图像的双缓存问题！

Question

我简单的作了一个程序，发现图像画不出来，不知道我的错误在那里指点一下吧？procedure TForm1.Button1Click(Sender: TObject);
begin
with TBitmap.Create do try
canvas.Pen.Color:=clblue;
canvas.Brush.Style:=bsclear;
canvas.Ellipse(rect(100,200,300,400));
canvas.Ellipse(rect(130,230,330,430));
bitblt(Form1.Canvas.Handle,0,0,width,height,canvas.Handle,0,0,srccopy);
finally free;
end;
end;

Answer 1

with TBitmap.Create do try
Height := 800;
width := 600;
PixelFormat:= pf8bit; //加这句
canvas.Pen.Color:=clblue;
canvas.Brush.Style:=bsclear;
canvas.Ellipse(rect(100,200,300,400));
canvas.Ellipse(rect(130,230,330,430));
bitblt(Form1.Canvas.Handle,0,0,width,height,canvas.Handle,0,0,srccopy);
finally free;

Answer 2

？记得好像昨天刚回答了啊？
tbitmap没有初始化大小！比如加上：
Height := 100;
width := 100;