I am implementing layers in a 2D engine of mine and I would like layers to be stackable, and I would also like a feature to 'cut holes' in layers - this means using alpha. However when writing it standalone I can't seem to get anything to use true alpha, it tried to fake it by blending colours together, for instance (my code):
BufferedImage background, foreground;
public GraphicsTest() {
background = new BufferedImage(500,500,BufferedImage.TYPE_INT_ARGB);
foreground = new BufferedImage(500,500,BufferedImage.TYPE_INT_ARGB); // Fully capable of alpha.
Random r = new Random();
int white = Color.white.getRGB();
// Draw random white dots
for (int i=0; i<500; i++) {
int
x = r.nextInt(500),
y = r.nextInt(500);
background.setRGB(x, y, white);
}
}
@Override
protected void paintComponent(Graphics g) {
BufferedImage output = new BufferedImage(500,500,BufferedImage.TYPE_INT_ARGB); // Fully capable of alpha.
Graphics2D canvas = output.createGraphics();
Graphics2D overlay = foreground.createGraphics();
canvas.drawImage(background, 0, 0, null);
overlay.setColor(Color.white);
overlay.fillRect(0, 0, 500, 500);
// Start drawing with alpha
overlay.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 1f));
overlay.setColor(new Color(0xFF000000)); // Overwrite/draw full alpha, colour doesn't matter when alpha is 100%
overlay.fillRect(100, 100, 125, 87);
//canvas.setColor(Color.red);
//canvas.fillRect(0, 0, 500, 500);
canvas.drawImage(foreground, 0, 0, null);
overlay.dispose();
canvas.dispose();
g.drawImage(output, 0, 0, null);
// Also write to a file for manual raw pixel checking
try {
// Does output a 32-bit depth image
ImageIO.write(output, "PNG", new File("c:/output.png"));
} catch (IOException e) {
e.printStackTrace();
}
}
This is the most basic test I could think of, I have two images, one for the background and one for the foreground, I am needing to see the background through the foreground in the 127x87 (random sized) box.
Currently it results in a white screen with a black box, the back box should be that part of the background.
I have tried all sorts of methods here, settings the composite and drawing black with full alpha but when combined I never see the background, the setColor(0xFF000000) doesn't seem to be doing anything but drawing black and the composite is the culprit of this 'faking', instead of overwriting FF000000 (black) on a 00FFFFFF (white with no alpha) background yielding FF000000 (what I set it to) it is instead 007F7F7F (grey with no alpha).
The only reason I can see for this is the fact that everything is going through a Graphics2D object, I cannot use output.setRGB as it is slow and I wouldn't know how to draw custom shapes with it.