Bug 13842 – Simplify Color::light() and Color::dark()

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

The RGB->HSV->RGB conversion Color::light() and Color::dark() do is an overkill. I don't think those functions are hot but what they do can be described and implemented in simpler terms.

Created attachment 14683 [details]
Simpler implementation

Created attachment 14684 [details]
Simpler implementation

[Darin Adler]

Comment on attachment 14684 [details]
Simpler implementation

Does this really give the same values as before? If so, seems fine. But I was under the impression that scaling value didn't affect the 3 channels equally.

I don't think dark() properly handles the case where all three of r, g, and b are zero. So review- because of that. Otherwise, would be r=me.

Comment on attachment 14684 [details]
Simpler implementation

(In reply to comment #3)
> (From update of attachment 14684 [details] [edit])
> Does this really give the same values as before? If so, seems fine. But I was
> under the impression that scaling value didn't affect the 3 channels equally.

If you look at convertHSVToRGB() you'll see that its result can be expressed as "v times some vector x whose components do not depend on v", so indeed for given h and s components, scaling v affects the 3 channels equally. (IIRC in the HSL space, L doesn't affect all channels equally, since L=1.0 maps to white).

> I don't think dark() properly handles the case where all three of r, g, and b
> are zero.

I verified that in that case (v - 0.33f) / v is -inf and therefore the multiplier is 0, so the result is <0,0,0,alpha>, which is what I would expect.

[Darin Adler]

Comment on attachment 14684 [details]
Simpler implementation

r=me

[Mark Rowe (bdash)]

Landed in r21798.