How to Create QGraphicsItem(Lines, Rectangles, etc.) in QGraphicsScence by mouse?

darrenleeleelee1

@JonB thanks, I will try it.
I also wondering could I create somthing like this.(pen)

I know how to do in QPainter, But I want create as QGraphicsItem.

darrenleeleelee1

@JonB And I also wondering I should override mousePressedEvent in QGraphicsScence or QGraphicsView, both of them have mousePressedEvent but I don't know which to override.

JonB

@darrenleeleelee1
If you want to create those "freehand" letter drawings as a GraphicsItem you would have to add it as a QGraphicsPathItem composed from a multi-item QPainterPath. Unless you are prepared to do it as a QGraphicsPixmapItem, and lose the ability to manipulate the points.

It probably doesn't matter which of QGraphicsScence or QGraphicsView to catch the mouse event, so long as it works. I did refer you to the DiagramScene example which seems to use the scene's mouse event.

darrenleeleelee1

@JonB Sorry, maybe I was misled you, I want a pen that I can draw anything I want, kind of doodle?Just one stroke when the mouse released the stroke become an object.

kind of this.

JonB

@darrenleeleelee1
You might get some clues from https://doc.qt.io/qt-5/qtwidgets-widgets-scribble-example.html in combination with https://forum.qt.io/topic/94586/draw-line-on-mouse-click & https://forum.qt.io/topic/94622/need-help-with-qgraphicsitem-painter .

darrenleeleelee1

@JonB ok, sorry I still have some question.

How can I do like I pressed mouse and hold, to draw a line until I released mouse, the line will become an object.

JonB

@darrenleeleelee1
I don't know what to say, it's just code you need to write. Note where the mouse goes down, note where the mouse is released and at that stage create a QGraphicsLineItem or whatever between those two points.

darrenleeleelee1

@JonB But if I create the QGraphicsLineItem at mousedReleasd, when I holding the mouse pressed, I can't see the line.

jsulm

@darrenleeleelee1 said in How to Create QGraphicsItem(Lines, Rectangles, etc.) in QGraphicsScence by mouse?:

But if I create the QGraphicsLineItem at mousedReleasd, when I holding the mouse pressed

How can you get mouse released event if you hold mouse button pressed? Can you please explain better?

darrenleeleelee1

@jsulm I want to override mouseMoveEvent to get my mouse position when my mouse is holding.

darrenleeleelee1

@jsulm I am thinking if I can change the existing QGraphicsLineItem to keep update to where my mouse position, and the start position is the moused click position.But I don't know how to adjust existing QGraphicsLineItem.

JonB

@darrenleeleelee1 said in How to Create QGraphicsItem(Lines, Rectangles, etc.) in QGraphicsScence by mouse?:

But I don't know how to adjust existing QGraphicsLineItem.

Again, I don't know what to say. You have QGraphicsLineItem::setLine(). I don't see the problems you see.

darrenleeleelee1

@JonB You are right, sorry I am thinking too complicated