# GraphicsScene

class pyqtgraph.GraphicsScene(clickRadius=2, moveDistance=5, parent=None)

  Extension of QGraphicsScene that implements a complete, parallel mouse event system. (It would have been preferred to just alter the way QGraphicsScene creates and delivers events, but this turned out to be impossible because the constructor for QGraphicsMouseEvent is private)

  > - Generates MouseClicked events in addition to the usual press/move/release events. (This works around a problem where it is impossible to have one item respond to a drag if another is watching for a click.)

  > - Adjustable radius around click that will catch objects so you don’t have to click exactly over small/thin objects

  > - Global context menu–if an item implements a context menu, then its parent(s) may also add items to the menu.

  > - Allows items to decide _before_ a mouse click which item will be the recipient of mouse events. This lets us indicate unambiguously to the user which item they are about to click/drag on

  > - Eats mouseMove events that occur too soon after a mouse press.

  > - Reimplements items() and itemAt() to circumvent PyQt bug

  Signals |
  sigMouseClicked(event) | Emitted when the mouse is clicked over the scene. Use ev.pos() to get the click position relative to the item that was clicked on, or ev.scenePos() to get the click position in scene coordinates. See `pyqtgraph.GraphicsScene.MouseClickEvent`.
  sigMouseMoved(pos) | Emitted when the mouse cursor moves over the scene. The position is given in scene coordinates.
  sigMouseHover(items) | Emitted when the mouse is moved over the scene. Items is a list of items under the cursor.
  sigItemAdded(item) | Emitted when an item is added via addItem(). The item is given.
  sigItemRemoved(item) | Emitted when an item is removed via removeItem(). The item is given.

  Mouse interaction is as follows:

  1. Every time the mouse moves, the scene delivers both the standard hoverEnter/Move/LeaveEvents as well as custom HoverEvents.

  2. Items are sent HoverEvents in Z-order and each item may optionally call event.acceptClicks(button), acceptDrags(button) or both. If this method call returns True, this informs the item that _if_ the user clicks/drags the specified mouse button, the item is guaranteed to be the recipient of click/drag events (the item may wish to change its appearance to indicate this). If the call to acceptClicks/Drags returns False, then the item is guaranteed to not receive the requested event (because another item has already accepted it).

  3. If the mouse is clicked, a mousePressEvent is generated as usual. If any items accept this press event, then No click/drag events will be generated and mouse interaction proceeds as defined by Qt. This allows items to function properly if they are expecting the usual press/move/release sequence of events. (It is recommended that items do NOT accept press events, and instead use click/drag events) Note: The default implementation of QGraphicsItem.mousePressEvent will accept the event if the item is has its Selectable or Movable flags enabled. You may need to override this behavior.

  4. If no item accepts the mousePressEvent, then the scene will begin delivering mouseDrag and/or mouseClick events. If the mouse is moved a sufficient distance (or moved slowly enough) before the button is released, then a mouseDragEvent is generated. If no drag events are generated before the button is released, then a mouseClickEvent is generated.

  5. Click/drag events are delivered to the item that called acceptClicks/acceptDrags on the HoverEvent in step 1. If no such items exist, then the scene attempts to deliver the events to items near the event. ClickEvents may be delivered in this way even if no item originally claimed it could accept the click. DragEvents may only be delivered this way if it is the initial move in a drag.

  __init__(clickRadius=2, moveDistance=5, parent=None)
  addParentContextMenus(item, menu, event)

    Can be called by any item in the scene to expand its context menu to include parent context menus. Parents may implement getContextMenus to add new menus / actions to the existing menu. getContextMenus must accept 1 argument (the event that generated the original menu) and return a single QMenu or a list of QMenus.

    The final menu will look like:

    > Original Item 1
    > Original Item 2
    > …
    > Original Item N
    > ——————
    > Parent Item 1
    > Parent Item 2
    > …
    > Grandparent Item 1
    > …

    Arguments: |
    item | The item that initially created the context menu (This is probably the item making the call to this function)
    menu | The context menu being shown by the item
    event | The original event that triggered the menu to appear.

  itemsNearEvent(event, selMode=1, sortOrder=1, hoverable=False)

    Return an iterator that iterates first through the items that directly intersect point (in Z order) followed by any other items that are within the scene’s click radius.

  prepareForPaint()

    Called before every render. This method will inform items that the scene is about to be rendered by emitting sigPrepareForPaint.

    This allows items to delay expensive processing until they know a paint will be required.

  setClickRadius(r)

    Set the distance away from mouse clicks to search for interacting items. When clicking, the scene searches first for items that directly intersect the click position followed by any other items that are within a rectangle that extends r pixels away from the click position.

  setMoveDistance(d)

    Set the distance the mouse must move after a press before mouseMoveEvents will be delivered. This ensures that clicks with a small amount of movement are recognized as clicks instead of drags.