Dataflow::CableDragAutoScroller Class Reference

Scrolls a QGraphicsView while a cable is being dragged towards one of its edges, so that a port currently off-screen can be reached. More...

Inheritance diagram for Dataflow::CableDragAutoScroller:

Detailed Description

Scrolls a QGraphicsView while a cable is being dragged towards one of its edges, so that a port currently off-screen can be reached.

A QDrag runs its own event loop and only reports drag-move events when the cursor actually moves, and none at all once the cursor has left the view: a timer keeps the view scrolling from where the cursor really is, while it is inside the edge margins or not too far outside the viewport. After each scroll step the scene point under the (unmoved) cursor has changed, so onScrolled is invoked with the new scene position to let the caller update whatever follows the cursor (the drag line, the magnetic target port...).

Views that implement AutoScrollableView decide how their content moves; the others get their scroll bars moved.

Public Types
using	CursorProvider = std::function< QPoint(QWidget &viewport)>
	Where the cursor is, in viewport coordinates, for the given viewport.

Public Member Functions
	CableDragAutoScroller (std::function< void(QPointF scenePos)> onScrolled, CursorProvider cursor={})
void	track (QWidget *viewport, QPointF scenePos)
	To be called on each drag-move event.
void	continueFromCursor ()
	To be called when the drag leaves the view: there will be no more drag-move events, scrolling goes on from where the cursor really is.
void	stop ()
	Stops scrolling, e.g. on drop.
bool	active () const noexcept
QGraphicsView *	view () const noexcept

Static Public Member Functions
static QPoint	scrollStep (QPoint viewportPos, QSize sz) noexcept
	Scroll step for a cursor at viewportPos inside a viewport of size sz.
static bool	scrollViewBy (QGraphicsView &view, QPoint delta)
	Moves the view's content by delta pixels.
static bool	scrollBarsBy (QGraphicsView &view, QPoint delta)
	The scroll bar fallback of scrollViewBy().

Static Public Attributes
static constexpr int	margin = 32
	Distance from the viewport edge, in pixels, from which scrolling starts.
static constexpr int	maxStep = 24
	Scroll step per tick, in pixels, reached at the edge and beyond it.
static constexpr int	outsideLimit = 200
static constexpr int	intervalMs = 16

Constructor & Destructor Documentation

CableDragAutoScroller()

Dataflow::CableDragAutoScroller::CableDragAutoScroller ( std::function< void(QPointF scenePos)>  onScrolled, CursorProvider  cursor = {}  )

explicit

Parameters

onScrolled	Called after each scroll step with the scene position now under the cursor.
cursor	Where the cursor is; by default QCursor::pos() mapped into the viewport. Tests inject their own.

Member Function Documentation

scrollStep()

QPoint Dataflow::CableDragAutoScroller::scrollStep ( QPoint  viewportPos, QSize  sz  )

staticnoexcept

Scroll step for a cursor at viewportPos inside a viewport of size sz.

Zero outside the margins; otherwise grows linearly from 1 px at the inner border of the margin to maxStep at the edge, and stays at maxStep up to outsideLimit pixels beyond the edge. Viewports too small to have a useful middle never scroll.

scrollViewBy()

bool Dataflow::CableDragAutoScroller::scrollViewBy ( QGraphicsView &  view, QPoint  delta  )

static

Moves the view's content by delta pixels.

Views that implement AutoScrollableView decide how (panning an item, growing the scene...); the others get their scroll bars moved.

Returns

true if the content moved.

track()

void Dataflow::CableDragAutoScroller::track	(	QWidget *	viewport,
		QPointF	scenePos
	)

To be called on each drag-move event.

Parameters

viewport	The widget the scene event was sent to (the view's viewport).
scenePos	The cursor position in scene coordinates.

Member Data Documentation

outsideLimit

constexpr int Dataflow::CableDragAutoScroller::outsideLimit = 200

staticconstexpr

How far outside the viewport the cursor may be while scrolling goes on; further away (another window, another panel) the view is left alone.

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The documentation for this class was generated from the following files:

• CableDragAutoScroller.hpp
• CableDragAutoScroller.cpp