Is it possible to change the size of a dash of a line?

Question

Hello,

I am drawing a dashed line on the TImage Canvas and found out that the size of dashes is way too big for the drawing area. Is there a way to change the size of dashes of lines drawn on canvas?
This is what i do to be able to draw dashed lines.

Canvas.Pen.Style := psDash;
Canvas.Polyline(myPoints);

And i didn't find any Pen property which could change the dash size/length.

Thanks

Answer 1

I don't know, but, which is the implementation of Polyline()? When you control+click it, which code do you see? Is it using an property-exposed variable may be? If so, you can set it, otherwise -if it is hardcoded- you will see it, and know that you can't.

Answer 2

According to http://docwiki.embarcadero.com/VCL/e/index.php/Graphics.TPenStyle you can use psUserStyle

The docs for ExtCreatePen are at http://msdn.microsoft.com/en-us/library/dd162705(VS.85).aspx

Here's my interpretation of how ExtCreatePen is meant to be used in combination with TPen:

const
  NumberOfSections = 8;
  LineLengths: array[0..NumberOfSections-1] of DWORD =
    (20, 15, 14, 17, 14, 8, 16, 9);
var
  logBrush: TLogBrush;
begin

  logBrush.lbStyle := BS_SOLID;
  logBrush.lbColor := DIB_RGB_COLORS;
  logBrush.lbHatch := HS_BDIAGONAL; // ignored

  Canvas.Pen.Handle := ExtCreatePen(PS_GEOMETRIC or PS_USERSTYLE or PS_ENDCAP_ROUND or PS_JOIN_BEVEL,
                      4, logBrush, NumberOfSections, @LineLengths[0]);
  // now Canvas.Pen.Style = psUserStyle

  Canvas.Polyline([Point(0,0), Point(100,100), Point(200, 100)]);

end;