I have a question regarding setting the Alpha value of pixels in a window of a
Java desktop application running under Linux. A simplified version of the code
from my paint function is shown below:
public void paint(Graphics g) {
int alpha;
Graphics2D g2d = (Graphics2D) g;
Composite c = AlphaComposite.getInstance(AlphaComposite.SRC_OVER);
g2d.setComposite(c);
// Draw transparent rectangle
alpha = 128;
g2d.setPaint(new Color(0, 0, 255, alpha));
g2d.fill(new Rectangle(0, 0, 100, 100));
// Draw opaque rectangle
alpha = 255;
g2d.setPaint(new Color(0, 0, 255, alpha));
g2d.fill(new Rectangle(100, 0, 100, 100));
}
I am using Graphics2D to draw rectangles with different values of alpha. Now,
what I am really trying to do is change the alpha value of pixels in the
window, however, what appears to be happening is that the alpha value I specify
is used for the drawing operation and then discarded.
Just as background info, I use the application window in another program that
exploits the Composite extension of the X server. This program redirects the
window and performs some additional processing based on the alpha value of
pixels in the window. If I draw the graphics using X then the alpha value of
pixels in the window is modified but not when I use Java.
To summarise my question, is there a way in Java to modify the alpha value of
pixels in a window?
Thanks for looking at my post, any advise or suggestions gratefully received.
Steve
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