I want to trigger where I click with the mouse on my QGraphicsView.
Problem here: this QGraphicsView is always zoomed in. But I want to get the point relative to the whole widget and not only to the viewport.
Or in other words: when I zoomed in and click on the upper left corner, the location should NOT be 0,0 (the QMousePressEvent just gives me this point). It should be the distance from there to the upper left corner of the whole sceneRectangle (or to the middle, doesn't matter).
Is there any way to do this?
Thanks for answers.
You can do what you want with Qt's mapToScene function.
Related
event->scenePosition().x();
event->scenePosition().y();
This way I can only get the current position of the cursor on the widget. It just tells me what position on the screen I clicked. I want to get the actual location of the widget when I scroll or zoom the widget.
I made a mathematical formula to get the actual position when zoomed in , zoomed out or scrolled the widget and was manipulating the screen coordinates according to scaling and scrolling , but this was not giving me high precision. Are there special functions for this in Qt?
I've seen that there can be an event handler for mouse click in viz, but not an equivalent for the Widget.
Is there any way to use the Point returned from viz::MouseEvent() to detect a click on a widget?
No, Widgets are not clickable.
You can:
get an MouseEvent
check the click checking if type == MouseButtonPress
get the Point in window where click happened
use converTo3DRay to get a ray representing click's all depths in 3D
iterate your widgets looking for intersection. Intersection is computed differently in each king of widget.
getWidgetPose gives you the pose in reference to the camera. getWidgetPose(...).translation() gives you the place the widget is. If you aren't comfortable with this translation, you can apply converTo3DRay.
If you find many widgets, you can order by z coordinate (the lower, the closer to camera). It works for points, it's harder for other geomtry.
I am implementing a function (Using Qt) that is supposed to move a widget to the cursor position as part of a drag and drop functionality.
I have three events that get triggered, mouse down, mouse move, and mouse up. When the mouse moves and is down, a signal is sent to the widget to move itself to the cursor; however, I have encountered some strange behavior.
This simple code:
void Block::moveToCursor()
{
block->move(block->mapFromGlobal(QCursor::pos()));
qDebug() << block->mapFromGlobal(QCursor::pos());
}
where "block" is a QLabel that is a member of Block and is a child of the window's central widget.
It produces this result:
As it can be seen in the debug output, the coordinates are flip flopping (or flickering) every time there is a pixel move. The first coordinated are correct but the second set of coordinates seem to be relative to the top right corner of the window.
I have tried all the mapping functions:
block->move(block->mapFromParent(QCursor::pos()));
-Produces a similar result with the second set of coordinates relative to the center of the window.
block->move(block->mapFrom(this->block, QCursor::pos()));
-This produces an even stranger result. The block does not flicker and moves correctly with respect to the mouse, but the initial position of the block seems to be off by the distance from the top right corner of the computer screen. It also only shows one point when printed out in debug, yet it is moving on the screen. Every time you see Continue Drag, the mouse has moved at least one pixel.
Can someone explain this strange behavior to me and show me the correct way of moving the widget to the cursor at the exact position from where it was originally clicked?
To get the coordinate in relation to the parent (like wanted from move()-Method), you need to use the mapFromGlobal on the parent like this:
block->move(block->parentWidget()->mapFromGlobal(QCursor::pos()));
Just give it a try. The reason for this is, lets consider what happens when you are at position 1,1 inside the child. But the child is for example at position 123,123 from its parent top-left. You would now move it to 1,1, causing it to jump 122 pixels each.
I have a rectangle class that has 2 points, the center axes point and the size of the rectangle. Lets say I want to drag the bottom of the rectangle with the mouse but keep the top of it in the same position. What is the algorithm to find the center position and the new rectangle size based on the mouse? Thanks in advance :)
Move the center in the same direction and half the distance (in either or both X and Y) as the bottom (right-hand corner) was dragged.
I would assume a graphics API is at hand here, what is it? I also assume that you have worked out how to detect that mouse clicking onto the edge of your box, have you decided exactly how that works though? do they just need to click near it, and they then drag the exact corner or what?
I can tell you that you are going to need to log the position of the mouse when they first click and get the differance to where they are now. Half that distance, and then add it to the original centre.
EDIT
oh, for the new size, its the difference of the mouse position added onto the original size. so if the mouse has moved down (increasing y) and left (decreasing x) say 10 units each way, you make the box ten units taller and ten narrower, the centre will be 5 down and 5 left.
It would be easier to tell the difference in the mouse movement, and create a new rectangle that size. Then use the rectangle class to check for the center point. Far easier than offsetting the old center.
This is my first attempt at writing a QT app, and I'm just trying to get a feel for how it works. My goal is to have a 400x400 widget which knows the exact position of the mouse when the mouse is hovering over it. For example, if the mouse was hovering in the top left corner, the position might be 10,10 (or something similar). If the mouse is in the bottom right corner, it might say 390,390.
Eventually, these coordinates will be displayed in a label on the main window, but that should be trivial. I'm stuck at the actual fetching of the coordinates. Any ideas?
For your widget, you must enable mouse tracking.
Then, you can either install an event filter, paying attention to mouse events and looking for the move event, or you can inherit from QWidget and override the mouse event, looking for mouse move events.
http://doc.qt.io/qt-4.8/qwidget.html#mouseTracking-prop
http://doc.qt.io/qt-4.8/eventsandfilters.html
http://doc.qt.io/qt-4.8/qmouseevent.html
If you are ever in a situation when you don't need actual tracking, just position at the moment, you can use QCursor::pos().