How to change PolyLine colour?
lazarus / 39-Graphics

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JoshM · 2014-01-02 20:37

I'm using the function:

function Polyline(DC: HDC; var Points; Count: Integer): BOOL; external
'gdi32' name 'Polyline';

Using the Canvas.Pen.Color code doesn't work, as (I think) the
function I'm using a built-in Windows one, and not a Pascal/Lazarus
one. Does anyone know how I could change the colour of the PolyLine,
or where I could go about getting this info?

Here's the code I've got, with comments to explain what I want:

Code: [Select]
procedure TNewPageControl.PaintWindow(DC: HDC);
begin
  inherited PaintWindow(DC);
  //set colour = black
  PolyLine(DC, Points, PointNum);
  //set colour = red
  PolyLine(DC, VerVec, PointNumVec);
  //set colour = green
  PolyLine(DC, HorVec, PointNumVec);
end;
        


Thanks.

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howardpc · 2014-01-02 21:20

You use a valid canvas (of a form or other control), setting its
Pen/Brush colour as desired, and then pass
Code: [Select]canvas.Handle
as the first parameter to Polyline(...);

You probably don't need to call PaintWindow() at all.

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taazz · 2014-01-02 21:23

Canvas.Polyline is not good enough? In short you have to make sure
that the dc has everything setup before you try do anything. Try
saving the canvas.handle in to a local variable that will force the
canvas to set up the dc correctly for you, using its internal brush,
pen and font classes. In case that you want to avoid using the canvas
all together then you need to use createpen, createbrush etc after
that you call the SelectObject function to let the dc know which pen
and brush you want to use and then you draw your polyline.

Reference :http://msdn.microsoft.com/en-
us/library/windows/desktop/dd162957%28v=vs.85%29.aspx