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