particles in Ruby/SDL

gistfile1.rb

require 'sdl' 

WINDOW_SIZE = [1280, 768]
PARTICLE_SIZE = 8
EFFECT_LENGTH = 16

class GameManager	
	def initialize(screen)
		@screen = screen
		@particles = Array.new
		
		for i in 0..300
			x = Float(rand WINDOW_SIZE[0]) + rand()
			y = Float(rand  WINDOW_SIZE[1]) + rand()
			@particles.push(Particle.new(x, y))
		end
	end

	def collision1()
		for p1 in @particles
			for p2 in @particles
				next if p1.equal?(p2)

				dx = p1.x - p2.x
				dy = p1.y - p2.y
				r = (dx**2 + dy**2) ** 0.5

				next if r > EFFECT_LENGTH 
				r += 0.001
				cos = dx / r
				sin = dy / r
				vec = 40 / (r ** 2)				
				p1.vx += vec * cos 
				p1.vy += vec * sin  
			end
		end	
	end

	def collision2()
		w = WINDOW_SIZE[0] / EFFECT_LENGTH
		h = WINDOW_SIZE[1] / EFFECT_LENGTH
		#p w,h
		
		grid = Array.new(h, nil)
		h.times{|i|
			grid[i] = Array.new(w, Array.new())
		}
		
		for p in @particles
			x = Integer(p.x / EFFECT_LENGTH)
			y = Integer(p.y / EFFECT_LENGTH)
			grid[y][x].push(p)
		end
		
		
		for p1 in @particles
			x = Integer(p1.x / EFFECT_LENGTH)
			y = Integer(p1.y / EFFECT_LENGTH)
			
			nearParticles = []
			nearParticles.concat(grid[y][x])
			nearParticles.concat(grid[y-1][x-1]) if (x > 0 && y > 0)
			nearParticles.concat(grid[y-1][x]) if (y > 0)
			nearParticles.concat(grid[y-1][x+1]) if (x < w-1 && y > 0)
			
			nearParticles.concat(grid[y][x-1]) if (x > 0)
			nearParticles.concat(grid[y][x+1]) if (x < w-1 )
			
			nearParticles.concat(grid[y+1][x-1]) if (x > 0 && y < h-1)
			nearParticles.concat(grid[y+1][x]) if (y < h-1)
			nearParticles.concat(grid[y+1][x+1]) if (x < w-1 && y < h-1)
				
			for p2 in nearParticles
				next if p1.equal?(p2)

				dx = p1.x - p2.x
				dy = p1.y - p2.y
				r = (dx**2 + dy**2) ** 0.5

				next if r > EFFECT_LENGTH 
				r += 0.001
				cos = dx / r
				sin = dy / r
				vec = 40 / (r ** 2)				
				p1.vx += vec * cos 
				p1.vy += vec * sin  
			end
		end
	
		
	end
	
	def mouseAction()
		mouseState = SDL::Mouse.state
		return if not mouseState[2]
		
		mx = mouseState[0]
		my = mouseState[1]
		for p in @particles
			dx = p.x - mx
			dy = p.y - my
			r = (dx**2 + dy**2) ** 0.5

			if r == 0
				next
			end
				
			cos = dx / r
			sin = dy / r
			
			vec = 100 / (r + 100)
			p.vx += vec * cos
			p.vy += vec * sin
			
		end

	end

	def run()
		#collision1()
		collision2()
		mouseAction()
		for particle in @particles
			particle.run()
		end
	end
	
	def draw()
		@screen.fillRect(0, 0, @screen.w, @screen.h, [0, 0, 0])
		for particle in @particles
			particle.draw(@screen)
		end
	end	
end

class Particle
	def initialize(x, y)
		@x = x
		@y = y
		@vx = 0
		@vy = 0
	end
	attr_accessor :x, :y, :vx, :vy
	
	def run()
		@x += @vx
		@y += @vy
		@vx *= 0.9
		@vy *= 0.9

		#@vy += 0.1
		
		cx = WINDOW_SIZE[0] / 2
		cy = WINDOW_SIZE[1] / 2
		dx = @x - cx
		dy = @y - cy
		r = (dx**2 + dy**2) ** 0.5
		if r > 10		
			cos = dx / r
			sin = dy / r
			
			@vx -= cos / 10
			@vy -= sin / 10
		end
		
		if @x < PARTICLE_SIZE
			@vx = 0
			@x = PARTICLE_SIZE
		end
		
		if @y < PARTICLE_SIZE
			@vy = 0 
			@y = PARTICLE_SIZE
		end

		if @x > WINDOW_SIZE[0] - PARTICLE_SIZE
			@vx = 0
			@x = WINDOW_SIZE[0] - PARTICLE_SIZE
		end
		if @y > WINDOW_SIZE[1] - PARTICLE_SIZE
			@vy = 0
			@y = WINDOW_SIZE[1] - PARTICLE_SIZE
		end
	end
	
	def draw(screen)
		screen.drawCircle(@x, @y,  PARTICLE_SIZE, [ 255, 255, 255 ])
	end	
end


def main()
	SDL.init( SDL::INIT_VIDEO ) 
	screen = SDL.setVideoMode( WINDOW_SIZE[0], WINDOW_SIZE[1], 16, SDL::SWSURFACE ) 

	gameManager = GameManager.new(screen)

	loop do  # (4)
		while event = SDL::Event2.poll
			case event
			when SDL::Event2::Quit, SDL::Event2::KeyDown
				exit
			end		
		end

		#update
		gameManager.run()
		
		#draw
		gameManager.draw()
		screen.updateRect( 0, 0, 0, 0 ) 

	end
end


main