[webkit-qt] QImage vs QPixmap

[Zack Rusin]

On Wednesday 03 March 2010 14:35:03 Antti Koivisto wrote:
> Sure, QPixmap is faster if you are doing server side rendering on X11
> which I suppose was the platform you were optimizing for during the
> switch. The question is if that graphics pipeline makes much sense at
> all.

It was really the GL pipeline we were thinking about and I think that is still 
very valid.
 
> Most (all? at least CG and Skia) other WebKit ports use client side
> software rasterization (except for special cases like compositing
> layers). They deliver very good graphics performance, generally better
> than Qt.
> 
> Was this considered before switching to QPixmaps?

Back then that wasn't even an option, since the #1 priority for general web 
rendering was text and text on a qimage on anything but Windows was just not 
good enough. So the question was simply about rendering pure images and on all 
platforms qpixmap's were better (because they are always the native rendering 
format).

Software renders are a great answer to the question of quality, rather than 
performance. It's especially the case for mobile devices where even though 
GPU's are usually slower than the CPU's they use a very small fraction of the 
power that it would take to rasterize something on the CPU. So it's a 
combination of factors, if you end up using GPU's through and through you 
optimize for power usage, memory consumption and more often than not speed, if 
you end up using CPU's you usually optimize for the quality of rendering and 
simplicity of usage.

z