Request to add 2 small functions in JclGraphUtils unit;

[devEric69]

type

.../...

type TColorSwap
private
public
class function ComplementaryColorFromHtmlColor(AHtmlColor: TColor; bSwapRedBlue: Boolean = False): TColor;
class function ComplementaryColor(AColor: TColor): TColor;
class function HighContrastColor(AColor: TColor): TColor;
class function SwappedRedGreenColor(AColor: TColor): TColor;
class function SwappedRedBlueColor(AColor: TColor): TColor;
end;
.../...

implementation

.../...

class function TColorSwap.ComplementaryColorFromHtmlColor(AHtmlColor: TColor; bSwapRedBlue: Boolean = False): TColor;
{$REGION 'Xls: Comments section'}
{
@param bSwapRedBlue: this parameter depends from your material context, and the purpose of this call:

• from the logic of use: let's say you found and copy a pretty #aabbcc color on a website, i.e. a hexdecimal representation in a string type, and you are looking for its complementary color to highlight TLabels on a TPanel for exemple, in Free Pascal. #aabbcc means that Red='#aa', Green='#bb', and Blue='#cc'. Even before calculating the complementary, it must be known that if you want to copy this color in Free Pascal, as it is, ie $aabbcc to a Canvas.Color property for example, it will not always work (depending on CPU type): indeed, the binary bits are read from right to left. So, the compiled equivalent will \ could have to be Red=$cc, Green=$bb Blue=$cc on your machine.
• from your CPU: into a file, Motorola writes AColor's RGB in that order ie RGB; but Intel writes it inversed ie BGR.

Trick, to check first, which convention is used:

• HTML writes the hex code in Motorola format, and the GIMP shows the color hex code in Motorola Format too ==> with such a format, if you take this color code from HTML or from the GIMP, then you'll have to swap red and blue.
• easy other test: fill some component's Color property, with Color:= $FF ==> if it is red you are on an Intel machine (swap needed, if we use a HTML color's display).
  Otherwise if it is blue you are on a Motorala machine (no swap needed, if we use a HTML color's display).

NB: if you use reference colors like clBlack, clLime, etc., from the LCL to find the complementary color of these, then leave bSwapRedBlue to false: the colors of the components are already natively - with respect to your machine's CPU - correctly managed. Or even better: use ComplementaryColor.
}
{$ENDREGION}

      function SwapRedBlue(AColor: TColor): TColor;
     {$REGION 'Xls: Comments section'}
      { See ComplementaryColorFromHtmlColor explanations. }
     {$ENDREGION}
      begin
      Result:= RGBToColor(Graphics.Blue(AColor), Graphics.Green(AColor), Graphics.Red(AColor))
      end;

begin
if bSwapRedBlue then
SwapRedBlue(AHtmlColor);
Result:= RGBToColor(255 - Graphics.Red(AHtmlColor), 255 - Graphics.Green(AHtmlColor), 255 - Graphics.Blue(AHtmlColor));
end;

class function TColorSwap.ComplementaryColor(AColor: TColor): TColor;
{$REGION 'Xls: Comments section'}
{ most efficient for complementary color. }
{$ENDREGION}
begin
Result := clWhite - ColorToRGB(AColor);
end;

class function TColorSwap.HighContrastColor(AColor: TColor): TColor;
{$REGION 'Xls: Comments section'}
{ The one that returns the color with the most contrast, in the middle of grey or pastel colors. }
{$ENDREGION}
begin
AColor := ColorToRGB(AColor);
if Red(AColor) + Green(AColor) + Blue(AColor) < 3*128 then
Result := clWhite
else
Result := clBlack;
end;

class function TColorSwap.SwappedRedGreenColor(AColor: TColor): TColor;
{$REGION 'Xls: Comments section'}
{ inspired from the "triadic color scheme": if color_base=RGB ==> sequencing triad_1=GBR, triad_2=BRG... }
{$ENDREGION}
begin
AColor := ColorToRGB(AColor);
Result := RGBToColor(Green(AColor), Red(AColor), Blue(AColor));
end;

class function TColorSwap.SwappedRedBlueColor(AColor: TColor): TColor;
{$REGION 'Xls: Comments section'}
{ inspired from the "triadic color scheme": if color_base=RGB ==> sequencing triad_1=GBR, triad_2=BRG... }
{$ENDREGION}
begin
AColor := ColorToRGB(AColor);
Result := RGBToColor(Blue(AColor), Green(AColor), Red(AColor));
end;

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Best regards.