AlphaBlend 是指定映像混合透明的函數, 在 Graphics、GraphUtil、RibbonStyleActnCtrls 單元用到.
下面的測試是把一張圖片顯示在表單, 並可以調整透明度.
本例:
代碼檔案:
unit Unit1;interfaceuses 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, {目標 DC} 30, 10, bit.Width, bit.Height, {目標位置與大小} bit.Canvas.Handle, {源 DC} 0, 0, bit.Width, bit.Height, {源位置與大小} BlendFunc {透明相關的結構} );end;procedure TForm1.TrackBar1Change(Sender: TObject);begin Repaint;end;end.
表單檔案:
object Form1: TForm1 Left = 0 Top = 0 Caption = 'Form1' ClientHeight = 206 ClientWidth = 223 Color = clBtnFace Font.Charset = DEFAULT_CHARSET Font.Color = clWindowText Font.Height = -11 Font.Name = 'Tahoma' Font.Style = [] OldCreateOrder = False OnCreate = FormCreate OnDestroy = FormDestroy OnPaint = FormPaint PixelsPerInch = 96 TextHeight = 13 object TrackBar1: TTrackBar Left = 8 Top = 175 Width = 207 Height = 23 ShowSelRange = False TabOrder = 0 OnChange = TrackBar1Change endend