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How to draw a rotated ellipse at a specific angle (2) (Views: 21)


Problem/Question/Abstract:

I created an object based off of TGraphicControl and I used the TCanvas.Ellipse method to create an ellipse. I would like to give the user the ability to rotate this ellipse. I would also like to give the user the ability after rotating the ellipse to still adjust the size and shape.

Answer:

You can use Win32GDI Routines. It works like this:


procedure RotatedEllipse(aCanvas: TCanvas; X1, Y1, X2, Y2: Integer);
var
  T, O: TXForm; {in unit Windows}
begin
  { ... }
  SetGraphicsMode(aCanvas.Handle, GM_Advanced);
  GetWorldTransform(aCanvas.Handle, O);
  {Angle in degree}
  T.eM11 := 1 * Cos(w / 360 * Pi * 2);
  T.eM22 := 1 * Cos(w / 360 * Pi * 2);
  T.eM12 := 1 * Sin(w / 360 * Pi * 2);
  T.eM21 := 1 * -Sin(w / 360 * Pi * 2);
  T.eDX := Round((X1 + X2) / 2);
  T.eDY := Round((Y1 + Y2) / 2);
  ModifyWorldTransform(aCanvas.Handle, T, MWT_LEFTMULTIPLY);
  Canvas.Ellipse(X1, Y1, X2, Y2);
  SetWorldTransform(TheDraw.Handle, O);
end;

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