17 pen%

class
pen% : class?

superclass: object%

A pen is a drawing tool with a color, width, and style. A pen draws lines and outlines, such as the outline of a rectangle. In a monochrome destination, all non-white pens are drawn as black.

In addition to its color, width, and style, a pen can have a pen stipple bitmap. Drawing with a stipple pen is similar to calling draw-bitmap with the stipple bitmap in region painted by the pen.

A pen style is one of the following:

'transparent — Draws with no effect (on the outline of the drawn shape).
'solid — Draws using the pen’s color. If a (monochrome) pen stipple is installed into the pen, black pixels from the stipple are transferred to the destination using the brush’s color, and white pixels from the stipple are not transferred.
'xor — The same as 'solid, accepted only for partial backward compatibility.
'hilite — Draws with black and a 0.3 alpha.
The following special pen modes use the pen’s color, and they only apply when a pen stipple is not used:
- 'dot
- 'long-dash
- 'short-dash
- 'dot-dash
- 'xor-dot
- 'xor-long-dash
- 'xor-short-dash
- 'xor-dot-dash

To avoid creating multiple pens with the same characteristics, use the global pen-list% object the-pen-list, or provide a color, width, and style to set-pen in dc<%>.

When drawing in 'smoothed or 'aligned mode, a pen’s size is truncated after scaling to an integral size. A pen of size 0 (after truncation, if applicable) uses a non-zero, scale-insensitive line size for the destination drawing context: 1/4 unit (after scaling) for post-script-dc% or pdf-dc% contexts in 'smoothed mode, or 1 unit (after scaling) for any other context. For example, in unscaled canvas and bitmap contexts, a zero-width pen behaves the same as a pen of size 1.

See also make-pen.

constructor
(new pen%
    [ [color color]
    [width width]
    [style style]
    [cap cap]
    [join join]
    [stipple stipple]]) → (is-a?/c pen%)
  color : (or/c string? (is-a?/c color%)) = "black"
  width : (real-in 0 255) = 0
  style : pen-style/c = 'solid
  cap : pen-cap-style/c = 'round
  join : pen-join-style/c = 'round
  stipple : (or/c #f (is-a?/c bitmap%)) = #f

Creates a pen with the given color, width, pen style, cap style, join style, and pen stipple bitmap. For the case that the color is specified using a name, see color-database<%> for information about color names; if the name is not known, the pen’s color is black.

method
(send a-pen get-cap) → pen-cap-style/c

Returns the pen cap style, which determines the shape of a line at each of its ending points when drawn by draw-line or at the non-connecting ends of lines when drawn by draw-lines or draw-path. The default is 'round, which draws the end of a line as a semi-circle. The 'projecting style draws a square in place of the semi-circle (i.e., past the point at which the line stops). The 'butt style ends the line with a straight edge, instead of projecting past the ending point of the line.

This code draws three diagonal lines, one with each of the possible caps ('round, 'butt, and then 'projecting) and puts a little red dot on the end points of the line.

Examples:

> (define (plot-line dc x1 y1 x2 y2 cap)
    (send dc set-pen
          (send the-pen-list find-or-create-pen
                "black" 40 'solid cap))
    (send dc draw-line x1 y1 x2 y2)
    (send dc set-brush "red" 'solid)
    (send dc set-pen "black" 1 'transparent)
    (send dc draw-ellipse (- x1 4) (- y1 4) 8 8)
    (send dc draw-ellipse (- x2 4) (- y2 4) 8 8))
> (dc
   (λ (dc dx dy)
     (define old-pen (send dc get-pen))
     (define old-brush (send dc get-brush))

     (plot-line dc 20 30 80 90 'round)
     (plot-line dc 100 30 160 90 'butt)
     (plot-line dc 180 30 240 90 'projecting)

     (send dc set-pen old-pen)
     (send dc set-brush old-brush))
   270 120)

method
(send a-pen get-color) → (is-a?/c color%)

Returns the pen’s color object.

method
(send a-pen get-join) → pen-join-style/c

Returns the pen join style that is used between multiple lines connected through draw-lines, draw-rectangle, draw-polygon, or draw-path. The join style fills the space that would be left at the outside corner of two lines if they were draw separately with 'butt line endings. The default join style is 'round, which fills under an arc that lines up with the outside of each of the two lines. The 'bevel style fills in the gap without adding extra pixels (i.e., it makes a blunt corner). The 'miter style fills the gap by adding pixels that would be covered by both lines if they were extended past the corner (i.e., it makes a sharp corner).

This code shows the three join styles ('round, 'bevel and then 'miter) by drawing a sequence of lines, first with a sharp corner and then with a right-angle. Each of the end points of the lines i with a red dot.

Examples:

> (define points '((100 . 100)
                   (0 . 0)
                   (0 . 100)
                   (40 . 100)))
> (define (connect-points dc dx dy join)
    (send dc set-pen
          (send the-pen-list find-or-create-pen
                "black" 40 'solid 'round join))
    (send dc draw-lines points dx dy)
    (send dc set-brush "red" 'solid)
    (send dc set-pen "black" 1 'transparent)
    (for ([pt (in-list points)])
      (send dc draw-ellipse
            (+ dx (car pt) -4) (+ dy (cdr pt) -4)
            8 8)))
> (dc
   (λ (dc dx dy)
     (define old-pen (send dc get-pen))
     (define old-brush (send dc get-brush))

     (connect-points dc 20 50 'round)
     (connect-points dc 180 50 'bevel)
     (connect-points dc 340 50 'miter)

     (send dc set-pen old-pen)
     (send dc set-brush old-brush))
   460 170)

method
(send a-pen get-stipple) → (or/c (is-a?/c bitmap%) #f)

Gets the current pen stipple bitmap, or returns #f if no stipple bitmap is installed.

method
(send a-pen get-style) → pen-style/c

Returns the pen style. See pen% for information about possible styles.

method
(send a-pen get-width) → (real-in 0 255)

Returns the pen width.

method
(send a-pen is-immutable?) → boolean?

Returns #t if the pen object is immutable.

method
(send a-pen set-cap cap-style) → void?
cap-style : pen-cap-style/c

Sets the pen cap style. See get-cap for information about cap styles.