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Frequently Asked Questions

Color problems in 256 color mode.

Question:

When I am drawing graphics with my application in 256 color mode (or less), some pen and text colors do not match my brush colors.

Answer:

Unless you are using a palette, Windows will attempt to 

convert pen and text colors to the nearest pure color 

available. You can determine the nearest pure color, a given 

color will map to, by calling the Windows API function 

GetNearestColor(). If you wish to use dithered colors for a 

pen, you can also set the pen style to the psInsideFrame 

style. When using this style, the pen draws lines within the 

frame of closed shapes that specify a bounding rectangle 

instead of centering the line over the shape. For the 

psInsideFrame style to have an effect, the pen width must be 

larger than 1 pixel.



Example:



procedure TForm1.Button1Click(Sender: TObject);

var NearestColor : TColorRef;

begin

  Form1.Canvas.Brush.Color := RGB(143, 53, 22);

  Form1.Canvas.Pen.Color := RGB(143, 53, 22);

  Form1.Canvas.Pen.Width := 10;

  Form1.Canvas.Ellipse(10, 10, 100, 100);

  Form1.Canvas.Pen.Style := psInsideFrame;

  Form1.Canvas.Ellipse(10, 110, 100, 200);

  Memo1.Lines.Add(

     'The nearest displayable color to RGB(143, 53, 22) is:');

  NearestColor :=

    GetNearestColor(Form1.Canvas.Handle,

                    RGB(143, 53, 22));

  Memo1.Lines.Add('Red := ' +

                  IntToStr(GetRValue(NearestColor)));

  Memo1.Lines.Add('Red := ' +

                  IntToStr(GetGValue(NearestColor)));

  Memo1.Lines.Add('Blue := ' +

                  IntToStr(GetBValue(NearestColor)));

end;

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