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/**
* Creates a 'ghost' bitmap version of the given source drawable (ideally a BitmapDrawable).
* In the ghost bitmap, the RGB values take on the values from the 'color' argument, while
* the alpha values are derived from the source's grayscaled RGB values. The effect is that
* you can see through darker parts of the source bitmap, while lighter parts show up as
* the given color. The 'invert' argument inverts the computation of alpha values, and looks
* best when the given color is a dark.
*/
private Bitmap createGhostIcon(Drawable src, int color, boolean invert) {
int width = src.getIntrinsicWidth();
int height = src.getIntrinsicHeight();
if (width <= 0 || height <= 0) {
throw new UnsupportedOperationException("Source drawable needs an intrinsic size.");
}
Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
Paint colorToAlphaPaint = new Paint();
int invMul = invert ? -1 : 1;
colorToAlphaPaint.setColorFilter(new ColorMatrixColorFilter(new ColorMatrix(new float[]{
0, 0, 0, 0, Color.red(color),
0, 0, 0, 0, Color.green(color),
0, 0, 0, 0, Color.blue(color),
invMul * 0.213f, invMul * 0.715f, invMul * 0.072f, 0, invert ? 255 : 0,
})));
canvas.saveLayer(0, 0, width, height, colorToAlphaPaint, Canvas.ALL_SAVE_FLAG);
canvas.drawColor(invert ? Color.WHITE : Color.BLACK);
src.setBounds(0, 0, width, height);
src.draw(canvas);
canvas.restore();
return bitmap;
}
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