Mega Code Archive

Rotate an ellipse

Title: Rotate an ellipse Question: How to draw a rotated Ellipse? Answer: I wrote a procedure "CentralRotatedEllipse" to rotate an ellipse. It works exactly enougth for simple graphics. The Ellipse is maked with two connected beziercurves. Rotatingpoint of the Ellipse is its centralpoint. The Parameter canvas for the Destinationcanvas, coordinates like "common" Ellipse and in alpha the rotatingangle. The function "Rotate2DPoint" you have to put in your code too, its called by the CentralRotatedEllipse-Procedure. And dont forget uses Math! enjoy it function Rotate2DPoint(P,Fix :TPoint; alpha:double): TPoint; var sinus, cosinus : Extended; begin SinCos(alpha, sinus, cosinus); P.x := P.x - Fix.x; P.y := P.y - Fix.y; result.x := Round(p.x*cosinus + p.y*sinus) + fix.x ; result.y := Round(-p.x*sinus + p.y*cosinus) + Fix.y; end; procedure CentralRotatedEllipse(Canvas : TCanvas; x1, y1, x2, y2:Integer; alpha : Extended); var PointList: array[0..6] of TPoint; f : TPoint; dk : Integer; begin dk := Round(0.654 * Abs(y2-y1)); f.x := x1 + (x2-x1) div 2; f.y := (y1 + (y2-y1) div 2) -1; PointList[0] := Rotate2DPoint(Point(x1, f.y), f, Alpha) ; // Startpoint PointList[1] := Rotate2DPoint(Point(x1, f.y - dk), f, Alpha); //Controlpoint of Startpoint first part PointList[2] := Rotate2DPoint(Point(x2- 1, f.y - dk), f, Alpha); //Controlpoint of secondpoint first part PointList[3] := Rotate2DPoint(Point(x2 -1 , f.y), f, Alpha); // Firstpoint of secondpart PointList[4] := Rotate2DPoint(Point(x2-1 , f.y + dk), f, Alpha); // Controllpoint of secondpart firstpoint PointList[5] := Rotate2DPoint(Point(x1, f.y + dk), f, Alpha); // Conrollpoint of secondpart endpoint PointList[6] := PointList[0]; // Endpoint of // Back to the startpoint PolyBezier(canvas.handle, Pointlist[0], 7); end;