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;;; Sly
;;; Copyright (C) 2016 David Thompson <davet@gnu.org>
;;;
;;; This program is free software: you can redistribute it and/or
;;; modify it under the terms of the GNU General Public License as
;;; published by the Free Software Foundation, either version 3 of the
;;; License, or (at your option) any later version.
;;;
;;; This program 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
;;; General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program. If not, see
;;; <http://www.gnu.org/licenses/>.
;;; Commentary:
;;
;; Particle simulations.
;;
;;; Code:
(define-module (sly render particles)
#:use-module (srfi srfi-9)
#:use-module (sly math vector)
#:use-module (sly math rect)
#:use-module (sly render)
#:use-module (sly render mesh)
#:use-module (sly render texture)
#:use-module (sly render sprite-batch)
#:export (make-simple-particle-renderer
make-particle-system
particle-system?
particle-system-texture
particle-system-duration
particle-system-emit-rate
particle-system-life-span
particle-system-renderer
render-particles))
(define (make-simple-particle-renderer proc)
"Create a particle renderer using PROC to define the position of
each particle. PROC must accept 3 numeric arguments: the particle ID,
time, and life span. PROC must return a 2D vector."
(lambda (gfx batch texture rect n time life-span)
(let* ((v (proc n time life-span)))
(sprite-batch-add! batch gfx texture (rect-move rect v)))))
(define default-particle-renderer
(make-simple-particle-renderer
(lambda (n time life-span)
(polar2 time n))))
(define-record-type <particle-system>
(%make-particle-system texture sprite-rect duration emit-rate
life-span renderer)
particle-system?
(texture particle-system-texture)
(sprite-rect particle-system-sprite-rect)
(duration particle-system-duration)
(emit-rate particle-system-emit-rate)
(life-span particle-system-life-span)
(renderer particle-system-renderer))
(define* (make-particle-system #:key (texture null-texture) duration
(emit-rate 1) (life-span 60)
(renderer default-particle-renderer))
"Create a new particle system where each particle is rendered using
TEXTURE. Particles are emitted at a rate of EMIT-RATE per tick of the
game clock for DURATION ticks and each particle exists for LIFE-SPAN
ticks. The procedure RENDERER is responsible for placing and
rendering each particle, and takes the following arguments: graphics
context, sprite batch, texture, sprite rectangle, particle ID, time,
and life span."
(let* ((w (texture-width texture))
(h (texture-height texture))
(sprite-rect (make-rect (- (/ w 2)) (- (/ h 2)) w h)))
(%make-particle-system texture sprite-rect duration emit-rate
life-span renderer)))
(define (render-particles particle-system batch time)
"Create a renderer for PARTICLE-SYSTEM at TIME. The particles will
be rendered using BATCH, a sprite batcher."
(let* ((life-span (particle-system-life-span particle-system))
(emit-rate (particle-system-emit-rate particle-system))
(duration (particle-system-duration particle-system))
(count (* emit-rate life-span))
(first (* (- time life-span) emit-rate))
(last (if duration
(min (+ first count)
(floor (* duration emit-rate)))
(+ first count)))
(render (particle-system-renderer particle-system))
(texture (particle-system-texture particle-system))
(sprite-rect (particle-system-sprite-rect particle-system)))
(lambda (gfx)
(with-sprite-batch batch gfx
(let loop ((particle (max first 0)))
(when (< particle last)
(let* ((start-time (/ particle emit-rate))
(current-time (- time start-time)))
(render gfx batch texture sprite-rect particle
current-time life-span))
(loop (1+ particle))))))))
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