Downscaling with Lanczos

[dsiders]

has anyone questioned the popup doc for the canvas.Draw(.....) ?

It states it calls the StretchDraw and so on, read the rest.

What is it specifically that *you* question? Give a fellow a goal...

[jamie]

it's a misleading description of what happens in the end.

you call DRAW, which does not resize the image but the docs leads you to believe the image is going to be resized because it's calling the StretchDraw.

 In reality, the image does not get resized at all, it just gets clipped off.


in any case, if you are on windows and want to natively use StretchDraw for a faster experience for a real stretch of an image.

Code: Pascal  [Select][+][-]

1.   SetStretchBltMode(hDC,HALFTONE);
2.                 StretchBlt(hDC,630,500,200,200, hDC, 0,0,400,400, SRCCOPY);
3.  

[dsiders]

it's a misleading description of what happens in the end.

you call DRAW, which does not resize the image but the docs leads you to believe the image is going to be resized because it's calling the StretchDraw.

 In reality, the image does not get resized at all, it just gets clipped off.

Thank you. That I can address.

[lainz]

Try with BGRABitmap:
https://forum.lazarus.freepascal.org/index.php/topic,41745.msg290230.html#msg290230

Code: Pascal  [Select][+][-]

1. var
2.   bgra: TBGRABitmap;
3. begin
4.   bgra := TBGRABitmap.Create('file.jpg');
5.   BGRAReplace(bgra, bgra.Resample...)
6.  
7. end;

[dsiders]

it's a misleading description of what happens in the end.

you call DRAW, which does not resize the image but the docs leads you to believe the image is going to be resized because it's calling the StretchDraw.

 In reality, the image does not get resized at all, it just gets clipped off.
[/code]

I am planning to patch the topic to the following:

Code: Text  [Select][+][-]

1. Draws the image content in SrcGraphic on the canvas at the specified position.
2.  
3. Draw is reintroduced method in TCanvas; it reimplements the
4. inherited method to use the TGraphic instance in SrcGraphic as the
5. container with the image content drawn in the method.
6.  
7. No actions are performed in the method if SrcGraphic has not been assigned.
8.  
9. Draw calls the StretchDraw method to render the content in SrcGraphic on the
10. canvas at the position specified in X and Y. The Width and Height in SrcGraphic
11. set the bounds for the image rectangle applied to the canvas using StretchDraw.
12. Since a stretch mode is not enabled when StretchDraw is called, the source
13. graphic is not enlarged or shrunk to the canvas size. The source graphic is
14. clipped if its bounds exceeds the canvas bounds. The Draw method in SrcGraphic
15. performs the actions needed to position and rendering the content to the Pixels
16. in the canvas.
17.  
18. CopyMode determines the raster operation performed for the Pixels affected on
19. the canvas.
20.  
21. Calling Draw causes the OnChanging and OnChange events to be signalled (when
22. assigned). OnChanging occurs prior to calling Draw in the TGraphic instance.
23. OnChange occurs after calling Draw in the TGraphic instance.
24.  

Is that more accurate?

[jamie]

Yes, that looks much better.
Thank you

[dsiders]

Yes, that looks much better.
Thank you

Thanks for the heads-up.