bitmap not displaying in android

Question

I have the following code;

@Override
public void run()
{
    tickCount = 0L;
    Log.d(TAG, "Starting game loop");
    while (running)
    {

        try
        {
            gameCanvas = surfaceHolder.lockCanvas();
            synchronized (surfaceHolder)
            {
                // Log.d(TAG, tickCount + " ticks so far");
                tickCount++;
                updateGameState();

                render(gameCanvas);
            }
        } finally
        {
            if (gameCanvas != null)
            {
                // 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
                    surfaceHolder.unlockCanvasAndPost(gameCanvas);
            }
        }
    }
}

The problem I am having is when I test the application the bitmap doesnt display. I have tried copying a drawable using and using setBitmap.

eg.

mutableBackground = backgroundImage.copy(Bitmap.Config.ARGB_8888, true);

where backgroundImage is a decoded drawable resource.

and..

    mutableBackground = Bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);
    gameCanvas = new Canvas();
    gameCanvas.setBitmap(mutableBackground);
    gameCanvas.drawColor(Color.GREEN);

and..

gameCanvas = new Canvas(mutableBackground);

If I draw a line in the render method, it does indeed draw.. but on a black background. Strangely enough if I do

int myColor = mutableBackground.getPixel(100, 100);
    int greeness = Color.green(myColor);;
    Log.d(TAG, "Greeness - " + greeness);

The log shows.. Greeness - 255

So the bitmap is being colored green but it displays as black. This is really confusing me and I have to sort this out real soon.

Thanks anybody that can help.

George Freeman · Accepted Answer · 2011-05-17 15:44:16Z

1

This is a little bit outside my normal ken, but since no one else has answered, I will take a stab. :-)

When you draw this way (i.e. with surfaceHolder.lockCanvas) you need to work with the canvas you get...you cannot just create a new canvas and send that to unlockCanvasAndPost. Nor should you, under normal circumstances, futz with the canvas's underlying bitmap. In your render function, why don't you just draw into the canvas (first the color for the background, or even a whole bitmap, and then whatever else you need). For example, something like:

render(Canvas c) {
    c.drawColor(Color.GREEN);
    c.drawBitmap(sprite, x, y, null);
}

answered May 17, 2011 at 15:44

George Freeman

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2 Comments

Finn Over a year ago

Thanks. I thought I was doing it wrong by sending the canvas my own bitmap. Just couldnt figure out a way to reference it afterwards.

George Freeman Over a year ago

@Finn I'm glad we resolved your issue; thank you for taking the time to accept my answer. :-) Android animation is not trivial...I have found it helpful to use sample code as a point of departure whenever possible. Off the top my head, the closest thing I can think of to what you have shown is the Lunar Lander example in the SDK. Good luck!

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