59 lines
1.9 KiB
Racket
59 lines
1.9 KiB
Racket
#lang frtime
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;; Needles
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;; Written by Robb Cutler
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;; July, 2004
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;;
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;; Demonstrates a grid of animated needles that follow the mouse cursor
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;; using the FrTime language.
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;; Require the animation library and the library
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;; containing the build-list function.
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(require frtime/animation
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frtime/gui)
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;; How many needles on one side of the grid of needles
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(define GRID-SIZE (make-slider "Grid size:" 1 12 8))
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;; The length of a needle in pixels
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(define NEEDLE-LENGTH 10)
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;; The distance between the centers of two adjacent needles
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(define SPACING 25)
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;; A useful constant.
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(define PI 3.1415626535)
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(define (distance x1 y1 x2 y2)
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(sqrt (+ (sqr (- x1 x2)) (sqr (- y1 y2)))))
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;; create-needle : number -> line
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;; Define one needle. A needle's orientation is such that it
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;; lies on a line between the center of the needle and the
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;; position of mouse cursor. num is the needle's row-major
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;; location on the grid (from 0 to GRID-SIZE^2-1).
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(define (create-needle num)
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(let* ([row (quotient num GRID-SIZE)]
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[col (remainder num GRID-SIZE)]
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[x (+ (* row SPACING) SPACING)]
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[y (+ (* col SPACING) SPACING)]
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[delta-x (- (posn-x mouse-pos) x)]
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[delta-y (- (posn-y mouse-pos) y)]
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[theta1 (atan (/ delta-y (exact->inexact delta-x)))]
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[theta2 (- theta1 PI)]
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[x1-pos (+ x (* NEEDLE-LENGTH (cos theta1)))]
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[y1-pos (+ y (* NEEDLE-LENGTH (sin theta1)))]
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[x2-pos (+ x (* NEEDLE-LENGTH (cos theta2)))]
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[y2-pos (+ y (* NEEDLE-LENGTH (sin theta2)))]
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[color-density (min 1 (/ (distance x1-pos y1-pos (posn-x mouse-pos) (posn-y mouse-pos)) 150.0))]
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)
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(make-line (make-posn x1-pos y1-pos)
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(make-posn x2-pos y2-pos)
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(make-rgb (- 1 color-density) 0 0))))
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;; Define a list of needles
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(define needles (build-list (sqr GRID-SIZE) create-needle))
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;; Draw the needles!
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(display-shapes needles)
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