Surfaces are double (or even triple) buffered. You are indeed not getting in your canvas what's currently on screen but what was on screen a frame ago. The easiest way to clear the surface is to call canvas.drawColor(0, PorterDuff.Mode.CLEAR) (you can also use 0xff000000, PorterDuff.Mode.SRC).
On Sun, Nov 25, 2012 at 3:42 PM, Johan <[email protected]> wrote: > I have some strange behaviour when repainting the screen with my live > wallpaper. I'm scaling an image and drawing it to the screen, but on each > draw (as the image is scaled smaller than the previous draw), I can still > see the previous image below the new image. > How do I clear the previous image out so that only the new scaled image is > displayed? > > This is my code: > > private final Runnable mDraw = new Runnable() { > public void run() { > draw(); > } > }; > > void draw() { > SurfaceHolder holder = getSurfaceHolder(); > Canvas canvas = null; > try { > canvas = holder.lockCanvas(); > if(canvas != null) { > this.paintScreen(canvas); > } > }finally { > if(canvas != null) { > holder.unlockCanvasAndPost(canvas); > } > } > mHandler.removeCallbacks(mDraw); > if (mVisible) { > mHandler.postDelayed(mDraw, 60000); > } > } > > Every minute my paintSurface function scales a bitmap (image loaded from > resources), then uses canvas.drawBitmap to put the image on the screen. As > I understand from the documentation, holde.lockCanvas()is not supposed to > contain the image currently on the screen and every pixel has to be > drawn... this doesn't seem to be the case since the previous pixels are > obviously under the new pixels. > > Thanks, > J > (26 Sept '12 - 10:45 AM) > > -- > You received this message because you are subscribed to the Google > Groups "Android Developers" group. > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/android-developers?hl=en -- Romain Guy Android framework engineer [email protected] -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
