unit1.pas

Delphi7应用编程150例附书源码.rar

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, StdCtrls;

type
  TfrmMain = class(TForm)
    Image1: TImage;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  frmMain: TfrmMain;
  Bitmap:TBitmap;
implementation

{$R *.dfm}

procedure TfrmMain.Button1Click(Sender: TObject);
var
  sBlendFunction: BlendFunction;
  // 这是Alpha混合时需要的一个类型参数
  i: byte;
begin
    if Button1.Caption='淡入' then
    begin
        Button1.Caption:='淡出';
        with sBlendFunction do
        // 设置初值
        begin
            BlendOp := AC_SRC_OVER;
            // 目前唯一支持的一种混合方式
            BlendFlags := 0;
            // 必须为零
            AlphaFormat := 0
            // 缺省
        end;
        for i := 0 to 51 do // 共有51帧
        begin
            sBlendFunction.SourceConstantAlpha:= i * 5;
            // 从全透明到不透明，每次渐变5级
            Windows.AlphaBlend(Image1.Canvas.Handle,0,0,Image1.Width,
               Image1.Height,Bitmap.Canvas.Handle,0,0,
               Bitmap.Width,Bitmap.Height,sBlendFunction);
               // Alpha混合处理
            sleep(50);
            // 延时50毫秒，适当的延时可让效果看起来更逼真
            Image1.Refresh;
            // 一定要实时刷新Image1，才能看出变化
        end;
    end
    else
    begin
        Button1.Caption:='淡入';
        with sBlendFunction do
        begin
            BlendOp := AC_SRC_OVER;
            BlendFlags := 0;
            AlphaFormat := 0;
        end;
        for i := 0 to 51 do
        begin
            sBlendFunction.SourceConstantAlpha:= i * 5;
            Windows.AlphaBlend(Image1.Canvas.Handle,0,0,Image1.Width,
               Image1.Height,Bitmap.Canvas.Handle,0,0,
               1,1,sBlendFunction);
            sleep(50);
            Image1.Refresh;
        end;
    end;
end;

procedure TfrmMain.FormCreate(Sender: TObject);
begin
    Bitmap:=TBitmap.Create;
    Bitmap.LoadFromFile('鸟.bmp');
end;

procedure TfrmMain.FormDestroy(Sender: TObject);
begin
    Bitmap.Free;
end;

end.