PtArc

An elliptical arc

Class hierarchy:

PtWidget → PtBasic → PtGraphic → PtArc

For more information, see the diagram of the widget hierarchy.

PhAB icon:

Public header:

<photon/PtArc.h>

Description:

You can use PtArc to create an elliptical arc that's defined by:

• the origin
• an ellipse
• a start angle
• an end angle.

Instances of PtArc: arcs, circles, ellipses, wedges, and chords.

The ellipse is specified using two control points stored in Pt_ARG_POINTS. These points are relative to the widget's origin, Pt_ARG_ORIGIN (see PtGraphic). If the points aren't set, the ellipse is specified by the widget's dimensions, Pt_ARG_DIM.

An arc is drawn along the ellipse in a counter-clockwise direction, starting at the start angle and finishing at the end angle. The start and end angles are specified by two resources: Pt_ARG_ARC_START and Pt_ARG_ARC_END.

The arc may be scaled directly by scaling its defining points. Scaling a circular arc by unequal amounts in the x and y directions results in an elliptical arc.

The arc may also be drawn as a closed curve by specifying the arc type with the Pt_ARG_ARC_TYPE resource:

• Pt_ARC_CURVE — draws the arc inscribed by the points
• Pt_ARC_PIE — draws the arc inscribed by the points with lines drawn from the two end points to the centroid of the arc, creating a pie-slice
• Pt_ARC_CHORD — draws the arc inscribed by the points with the chord connecting the two end points closing the curve.

New resources:

Pt_ARG_ARC_END

The end angle, in tenths of a degree.

Pt_ARG_ARC_START

The start angle, in tenths of a degree. If this angle is 0, the arc starts on the horizon, to the right of the center. Angles increase in a counter-clockwise direction.

Pt_ARG_ARC_TYPE

The type of arc; one of:

Pt_ARC_CHORD

Curve with ends connected by a straight line.

Pt_ARC_CURVE

Curve only.

Pt_ARC_PIE

Curve with ends connected to the center.

Inherited resources:

If the widget modifies an inherited resource, the “Default override” column indicates the new value. This modification affects any subclasses of the widget.