WinAPI: IntersectRect、SubtractRect、UnionRect 用两个矩形合成一个新的矩形

本例效果图:

---

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{定义两个矩形常量}
const
  R1: TRect = (Left:20; Top:30; Right:160; Bottom:100);
  R2: TRect = (Left:100; Top:10; Right:180; Bottom:120);

{初始化按钮显示}
procedure TForm1.FormCreate(Sender: TObject);
begin
  Button1.Caption := '两个原始矩形';
  Button2.Caption := '相交';
  Button3.Caption := '减去';
  Button4.Caption := '联合';
end;

{画出两个原始矩形}
procedure TForm1.Button1Click(Sender: TObject);
begin
  Refresh;
  Canvas.Brush.Color := clOlive;
  Canvas.Rectangle(R2);
  Canvas.Brush.Color := clBlue;
  Canvas.Rectangle(R1);
end;

{相交: IntersectRect}
procedure TForm1.Button2Click(Sender: TObject);
var
  R: TRect;
begin
  Refresh;
  IntersectRect(R, R1, R2);
  Canvas.Brush.Color := clRed;
  Canvas.Rectangle(R);
end;

{减去: SubtractRect}
procedure TForm1.Button3Click(Sender: TObject);
var
  R: TRect;
begin
  Refresh;
  SubtractRect(R, R1, R2);
  Canvas.Brush.Color := clRed;
  Canvas.Rectangle(R);
end;

{联合: UnionRect}
procedure TForm1.Button4Click(Sender: TObject);
var
  R: TRect;
begin
  Refresh;
  UnionRect(R, R1, R2);
  Canvas.Brush.Color := clRed;
  Canvas.Rectangle(R);
end;

end.