WinAPI: CombineRgn 区域合成

CombineRgn(
  p1: HRGN;     {合成后的区域}
  p2, p3: HRGN; {两个原始区域}
  p4: Integer   {合并选项; 见下表}
): Integer;     {有四种可能的返回值}

//合并选项:
RGN_AND  = 1;
RGN_OR   = 2;
RGN_XOR  = 3;
RGN_DIFF = 4;
RGN_COPY = 5; {复制第一个区域}

//返回值:
ERROR         = 0; {错误}
NULLREGION    = 1; {空区域}
SIMPLEREGION  = 2; {单矩形区域}
COMPLEXREGION = 3; {多矩形区域}

本例效果图:

---

代码文件:

---

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    RadioGroup1: TRadioGroup;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure FormActivate(Sender: TObject);
    procedure RadioGroup1Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

var
  Rgn1,Rgn2,Rgn: HRGN;

//初始化
procedure TForm1.FormCreate(Sender: TObject);
begin
  {建立两个原始区域}
  Rgn1 := CreateEllipticRgn(20, 20, 120, 160);
  Rgn2 := CreateEllipticRgn(70, 20, 170, 160);

  {Rgn 是用来接受运算结果的, 但函数 CombineRgn 要求它必须是已存在的区域, 这里虚拟一个}
  Rgn := CreateRectRgnIndirect(BoundsRect);

  RadioGroup1.Items.CommaText := '两个原始区域,RGN_AND,RGN_OR,RGN_XOR,RGN_DIFF,RGN_COPY';
  RadioGroup1.ItemIndex := 0;
end;

//见到窗体时先绘制一次
procedure TForm1.FormActivate(Sender: TObject);
begin
  RadioGroup1Click(nil);
end;

//主要代码
procedure TForm1.RadioGroup1Click(Sender: TObject);
begin
  Repaint;
  if RadioGroup1.ItemIndex = 0 then
  begin
    Canvas.Brush.Color := clSilver;
    Canvas.Brush.Style := bsDiagCross;
    FillRgn(Canvas.Handle, Rgn1, Canvas.Brush.Handle);
    FillRgn(Canvas.Handle, Rgn2, Canvas.Brush.Handle);

    Canvas.Brush.Style := bsSolid;
    Canvas.Brush.Color := clRed;
    FrameRgn(Canvas.Handle, Rgn1, Canvas.Brush.Handle, 2, 2);
    FrameRgn(Canvas.Handle, Rgn2, Canvas.Brush.Handle, 2, 2);
  end else begin
    CombineRgn(Rgn, Rgn1, Rgn2, RadioGroup1.ItemIndex);

    Canvas.Brush.Color := clSilver;
    Canvas.Brush.Style := bsDiagCross;
    FillRgn(Canvas.Handle, Rgn, Canvas.Brush.Handle);

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

procedure TForm1.FormDestroy(Sender: TObject);
begin
  DeleteObject(Rgn1);
  DeleteObject(Rgn2);
  DeleteObject(Rgn);
end;

end.

窗体文件:

---

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 182
  ClientWidth = 300
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  OnActivate = FormActivate
  OnCreate = FormCreate
  OnDestroy = FormDestroy
  PixelsPerInch = 96
  TextHeight = 13
  object RadioGroup1: TRadioGroup
    Left = 189
    Top = 8
    Width = 106
    Height = 166
    Caption = 'RadioGroup1'
    TabOrder = 0
    OnClick = RadioGroup1Click
  end
end