Stefan Schimanski wrote:
Some profiling on Mac with Qt 4.2.x tells me:
* 18% QPainter::drawTextItem
* 18% QTextEngine::shape
* 70% paintPar (includes the upper two)
* 11% updateMetrics
So 70% of the whole painting process goes into paintPar. Am I wrong that
this part would go down more or less linearly in the number of
paragraphs we draw?
It should be possible to cache the Paragraph painting. That is, instead
of the word level caching. The key would then be the paragraph id.
Sounds promising...
Only 36% seem to be spent in Qt though.
I suspect there is more than that that does not immediately show in your
profile.
Those numbers come from sliding around the User Manual with the
scrollbar. Probably all that needs a deeper analysis, e.g. maybe the
numbers for other items go up without drawing (by caching effects...).
Instead of doing partial redraw, I would use a QPixmapCache to cache
word painting. The main problem in Mac is that Qt is damned slow at
font metrics calculation. And Qt needs to recalculate the font metrics
for each text painting. But caching small transparent pixmaps of
painted words inside QLPainter we can speedup painting tremendously.
I've played a bit with this approach some months ago and it is
certainly doable.
Interesting approach. One should implement a prototype and see what
happens.
I had a prototype once. It was quite easy to implement. Once I find some
time I'll try to redo it again.
Abdel.
