ParticleSystems in Rebound

[Santos]

So, I think the particle effects in Rebound (0.8.0 compatible version here) by TechnoCat look really really cool, so thought I'd try to figure out how they work.

xP3qHAu.png (51.91 KiB) Viewed 877 times

Here are some files with the individual particle systems in them for playing around with:

reboundparticlesystems.zip

(7.17 KiB) Downloaded 420 times

Note: What I describe isn't necessarily exactly what is in the game!

So basically...

• Each paddle has two particle systems, each going in opposite directions.
• The ball is made from a circle two particle systems and doesn't have any speed, the effect is created just by moving it. The circle and one of the particle systems changes colour depending on which paddle it bounced off last.
• The upgrades are made from a particle system with its direction being spun around.
• The background is made from two particle systems, one for the rotating larger pieces and one for the slower, finer pieces.
• Additive blend mode makes everything look all glowy.

Also the background is a dark grey:

love.graphics.setBackgroundColor(30, 30, 30)

And vsync is off.



Paddles!

The paddle's particle systems use this image:

HoBaUmU.png (978 Bytes) Viewed 877 times

Here are the beginnings of the top part of a paddle:

oVnX4jI.png (1.87 KiB) Viewed 877 times

Code: Select all

function love.load()
	square = love.graphics.newImage('square.png')

	p = love.graphics.newParticleSystem(square, 200)
	p:setPosition(x, y)
	p:setDirection(math.pi/2)
	p:setParticleLife(0.6)
	p:setEmissionRate(10) -- Temporary!
	p:setSpeed(200) -- Temporary!
	
	love.graphics.setBackgroundColor(30, 30, 30)	
end

function love.update(dt)
	p:update(dt)
end

function love.draw()
	love.graphics.draw(p1, 0, 0)
end

The "200" in love.graphics.newParticleSystem means this particle system has a maximum of 200 particles.

The setDirection sets the direction in radians, and math.pi/2 points down.

setParticleLife(0.6) means the particles are removed after 0.6 seconds.

4u3e0um.png (2.95 KiB) Viewed 877 times

setSpread(math.pi/16) sets the initial direction to a direction within the angle of math.pi/16.

This arc shows the angle:

2ywzVWU.png (3.27 KiB) Viewed 877 times

TZXT6Uh.png (1.79 KiB) Viewed 877 times

setSizes(1, 0) changes the particle size from full size (1 times the size) at the start of the particle's life, and no size at the end (0 times the size).

Dh6tebi.png (2.21 KiB) Viewed 877 times

setEmissionRate(100) means 100 particles are emitted every second.

F9yZi8e.png (2.81 KiB) Viewed 877 times

setSpeed(0, 400) sets a random speed between 0 and 400.

R24YbU1.png (5.03 KiB) Viewed 877 times

setColors(r,g,b,128, r/2,g/2,b/2,0) fades the colour from the paddle's colour at half transparency at the start of the particle's life, and half the paddle's colour value completely transparent at the end of the particle's life.

TxeQOeJ.png (6.18 KiB) Viewed 877 times

love.graphics.setBlendMode('additive') sets the blend mode to additive.

I think the equation for additive blend mode is this, for each colour component (red, green and blue):

final colour = whatever is already there + (new colour component value * new colour alpha)

(You can check out the other formulas here.)

There is another particle system for each paddle which is pretty much identical except that it's further down and the direction is up. And that's it!

jc3S0PH.png (11.83 KiB) Viewed 877 times

Ball!

The ball, upgrades, and background all use this image in their particle systems:

GhRlKLA.png (663 Bytes) Viewed 877 times

So, here's a start:

52Q2HcP.png (925 Bytes) Viewed 877 times

p1 = love.graphics.newParticleSystem(ball, 200)
p1:setEmissionRate(10) -- Temporary!
p1:setSpeed(250) -- Just for demonstration!
p1:setParticleLife(0.5)

The ball has no speed, and the emitter itself is what moves. This means the direction has no effect.

The particles are alive for half a second.

ZvRuSkc.png (1.76 KiB) Viewed 877 times

setSizes(1, 0.5)

The particle sizes transition from full size to half size.

uKGV6Rr.png (1.56 KiB) Viewed 877 times

setEmissionRate(100)

There are 100 particles emitted per second.

FFmOaF3.png (3.37 KiB) Viewed 877 times

setColors(220,105,20,255, 194,30,18,0)

The colour transitions from opaque orange to a fully transparent red.

nB6Ur2q.png (4.13 KiB) Viewed 877 times

And now with additive blending!
love.graphics.setBlendMode('additive')

Now for the the ball's second particle system.

RL55Vdx.png (1016 Bytes) Viewed 877 times

p2 = love.graphics.newParticleSystem(ball, 200)
p2:setEmissionRate(10) -- Temporary!
p2:setParticleLife(0.75)
p2:setSizes(0.25, 1)
p2:setColors(220,105,20,20, 194,30,18,0)
p1:setSpeed(250) -- Just for demonstration!

AZxqGnn.png (2.22 KiB) Viewed 877 times

setSizes(0.25, 1)

EIxI3gr.png (2.16 KiB) Viewed 877 times

setEmissionRate(50)

Iv7OYj7.png (3.63 KiB) Viewed 877 times

setColors(r,g,b,255, 194,30,18,0)

The colour fades from the colour of the paddle which it last bounced off, and the same transparent red as in the ball's other particle system.

NhHdK8P.png (4.42 KiB) Viewed 877 times

love.graphics.setBlendMode('additive')

Q4oHuis.png (339 Bytes) Viewed 877 times

And there's a circle too, also in the same colour as the last bounced paddle.

Here's everything together, it both colours.

uONB3LT.png (15.04 KiB) Viewed 877 times

Upgrades!

q31KnyK.png (1.05 KiB) Viewed 877 times

p = love.graphics.newParticleSystem(ball, 200)

p = love.graphics.newParticleSystem(ball, 200)
p:setPosition(x, y)
p:setEmissionRate(10) -- Temporary!
p:setParticleLife(0.5)
p:setSpeed(200)

sEYBUqp.png (1.74 KiB) Viewed 877 times

p:setSizes(1, 0.5)

tz7KfoR.png (1.45 KiB) Viewed 877 times

setEmissionRate(100)

RRXbFXF.png (3.32 KiB) Viewed 877 times

setColors(r,g,b,255, 64,64,128,128)

Colours fade between green (0, 255, 0) or red (255, 0, 0) and a half transparent blue.

SCqNKl5.png (3.9 KiB) Viewed 877 times

love.graphics.setBlendMode('additive')

aHAjKRI.png (5.02 KiB) Viewed 877 times

setTangentialAcceleration(500)

YG3RXeS.png (3.54 KiB) Viewed 877 times

setRadialAcceleration(-1200)

vl7J9MM.png (4.66 KiB) Viewed 877 times

p1:setSpread(2)

The direction of the emitter is rotated in love.update.

Code: Select all

d = d - (30*dt)
if d < 0 then
	d = d + 2*math.pi
end

p:setDirection(d)
p:update(dt)

And that's it!

x5jSyTK.png (8.91 KiB) Viewed 877 times

Additive blend mode makes the upgrades looks super cool when they overlap.

erPyiRn.png (6.23 KiB) Viewed 877 times

Background!

Here's one part of the background:

jdOFxEG.png (9.18 KiB) Viewed 877 times

p1 = love.graphics.newParticleSystem(ball, 200)

p1:setSpread(2*math.pi)
p1:setParticleLife(5)
p1:setSpeed(0, 200)
p1:setColors(0,0,0,128, 50,50,50,0)

p1:setEmissionRate(20)
p1:setSizes(1, 4)
p1:setTangentialAcceleration(200)

There are 2 * math.pi radians in a circle, so setSpread(2*math.pi) makes the emitter emit particles in all directions.

Here's the other part:

EiQIC97.png (2.04 KiB) Viewed 877 times

p2 = love.graphics.newParticleSystem(ball, 200)

p2:setSpread(2*math.pi)
p2:setParticleLife(5)
p2:setSpeed(0, 200)
p2:setColors(0, 0, 0, 128, 50, 50, 50, 0)

p2:setEmissionRate(10)
p2:setSizes(0, 1)
p2:setRadialAcceleration(-10)

setRadialAcceleration(-10) sets some acceleration toward the emitter, making the particles slow down.

And here's the background with both layers:

jxnzRRd.png (11.35 KiB) Viewed 877 times

[bashlook]

This is what i'm looking for! Kudos!

[seanmd]

What a great writeup, and of some pretty creative uses of particle systems to boot. Thanks to both of you.

[CaptainMaelstrom]

Very helpful explanation, thanks.

[verilog]

Santos,
Thank you for this excellent and detailed explanation, this is awesome! cheers!

[TechnoCat]

Popped back onto the forum to check something out. Pretty cool analysis.