Qt4-preview-feedback Archive, April 2007
drawText on QGraphicsView
Message 1 in thread
Hello,
I am looking for ways to speed up the drawing of small portions of text
on my graphics items. Or alternatively, I am looking for assurance that
text drawing on graphics views will be vastly improved in Qt 4.3.
On a graphics view with about 10 graphics items, if I remove all the
calls to QPainter::drawText from inside the derives classes paint method
and just leave the painting for other parts of the graphics item (lines,
rectangles, curves) I achieve resonable performance. However, as soon as
I turn on the drawing of small pieces of text on the graphics items,
typically one or two latin character words on each graphics item,
centered in a rectangle, the performance degrades beyond usable. Drawing
text 10 or 20 times makes repainting of the entire scene take over a
second at certain scale settings of the graphics view QMatrix.
Regards,
Andy.
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Message 2 in thread
Hi Andy,
You may try to draw text out of your own classes - just using
QGraphicSimpleTextItem (with Z greater then your classes Z). May be drawing
in rect takes the time?
Best regards,
Igor Grivko
5 ÐÐÑÐÐÑ 2007 10:28, Andrew Ward ÐÐÐÐÑÐÐ:
> Hello,
> I am looking for ways to speed up the drawing of small portions of text
> on my graphics items. Or alternatively, I am looking for assurance that
> text drawing on graphics views will be vastly improved in Qt 4.3.
>
> On a graphics view with about 10 graphics items, if I remove all the
> calls to QPainter::drawText from inside the derives classes paint method
> and just leave the painting for other parts of the graphics item (lines,
> rectangles, curves) I achieve resonable performance. However, as soon as
> I turn on the drawing of small pieces of text on the graphics items,
> typically one or two latin character words on each graphics item,
> centered in a rectangle, the performance degrades beyond usable. Drawing
> text 10 or 20 times makes repainting of the entire scene take over a
> second at certain scale settings of the graphics view QMatrix.
>
> Regards,
> Andy.
>
> To unsubscribe - send "unsubscribe" in the subject to
> qt4-preview-feedback-request@xxxxxxxxxxxxx
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Message 3 in thread
Andrew Ward wrote:
> Hello,
> I am looking for ways to speed up the drawing of small portions of
> text on my graphics items. Or alternatively, I am looking for
> assurance that text drawing on graphics views will be vastly improved
> in Qt 4.3.
>
> On a graphics view with about 10 graphics items, if I remove all the
> calls to QPainter::drawText from inside the derives classes paint
> method and just leave the painting for other parts of the graphics
> item (lines, rectangles, curves) I achieve resonable performance.
> However, as soon as I turn on the drawing of small pieces of text on
> the graphics items, typically one or two latin character words on each
> graphics item, centered in a rectangle, the performance degrades
> beyond usable. Drawing text 10 or 20 times makes repainting of the
> entire scene take over a second at certain scale settings of the
> graphics view QMatrix.
Have you tried disabling anti-aliasing of text with
graphicsView->setRenderHint( QPainter::TextAntialiasing, false );
--Dave
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Message 4 in thread
Thanks for your replies Igor and Dave,
Using a QGraphicsSimpleTextItem is not an option for me, however I
checked and it uses much the same code behind the scenes as
QPainter::drawText does anyway.
With regard to TextAntialiasing I don't even think this flag is used on
Windows, I could not see it referenced anywhere in the Qt code while
stepping through a call to QPainter::drawText, and the output looks the
same whether it is set or not.
I must admit that I am surprised by the huge amounts of code run before
the final call to the Windows function 'ExtTextOutW' to actually draw
the text.
Here is a profile constructed using LTProf of the call trace using most
of the CPU time in the application. Percents are the total application
time spent in that particular function.
49.59% QPainter::drawText
49.58% qt_format_text
49.35% QTextLine::draw
49.22% drawMenuText
49.15% QPainter::drawTextItem
48.53% QRasterPaintEngine::drawTextItem
41.55% QRasterPaintEngine::drawTextInFontBuffer
I am not sure I trust this profile completely, because it says that 98%
of the time spent in QRasterPaintEngine::drawTextInFontBuffer is spent
in the line:
d->fontRasterBuffer->resetBuffer(255);
Which simply does a memset, which should be very quick.
Looking at the docs for QRasterPaintEngine it says this class is only
available in Qtopia, but I am using Windows XP, maybe the docs are
misleading?
Andy.
Dave Smith wrote:
> Andrew Ward wrote:
>> Hello,
>> I am looking for ways to speed up the drawing of small portions of
>> text on my graphics items. Or alternatively, I am looking for
>> assurance that text drawing on graphics views will be vastly improved
>> in Qt 4.3.
>>
>> On a graphics view with about 10 graphics items, if I remove all the
>> calls to QPainter::drawText from inside the derives classes paint
>> method and just leave the painting for other parts of the graphics
>> item (lines, rectangles, curves) I achieve resonable performance.
>> However, as soon as I turn on the drawing of small pieces of text on
>> the graphics items, typically one or two latin character words on
>> each graphics item, centered in a rectangle, the performance degrades
>> beyond usable. Drawing text 10 or 20 times makes repainting of the
>> entire scene take over a second at certain scale settings of the
>> graphics view QMatrix.
>
> Have you tried disabling anti-aliasing of text with
> graphicsView->setRenderHint( QPainter::TextAntialiasing, false );
>
>
> --Dave
>
> To unsubscribe - send "unsubscribe" in the subject to
> qt4-preview-feedback-request@xxxxxxxxxxxxx
>
>
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