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;;; guile-2d
;;; Copyright (C) 2013 David Thompson <dthompson2@worcester.edu>
;;;
;;; Guile-2d is free software: you can redistribute it and/or modify it
;;; under the terms of the GNU Lesser General Public License as
;;; published by the Free Software Foundation, either version 3 of the
;;; License, or (at your option) any later version.
;;;
;;; Guile-2d is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this program. If not, see
;;; <http://www.gnu.org/licenses/>.
;;; Commentary:
;;
;; Rects are axis-aligned bounding boxes that can be used for
;; performing simple collision detection.
;;
;;; Code:
(define-module (2d rect)
#:use-module (srfi srfi-9)
#:export (<rect>
make-rect
rect?
rect-x
rect-y
rect-x2
rect-y2
rect-width
rect-height
rect-move
rect-inflate
rect-union
rect-clip
rect-within?
rect-intesects?
rect-contains?))
;; The rect API is very similar to the Pygame rect API, but rects are
;; immutable.
(define-record-type <rect>
(make-rect x y width height)
rect?
(x rect-x)
(y rect-y)
(width rect-width)
(height rect-height))
(define (rect-x2 rect)
(+ (rect-x rect) (rect-width rect) -1))
(define (rect-y2 rect)
(+ (rect-y rect) (rect-height rect) -1))
(define (rect-move rect x y)
"Moves a rect by the given offset."
(make-rect (+ (rect-x rect) x)
(+ (rect-y rect) y)
(rect-width rect)
(rect-height rect)))
(define (rect-inflate rect width height)
"Grows the rect by the given amount. The rect stays centered around
its current center."
(make-rect (+ (rect-x rect) (/ width 2))
(+ (rect-y rect) (/ height 2))
(+ (rect-width rect) width)
(+ (rect-height rect) height)))
(define (rect-union rect1 rect2)
"Returns a rect that covers the area of rect1 and rect2."
(let ((x1 (min (rect-x rect1) (rect-x rect2)))
(x2 (max (rect-x2 rect1) (rect-x2 rect2)))
(y1 (min (rect-y rect1) (rect-y rect2)))
(y2 (max (rect-y2 rect1) (rect-y2 rect2))))
(make-rect x1 y1 (- x2 x1) (- y2 y1))))
(define (rect-clip rect1 rect2)
"Returns the overlapping region of rect1 and rect2. If the rects do
not overlap, a rect of size 0 is returned."
(let ((x1 (max (rect-x rect1) (rect-x rect2)))
(x2 (min (rect-x2 rect1) (rect-x2 rect2)))
(y1 (max (rect-y rect1) (rect-y rect2)))
(y2 (min (rect-y2 rect1) (rect-y2 rect2))))
(make-rect x1 y1 (max (- x2 x1) 0) (max (- y2 y1) 0))))
(define (rect-within? rect1 rect2)
"Tests if rect2 is completely within rect1."
(and (>= (rect-x rect2) (rect-x rect1))
(<= (rect-x rect2) (rect-x2 rect1))
(>= (rect-x2 rect2) (rect-x rect1))
(<= (rect-x2 rect2) (rect-x2 rect1))
(>= (rect-y rect2) (rect-y rect1))
(<= (rect-y rect2) (rect-y2 rect1))
(>= (rect-y2 rect2) (rect-y rect1))
(<= (rect-y2 rect2) (rect-y2 rect1))))
(define (rect-intersects? rect1 rect2)
"Tests if rect2 overlaps rect1."
(or (and (>= (rect-x rect2) (rect-x rect1))
(<= (rect-x rect2) (rect-x2 rect1)))
(and (>= (rect-x2 rect2) (rect-x rect1))
(<= (rect-x2 rect2) (rect-x2 rect1))))
(or (and (>= (rect-y rect2) (rect-y rect1))
(<= (rect-y rect2) (rect-y2 rect1)))
(and (>= (rect-y2 rect2) (rect-y rect1))
(<= (rect-y2 rect2) (rect-y2 rect1)))))
(define (rect-contains? rect x y)
"Tests if the given point is within rect."
(and (>= x (rect-x rect))
(<= x (rect-x2 rect))
(>= y (rect-y rect))
(<= y (rect-y2 rect))))
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