QwtScaleCorner Namespace Reference

Helpers for the corners where perpendicular scale backbones meet. More...

Classes
struct	Targets
	Target positions of the perpendicular backbones at one corner. More...

Functions
QWT_EXPORT void	cornerAxes (QwtAxisId axisId, QwtAxisId &startAxis, QwtAxisId &endAxis)
	The perpendicular axes sharing the start/end corner of an axis.
QWT_EXPORT qreal	nearEdgeShift (QwtAxisId axisId)
	Logical offset of the near band edge from the scale position.
QWT_EXPORT QwtScaleDraw::CornerMiter	miterFlags (const QwtPlot *plot, QwtAxisId axisId)
	Compute the corner miter flags for an axis of a plot.
QWT_EXPORT Targets	widgetTargetPositions (const QwtPlot *plot, QwtAxisId axisId)
	Target positions derived from the axis widgets of the whole plot family.
QWT_EXPORT Targets	layoutTargetPositions (const QwtPlot *plot, QwtAxisId axisId)
	Target positions derived from the plot layout (for QwtPlotRenderer)
QWT_EXPORT void	widgetExtensions (const QwtPlot *plot, QwtAxisId axisId, qreal devicePixelRatio, int &startExtension, int &endExtension)
	Logical pixels an axis widget must reserve at its ends for the miter.

Detailed Description

Helpers for the corners where perpendicular scale backbones meet.

When two perpendicular axes are visible, their backbones should intersect at the shared canvas corner instead of ending in a diagonal step. QwtScaleDraw extends (miters) the backbone into the corner for this purpose. These helpers answer the questions around that extension:

• which corners exist (miterFlags()),
• where the perpendicular backbone actually is, so that the extension reaches it exactly (widgetTargetPositions() for the on-screen widgets, layoutTargetPositions() for QwtPlotRenderer, which lays out independently of the widget geometries),
• how many logical pixels an axis widget has to reserve beyond its ends, so that the extension is not clipped away by the widget rectangle (widgetExtensions()).

Parasite plots share the canvas of their host and stack their axis bands outside of the bands of the host, so the perpendicular band adjacent to the canvas may belong to any plot of the family. The target is the near edge of that innermost band - the band a border tick sits on. Bands stacked farther out are not crossed: extending a backbone to them would draw long lines through the whole axis stack and close the corners of unrelated bands.

All positions are in logical coordinates of the plot the axis belongs to; qQNaN() means "no corner at this end".

Function Documentation

cornerAxes()

void QwtScaleCorner::cornerAxes	(	QwtAxisId	axisId,
		QwtAxisId &	startAxis,
		QwtAxisId &	endAxis
	)

The perpendicular axes sharing the start/end corner of an axis.

Parameters

	axisId	Axis
[out]	startAxis	Perpendicular axis at the start of the scale
[out]	endAxis	Perpendicular axis at the end of the scale

layoutTargetPositions()

QwtScaleCorner::Targets QwtScaleCorner::layoutTargetPositions	(	const QwtPlot *	plot,
		QwtAxisId	axisId
	)

Target positions derived from the plot layout (for QwtPlotRenderer)

Compute where the backbone miter should reach, from the plot layout.

Parameters

plot	Plot the axis belongs to
axisId	Axis

Returns

Target positions in logical coordinates of the plot layout

Variant of widgetTargetPositions() for QwtPlotRenderer: the renderer activates the plot layout for the paint device and positions the scales from the layout rectangles, so the widget geometries are not a reliable source here. Stacked parasite axes are not rendered into documents and are ignored. The plot layout must be activated when calling.

miterFlags()

QwtScaleDraw::CornerMiter QwtScaleCorner::miterFlags	(	const QwtPlot *	plot,
		QwtAxisId	axisId
	)

Compute the corner miter flags for an axis of a plot.

Returns

the corner miter flags for an axis of a plot

Parameters

plot	Plot the axis belongs to
axisId	Axis

Returns

Miter flags for the corners shared with visible perpendicular axes

A corner exists when a perpendicular axis is visible and paints a backbone - in the plot itself or anywhere in its family (the host and the sibling parasites sharing the canvas).

nearEdgeShift()

qreal QwtScaleCorner::nearEdgeShift

(

QwtAxisId

axisId

)

Logical offset of the near band edge from the scale position.

Returns

1 for top/left axes, 0 for bottom/right axes

Added to a band position before rounding it to device pixels, and subtracted again afterwards: the near edge of a top/left backbone band is the last device pixel of its logical pixel, while the near edge of a bottom/right band is the first one.

Parameters

axisId

Axis the backbone band belongs to

Returns

1 for top/left axes, 0 for bottom/right axes

The near ( canvas side ) edge of a top/left backbone band is the last device pixel of the logical pixel of the scale position, while the near edge of a bottom/right band is the first one: rounding position + shift to device pixels and subtracting the shift again yields the near edge for both cases.

widgetExtensions()

void QwtScaleCorner::widgetExtensions	(	const QwtPlot *	plot,
		QwtAxisId	axisId,
		qreal	devicePixelRatio,
		int &	startExtension,
		int &	endExtension
	)

Logical pixels an axis widget must reserve at its ends for the miter.

Compute how much an axis widget has to reserve for the corner miter.

Parameters

	plot	Plot the axis belongs to
	axisId	Axis
	devicePixelRatio	Device pixel ratio of the axis widget
[out]	startExtension	Logical pixels to reserve at the start of the scale
[out]	endExtension	Logical pixels to reserve at the end of the scale

QwtScaleWidget clips everything painted outside of its rectangle, so a backbone miter reaching the perpendicular backbone is only visible when the widget covers the corner pixels. The extensions are the gap between the widget borders and the outer edge of the perpendicular backbone band the miter reaches, rounded up to whole logical pixels. The caller grows the widget rectangle accordingly and passes the same values to QwtScaleWidget::setCornerExtension(), which keeps the scale span unchanged by absorbing them into the border distances.

widgetTargetPositions()

QwtScaleCorner::Targets QwtScaleCorner::widgetTargetPositions	(	const QwtPlot *	plot,
		QwtAxisId	axisId
	)

Target positions derived from the axis widgets of the whole plot family.

Compute where the backbone miter should reach, from the axis widgets.

Parameters

plot	Plot the axis belongs to
axisId	Axis

Returns

Target positions in logical coordinates of plot

The targets are derived from the geometry and scale draw positions of the perpendicular axis widgets of the whole plot family. Per end the target is the near edge of the innermost band - the one closest to the canvas, where a border tick sits. Bands stacked farther out are not crossed. Call after the plot layout has been applied to the widgets of the family.