( ilen >= imageCount ) ilen=0;
        }
        catch (Exception e) { e.printStackTrace(); }
            }
        } finally {
            if (c != null) holder.unlockCanvasAndPost(c);
        }

        // Reschedule the next redraw
        mHandler.removeCallbacks(mDrawCube);
        if (mVisible) {
            mHandler.postDelayed(mDrawCube, fps);
        }
    }

where "transMatrix" is a scaling and rotation matrix predefined before.

It's supposed to render at 30fps but of course it doesn't do that. My initial guess is that the BufferedInputStream is one factor. I should probably cache a few of these as I go along along with the Bitmaps. But any other ideas? Will I have to use the OpenGL hack for live wallpapers?

Answer 1

Yes, the BufferedInputStream and BitmapFactory really shouldn't be in drawFrame() at all. You're loading and creating resources on every single frame, and that's a huge waste. Like you said, cache as many as you can beforehand, and if you find the need to load more during drawing, use a separate thread to do it so it doesn't slow the drawing.