Table of Contents

• 1. arcn
  • 1.1. Syntax
  • 1.2. Stack Effects
  • 1.3. Description
  • 1.4. PostScript Level
  • 1.5. Examples
  • 1.6. Common Use Cases
    • 1.6.1. Creating Ring Shapes
    • 1.6.2. Drawing Pac-Man
    • 1.6.3. Creating Donut Charts
  • 1.7. Common Pitfalls
  • 1.8. Error Conditions
  • 1.9. Implementation Notes
  • 1.10. Performance Considerations
  • 1.11. See Also

1. arcn

Appends a clockwise circular arc to the current path.

1.1. Syntax

x y r ang1 ang2 arcn → -

1.2. Stack Effects

Table 1. Before

Level	Object
4	ang2 (number - ending angle in degrees)
3	ang1 (number - starting angle in degrees)
2	r (number - radius)
1	y (number - center y-coordinate)
0	x (number - center x-coordinate)

Table 2. After

Level	Object
(empty)	Stack cleared of operands

1.3. Description

arcn (arc negative) behaves like arc, but builds its arc segment in a clockwise direction in user space instead of counterclockwise.

The arc has (x, y) as center, r as radius, ang1 as the angle from (x, y) to the first endpoint, and ang2 as the angle from (x, y) to the second endpoint. Angles are measured in degrees counterclockwise from the positive x-axis.

If there is a current point, arcn includes a straight line segment from the current point to the first endpoint of the arc. The second endpoint of the arc becomes the new current point.

1.4. PostScript Level

Level 1 and later

1.5. Examples

Drawing a clockwise arc

newpath
200 200 50 90 0 arcn     % Clockwise from 90° to 0°
stroke

Creating a windshield wiper shape

newpath
200 200 100 0 90 arc     % Outer arc counterclockwise
200 200 50 90 0 arcn     % Inner arc clockwise
closepath
fill

Drawing a crescent moon

newpath
200 200 50 90 -90 arc    % Outer arc (right half)
180 200 50 -90 90 arcn   % Inner arc (offset left)
closepath
fill

1.6. Common Use Cases

1.6.1. Creating Ring Shapes

/drawRing {
  % cx cy outerRadius innerRadius
  /ir exch def
  /or exch def
  /cy exch def
  /cx exch def

  newpath
  cx cy or 0 360 arc      % Outer circle counterclockwise
  cx cy ir 0 -360 arcn    % Inner circle clockwise (cuts hole)
  closepath
} def

200 200 80 50 drawRing
fill

1.6.2. Drawing Pac-Man

/drawPacMan {
  % x y radius mouthAngle
  /mouth exch def
  /r exch def
  /y exch def
  /x exch def

  newpath
  x y moveto
  x y r mouth 360 mouth sub arc
  closepath
} def

200 200 50 45 drawPacMan
1 1 0 setrgbcolor
fill

1.6.3. Creating Donut Charts

/drawSegment {
  % cx cy outer inner startAng endAng
  /endAng exch def
  /startAng exch def
  /inner exch def
  /outer exch def
  /cy exch def
  /cx exch def

  newpath
  cx cy outer startAng endAng arc
  cx cy inner endAng startAng arcn    % Reverse direction
  closepath
} def

% Draw donut chart segments
200 200 100 60 0 120 drawSegment
0.8 0.2 0.2 setrgbcolor fill

200 200 100 60 120 240 drawSegment
0.2 0.8 0.2 setrgbcolor fill

200 200 100 60 240 360 drawSegment
0.2 0.2 0.8 setrgbcolor fill

1.7. Common Pitfalls

Clockwise Means Negative Direction - Even though you specify ang1 to ang2, arcn draws clockwise (decreasing angles).

% These produce the same arc shape:
200 200 50 90 0 arcn     % Clockwise from 90° to 0°
200 200 50 0 90 arc      % Counterclockwise from 0° to 90°

Angle Order Still Matters - ang1 is the start angle, ang2 is the end angle, but the arc goes clockwise from start to end.

200 200 50 0 90 arcn     % Goes 270° clockwise (0→-90→-180→-270→90)
200 200 50 90 0 arcn     % Goes 90° clockwise (90→45→0)

Use for Interior Paths - arcn is essential for creating holes in shapes when combined with arc, as opposite directions create non-overlapping regions.

1.8. Error Conditions

Error	Condition
[limitcheck]	Path becomes too complex for implementation
[stackunderflow]	Fewer than 5 operands on stack
[typecheck]	Any operand is not a number

1.9. Implementation Notes

• Internally represented as Bézier cubic curves

• Direction matters for fill rules (non-zero winding number)

• Clockwise and counterclockwise arcs can create holes in filled shapes

• Same accuracy considerations as arc

• Produces elliptical curves if CTM has non-uniform scaling

1.10. Performance Considerations

• Same performance characteristics as arc

• No additional overhead for clockwise direction

• Useful for efficient hole creation in complex paths

1.11. See Also

• arc - Counterclockwise arc

• arct - Arc defined by tangent lines

• arcto - Like arct but returns tangent points

• closepath - Close current subpath

• moveto - Set current point