WinAPI: SelectClipRgn、ExtSelectClipRgn、SelectClipPath - 定义剪切区域

剪切区域也是区域的一种, 窗口在重绘时只会重绘剪切区域中的内容.

SelectClipRgn 和 ExtSelectClipRgn 是通过指定区域来定义剪切区域;

SelectClipPath 是通过指定路径来定义剪切区域;

ExtSelectClipRgn 和 SelectClipPath 比 SelectClipRgn 多出一个与原剪切区域混合方式的参数:

RGN_AND  = 1;

RGN_OR   = 2;

RGN_XOR  = 3;

RGN_DIFF = 4;

RGN_COPY = 5;


 
   

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 FormPaint(Sender: TObject);

    procedure RadioGroup1Click(Sender: TObject);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



var

  bit: TBITMAP;



procedure TForm1.FormCreate(Sender: TObject);

begin

  RadioGroup1.Caption := '定义剪切区域';

  RadioGroup1.Items.CommaText := '无剪切区域,根据区域,根据路径';

  RadioGroup1.ItemIndex := 0;



  bit := TBitmap.Create;

  bit.LoadFromFile('c:\temp\Test.bmp');

end;



procedure TForm1.FormPaint(Sender: TObject);

var

  Rgn: HRGN;

begin

  case RadioGroup1.ItemIndex of

    1: begin

         Rgn := CreateEllipticRgn(30,30,140,140);

         SelectClipRgn(Canvas.Handle, Rgn);

         DeleteObject(Rgn);

       end;

    2: begin

         Canvas.Font.Size := 160;

         Canvas.Font.Style := [fsBold];

         SetBkMode(Canvas.Handle, TRANSPARENT);

         BeginPath(Canvas.Handle);

         Canvas.TextOut(-15,-30,'A');

         EndPath(Canvas.Handle);

         SelectClipPath(Canvas.Handle, RGN_COPY);

       end;

  end;



  Canvas.Draw(0,0,bit);

end;



procedure TForm1.RadioGroup1Click(Sender: TObject);

begin

  Repaint;

end;



procedure TForm1.FormDestroy(Sender: TObject);

begin

  bit.Free;

end;



end.


 
   

窗体文件:

---

object Form1: TForm1

  Left = 366

  Top = 307

  Caption = 'Form1'

  ClientHeight = 206

  ClientWidth = 309

  Color = clBtnFace

  Font.Charset = DEFAULT_CHARSET

  Font.Color = clWindowText

  Font.Height = -11

  Font.Name = 'Tahoma'

  Font.Style = []

  OldCreateOrder = False

  Position = poDesigned

  OnCreate = FormCreate

  OnDestroy = FormDestroy

  OnPaint = FormPaint

  PixelsPerInch = 96

  TextHeight = 13

  object RadioGroup1: TRadioGroup

    Left = 209

    Top = 93

    Width = 95

    Height = 105

    Caption = 'RadioGroup1'

    TabOrder = 0

    OnClick = RadioGroup1Click

  end

end