CODEWITHSUNDEEP
qtsvgrotationrotational-matricesqtsvg
flatronka
flatronka

Reputation: 1081

QGraphicsSvgItem positioning after rotation

I encountered a strange issue/feature when I try to rotate a QGraphicsSvgItem object and set a position.

Check the following example: I have one .svg for the sake of simplicity that is a blue rectangle. I create two QGraphicsSvgItem using the file and I rotate on of them with 90 degree. I set both of them to the same position, however the rotated one positioned 'wrongly'(maybe that is the correct behaviour). It looks like that the x,y coordinate(top-left corner) is now the top-right corner, remains like that it is not rotated. It looks strange from my viewpoint, I expect that when I rotate and set the position the 'first point' of the shape should be where the shape 'starts'.

I hope with the source code is more understandable that I wrote above:

    SVGDom *bubbleDom = shadowgram->bubble();
    _bubble = new DrawableSvgItem(sh->message(), bubbleDom->byteArray());
    this->addItem(_bubble);
    _bubble->setPos((this->width()-_bubble->sceneBoundingRect().width()) / 2, (this->height() - _bubble->sceneBoundingRect().height()) / 2);
    qDebug() <<"Bubble pos: " << _bubble->pos();
    qDebug() <<"Bubble boundindRect: " << _bubble->boundingRect();
    qDebug() << "Bubble rect: " <<_bubble->sceneBoundingRect();
    qDebug() << "Bubble topleft: " <<_bubble->sceneBoundingRect().topLeft();

    DrawableSvgItem *bubble2 = new DrawableSvgItem(sh->message(), bubbleDom->byteArray());
    this->addItem(bubble2);
    bubble2->setRotation(90);
    bubble2->setPos(_bubble->pos());
    qDebug() << "Bubble2 pos: " << bubble2->pos();
    qDebug() <<"Bubble2 boundindRect: " << bubble2->boundingRect();
    qDebug() << "Bubble2 rect: " <<bubble2->sceneBoundingRect();
    qDebug() <<"Bubble2 topleft: " << bubble2->sceneBoundingRect().topLeft();

DrawableSvgItem is only an extension of QGraphicsSvgItem, I created for drawing sourcepaths into the item. Currently I am not using it.

Output:

Bubble pos:  QPointF(413.5, 297)
Bubble boundindRect:  QRectF(0,0 171x117)
Bubble rect:  QRectF(296.5,297 117x171)
Bubble topleft:  QPointF(296.5, 297)
Bubble2 pos:  QPointF(413.5, 297)
Bubble2 boundindRect:  QRectF(0,0 171x117)
Bubble2 rect:  QRectF(411.458,297 173.016x119.967)
Bubble2 topleft:  QPointF(411.458, 297)

In pictures, I expect the following:

enter image description here

But I got the following image:

enter image description here

I found a similar problem here.

Upvotes: 0

Views: 1318

Answers (1)

a_manthey_67
a_manthey_67

Reputation: 4286

bubble2 is rotated around its transform origin point. That is by default 0,0 in the coordinates of bubble2. Additionally bubble2->setPos() sets this point to the 0,0 of _bubble, so you only need to adjust bubble2->setPos() to the wanted pos. You can change the transform origin point by setTransformOriginPoint().

edit 5.11.2014:

Top-left of bubble2 is defined in bubble2-coordinates. These coordinates are not changed by items transformations, after rotation the top-left corner of the item is the same corner as before. This point is placed by setPos(). So picture 2 shows the correct behaviour. The corner, you want to place on bubble(x,y), is bubble2's bottom-left corner. To get picture 1 you only need to add 1 line to your code: either move bubble2 in last step by its height to the right

bubble2->setpos(413.5 + 117, 297)

or as first step set transformation origin point of bubble2 to bottem left corner

bubble2->setTransformOriginPoint(0,117)

Upvotes: 1

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