Is TFPImageCanvas.StretchDraw slow

[Zaher]

My project is small bitmap font editor, I am adding new control to edit small png transparent image with alpha pixles.

Drawing pixels started being slow at size > 64, with scaling it 10 times

here the part of code of painting it

Code: Pascal  [Select][+][-]

1. var
2.   Img: TBitmap;
3.   fpimage: TLazIntfImage;
4. begin
5.   if IsChanged then
6.   begin
7.     IsChanged := False;
8.     if (PaintTool <> nil) and not (ptsDirect in PaintTool.Style) then
9.     begin
10.       ScrachImage.CopyPixels(FImage);
11.       PaintTool.Paint(FScrachCanvas);
12.       fpimage := ScrachImage;
13.     end
14.     else
15.       fpimage := Image;
16.  
17.     ScaledImage.CopyPixels(BackgroundImage);
18.     ScaledCanvas.DrawingMode := dmAlphaBlend;
19.     //ScaledCanvas.Interpolation := TFPBoxInterpolation.Create; moved to after create ScaledCanvas
20.     ScaledCanvas.StretchDraw(0, 0, ScaledImage.Width, ScaledImage.Height, fpimage);
21.   end;
22.  
23.   Img := TBitmap.Create;
24.   try
25.     Img.LoadFromIntfImage(ScaledImage);
26.     vCanvas.Draw(0, 0, Img);
27.   finally
28.     Img.Free;
29.   end;
30. end;
31.  

and images created here

Code: Pascal  [Select][+][-]

1.   FImage := TLazIntfImage.Create(cDefaultWidth, cDefaultHeight, [riqfRGB, riqfAlpha]);
2.   FCanvas := TFPImageCanvas.Create(FImage);
3.   FDrawer := TIntfFreeTypeDrawer.Create(FImage);
4.   FFont := TFreeTypeFont.Create;
5.   FFont.Name := 'c:\Windows\fonts\Arial.ttf';
6.   FFont.SizeInPixels := 9;
7.   FFont.Hinted := False;
8.   FFont.ClearType := False;
9.   FFont.Quality := grqLowQuality;
10.  
11.   FScrachImage := TLazIntfImage.CreateCompatible(FImage, cDefaultWidth, cDefaultHeight);
12.   FScrachCanvas := TFPImageCanvas.Create(FScrachImage);
13.  
14.   ScaledImage := TLazIntfImage.CreateCompatible(ScrachImage, ScrachImage.Width * DotSize, ScrachImage.Height * DotSize);
15.   ScaledCanvas := TFPImageCanvas.Create(ScaledImage);
16.   ScaledCanvas.Interpolation := TFPBoxInterpolation.Create;
17.  
18.   BackgroundImage := TLazIntfImage.CreateCompatible(ScrachImage, ScrachImage.Width * DotSize, ScrachImage.Height * DotSize);
19.   BackgroundCanvas := TFPImageCanvas.Create(BackgroundImage);
20.  
21.   FHistory := TntvHistory.Create;
22.  
23.   SetSize(cDefaultWidth, cDefaultHeight);
24.  

my project is opensource https://github.com/parmaja/minictrls/blob/master/native/ntvPixelGrids.pas#L612

Where is my fault, or Is there any way to make it faster painting or generating scaled image?