I have a QGraphicsScene and i want to do zooming ( in and out ) with a qpushbutton , i have this code :
void fonction(){
Scene = new QGraphicsScene(this);
ui->graphicsView->setScene(Scene);
QPen Pen ;
QBrush Brush(Qt::red) ;
Pen.setWidth(5);
ellipse = Scene->addEllipse(2,2,30,30,Pen,Brush);
}
How to do it ?
I have tried :
void HomePage::on_pushButton_4_clicked()
{
if(Zoom!=10 ){
Zoom=Zoom+0.1 ;
}
ui->graphicsView->show();
}
But something does not happen .
You haven't used your Zoom variable to do anything with QGraphicsView. You'll need to call:
ui->graphicsView->scale (Zoom, Zoom);
This will change the zoom level. The method scales the current transformation by the value of Zoom. Your code doesn't show what Zoom starts as, but you'll want it to start 1, I suspect. If it starts at 0, so that the first Zoom level is 0.1, then your scene will zoom very far out on the first button press.
In order to control this, you may want to use ui->graphicsView->transform() to get the current transformation matrix and look at the m11 and m22 values for the current zoom levels.
Again, the scale method scales the current transformation, so each time you call it, you're scaling from the current scale factors, not the original values (which are 1 by default, indicating no scaling transformation).
Related
I am trying to implement the same functionality in my widget as it is in cv:: namedWindow.
The goal is to enable zooming and to make the overlay with the grid and the values of pixel's colors directly over the original pixmap. Here is the example: сv picture zoomed:
I inherited the QGraphicsView widget, added to QGraphicsScene the QGraphicsPixmapItem and reimplemented the QWheelEvent so that zooming in and out works correctly now. The problem starts with creating an overlay.
Instead of creating a pack of QGraphicsLineItems and adding them to the scene in order to make the grid, I inherit the QGraphicsRectItem and draw the whole grid on it.
void QGraphicsOverlayItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
QPen pen(Qt::black);
pen.setWidthF(0.02);
painter->setPen(pen);
painter->setBrush(Qt::BrushStyle::NoBrush);
QVector<QLineF> crossLines = createCrossLines();
painter->drawLines(crossLines);
}
This works very fast. But when I try to drawText with the QPainter and set the QFont:: pointSizeF() as small as possible, it works incorrectly (symbols change their size from small to huge during zooming or even disappear at all). Nevertheless, the best result that I get this way is the following:
the QPainter's drawText() result:
QFont font(painter->font());
font.setPointSizeF(0.1);
font.setLetterSpacing(QFont::SpacingType::AbsoluteSpacing,0.01);
painter->setFont(font);
painter->drawText(432,195,"123");
The easiest way is to add to scene a lot of QGraphicsTextItems and scale them to correct size, but it is too slow.
So the question is how can I subscribe the pixel's color value in the QGraphicsScene directly over the QPixmapItem?
I finally watched through the openCV source code and found what I looked for.
The answer for me was the QTransform matrix. OpenCV developers show the image not by using the scene in the QGraphicsView, but actually painting the image directly on the viewport in the paintEvent.
The QTransform matrix is stored in the class and is passed to QPainter in the beginning of the paintEvent.
void DefaultViewPort::paintEvent(QPaintEvent *event)
{
QPainter painter(viewport());
painter.setWorldTransform(param_matrixWorld);
painter.drawImage(QRect(0,0,viewport()->width(),viewport()->height()),image2Draw,QRect(0,0,image2Draw.width(),image2Draw.height()));
If you know the ratio of the image's size to the widget's size, and you also know the scale of QTransform matrix used to paint the image, it is easy to calculate how much area does the single source pixel take on the screen:
qreal ratioX = width() / float(image2Draw.width());
qreal ratioY = height() / float(image2Draw.height());
double pixel_width = qtransform_matrixWorld.m11()*ratioX;
double pixel_height = qtransform_matrixWorld.m11()*ratioY;
If we know the pixel_height, we can just set the QFont::pixelSize like this:
QFont font = painter->font();
font.setPixelSize(pixel_height/5);
painter->setFont(font);
I need to draw a circle with QPainter. When I used drawEllipse function like :
void UserClass::Draw(QPainter &painter) {
painter.save();
painter.setBrush( GetColor() );
QPoint centerPosition = GetCenterPosition();
painter.drawEllipse( centerPosition, m_CircleOuterRadius, m_CircleOuterRadius);
painter.setBrush(QColor(0, 0, 0, 0));
painter.drawEllipse( centerPosition, m_CircleInnerRadius, m_CircleInnerRadius);
painter.restore();
}
Unfortunately result is not what I desired. I want to have inner circle not be filled. That is why I put alpha value as zero but ofcourse it didn't work. How can I have a circle which is not until a certain radius with qt ?
You should create a QPainterPath then add the two circles to it via addEllipse(), the outer first, then the inner. This will effectively give you a shape that is the outer circle with the inner circle punched as a hole.
Then you fill the painter path with a green brush, which will result in a hollow ring. Afterwards, if you want the white outlines, you can stroke the path with a white pen as well.
Also note that the painter path can be created only once and stored for reuse instead of creating it anew every time you redraw.
I wanted to have an online monitoring system that could tell where the shape is currently, but am getting very weird coordinates of the item, also the dimensions of it get higher by 1 each time I create new one and drag it.
Initial position (map size is 751 by 751, checked by outputting to qDebug(), scene bound to yellow space) :
Dragging it to the left top corner.
As you can see in the beginning it was on (200;200), but after dragging it is on (-201;-196). After deleting it and creating new shape on the same position with the same properties, new shape can't be seen because it is outside of the map, which suggests that edits don't show correct data.
Here is the code of updating the edits:
void CallableGraphicsRectItem::mouseReleaseEvent(QGraphicsSceneMouseEvent* event)
{
QGraphicsRectItem::mouseReleaseEvent(event);
ptr->updateEdits(this);
}
Here is what I managed to cut down into updateEdits():
void MainWindow::updateEdits(QAbstractGraphicsShapeItem* item)
{
//stuff not related to scene
auto posReal = item->scenePos();
auto pos = posReal.toPoint();
//create QString from coordinates
QString coordinate;
coordinate.setNum(pos.x());
ui->leftXEdit->setText(coordinate);
coordinate.setNum(pos.y());
ui->upperYEdit->setText(coordinate);
//get width and height for rect, radius for circle
auto boundingRectReal = item->sceneBoundingRect();
auto boundingRect = boundingRectReal.toRect();
ui->widthEdit->setText(QString::number(boundingRect.width()));
//disables height edit for circles, not really relevant
if (!items[currentShapeIndex].isRect)
{
ui->heightEdit->setDisabled(true);
}
else
{
ui->heightEdit->setDisabled(false);
ui->heightEdit->setText(QString::number(boundingRect.height()));
}
}
Here is how I anchor the QGraphicsScene to the left top corner of the yellow area:
scene->setSceneRect(0, 0, mapSize.width() - 20, mapSize.height() - 20);
ui->graphicsView->setScene(scene);
How can I report the right data to the edits?
You're better off overriding the itemChange method and using the ItemPositionHasChanged notification. You have to set the ItemSendsGeometryChanges flag on the item so that it receives these notifications.
I'm not sure that your item's final position has been set when you're still in the mouseReleaseEvent method. Tracking it in itemChange will ensure that the data is valid, and this kind of thing is what it's for.
Also, note that "pos" is in the item's parent coordinates, and "boundingRect" is in the item's coordinate space. You should use "scenePos" and "sceneBoundingRect" if you want to be sure you're using scene coordinates. If the item doesn't have a parent, then "pos" and "scenePos" will return the same values, but "boundingRect" and "sceneBoundingRect" will generally differ.
I'm building a very simple image editor on Qt creator.I have my image displayed on a QGraphicsView and i want to give the user the ability to zoom in and out by a pushbutton.
I've searched a lot and found how to zoom in and out through the mouse wheel.As i am very new to Qt i can't adjust it to the pushbutton because i don't understand everything clearly.
I' ve tried this(without understanding completely what i'm doing)but the result isn't the wanted.It zooms in only once and quite abruptly.I want a smoother zoom and as many times as i want.
void MainWindow::on_pushButton_clicked(){
QMatrix matrix;
ui->graphicsView->setTransformationAnchor(QGraphicsView::AnchorViewCenter);
matrix.scale(1.0,1.0);
ui->graphicsView->setMatrix(matrix);
ui->graphicsView->scale(1,-1);
}
I would be very grateful if you guys can help
Below is how I implemented zooming in my subclass of QGraphicsView. Note that you'd need to pass in different values of "zoom" to get different magnifications as the zoom factor is an absolute value, not a relative one.
(The optMousePos argument can be set to point to a QPoint indicating the spot that should be the central-point of the zoom transformation, or it can be left NULL if you don't care about that. I use it because I zoom in and out based on the user turning the wheel in his mouse, and when doing that, the user usually wants to zoom in towards the point where his mouse point is currently positioned, rather than in towards the center of the graphics area)
qreal _zoom = 0.0;
[...]
void MyQGraphWidgetSubclass :: SetZoomFactor(qreal zoom, const QPoint * optMousePos)
{
if ((zoom != _zoom)&&(zoom >= 0.02f)&&(zoom <= 1000000.0f))
{
QPointF oldPos;
if (optMousePos) oldPos = mapToScene(*optMousePos);
// Remember what point we were centered on before...
_zoom = zoom;
QMatrix m;
m.scale(_zoom, _zoom);
setMatrix(m);
if (optMousePos)
{
const QPointF newPos = mapFromScene(oldPos);
const QPointF move = newPos-*optMousePos;
horizontalScrollBar()->setValue(move.x() + horizontalScrollBar()->value());
verticalScrollBar()->setValue(move.y() + verticalScrollBar()->value());
}
}
}
void MyQGraphWidgetSubclass :: wheelEvent(QWheelEvent* event)
{
QPoint pos = event->pos();
SetZoomFactor(_zoom*pow(1.2, event->delta() / 240.0), &pos);
event->accept();
}
I have a class MaskGraphicsWidget.cpp inheriting from QGraphicsView which contains several functions, the constructor is:
MaskGraphicsWidget::MaskGraphicsWidget(QTreeWidget * tree, QWidget* parent) : QGraphicsView(parent), m_tree_widget(tree){
setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
m_mask_scene = new QGraphicsScene;
m_mask_scene->setSceneRect(0, 0, 250, 250);
setScene(m_mask_scene);
primitive = 0;
minX = 0;
minY = 0;
}
where I initialize my scene m_mask_scene and I set the coordinate system.
I also have a function MousePressEvent :
http://pastebin.com/wjwDTQzw
And my MaskGraphicsWidget.h is like that :
QGraphicsScene* m_mask_scene;
QList<QPointF> m_polygon_points;
QList<QGraphicsLineItem*> m_polygon_lines;
int minX;
int minY;
My problem is that, I want to set the Pos of the QGraphicsPolygonItem poly but if I set it to the value min and max (that I calculate somewhere else), the item moves from the current Pos to the Pos of min and max. Basically it sets the Pos of the item in his own coordinate system. How can I write that I want to set the Pos in the coordinate system of the m_mask_scene ?
Sorry for my English, if you did not understand, feel free to add a comment !
Edit 1 :
m_polygon_points and m_polygon_lines are filled somewhere else and it's working. (see pastebin)
Edit 2 : Added the plan, see below for better (I hope) understanding !
Explanation of the plan : the black polygon is what I got (I do not set any Pos), but if I do set the Pos at min and max, I get the red polygon. I want to set the Pos at min and max AND still have the black polygon ! Sorry for my poor paint skills
Edit 3 : Of course, if I print the Pos of the QGraphicsPolygonItem poly, it shows (0,0).
Edit 4 : Added a pastebin to not overload the post, I've put everything in it, please ignore the PrimitiveItem things, and the case 0 and 1 which are not for the QGraphicsPolygonItem.
Edit 5 : To clarify, I catch the event on MousePressEvent:
if it's a left click, I use it to create a new point (creating new lines for my polygon)
if it's a right click, I don't use the event but instead I just close my polygon, delete all the lines added to the scene and adding the polygon in the scene.
QPointF point(event->x(), event->y());
With event being a QMouseEvent, a call to x() and y() returns coordinates relative to the widget that receives the event. In this case, MaskGraphicsWidget, which is a QGraphicsView.
If you add an item to a scene and want to set its position, you're setting its position relative to its parent. In the case of an item with no parent, the position is relative to the scene (in scene coordinates).
So your current code is trying to set view coordinates, not scene coordinates. You need to convert the position of the mouse coordinates to the scene: -
QPointF scenePoint = mapToScene(event->pos());
Then use this to set the position of the newly created item.
Note that a QGraphicsView is like a window looking into a world (the QGraphicsScene), so it may not match the scene coordinates.