QGraphicsView 90 degree Rotation

[keksi venksi]

Hi all ,

I try to apply rotation through transform.rotate(90) , Rotation works fine in this case . But when i try to apply zoom , the view disappears in this case . So I wish to find some other way for rotation .

I have found some example for rotation . Among all transform.setmatrix (m11,m12,m13,m21,m22,m23,m31,m32,m33) works fine .But In the example the matrix values are calculated for 180 degree .
I want to find the values for 90 degree .
Means can any one help me to find the values of the matrix for 90 degree

[A Former User]

Hi!

See Rotation matrix, Affine transformations, Homogeneous coordinates.

[keksi venksi]

Hi !!!!

Thanks for your reply .
There is a correction in my angle im using clokwise 90 degree So the angle is -90 degree
I got the coordinates for the -90 degree matrix
m11= 0 m12 = 1 m13 = 0
m21 = -1 m22 = 0 m23 = 0
m31 = 0 m32 = 0 m33 = 1

I got the actual transformation which i want .
But I got another one issue by achieving this.
When you look into the matrix the value m11 and m22 are equal to zero .
These m11 is for horizontal scaling and m22 is for vertical scaling
So in wheelevent when i try to scale the value of horizontal and vertical scaling coordinates it becomes zero
**view.scale(view.transform().m11()1.05 , view.transform().m22()1.05)
The value becomes zero in both X and Y.
So Now my questions i have achieved the transformation but I want some help for handling the wheel vent to zoom the view along -90 degree
Please can anyone help me on this issue to handle the wheelevent to acheive zoomIn() and zoomOut()

[A Former User]

See example code below.

customgraphicsview.h

#ifndef CUSTOMGRAPHICSVIEW_H
#define CUSTOMGRAPHICSVIEW_H

#include <QGraphicsView>

class CustomGraphicsView : public QGraphicsView
{
    Q_OBJECT
public:
    explicit CustomGraphicsView(QWidget *parent = nullptr);
    void reset();

protected:
    void wheelEvent(QWheelEvent* event) override;

private:
    void updateTransform();
    double m_scale = 1.0;
    double m_angle = 0.0;
};

#endif // CUSTOMGRAPHICSVIEW_H

customgraphicsview.cpp

#include "customgraphicsview.h"
#include <QBrush>
#include <QColor>
#include <QWheelEvent>

CustomGraphicsView::CustomGraphicsView(QWidget *parent)
    : QGraphicsView(parent)
{
    setBackgroundBrush(QBrush(QColor("grey")));
}

void CustomGraphicsView::reset()
{
    m_scale = 1.0;
    m_angle = 0.0;
    updateTransform();
}

void CustomGraphicsView::wheelEvent(QWheelEvent *event)
{
    auto const delta = (event->delta() <0.0) ? -1.0 : 1.0;
    if (event->modifiers() & Qt::ShiftModifier)
        m_scale += 0.1 * delta;
    else
        m_angle += 15.0 * delta;
    updateTransform();
}

void CustomGraphicsView::updateTransform()
{
    QTransform t;
    t.scale(m_scale, m_scale);
    t.rotate(m_angle);
    setTransform(t);
}

[keksi venksi]

@Wieland said in QGraphicsView 90 degree Rotation:

void CustomGraphicsView::updateTransform()
{
QTransform t;
t.scale(m_scale, m_scale);
t.rotate(m_angle);
setTransform(t);
}

Thanks for your kind reply with full code .
When i try to apply this code the code scales the view in x direction . In my caes if i rotate my view 90 clockwise it should scale in Y direction .

Means in normal mode when i try to zoom , the view should expand by width mean while when i rotate and zoom in that rotated view it should expand in height

[keksi venksi]

A Short note to all regarding this issue .

Currently I have achieved the 90 degree clockwise rotation thourgh

QTransform transform1;
transform1.rotate(90);
// Set the Views transformation
view()->setTransform(transform1);

Rotation works fine

I try to achieve zooming functionality using fitInView()

Normal case
fitInView(0,0,calcValue,viewRect.height())

In this case , zooming works fine

90 rotation case
fitInView(0,0,viewRect.weight(),calcValue)

In this case , zooming is not not achieved . Please help me .

I dont want to use scale() method because I set some restrictions in zooming through calcValue depending on the delta of the wheelEvent

[keksi venksi]

Please some one look into this issue . Timely helps are really appreciable .

[A Former User]

Sry, I think I don't understand exactly what you want to do. Maybe you can draw a few pictures to help my imagination :)

[keksi venksi]

I tried to add image in my post but i cant .
Can you help me on it

[keksi venksi]

@Wieland

X Mode

**-----------------------------|

-----------------------------**
Width

This is how I locate my graphicsview at initial stage

Im achieving zooming through wheel event .

I have currentZoomingWidth level if the delta is +ve then i will increase the currentZoomingWidth level and if it is -ve then i will decrease the currentZoomingWidth
So finally i find the width to expand (currentZoomingWidth )

wheelvent()
{
fitInVieW(0,0,currentZoomingWidth ,view().geometry().height())
}
So zooming is achieved through fitInView()

Y MODE
| |
| |
| |
| |
| | Height
| |
| |

Width

Like same case im calculating the currentZoomingWidth depending upon the delta and applying it to fitInView() height

wheelvent()
{
fitInVieW(0,0 ,view().geometry().width(),currentZoomingWidth)
}

In X mode i apply the calculated zoom factor to width and in Y mode I apply it to the height

My problem is In X mode the fit in view works fine but in Y mode it works weird

[A Former User]

@keksi-venksi said in QGraphicsView 90 degree Rotation:

I tried to add image in my post but i cant .
Can you help me on it

Hi! The image-upload feature on our forum is broken, you might see the picture but other users don't. Please upload your image to a image hoster of your choice (e.g. postimage.org) and embed the pic here with the following markup: ![alternate text](image-url). See also How to insert image on this forum and Hitchhiker's Visual Guide to the Qt Forum.

[keksi venksi]

@Wieland

I have explained my query in my previous post . Please give your suggestions

Any how i have added the image here .This is how my graphicsview rotated .
Now i wanna apply zooming functionality using fitinview in this 90 degree rotated graphicsview .

This is how Y Mode looks

[kshegunov]

Use two QTransform objects - one for rotation and one for scaling, then multiply them in the proper order (the order of multiplication matters as scaling and rotation don't commute). After that apply your transform to whatever you need.

[keksi venksi]

@kshegunov
Thanks for your reply .
Can you give some example code .

[kshegunov]

QTransform rotation;
rotation.rotate(90);

QTransform scaling;
scaling.scale(0.5, 1);

setTransform(rotation * scaling);
// Or
QVector2D vector;
vector = rotation * scaling * vector;

Modify according to your needs.

[keksi venksi]

@kshegunov

Thanks for your reply .

In my case I dont want to use scale to zoom

I wish to use fitInView() to achieve zoom.

In short note after applying transform (rotate 90 degree) fitInView() does not works fine . I want fitInView() to do zoom

[keksi venksi]

@keksi-venksi

Can any one help me on it .
Helps are really appreciable

[A Former User]

customgraphicsview.h

#ifndef CUSTOMGRAPHICSVIEW_H
#define CUSTOMGRAPHICSVIEW_H

#include <QGraphicsView>

class CustomGraphicsView : public QGraphicsView
{
    Q_OBJECT
public:
    enum class Mode
    {
        x,
        y
    };

    explicit CustomGraphicsView(QWidget *parent = nullptr);
    void reset();
    void fit();
    void setMode(Mode mode);

protected:
    void wheelEvent(QWheelEvent* event) override;

private:
    void updateTransform();
    Mode m_mode = Mode::x;
    double m_scale = 1.0;
};

#endif // CUSTOMGRAPHICSVIEW_H

customgraphicsview.cpp

#include "customgraphicsview.h"
#include <QBrush>
#include <QColor>
#include <QWheelEvent>
#include <QDebug>

CustomGraphicsView::CustomGraphicsView(QWidget *parent)
    : QGraphicsView(parent)
{
    setBackgroundBrush(QBrush(QColor("grey")));
}

void CustomGraphicsView::reset()
{
    m_mode = Mode::x;
    m_scale = 1.0;
    updateTransform();
}

void CustomGraphicsView::fit()
{
    auto const r = scene()->itemsBoundingRect();
    switch (m_mode) {
    case Mode::x: {
        double f1 = width() / (r.width() + 2);
        double f2 = height() / (r.height() + 2);
        m_scale = qMin(f1,f2);
        updateTransform();
        break;
    }
    case Mode::y: {
        double f1 = height() / (r.width() + 2);
        double f2 = width() / (r.height() + 2);
        m_scale = qMin(f1,f2);
        updateTransform();
        break;
    }
    }
}

void CustomGraphicsView::setMode(CustomGraphicsView::Mode mode)
{
    if (m_mode == mode)
        return;
    m_mode = mode;
    updateTransform();
}

void CustomGraphicsView::wheelEvent(QWheelEvent *event)
{
    auto const delta = (event->delta() <0.0) ? -1.0 : 1.0;
    m_scale += 0.1 * delta;
    updateTransform();
}

void CustomGraphicsView::updateTransform()
{
    QTransform t;
    if (m_mode == Mode::y)
        t.rotate(90);
    t.scale(m_scale, m_scale);
    setTransform(t);
}

[keksi venksi]

@keksi-venksi

I would like to continue with this thread

in the normal mode im using view->fitInView(rect.x(),0,rect.width(),30)

in the 90 degree rotated mode im using view->fitInView(0,rect.y(),30,rect.height())

I have tried with different combinations of fitInView for 90 degree rotataion Nothing works

Can any one suggest me the coordinates for the fitInView() for the rotated view

Help me on it

[A Former User]

@keksi-venksi Please try the code above that I just posted. If I understood you right, then it should meet your requirements :)