Delphi 與 DirectX 之 DelphiX(12): TPictureCollectionItem.DrawAlpha

　本例效果圖:

　　代碼文件:

unit Unit1;
interface
uses
　Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
　Dialogs, DXDraws, StdCtrls, DXClass, ComCtrls;
type
　TForm1 = class(TForm)
　　DXDraw1: TDXDraw;
　　DXImageList1: TDXImageList;
　　TrackBar1: TTrackBar;
　　procedure FormCreate(Sender: TObject);
　　procedure TrackBar1Change(Sender: TObject);
　end;
var
　Form1: TForm1;
implementation
{$R *.dfm}
var
　PicItem: TPictureCollectionItem;
procedure TForm1.FormCreate(Sender: TObject);
const
　ImgPath1 = 'C:TempDelphiX.bmp';
begin
　DXImageList1.DXDraw := DXDraw1;
　PicItem := TPictureCollectionItem(DXImageList1.Items.Add);
　PicItem.Picture.LoadFromFile(ImgPath1);
　TrackBar1.Max := 255;
　TrackBar1.Min := 0;
　TrackBar1.Height := 22;
　TrackBar1.ShowSelRange := False;
　TrackBar1.Align := alBottom;
end;
procedure TForm1.TrackBar1Change(Sender: TObject);
var
　r: TRect;
begin
　r := Bounds((DXDraw1.Width - PicItem.Width) div 2,
　　　　　　　(DXDraw1.Height - PicItem.Height) div 2,
　　　　　　　 PicItem.Width,
　　　　　　　 PicItem.Height);
　DXDraw1.Surface.Fill(0);
　PicItem.DrawAlpha(DXDraw1.Surface, r, 0, TrackBar1.Position);
　DXDraw1.Flip;
end;
end.