Question

GDI+ methods - Flip a figure

Asked by: jaja2005

Hi. I am using GDI+ methods for drawing shape with GraphicsPath object.
If the figure is symmetric with respect to the y-axis, how i can clone
the current path and flip it before drawing on canvas?

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Asked On
2009-11-05 at 14:08:32ID24876287
Topics

Graphics and Delphi Programming

,

Delphi Programming

,

Windows Programming

Participating Experts
1
Points
500
Comments
2

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Answers

 

by: epasquierPosted on 2009-11-05 at 15:35:39ID: 25755299

assuming that you use the same library some other expert talked about a few weeks ago, or one compatible with the help file I'm looking at, I think you'll have to use the Transform method of a path with a matrix that codes the Y-axis symetry. That's for theory, and I'll try to put the code right
I believe the scale transformation is what we are looking at.

var
  AGraphics : IGPGraphics;
  APath     : IGPGraphicsPath;
  AMatrix   : IGPMatrix; 
begin
  AGraphics := TGPGraphics.Create( ACanvas );
  APath := TGLPath.Create();
// add some drawings
  APath.AddRectangle( MakeRect(40, 10, 200, 50)); 
  // Draw the path in blue before applying a transformation.
  AGraphics.DrawPath( TGPPen.Create( aclBlue )), APath); 
  // Transform the path.
  AMatrix := TGPMatrix.Create();
// Y-Axis Symetry : X:=-OldX , Y:=OldY
  AMatrix.Scale(-1,1, MatrixOrderAppend );
  path.Transform( AMatrix ); 
  // Draw the transformed path in red.
  graphics.DrawPath( TGPPen.Create( aclRed ), APath);
end;

                                              
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by: epasquierPosted on 2009-11-05 at 15:41:25ID: 25755340

I don't know exactly, but if there is not a translation somewhere before drawing, won't negative coordinates be outside the canvas ? If so then it's possible that the second drawing won't show.

A solution would be to have some path on both sides of the Y axis in the first place, that way we would be sure the transformation has effects. like

// add some drawings
APath.AddLine(-30,10,80,80);

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