While debugging tdf#163945, Xcode's Instruments application uncovered
the following performance bottlenecks when using Skia/Metal:
1. Very slow rendering an NSBox:
Many system colors have the NSColorTypeCatalog color type. For
some unkown reason, setting the NSBox's fill color to a color set
to NSColorTypeCatalog causes drawing to take at least twice as
long as when the fill color is set to NSColorTypeComponentBased.
So, only draw with a fill color set to NSColorTypeComponentBased.
2. Excessively large offscreen buffers when drawing native controls:
The temporary bitmap was set to the control region expanded by
50 * mScaling (e.g. both width and height were increased by 200
pixels when running on a Retina display). This caused temporary
bitmaps to be up to several times larger than needed. Also,
drawing NSBox objects to a CGBitmapContext is noticeably slow
so filling all that unneeded temporary bitmap area can slow down
performance when a large number of NSBox objects like the status
bar are redrawn in quick succession.
Using getNativeControlRegion() isn't perfect, but it does try to
account for the focus ring as well as the minimum width and/or
height of the native control so union the two regions set by
getNativeControlRegion() and add double the focus ring width on
each side just to be safe. In most cases, this should ensure
that the temporary bitmap is large enough to draw the entire
native control and a focus ring.
3. Unncessary copying of bitmap buffer when drawing native controls:
Let Skia own the CGBitmapContext's buffer so that an SkImage
can be created without Skia making a copy of the buffer.
Change-Id: Ibd3abb4b9d7045c47268319772fe97a5c4dba3c6
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/177225
Tested-by: Jenkins
Reviewed-by: Patrick Luby <guibomacdev@gmail.com>
0807fe3628