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Apply a radial mask vignette to a bitmap using PorterDuffXfermode

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/**
 * Apply a radial mask (vignette, i.e. fading to black at the borders) to a bitmap
 * @param imageToApplyMaskTo Bitmap to modify
 */
public static void radialMask(final Bitmap imageToApplyMaskTo) {
    Canvas canvas = new Canvas(imageToApplyMaskTo);

    final float centerX = imageToApplyMaskTo.getWidth() * 0.5f;
    final float centerY = imageToApplyMaskTo.getHeight() * 0.5f;
    final float radius = imageToApplyMaskTo.getHeight() * 0.7f;

    RadialGradient gradient = new RadialGradient(centerX, centerY, radius,
            0x00000000, 0xFF000000, android.graphics.Shader.TileMode.CLAMP);

    Paint p = new Paint();
    p.setShader(gradient);
    p.setColor(0xFF000000);
    p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
    canvas.drawRect(0, 0, imageToApplyMaskTo.getWidth(), imageToApplyMaskTo.getHeight(), p);
}
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PorterDuff Mode:
* PorterDuff Mode
* Creating a PorterDuff ColorFilter
* Creating a PorterDuff XferMode
* Apply a radial mask vignette to a bitmap using PorterDuffXfermode
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