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