Delphi中图像混合透明的函数AlphaBlend的使用

时间：2011/9/3 14:51:23 点击：

　　核心提示：下面的测试是把一张图片显示在窗体, 并可以调整透明度.unit Unit1;interfaceuses Windows, Messages, SysUtils, Variants, Classes,...

下面的测试是把一张图片显示在窗体, 并可以调整透明度.

unit Unit1;

interface

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

type
TForm1 = class(TForm)
    TrackBar1: TTrackBar;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure TrackBar1Change(Sender: TObject);
    procedure FormPaint(Sender: TObject);
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

var
bit: TBitmap;

procedure TForm1.FormCreate(Sender: TObject);
begin
bit := TBitmap.Create;
bit.LoadFromFile('c:\temp\Test.bmp');

TrackBar1.Min := 0;
TrackBar1.Max := 255;
TrackBar1.Position := 128;

DoubleBuffered := True;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
bit.Free;
end;

procedure TForm1.FormPaint(Sender: TObject);
var
BlendFunc: TBlendFunction;
begin
BlendFunc.BlendOp := AC_SRC_OVER;
BlendFunc.BlendFlags := 0;
BlendFunc.SourceConstantAlpha := TrackBar1.Position;

if bit.PixelFormat = pf32bit then
    BlendFunc.AlphaFormat := AC_SRC_ALPHA
else
    BlendFunc.AlphaFormat := 0;

Windows.AlphaBlend(Canvas.Handle,                 {目标 DC}
                     30, 10, bit.Width, bit.Height, {目标位置与大小}
                     bit.Canvas.Handle,             {源 DC}
                     0, 0, bit.Width, bit.Height,   {源位置与大小}
                     BlendFunc                      {透明相关的结构}
                     );
end;

procedure TForm1.TrackBar1Change(Sender: TObject);
begin
Repaint;
end;

end.