[Solved] Darken TColor

[Mike.Cornflake]

I'm ignorant in the world of image processing.   I'm highlighting rows in a grid by setting Color in OnPrepareCanvas (according to calculated criteria - bad = red, good = green, OKish = Yellow or Orange.  Unimportant = white.  The unimportant selected rows are highlighted in light gray automatically for me by the grid itself)

If the row is the selected row, I want to to highlight the row with a slighter darker version of the color.  Instead of hard-coding alternatives, is there a simple DarkenColor(AColor: TColor; APercent: Double): TColor anywhere?  (Or equivalent)

I've looked, and the ones I can find are in dedicated image processing libraries, which I *think* involves introducing levels of complexity beyond what I'm actually after...

[taazz]

use GraphUtil.ColorAdjustLuma or search for colorblend for alphablending two colors with a standart alpha value creating something like a chromasity ee a blue window on top of the back color.

[wp]

That's the way I did it in fpspreadsheetgrid. It darkens a bright color and brightens a dark color:

Code: [Select]

function CalcSelectionColor(c: TColor; ADelta: Byte) : TColor;
type
  TRGBA = record R,G,B,A: Byte end;
begin
  c := ColorToRGB(c);
  TRGBA(Result).A := 0;
  if TRGBA(c).R < 128
    then TRGBA(Result).R := TRGBA(c).R + ADelta
    else TRGBA(Result).R := TRGBA(c).R - ADelta;
  if TRGBA(c).G < 128
    then TRGBA(Result).G := TRGBA(c).G + ADelta
    else TRGBA(Result).G := TRGBA(c).G - ADelta;
  if TRGBA(c).B < 128
    then TRGBA(Result).B := TRGBA(c).B + ADelta
    else TRGBA(Result).B := TRGBA(c).B - ADelta;
end;


[Mike.Cornflake]

Many thanks @taazz and @wp, I'll play with both solutions :-)

[Blaazen]

use GraphUtil.....

I didn't know this unit at all! I reinvented some methods in EC-Controls (NormalizeRect, GetMonochromaticColor, maybe more). I'll refactore the code.
Also unit GraphMath is interesting.
Anyway, thanks.

[Mike.Cornflake]

use GraphUtil.....

I didn't know this unit at all!

There's a bucketload of undiscovered goodies all around :-)

And I've just noticed your tagline

POKE 54296,15

Wow, that takes me back :-)

[Mike.Cornflake]

Again, many thanks all.  I ended up going with

Code: [Select]

oColor := GetHighLightColor(oColor, 32);GetHighlightColor is defined in GraphUtil.

[Mike.Cornflake]

That's the way I did it in fpspreadsheetgrid. It darkens a bright color and brightens a dark color:

Apologies for re-opening an old topic, but thanks are due:   I just had to fix an issue where I was darkening a row all the way to blackness.  I resolved by popping back here and using @wp's solution instead.  So many thanks @wp :-)