如何将椭圆或多边形从一个位图复制到另一个位图

Question

How Can I copy an ellipse or polygon shape from one bitmap to another Bitmap. BitBlt is only useful for copying Rectangles.

I currently use GDI but If it is easier to use GDI+, I can use it. I only need a general guidance to show me the right direction.

Answer 1

You could select an elliptic/polygon clip region into the target device context and then use BitBlt as usual.

var
  Rgn: HRGN;
  Points: array[0..2] of TPoint;
begin
  //Rgn := CreateEllipticRgn(0, 0, 100, 100);

  Points[0] := Point(0, 0);
  Points[1] := Point(50, 50);
  Points[2] := Point(50, 0);
  Rgn := CreatePolygonRgn(Points, 3, WINDING);

  SaveDC(Canvas.Handle);
  SelectClipRgn(Canvas.Handle, Rgn);
  DeleteObject(Rgn); // SelectClipRgn copies the region

  BitBlt(Canvas.Handle, 0, 0, 100, 100, BmpDC, 0, 0, SRCCOPY);

  RestoreDC(Canvas.Handle, -1);
end;