[Solved] Darken TColor
lazarus / 39-Graphics

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Mike.Cornflake · 2014-06-26 07:36

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...

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taazz · 2014-06-26 08:04

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.

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wp · 2014-06-26 08:06

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;

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Mike.Cornflake · 2014-06-26 08:34

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

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Blaazen · 2014-06-26 09:12

Quoteuse 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.

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Mike.Cornflake · 2014-06-26 09:21

Quote from: Blaazen on June 26, 2014, 11:12:57 amQuoteuse
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
QuotePOKE 54296,15Wow, that takes me back :-)

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Mike.Cornflake · 2014-06-26 16:28

Again, many thanks all.  I ended up going with
Code: [Select]oColor := GetHighLightColor(oColor,
32);GetHighlightColor is defined in GraphUtil.

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Mike.Cornflake · 2018-08-29 17:41

Quote from: wp on June 26, 2014, 10:06:42 amThat'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 :-)