AlphaBlend 是指定图像混合透明的函数, 在 Graphics、GraphUtil、RibbonStyleActnCtrls 单元用到.
下面的测试是把一张图片显示在窗体, 并可以调整透明度.
代码文件:
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: empTest.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.
窗体文件:
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
end
end