WinAPI: AlphaBlend

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WinAPI: alphablend - 图像透明度

alphablend( DC: HDC; {目标设备环境句柄} p2, p3, p4, p5: Integer; {目标位置与宽高} DC6: HDC; {源设备环境句柄} p7, p8, p9, p10: Integer; {源位置与宽高} p11: TBlendFunction {合成方式的数据结构, 见下表} ): BOOL; //TBlendFunction 结构是 _BLENDFUNCTION 的重命名: _BLENDFUNCTION = packed record BlendOp: BYTE; {本例使用了: AC_SRC_OVER = 0} BlendFlags: BYTE; {必须为 0} SourceConstantAlpha: BYTE; {透明度: 0..255} AlphaFormat: BYTE; {通常为 0，如果源位图为32位真彩色，可为 AC_SRC_ALPHA } end; 本例效果图:

代码文件: unit Unit1; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, ExtCtrls, ComCtrls; type TForm1 = class(TForm) TrackBar1: TTrackBar; procedure FormCreate(Sender: TObject); procedure FormPaint(Sender: TObject); procedure TrackBar1Change(Sender: TObject); procedure FormDestroy(Sender: TObject); end; var Form1: TForm1; implementation {$R *.dfm} var Bit,BitBack: TBitmap; Transparency: Byte = 255; {透明度} procedure TForm1.FormCreate(Sender: TObject); begin {设定窗体背景} BitBack := TBitmap.Create; BitBack.LoadFromFile('c:\temp\Back.bmp'); Brush.Bitmap := BitBack; {调入图片} Bit := TBitmap.Create; Bit.LoadFromFile('c:\temp\test.bmp'); {给 TrackBar1 初始化} TrackBar1.Max := 255; TrackBar1.Min := 0; TrackBar1.ShowSelRange := False; TrackBar1.Position := TrackBar1.Max; end; procedure TForm1.FormPaint(Sender: TObject); var Blend: TBlendFunction; {定义 AlphaBlend 要使用的 TBlendFunction 结构} begin {给 TBlendFunction 结构赋值} Blend.BlendOp := AC_SRC_OVER; Blend.BlendFlags := 0; Blend.AlphaFormat := 0; Blend.SourceConstantAlpha := Transparency; Windows.alphablend(Canvas.Handle, {因 VCL 有同名属性, 所以指定了是来自 Windows 单元} 10, 10, Bit.Width + 10, Bit.Height + 10, Bit.Canvas.Handle, 0, 0, Bit.Width, Bit.Height, Blend ); end; procedure TForm1.TrackBar1Change(Sender: TObject); begin Transparency := TrackBar1.Position; Text := IntToStr(Transparency); Self.Repaint; {命令重绘} end; procedure TForm1.FormDestroy(Sender: TObject); begin Bit.Free; BitBack.Free; end; end. 窗体设计: object Form1: TForm1 Left = 352 Top = 238 Caption = 'Form1' ClientHeight = 209 ClientWidth = 211 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 TrackBar1: TTrackBar Left = 0 Top = 186 Width = 201 Height = 24 TabOrder = 0 OnChange = TrackBar1Change end end

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