Multithreaded filter about bgrabitmap HOT 7 CLOSED

I fixed it, with 2 threads now works fast and fine!
https://forum.lazarus.freepascal.org/index.php/topic,48085.msg345826.html#msg345826

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Here I tried
https://github.com/bgrabitmap/multithreadedfilter

But I get an exception, that i'm out of memory for creating the thread (like when I resize a lot the form). But it works at least is a start.

I asked in the forum
https://forum.lazarus.freepascal.org/index.php/topic,48085.0.html

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Now I fixed it, but the main form is not very fast or responsive, maybe it can be fixed with another technique.

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I close this since maybe it's good to process images in a background process, is not good for displaying on screen that's one if not the main way to use bgrabitmap.

Is faster using a single thread, at least on my machine. So don't worth the time trying if even the grayscale filter works badly.

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For blur, it is a bit more complicated than grayscale. It cannot be done in-place because the content of pixels influence other pixels. For example, if the first thread changes pixels at the bottom of its target rectangles before the second thread reads those, then the blur result would be different.

Then, the current algorithm for blur would not be adapted, because the source rectangle for pixels is wider than the destination rectangle. For example, if the second thread target area starts at row 100 and the blur radius is 10, then it needs to read pixels from row 90.

So one would need to write a new version of the blur algorithm that can take two rectangles as input, the source and the destination rectangle.

Second difficulty, in order to optimize blur, I've approximated it by a series of box blur one on another:

  if radiusX*radiusY >= 100 then
  begin
    tempDest := ADestination.NewBitmap;
    tempDest.SetSize(ADestination.Width,ADestination.Height);
    FilterBlurBox(bmp,bounds,radiusX/3.2,radiusY/3.2,tempDest);
    FilterBlurBox(tempDest,bounds,radiusX/2.9,radiusY/2.9,ADestination);
    FilterBlurBox(ADestination,bounds,radiusX/3.2,radiusY/3.2,tempDest);
    FilterBlurBox(tempDest,bounds,radiusX/2.3,radiusY/2.3,ADestination, ACheckShouldStop);
    tempDest.Free;
    exit;
  end; 

In this case, each thread need to wait for the others to have completed before going to the next box blur.

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Oh I see, well, it was a good experiment anyways =)

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Yeah threads are interesting. :)

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