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()