Be careful with QPainter::drawRect etc

[Thiago Macieira]

John Tapsell wrote:
>Hey all,
>
>  I have tracked down a bugs in KFormula where the problem was that:
>
>QPainterPath rect;
>rect.addRect(0, -baseLine(), width(), baseLine() );
>painter.drawPath( rect );
>
>and
>
>painter.drawRect(0, -baseLine(), width(), baseLine() );
>
>Draw different rectangles.  The reason for this is that addRect takes
>reals, and drawRect takes int.  The drawRect thus loses precision, and
>draws incorrectly.
>
>This is a very subtle and very nasty bug, as at 500% zoom, it's off by
>less than 10 pixels typically.
>
>I have grepped the koffice source code and found hundreds of uses of
>drawRect, drawLine etc.  I'm sure that many of this are wrong.
>
>Can we put a check for this use ebn?  There will be false positives,
>but I think we need to check all uses of this.

Please file this with qt-bugs and have Trolltech verify that this is the 
intended behaviour.

Someone today showed to me some rectangles drawn with incorrect sizes 
under some circumstances. He was showing some painter code. It could be 
the same problem.

When you see a problem in Qt, don't forget to tell Trolltech so we can fix 
it.
-- 
  Thiago Macieira  -  thiago (AT) macieira.info - thiago (AT) kde.org
    PGP/GPG: 0x6EF45358; fingerprint:
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