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add mode to arc' in dc-path%' to support right/bottom alignment

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This commit is contained in:
Matthew Flatt 2011-06-15 12:58:00 -06:00
parent c5b94831e4
commit 80bd949531
2 changed files with 22 additions and 9 deletions
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10
collects/racket/draw/private/dc-path.rkt
View File

@ -191,7 +191,7 @@
rev-open-points)))
(def/public (arc [real? x] [real? y]
[nonnegative-real? w] [nonnegative-real? h]
[real? w] [real? h]
[real? start] [real? end] [any? [ccw? #t]])
(do-arc x y w h start end ccw?))
@ -209,6 +209,8 @@
;; Change top-left to center:
(let ([x (+ x (/ w 2.0))]
[y (+ y (/ h 2.0))]
[w (abs w)]
[h (abs h)]
[pts null])
;; make up to 4 curves to represent the arc:
(let loop ([start start]
@ -382,13 +384,13 @@
(* (min w h) (- radius))
radius))])
(move-to (+ x (- w dx)) y)
(arc (+ x (- w (* 2 dx))) y (* 2 dx) (* 2 dy) pi/2 0.0 #f)
(arc (+ x w) y (* -2 dx) (* 2 dy) pi/2 0.0 #f)
(line-to (+ x w) (+ y dy))
(line-to (+ x w) (+ y (- h dy)))
(arc (+ x (- w (* 2 dx))) (+ y (- h (* 2 dy))) (* 2 dx) (* 2 dy) 0 (- pi/2) #f)
(arc (+ x w) (+ y h) (* -2 dx) (* -2 dy) 0 (- pi/2) #f)
(line-to (+ x (- w dx)) (+ y h))
(line-to (+ x dx) (+ y h))
(arc x (+ y (- h (* 2 dy))) (* 2 dx) (* 2 dy) (- pi/2) (- pi) #f)
(arc x (+ y h) (* 2 dx) (* -2 dy) (- pi/2) (- pi) #f)
(line-to x (+ y (- h dy)))
(line-to x (+ y dy))
(arc x y (* 2 dx) (* 2 dy) pi pi/2 #f)

21
collects/scribblings/draw/dc-path-class.scrbl
View File

@ -57,19 +57,30 @@ Adds the sub-paths of @scheme[path] to @this-obj[]. @tech{Closed
@defmethod[(arc [x real?]
[y real?]
[width (and/c real? (not/c negative?))]
[height (and/c real? (not/c negative?))]
[width real?]
[height real?]
[start-radians real?]
[end-radians real?]
[counter-clockwise? any/c #t])
void?]{
Extends or starts the path's @tech{open sub-path} with a curve that
corresponds to a section of an ellipse. The ellipse is the one
corresponds to a section of an ellipse. If @racket[width] and @racket[height]
are non-negative, the ellipse is the one
bounded by a rectangle whose top-left corner is @math{(@scheme[x],
@scheme[y])} and whose dimensions are @scheme[width] by
@scheme[height]. The ellipse section starts a the angle
@scheme[start-radians] (@scheme[0] is three o'clock and half-pi is
@scheme[height]; if @racket[width] is negative, then
the rectangle's right edge is @racket[x], and the ellipse
width is @racket[(abs width)], while a negative @racket[height]
similarly makes @racket[y] is the bottom edge of the ellipse and
the height @racket[(abs height)].
@margin-note*{Support for negative @racket[width] and @racket[height]
helps avoid round-off problems for aligned drawing in an eventual
destination, since @method[dc-path% arc] reduces its input to a sequence of curves.
In contrast, @xmethod[dc<%> draw-arc] can automatically correct for round off,
since the drawing mode is known immediately.}
The ellipse section starts a the angle
@scheme[start-radians] (@scheme[0] is three o'clock and half-π is
twelve o'clock) and continues to the angle @scheme[end-radians]; if
@scheme[counter-clockwise?] is true, then the arc runs
counter-clockwise from @scheme[start-radians] to