//举例:
{绘制直线}
procedure TForm1.Button1Click(Sender: TObject);
begin
  Canvas.Pen.Color := clRed; {设置画笔颜色}
  Canvas.Pen.Width := 2;     {设置画笔宽度}

  Canvas.MoveTo(10,10);      {直线起点}
  Canvas.LineTo(100,100);    {直线终点}

{这里的 Canvas 是简写, 也可以写做: Self.Canvas 或 Form1.Canvas }
end;

{矩形填充}
procedure TForm1.Button2Click(Sender: TObject);
begin
  Canvas.Brush.Color := clYellow; {设置画刷颜色, 也就是填充色}
  Canvas.FillRect(ClientRect);    {填充窗体客户区}
end;


//效果图: