Text does not drawn properly in RTOL locale on Mac OS X

[sanjayshelke]

Hi all,

I am facing very strange problem with the behavior of QPainter::drawText in RTOL locale on Mac OS X.

If i draw any text by providing bounding rect and specifying the alignment like drawText( rt, Qt::AlignLeft, text), it does not drawn properly.

ANy one knows why this is happening?


Thanks in advance.

regards,
~Sanjay

[wysota]

What does "not drawn properly" mean in this case?

[sanjayshelke]

I have customized QGraphicsItem to draw the custom fractions like "1000 1/2".
SO in RTOL locale this fraction should be displayed as "1/2 1000".
In Paint() i written code to draw the 1000 to the left of the bounding rect and 1/2 to the right of the bounding rect.
This is working properly on Windows in RTOL or LTOR locale.

But on Mac OS X these texts are getting overlapped on each other in RTOL locale.

[wysota]

Can we see the code?

[sanjayshelke]

I have attached the sources. please have a look.

[wysota]

To me it seems the layout of text has nothing to do with the effect you get. As you are drawing everything yourself, Qt can't decide on anything. The only thing it could do (I don't say it does) is to reverse the meaning of right and left when calling QPainter::drawText() but this is easy to check - simply reverse the flag in your code when doing RTOL on a Mac and see if it helps. If it's still wrong then you're probably calculating positions incorrectly. It also depends on what "overlapping" means in your case.

[sanjayshelke]

I tried with reversing the flag in the code when doing RTOL on a Mac, but it does not work.
The text gets overlapped means

1/2

and

1000

gets overlapped.

i guess there is problem while drawing text with the alignment flags on Mac OS X in RTOL locale.

As far as their positions are concerned their calculations are straightforward. I dont think so there is any problem.

The most notable thing is that this works fine on windows. I agree that the windows architecture is different but then the question is this problem should be there on windows for RTOL if the calculation is wrong.

[wysota]

The text gets overlapped means and gets overlapped.

Yes, that explains a lot

Are they drawn in exactly the same place or does only parts cover the same region? Maybe you could post a screenshot?

[sanjayshelke]

Sorry that was a typo mistake.

I have attached two screen shots for your reference. One screen shot contains overlapped text and other is required text.


Please have a look

[wysota]

To me it seems your item may simply be too narrow. Try increasing the boundingRect() and see if it changes anything.

[sanjayshelke]

Increasing the bounding rect does solve my problem.
BUt then this is the incorrect way to fix this issue. I am just finding out why this is been incorrect in RTOL locale.

If you can see the implementation of boundingRect() of this item, it has been implemented properly as far as my knowledge is concerned.

see this :

QRectF QFractionTextItem :: boundingRect()const
{
	return  QRectF( 0, 0 ,m_nWidth, m_nHeight*2 );
}

QRectF QFractionTextItem :: boundingRect()const
{
	return  QRectF( 0, 0 ,m_nWidth, m_nHeight*2 );
}

To copy to clipboard, switch view to plain text mode 

where m_nWidth is the addition of QFontMetrics::width("1000") and qMax( QFontMetrics::width("1") , QFontMetrics::width("2") )

SO i am just wondering what is going wrong behind the screen.

[wysota]

BUt then this is the incorrect way to fix this issue.

True. The correct way is to fix your code which apparently computes the bounding rect incorrectly.

where m_nWidth is the addition of QFontMetrics::width("1000") and qMax( QFontMetrics::width("1") , QFontMetrics::width("2") )

Maybe there is some margin somewhere? Try adding this code to your paint():

painter->save();
painter->setPen(Qt::red);
painter->drawRect(boundingRect());
painter->restore();

painter->save();
painter->setPen(Qt::red);
painter->drawRect(boundingRect());
painter->restore();

To copy to clipboard, switch view to plain text mode 

Also you don't tell the item that its bounding rect changes when you change the font. You should call prepareGeometryChange() after setting the font.

[sanjayshelke]

I tried this option of drawing rectangle around its bounding rect, but there is no margin.

The most important thing i like to point out that if you draw the text by specifying the x and y pos( do not provide rectt and alignment while drawing text ), it does draws the text properly without getting overlapped on each other.

But even though i have implemented the boundingRect() method correctly, it clips some part of the text from outside.

here are some points i have highlighted
1.QFontMetrics is not working properly and hence giving incorrect width of the text
2.boundingRect() is incorrect ( which looks like the root cause but its implemenation is very straight forward and correct )
3.QPainter::drawText() with the parameter rect and alignment flags behaves incorrectly in RTOL locale on Mac. ( this is sure a Qt bug )

[wysota]

(1) is impossible - it wouldn't work in many other cases as well and apparenty it does work otherwise every output in Qt would be a mess
(2) may only be your own fault
(3) is possible although if I were you I would refrain from using the word "surely" until you look at source code of the method and prove it is a bug. Right now I am closer to proving it is not a bug in Qt than you are to proving it is. At least I have taken a look into the source code and I can say there is no ifdef for mac in code responsible for drawing the text through your method.

[sanjayshelke]

ok. I agreed that i have not taken a look on the methods i have used. I do not have a source code of Qt. I will take it first.
But then i am still unable to find out the cause of this weird behavior.
What you suggest ion this?

[sanjayshelke]

Based on the points i have highlighted i troubleshoot the issue.
Further debugging the issue i could found some fruitful observations.
Observation are:

font used in the class is "Comic Sans Ms" and point size is 18
1.in LTOR locale
QFontMetrics::width("1000") returns 41 value
QFontMetrics::width("900") returns 33 value
QFontMetrics::width("90") returns 22 value

2.in RTOL locale
QFontMetrics::width("1000") returns 30 value
QFontMetrics::width("900") returns 22 value
QFontMetrics::width("90") returns 22 value


it looks that QFontMetrics::width() gives incorrect values on Mac OS X in RTOL locale.

You can also try out this by just drawing "1000" in your customized QGraphicsItem on Mac OS X in RTOL and LTOR locale. Just drawing text "1000" gets clipped.

[wysota]

Did you try other fonts as well? Maybe the font itself is broken...

[sanjayshelke]

Yes i have tried with other fonts also. But the problem still exist.

[wysota]

Run one of existing Qt applications (like Designer) with the -reverse parameter. See if widths of text (especially in message boxes where the texts are long) got screwed up.

[sanjayshelke]

Which message box your talking about in designer app? Can you please elaborate?
I can see none of the text displayed on designer app is screwed up.