XE8_TPaintBox画

procedure TForm1.PaintBox1Paint(Sender: TObject; Canvas: TCanvas);
var bitmap :TBitMap;
    pt1, pt2 :TPointF;
begin
  pt1 := TPointF.Create(0, 0);
  pt2 := TPointF.Create(PaintBox1.Width, PaintBox1.Width);

  //ShowMessage(‘yes‘);
  bitmap := TBitMap.Create(Trunc(PaintBox1.Width), Trunc(PaintBox1.Width));
  try
    bitmap.Canvas.BeginScene(); // ZC: 做画图工作时，这一句必须要
    bitmap.Canvas.Stroke.Kind := TBrushKind.bkSolid;
    bitmap.Canvas.Stroke.Color := TAlphaColorRec.Black;
    bitmap.Canvas.DrawLine(pt1, pt2, 1);
    bitmap.Canvas.EndScene;     // ZC: 做画图工作时，这一句必须要

    //TCanvas.CopyBitmap(bitmap, Canvas.Bitmap);
    //PaintBox1.Canvas.BeginScene(); // ZC: 这里，可以不执行这一句
    PaintBox1.Canvas.DrawBitmap(
      bitmap,
      TRectF.Create(0, 0, PaintBox1.Width, PaintBox1.Width),
      TRectF.Create(0, 0, PaintBox1.Width, PaintBox1.Width),
      1);
    //PaintBox1.Canvas.EndScene;     // ZC: 这里，可以不执行这一句
  finally
    if Assigned(bitmap) then
      bitmap.Free;
  end;
end;