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From Harbs <harbs.li...@gmail.com>
Subject Layout optimizations
Date Fri, 23 Mar 2018 11:46:23 GMT
I’m working on making layouts more efficient. Currently, there’s lots of setting and reading
of width and height which causes many browser reflows. While profiling performance in my app,
reflows is a major bottleneck. In one area, it’s taking about 150ms (on my I7 2.8 Ghz MacBook
Pro — on tablets it’s painfully slow) to execute on area of layout. Almost all of that
time is being spent measuring with and height of components. The width and height getters
trigger reflow because properties are recursively set in layout.

I was able to get about a 10% improvement by optimizing the width and height getters to return
the explicitWdith and explicitHeight if set. It looks to me like almost all of this bottleneck
could be eliminated by delaying the property setting until after the measurements are done.
I’m working on doing that, but I have a question:

LayoutBase.performLayout has the following code:

					// check sizes to see if layout changed the size or not
					// and send an event to re-layout parent of host
					if (host.width != oldWidth ||
						host.height != oldHeight)
					{
						isLayoutRunning = true;
						host.dispatchEvent(new Event("sizeChanged"));
						isLayoutRunning = false;
					}

Under what circumstances does this code get executed? This appears to be causing a recursive
layout. Can I assume that there will be an explicitWidth/height when this will be executed?
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