[webkit-qt] performance opportunities in graphics processing

[Ariya Hidayat]

>     (1) I see that since
> https://bugs.webkit.org/show_bug.cgi?id=41774 smooth pixmap transforms are
> enabled but with some overhead.
>           In my understanding we do not need such transforms if we
> draw/scale a pixmap to a smaller size. Isn't it?

Technically you still need it, otherwise the lack of filtering will
potentially yield the Moire pattern.

>  (2) Also from ImageQt.cpp I see statements due to
> https://bugs.webkit.org/show_bug.cgi?id=24229
>     if (!image->hasAlpha() && painter->compositionMode() ==
> QPainter::CompositionMode_SourceOver)
>         compositionMode = QPainter::CompositionMode_Source;
>
>     This statement often disable raster graphics engine optimization in
> void QRasterPaintEnginePrivate::recalculateFastImages()
> {
>     ......
>     s->flags.fast_images = !(s->renderHints &
> QPainter::SmoothPixmapTransform)
>                            && rasterBuffer->compositionMode ==
> QPainter::CompositionMode_SourceOver
>                            && s->matrix.type() <= QTransform::TxShear;
>     ......
> }
>    for some QImage::Format_RGB32 pages which are stored using a 32-bit RGB
> format (0xffRRGGBB) but regarded as without alpha channel according to
> qt/src/gui/image/qimage.cpp
>    I wonder if QImage::Format_RGB32 can be just regarded as a special case
> (always 0xFF alpha) of Format_ARGB32? What is the side-effect to keep the
> CompositionMode_SourceOver mode here beside the observed performance gain?

It's still useful for paint engines other than raster. But I agree,
maybe fast_images should include CompositionMode_Source as well?


-- 
Ariya Hidayat
http://www.linkedin.com/in/ariyahidayat