Philippe wrote:
> I run in release, yes.
>
> What is strange to me is this:
>
> One of my main and large widget draws thousands of lines (no
> antialisaing), a gradient background, a bit of to text, to display data
> changing in real time (hence the importance of speed).
>
> I need to maintain a cache hence I draw into a QImage. I choose a QImage
> because it is faster than drawing into a QPixmap, at least for the
> graphics I do, as I could test it.
>
> Now, if I do:
>
> QApplication::setGraphicsSystem("raster");
>
> then my widget display is much slower than if I do nothing (eg. "native").
> I don't understand this, as drawing into a QImage is "raster" (as far as
> I understand). So I don't know why there is any difference of speed at
> all.
Are you still drawing to a temporary QImage in the raster case?
Is drawing directly to a QImage followed by QPainter::drawImage() faster
than graphicssystem raster and drawing directly to QPainter?
> And as far as I remember, there was not this difference with 4.5.0.
> However, I don't have 4.5.x installed anymore to confirm today.
>
> BTW, one thing I don't understand, is that drawing so in a QImage is
> much faster under Windows than Mac (same machine). I know the difference
> of quality between VC++ and GCC, but the speed difference is large
> enough not to rely on this sole explanation, IMHO.
> Maybe the time needed to render a QImage onto screen is different
> between the two platforms?...
GCC is a lot worse than VC++, I've observed VC being up to 3x faster in
tight loops based for the same code in extreme cases, but the difference
doesn't bubble up to application level... Possibly a +/-10% difference.
Could it be that you are not getting SSE/MMX instructions on Mac? Are
you on 10.4 by any chance?
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