[QGIS-Developer] QGIS 3.0 Sluggish on MacOS 10.13 with Retina Display

[Jeremy Palmer]

Hi All,

For some time I've been noticing that QGIS 3.0 on MacOSX has sluggish
canvas redraw speeds. When comparing between QGIS 2.18 and 3.0 I see ~4x
more CPU activity in 3.0 when performing the same set of operations on the
same dataset.

My test case was using a single raster VRT with overviews, and zooming in
and panning around the map cavnas for 20 sec. On average each time I tested
this case the total used CPU time for 2.18 was about 6 secs, but in
3.0dev-64369f8099 (complied against QT 5.10.0 with homebrew) I get total
CPU time of 25 secs. In QGIS 3.0 most of the time the application is using
100% CPU (one core) and spikes to about 180-200% CPU when the canvas
redraws are performed. When using a profiler it seems much of the time is
taken up in QImage::copy(QRect const&) within two seperate, but equivalent,
call subtrees. See [1] for more info.

Is anyone else seeing slow map canvas performance in QGIS 3.0 on MacOSX?

Cheers,
Jeremy

[1]  - https://imgur.com/a/ZSRTf
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