Problem with StretchDraw()

[shyub]

You need to open the file with the picture:

Code: Pascal  [Select][+][-]

1. Bmp.LoadFromFile(OpenPictureDialog1.FileName);

Then scale:

Code: Pascal  [Select][+][-]

1. MyBmp:=TBitmap.Create;
2. MyBmp.Width:=100;
3. MyBmp.Height:=100;
4. MyBmp.Canvas.StretchDraw(Rect(0, 0, MyBmp.Width, MyBmp.Height), Bmp);

However, after MyBMP is displayed on the screen, only a white background is obtained. (Output from Bmp - works without scaling.)

[paweld]

What system, version of lazarus and fpc? It would be best to include an example showing the problem.
There is no such problem on the current version.

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. var
3.   bmp, bmpscale: TBitmap;
4. begin
5.   if not OpenDialog1.Execute then
6.     exit;
7.   Invalidate;
8.   bmp := TBitmap.Create;
9.   bmp.LoadFromFile(OpenDialog1.FileName);
10.   bmpscale := TBitmap.Create;
11.   bmpscale.Width := 100;
12.   bmpscale.Height := 100;
13.   bmpscale.Canvas.StretchDraw(Rect(0, 0, bmpscale.Width, bmpscale.Height), bmp);
14.   Canvas.Draw(10, 50, bmpscale);
15.   Canvas.Draw(10 + bmpscale.Width + 20, 50, bmp);
16.   bmp.Free;
17.   bmpscale.Free;
18. end;  
19.  

[shyub]

Windows-10 x64, Lazarus 2.0.12.
Problem still exists.

[Josh]

Hi

Tbitmap has very limited support of image filetypes.
TPicture has much better support.

Also note your drawing straight to form canvas, this is not persitant, any form repainting and the imagewill vanish.

IIRC When a bitmap is created with width, height its filled with $FF ie white, delphi fills with $00

Code: Pascal  [Select][+][-]

1. var myPic:TPicture;
2.     myBMP:Tbitmap;
3. begin
4.   try
5.     myPic := TPicture.Create;
6.     myPic.LoadFromFile(OpenDialog1.FileName);
7.     try
8.       myBMP := TBitmap.Create;
9.       myBMP.Width := 100;
10.       myBMP.Height :=100;
11.       myBMP.Canvas.StretchDraw(Rect(0, 0, myBMP.Width, myBMP.Height), myPic.Graphic);
12.       Canvas.Draw(10, 50, myBMP);
13.       Canvas.Draw(10 + myBMP.Width + 20, 50, myPic.Graphic);
14.     finally
15.       myBMP.Free;
16.     end;
17.   finally
18.     myPic.Free;
19.   end;
20. end;

[paweld]

I checked on version 2.0.12 and it is also ok.
But maybe you have a problem somewhere else - as @Josh writes such way of drawing on the form is non-permanent, i.e. every time you refresh the form the canvas will be cleared.
If you want to have "permanent" drawing on the form then use the OnPaint event.

i.e:

Code: Pascal  [Select][+][-]

1. var
2.   bmp, bmpscale: TBitmap;
3.  
4. procedure TForm1.Button1Click(Sender: TObject);
5. begin
6.   if not OpenDialog1.Execute then
7.     exit;    
8.   bmp.LoadFromFile(OpenDialog1.FileName);
9.   bmpscale.Canvas.StretchDraw(Rect(0, 0, bmpscale.Width, bmpscale.Height), bmp);
10.   Invalidate;
11. end;
12.  
13. procedure TForm1.FormCreate(Sender: TObject);
14. begin
15.   bmp := TBitmap.Create;
16.   bmpscale := TBitmap.Create;
17.   bmpscale.Width := 100;
18.   bmpscale.Height := 100;
19. end;
20.  
21. procedure TForm1.FormDestroy(Sender: TObject);
22. begin
23.   bmp.Free;
24.   bmpscale.Free;
25. end;
26.  
27. procedure TForm1.FormPaint(Sender: TObject);
28. begin
29.   if bmp.Width > 0 then
30.   begin;
31.     Canvas.Draw(10, 50, bmpscale);
32.     Canvas.Draw(10 + bmpscale.Width + 20, 50, bmp);
33.   end;
34. end;            

[KodeZwerg]

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. var
3.   bmp: TBitmap;
4. begin
5.   if OpenPictureDialog1.Execute then
6.     begin
7.       bmp := TBitmap.Create;
8.       try
9.         bmp.LoadFromFile(OpenPictureDialog1.FileName);
10.         Image1.Proportional := False;
11.         Image1.Stretch := False;
12.         Image1.Picture.Bitmap.Assign(bmp);
13.         Image1.Proportional := True;
14.         Image1.Stretch := True;
15.       finally
16.         bmp.Free;
17.       end;
18.     end;
19. end;

[shyub]

The problem was solved this way:

Code: Pascal  [Select][+][-]

1. MyBmp.Canvas.StretchDraw(Classes.Rect(0, 0, MyBmp.Width, MyBmp.Height), Bmp);