# How do i find out what color a certain pixel is?

Mike Miller
Greenhorn
Posts: 5
I'm writing a little applet using awt that draws a number of line of the screen. The lines are drawn as single points and move around the screen using velocity vectors. When they hit the edge they bounce at random. I need to detect when a line hits another line. I thought that if i look ahead of the line to see if the color is not the default background then the line could bounce. So what i need is a method that accepts x,y co-ords and returns the color at those co-ords.
With thanks.

Mike Miller
Greenhorn
Posts: 5
Could i use pixelGrabber? The screen is being drawn as an image.

Dirk Schreckmann
Sheriff
Posts: 7023
Hello,
This idea is perhaps not as slick as being able to test a pixel for its color...
What about maintaining an array of the pixels that you have already drawn to? Then just test the upcoming pixel with the current pixels in your array to determine if you should bounce or not.
Just an idea.
Good Luck.

Rob Ross
Bartender
Posts: 2205
java.awt.Robot rb = new java.awt.Robot();
Color aPixelColor = rb.getPixelColor(0,0);//gets the color of the pixel at screen coordinate 0,0.
Hope this helps!

Dirk Schreckmann
Sheriff
Posts: 7023
Very nice. Thanks Rob.

Mike Miller
Greenhorn
Posts: 5
in the end i used this...
class mikes extends Object {
public static boolean handlesinglepixel(int x, int y, int pixel,Color c) {
int alpha = (pixel >> 24) & 0xff;
int red = (pixel >> 16) & 0xff;
int green = (pixel >> 8) & 0xff;
int blue = (pixel ) & 0xff;
int blue2,red2,green2;
//System.out.println(red+"|"+green+"|"+blue);
red2 = c.getRed();
green2 =c.getGreen();
blue2 = c.getBlue();
if (((red==255)&&(green==255)&&(blue==255)) || ((red==0)&&(green==0)&&(blue==0)) || ((red==red2)&&(green==green2)&&(blue==blue2)) )
return true;
else return false;
}
public static boolean handlepixels(Image img, int x, int y, int w, int h,Color c) {
int[] pixels = new int[w * h];
PixelGrabber pg = new PixelGrabber(img, x, y, w, h, pixels, 0, w);
try {
pg.grabPixels();
} catch (InterruptedException e) {
System.err.println("interrupted waiting for pixels!");
return false;
}/*
if ((pg.getStatus() & ImageObserver.ABORT) != 0) {
System.err.println("image fetch aborted or errored");
return;
}*/
boolean white = true;
for (int j = 0; j < h; j++) {
for (int i = 0; i < w; i++) {
if (white) white = handlesinglepixel(x+i, y+j, pixels[j * w + i],c);
}
}
return white;
}
}