WinAPI: SetRectRgn - 将区域转换成矩形区域

本例效果图:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TForm1 = class(TForm)
    procedure FormClick(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

var f: Boolean;

procedure TForm1.FormClick(Sender: TObject);
const
  n = 50;
var
  Rgn: HRGN;
  x1,y1,x2,y2: Integer;
begin
  Repaint;

  x1 := n;
  y1 := n div 2;
  x2 := ClientWidth - n;
  y2 := ClientHeight - n;

  {建立椭圆区域}
  Rgn := CreateEllipticRgn(x1, y1, x2, y2);

  {转换为矩形区域 - 谈不上是转换, 是重新定制了一个矩形区域, 只是用了原来的区域句柄而已}
  if f then SetRectRgn(Rgn, 11, 11, 111, 111);
  f := not f;

  {绘制区域}
  Canvas.Brush.Color := clSilver;
  Canvas.Brush.Style := bsCross;
  FillRgn(Canvas.Handle, Rgn, Canvas.Brush.Handle);

  Canvas.Brush.Color := clRed;
  Canvas.Brush.Style := bsSolid;
  FrameRgn(Canvas.Handle, Rgn, Canvas.Brush.Handle, 2, 2);

  DeleteObject(Rgn);
end;

end.