Improve the pan-redraw rendering sub-system cycle
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Key: UDIG-1771
URL: https://jira.codehaus.org/browse/UDIG-1771
Project: uDIG
Issue Type: Improvement
Components: visualization using map layer and style
Affects Versions: UDIG 1.2.2
Environment: Ubuntu 10.04 LTS 64bit, JRE 1.6, Eclipse 3.6.1
Reporter: Kenneth Gulbrandsøy
Priority: Minor
Fix For: UDIG 1.2.x
Attachments: test-0000.mpeg, test-0001.mpeg, test-0002.mpeg,
test-0003.mpeg, test-0004.mpeg, test-0005.mpeg
When panning a map with a WMS layer as a "background map", the WMS layer
disappear (is cleared), from the moment that the mouse button is released,
until the new WMS image is received. This is a bit annoying, reducing the
overall user experience. It would be better if the rendering sub-system kept
all old caches as they were on mouse button release, only clearing the map
extents which require new data.
After some initial debugging of the rendering sub-system, it seems that other
renderers suffers from the same problem (shape and postgis tested so far). But
since these renders receives new data much faster then WMS, the "white-out"
phase is much shorter, and therefore appear to keep the panned map until new
data is received, just as described above.
My understanding of the rendering sub-system is not that good (it is hard to
debug), but it seems to me that there is a "white-out" gap between the request
for new map bounds and the actual rendering of it. My experiments show that
this gap increase with the latency metric (see video screen captures). Since
WMS has a significantly longer latency then f.ex. postgis, the problem become
more visible when using a WMS georesource as a background map.
I have attached six screen capture videos showing the problem for WMS, Shape
and PostGIS (one without break-points and another with break-points per
georesource). These show that all renderers clear the map before new data is
received, which underpin my conclusions.
If somebody with a better understanding of the sub-system than me can shed some
light on the reasons behind the "white-out" phase, and where this happens in
the redraw cycle, I would be happy to look into solutions that remove the gap.
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