VCL 中的 Windows API 函數(5): AlphaBlend

來源:互聯網
上載者:User
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
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