cairoArc: cairoArc

In RGtk2: R Bindings for Gtk 2.8.0 and Above

Description

Adds a circular arc of the given radius to the current path. The arc is centered at (xc, yc), begins at angle1 and proceeds in the direction of increasing angles to end at angle2. If angle2 is less than angle1 it will be progressively increased by 2*M_PI until it is greater than angle1.

Usage

cairoArc(cr, xc, yc, radius, angle1, angle2)

Arguments

cr	[Cairo] a cairo context
xc	[numeric] X position of the center of the arc
yc	[numeric] Y position of the center of the arc
radius	[numeric] the radius of the arc
angle1	[numeric] the start angle, in radians
angle2	[numeric] the end angle, in radians

Details

If there is a current point, an initial line segment will be added to the path to connect the current point to the beginning of the arc. If this initial line is undesired, it can be avoided by calling cairoNewSubPath before calling cairoArc.

Angles are measured in radians. An angle of 0.0 is in the direction of the positive X axis (in user space). An angle of M_PI/2.0 radians (90 degrees) is in the direction of the positive Y axis (in user space). Angles increase in the direction from the positive X axis toward the positive Y axis. So with the default transformation matrix, angles increase in a clockwise direction.

(To convert from degrees to radians, use degrees * (M_PI / 180.).)

This function gives the arc in the direction of increasing angles; see cairoArcNegative to get the arc in the direction of decreasing angles.

The arc is circular in user space. To achieve an elliptical arc, you can scale the current transformation matrix by different amounts in the X and Y directions. For example, to draw an ellipse in the box given by x, y, width, height:

cr$save()
cr$translate(x + width / 2, y + height / 2)
cr$scale(width / 2, height / 2)
cr$arc(0, 0, 1, 0, 2 * pi)
cr$restore()

Author(s)

Derived by RGtkGen from GTK+ documentation

RGtk2 documentation built on Oct. 14, 2021, 5:08 p.m.