How to clip and fill a canvas using an alpha mask

Posted by Jay Koutavas on Stack Overflow See other posts from Stack Overflow or by Jay Koutavas
Published on 2010-01-09T02:49:20Z Indexed on 2012/06/13 4:40 UTC
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I have some .png icons that are alpha masks. I need to render them as an drawable image using the Android SDK.

On the iPhone, I use the following to get this result, converting the "image" alpha mask to the 'imageMasked' image using black as a fill:

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(NULL, thumbWidth, 
    thumbHeight, 8, 4*thumbWidth, colorSpace, kCGImageAlphaPremultipliedFirst);
CGRect frame = CGRectMake(0,0,thumbWidth,thumbHeight);
CGContextClipToMask(context, frame, [image CGImage]);
CGContextFillRect(context, frame);

CGImageRef imageMasked = CGBitmapContextCreateImage(context);
CGContextRelease(context);

How do I accomplish the above in Android SDK?

I've started to write the following:

Drawable image = myPngImage;

final int width = image.getMinimumWidth();
final int height = image.getMinimumHeight();

Bitmap imageMasked = Bitmap.createBitmap(width,
    height, Config.ARGB_8888);
Canvas canvas = new Canvas(iconMasked);
image.draw(canvas); ???

I'm not finding how to do the clipping on imageMasked using image.

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