https://bugs.documentfoundation.org/show_bug.cgi?id=87485
--- Comment #53 from Clemens Eisserer <linuxhi...@gmail.com> ---
I did some digging, and although I am far from a solution (even a stop-gap
one), these are my findings:
- the gtk3 vcl plugin seems to render to a software surface, toms of cycles are
wasted scaling the input bitmap over and over in pixman library routines:
SvpSalGraphics::drawAlphaBitmap -> composite_boxes -> general_composite_rect
- the gtk and x11 vcl plugins seem to render to a native surface (which is
usually a lot better), however both are doing stupid stuff (extracting the
alpha values again and again) - therefore reading back image data from the
XServer using XGetImage (no-go for good performance):
drawinglayer::impBufferDevice::paint -> AlphaMask::AlphaMask -> Bitmap::Convert
-> ... -> X11SalBitmap::ImplCreateDIB -> XGetImage
Maybe I can find howto switch gtk3 to using a native XRender surface (these
days XRender is rather capable, layered above OpenGL (glamor) anyway) and then
work on the second issue...
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