106 lines
3.3 KiB
Racket
106 lines
3.3 KiB
Racket
#lang scribble/doc
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@(require "common.rkt" scribble/eval
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(for-label slideshow/pict))
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@(define class-eval (make-base-eval))
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@(interaction-eval #:eval class-eval (require racket/class racket/draw slideshow/pict))
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@defclass/title[linear-gradient% object% ()]{
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A @deftech{linear gradient} is used with a @racket[brush%] to fill
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areas with smooth color transitions.
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Color transitions are based on a line, where colors are assigned to
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stop points along the line, and colors for in-between points are
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interpolated from the stop-point colors. The color of a point on the
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gradient's line is propagated to all points in the drawing context
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that are touched by a line through the point and perpendicular to the
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gradient's line.
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@defconstructor[([x0 real?]
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[y0 real?]
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[x1 real?]
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[y1 real?]
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[stops (listof (list/c (real-in 0 1) (is-a?/c color%)))])]{
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Creates a linear gradient with a line from (@racket[x0], @racket[y0])
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to end point (@racket[x1], @racket[y1]). The @racket[stops] list
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assigns colors to stop points along the line, where @racket[0.0]
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corresponds to (@racket[x0], @racket[y0]), @racket[1.0] corresponds to
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(@racket[x1], @racket[y2]), and numbers in between correspond to
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points in between.
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Elements in @racket[stops] are implicitly sorted by point (i.e., by
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the number between @racket[0.0] and @racket[1.0]). Order is preserved
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for multiple elements for the same point, in which case the first
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element for a given point is treated infinitesimally before the point,
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and additional elements between the first and last for a stop point
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are effectively ignored.
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@examples[
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#:eval class-eval
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(define ellipse-brush
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(new brush%
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[gradient
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(new linear-gradient%
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[x0 0]
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[y0 200]
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[x1 200]
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[y1 00]
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[stops
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(list (list 0 (make-object color% 255 0 0))
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(list 0.5 (make-object color% 0 255 0))
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(list 1 (make-object color% 0 0 255)))])]))
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(define rectangle-brush
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(new brush%
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[gradient
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(new linear-gradient%
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[x0 0]
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[y0 100]
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[x1 100]
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[y1 0]
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[stops
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(list (list 0 (make-object color% 255 0 0))
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(list 0.5 (make-object color% 0 255 0))
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(list 1 (make-object color% 0 0 255)))])]))
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(dc
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(λ (dc dx dy)
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(define old-pen (send dc get-pen))
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(define old-brush (send dc get-brush))
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(define-values (ox oy) (send dc get-origin))
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(send dc set-pen "black" 1 'transparent)
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(send dc set-brush ellipse-brush)
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(send dc set-origin (+ ox dx 50) (+ oy dy 50))
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(send dc draw-ellipse 0 0 200 200)
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(send dc set-brush rectangle-brush)
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(send dc set-origin (+ ox dx 300) (+ oy dy 50))
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(send dc draw-rectangle 0 0 200 200)
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(send dc set-pen old-pen)
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(send dc set-brush old-brush)
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(send dc set-origin ox oy))
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550 300)
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]}
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@defmethod[(get-line)
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(values real? real? real? real?)]{
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Returns the gradient's control line as @racket[_x0], @racket[_y0],
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@racket[_x1], and @racket[_y1].
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}
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@defmethod[(get-stops)
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(listof (list/c (real-in/c 0 1) (is-a?/c color%)))]{
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Returns the gradient's list of color stops.
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}}
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@(close-eval class-eval)
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