zoom in/out on a qwidget

rest

hi! i'm trying to zoom on a widget were i draw lines/curves.
and my problem is that it zooms just on the top left . it could be something with the resize of the widget?

my code is like this:

void DrawShape::wheelEvent(QWheelEvent *event)
{

const int degrees = event->delta() / 8;

int steps = degrees / 15;
double scaleFactor = 1.0;
const qreal minFactor = 1.0;
const qreal maxFactor = 10.0;




    if(steps > 0)
    {
        m_ScaleFactor.scaleX = (m_ScaleFactor.scaleX >= maxFactor) ? m_ScaleFactor.scaleX : (m_ScaleFactor.scaleX + scaleFactor);
        m_ScaleFactor.scaleY = (m_ScaleFactor.scaleY >= maxFactor) ? m_ScaleFactor.scaleY : (m_ScaleFactor.scaleY + scaleFactor);
    }
    else
    {
        m_ScaleFactor.scaleX = (m_ScaleFactor.scaleX <= minFactor) ? minFactor : (m_ScaleFactor.scaleX - scaleFactor);
        m_ScaleFactor.scaleY = (m_ScaleFactor.scaleY <= minFactor) ? minFactor : (m_ScaleFactor.scaleY - scaleFactor);
    }



update();

}

where m_ScaleFactor is a struct

mrjj

Hi
How do you apply the scale values?
Or do u mean, you zoom the actual drawing in paintEvent and not the widget it self?

rest

@mrjj i zoom in the paintEvent

mrjj

@rest
ok, must be something in the draw code then :)
Can you show paintEvent.

Also you say it only zoom in top left corner.
Can you tell more about that?

rest

void DrawShape::paintEvent(QPaintEvent *)
{
// we use this to make the background white
QStyleOption option;
option.init(this);
QPainter painter(this);
style()->drawPrimitive(QStyle::PE_Widget, &option, &painter, this);

painter.setPen(QPen(Qt::black, 7));
// we draw all the current points
for(int i = 0; i < shapeWeDrawNow.getAllPoints().size(); i++)
    painter.drawPoint(shapeWeDrawNow.getAllPoints()[i].getX(), shapeWeDrawNow.getAllPoints()[i].getY());

painter.setPen(QPen(Qt::black, 2));
// we draw all the current lines
for(int i = 1; i < shapeWeDrawNow.getAllPoints().size(); i++)
    if(shapeWeDrawNow.getAllPoints()[i].getType() == 'l' && shapeWeDrawNow.getAllPoints()[i-1].getType() != 'b')
        painter.drawLine(shapeWeDrawNow.getAllPoints()[i-1].getX(), shapeWeDrawNow.getAllPoints()[i-1].getY(), shapeWeDrawNow.getAllPoints()[i].getX(), shapeWeDrawNow.getAllPoints()[i].getY());
    else if(i >= 3 && shapeWeDrawNow.getAllPoints()[i-2].getType() == 'b' && shapeWeDrawNow.getAllPoints()[i-1].getType() == 'b')
    {
        QPainterPath path;
        path.moveTo(shapeWeDrawNow.getAllPoints()[i-3].getX(), shapeWeDrawNow.getAllPoints()[i-3].getY());
        path.cubicTo(shapeWeDrawNow.getAllPoints()[i-2].getX(), shapeWeDrawNow.getAllPoints()[i-2].getY(), shapeWeDrawNow.getAllPoints()[i-1].getX(), shapeWeDrawNow.getAllPoints()[i-1].getY(), shapeWeDrawNow.getAllPoints()[i].getX(), shapeWeDrawNow.getAllPoints()[i].getY());
        painter.drawPath(path);
    }

painter.scale(m_ScaleFactor.scaleX, m_ScaleFactor.scaleY);

}

rest

@mrjj is like he zooms just on the top and i would like it to zoom on the mouse position

mrjj

@rest
Hi
http://doc.qt.io/qt-5/qtwidgets-painting-transformations-example.html

Think you need to call .translate before you call .scale. so you move the origin from
topleft corner to mouse. Make sure the mouse position is already converted from global to local before used.

rest

@mrjj thanks, solved somehow, but now i have the problem that when i make another object, the first comes after him

mrjj

@rest
Well did you try to reset the translate before adding a new object ?