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List:       kde-kimageshop
Subject:    Re: Krita performance.
From:       Boudewijn Rempt <boud () valdyas ! org>
Date:       2013-05-22 9:11:23
Message-ID: 3964298.XfyC7dvADJ () linux-ixka ! site
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On Wednesday 22 May 2013 May 10:16:30 Dmitry Kazakov wrote:
> > So, I guess, we could implement a kind of scaled down cache in the
> > > KisImage. Then some actions (which are designed to support it) may be
> > > applied by the strokes framework first on the scaled down image and later
> > > on the original one. As stroked framework works in the background the UI
> > > will not be blocked during these actions.
> > > 
> > 
> > I think you this would need to go through the entire layer stack.
> > 
> 
> Yes, sure. That's why I suggest doing an optimization of the stack and of
> the cache stack. And if we want to implement this incrementally, we could
> first implement a single-node cache and then extend it to a graph.

I am fairly sure that photoshop does actually two or three things here:

* keep the full data compressed
* mipmapping
* do a kind of reverse composition first, like this:

1) for every screen pixel, determine the area of the image that is responsible for \
it. 2) go down the layer stack (not up, like we do), and check at which point that \
pixel becomes 100% opaque, possibly by simply using a nearest neighbour on every \
pixel in the area responsible for the display pixel, on the nearest mipmap. This is \
easy because their stack is fully linear, they don't have groups like we, and also no \
clone layers (as far as I can tell) 3) from that point, go up again

Then, I am guessing, they start in the background to composite the full image and \
when that is done, scale it and show it.

Nuke works this way, too, and does it by scanlines. For every pixel in the scanline, \
get the area of pixels in the image resolution and calculate back and forth. It's \
illuminating to read the nuke plugin coding docs.


-- 
Boudewijn Rempt
http://www.valdyas.org, http://www.krita.org, http://www.boudewijnrempt.nl

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