How draw a rotated text in a QPainterPath?

[darksaga]

don't know exactly, coz i've not yet worked with QPainterPath,

but you should take a look @ the QMatrix class

you could do something like:

QMatrix mat;
mat.rotate(myAngle);

QMatrix mat;
mat.rotate(myAngle);

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and then you should use

//QPainterPath map ( const QPainterPath & path ) const 
//e.g.:
QPainterPath newPath = mat.map(oldPath);

//QPainterPath map ( const QPainterPath & path ) const 
//e.g.:
QPainterPath newPath = mat.map(oldPath);

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this shold get the job done, I think

[iw2nhl]

Thank you very much darksaga!!!
This was exactly what I was looking for!

Now the rotated rectangle is no more a problem.
Probably I can use the same way to make the text fit the rectangle: I could draw a text in a generic size (say 10 pts), than I can scale it's painter path in both x and y to fill the rectangle.
I'll post if it works or not :-)

[iw2nhl]

Thank you again because I solved the other problem too, in fact I could scale and rotate the text perfectly!
I just draw the text with the default size and then I scale it depending on the rectangle size.

Just I changed the rectangle mapping from a QPainterPath to a QPolygonF, because I think it is faster (QPainterPath handles curves too, while QPolygonF handles just points). I converted it to a QPainterPath after the mapping.

Here is the code (may be it can be useful to someone else):

{
            // Rectangle mapping
 
            QLineF rectBase = QLineF(begin, end);
            qreal angle = rectBase.angle(QLineF(QPointF(0, 0), QPointF(1, 0)));
            QMatrix rotationMatrix;
            rotationMatrix.translate(begin.x(), begin.y());
            rotationMatrix.rotate(angle);
            path.addPolygon(rotationMatrix.map(QPolygonF(textRectangle)));
 
            // Text mapping
 
            QFont font = QFont("courier");
            // Take text size
            QFontMetricsF fm(font);
            QSizeF textSize = fm.size(0, text);
            // Calculate how much to scale the text to fit the rectangle
            qreal scaleX = textRectangle.width() / textSize.width();
            qreal scaleY = textRectangle.height() / textSize.height();
            // Apply the scale factors
            rotationMatrix.scale(scaleX, -scaleY);
            // Draw the text
            QPainterPath textPath;
            textPath.addText(QPointF(0, -fm.descent()), font, text);
            path.addPath(rotationMatrix.map(textPath));
}

{
            // Rectangle mapping

            QLineF rectBase = QLineF(begin, end);
            qreal angle = rectBase.angle(QLineF(QPointF(0, 0), QPointF(1, 0)));
            QMatrix rotationMatrix;
            rotationMatrix.translate(begin.x(), begin.y());
            rotationMatrix.rotate(angle);
            path.addPolygon(rotationMatrix.map(QPolygonF(textRectangle)));

            // Text mapping

            QFont font = QFont("courier");
            // Take text size
            QFontMetricsF fm(font);
            QSizeF textSize = fm.size(0, text);
            // Calculate how much to scale the text to fit the rectangle
            qreal scaleX = textRectangle.width() / textSize.width();
            qreal scaleY = textRectangle.height() / textSize.height();
            // Apply the scale factors
            rotationMatrix.scale(scaleX, -scaleY);
            // Draw the text
            QPainterPath textPath;
            textPath.addText(QPointF(0, -fm.descent()), font, text);
            path.addPath(rotationMatrix.map(textPath));
}

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[iw2nhl]

I also added a little border to not have the text touching the rectangle:

{
            // [...]
 
            // Leave a 1 pixel wide border around the text
            const qreal borderSize = 1;
            const qreal doubleBorder = borderSize * 2;
            // Calculate how much to scale the text to fit the rectangle
            qreal scaleX = textRectangle.width() / (textSize.width() + doubleBorder);
            qreal scaleY = textRectangle.height() / (textSize.height() + doubleBorder);
            // Apply the scale factors
            rotationMatrix.scale(scaleX, -scaleY);
            // Center the text (because of the border)
            qreal offsetX = borderSize;
            qreal offsetY = borderSize;
            // Draw the text
            QPainterPath textPath;
            textPath.addText(QPointF(offsetX, -(offsetY + fm.descent())), font, text);
 
            // [...]
}

{
            // [...]

            // Leave a 1 pixel wide border around the text
            const qreal borderSize = 1;
            const qreal doubleBorder = borderSize * 2;
            // Calculate how much to scale the text to fit the rectangle
            qreal scaleX = textRectangle.width() / (textSize.width() + doubleBorder);
            qreal scaleY = textRectangle.height() / (textSize.height() + doubleBorder);
            // Apply the scale factors
            rotationMatrix.scale(scaleX, -scaleY);
            // Center the text (because of the border)
            qreal offsetX = borderSize;
            qreal offsetY = borderSize;
            // Draw the text
            QPainterPath textPath;
            textPath.addText(QPointF(offsetX, -(offsetY + fm.descent())), font, text);

            // [...]
}

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Now I have troubles in getting exact font size because QFontMetricsF seems to be very inaccurate and often the text goes outside the rectangle because it is bigger than what is reported.
Probably I'll make another post for this problem , anyway I think it is not easily solvable (Qt or X11 or KDE Bug?).