using bitshifting to change alpha value on color? - Processing Forum

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jedierikb

using bitshifting to change alpha value on color?

in Programming Questions • 9 months ago

Given a color, I want to use bitshifting to change the alpha value.

I am not sure how to use >> and << to do this.

I currently create the new color like this:

color newAlphaColor = color( red(oldColor), green(oldColor), blue(oldColor), newAlpha );

How would I use >> and << to do this?

Thanks!

1

Replies(2)

PhiLho

PhiLho

Re: using bitshifting to change alpha value on color?

9 months ago

The article What is a color in Processing? (first one of the Technical FAQ, in case Zoho messes up the link) should help you.

asimes

asimes

Re: using bitshifting to change alpha value on color?

9 months ago

Copy code

int alpha = 255;
void setup() {
size(200, 200, P2D);
loadPixels();
}
void draw() {
// Alpha-Alpha-Red-Red-Green-Green-Blue-Blue
background(0xffff0000); // Red underneath pixels, full opacity
for (int i = 0; i < width*height; i++) {
/* Note: This normally should be one line like this:
pixels[i] = (alpha<<24)|(red<<16)|(green<<8)|blue
But I separated it to make it easier to see */
pixels[i] = alpha<<24; // Alpha
pixels[i] += 0<<16; // Red
pixels[i] += 255<<8; // Green
pixels[i] += 0; // Blue
}
updatePixels();
alpha++;
if (alpha > 255) alpha = 0;
}

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