eirikbakke commented on PR #7930:
URL: https://github.com/apache/netbeans/pull/7930#issuecomment-2609964518
@neilcsmith-net Your main objection is with the fadeColor method that has a
hard-coded alpha value in it, right?
Is there any reason the alpha value cannot come from one of the
parameterized Color instances instead?
Here is a more general "blend" function that takes alpha values into account:
```
public static Color blendOver(final Color src, final Color dest, float
extraSourceAlpha) {
Preconditions.checkArgument(extraSourceAlpha >= 0.0f && extraSourceAlpha
<= 1.0f);
// Small optimization.
if (src.getAlpha() == 0 || extraSourceAlpha == 0.0f)
return dest;
/* Based on the formulas from the Porter and Duff paper, as presented in
the Javadoc for
java.awt.AlphaComposite. */
// "The 'extra' alpha component from the AlphaComposite instance"
final float Aac = extraSourceAlpha;
final float Csr[] = src.getRGBComponents(null);
final float Cdr[] = dest.getRGBComponents(null);
final float Asr = Csr[3];
final float Adr = Cdr[3];
final float As = Asr * Aac;
final float Ad = Adr;
// Use the functions for SRC_OVER.
final float Fs = 1.0f;
final float Fd = 1.0f - As;
final float Ar = As * Fs + Ad * Fd;
final float Adf = Ar;
// Avoid division by zero below.
if (Adf == 0.0f)
return new Color(0, 0, 0, 0);
final float Cdf[] = new float[3];
for (int i = 0; i < 3; i++) {
/* The zero check ensures correct behavior in the case of a zero-alpha
Color with NaN color
components. */
final float Cs = (As == 0.0f) ? 0.0f : Csr[i] * As;
final float Cd = (Ad == 0.0f) ? 0.0f : Cdr[i] * Ad;
final float Cr = Cs * Fs + Cd * Fd;
Cdf[i] = Cr / Ar;
}
return new Color(Cdf[0], Cdf[1], Cdf[2], Adf);
}
```
If useful, I could add it to org.openide.util.Utilities. I've been using it
for several years.
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