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Slides for the Reactive 3D Game Engine presented at ScalaDays 2014. Shows the demo of the 3D engine, followed by the description of the reactive 3D game engine - how reactive dependencies between input, time and game logic are expressed, how to deal with GC issues, how to model game state using Reactive Collections.
Citation preview
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A Reactive 3D Game Engine in Scala
Aleksandar Prokopec@_axel22_
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What’s a game engine?
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Simulation
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Real-time simulation
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15 ms
Real-time simulation
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Input Simulator
Interaction
Renderer
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Reactive values
Reactive[T]
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val ticks: Reactive[Long]
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ticks 1
1
2
2
3
3
4
4
60
60
61
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ticks onEvent { x => log.debug(s”tick no.$x”)}
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1 2 3 4 60 61
tick no.1tick no.2tick no.3tick no.4
tick no.60tick no.61
...
ticks foreach { x => log.debug(s”tick no.$x”)}
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1 2 3 4 60 61
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for (x <- ticks) { log.debug(s”tick no.$x”)}
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Reactive combinators
for (x <- ticks) yield { x / 60 }
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val seconds: Reactive[Long] = for (x <- ticks) yield { x / 60 }
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6061
val seconds: Reactive[Long] = for (x <- ticks) yield { x / 60 }
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ticks 1
1
2
2
3
3 60 61
seconds
0 0 0 1 1
ticks
seconds
00011
val days: Reactive[Long] = seconds.map(_ / 86400)
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val days: Reactive[Long] = seconds.map(_ / 86400)val secondsToday =
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val days: Reactive[Long] = seconds.map(_ / 86400)val secondsToday = (seconds zip days) { (s, d) => s – d * 86400 } 21
val days: Reactive[Long] = seconds.map(_ / 86400)val secondsToday = (seconds zip days) { _ – _ * 86400 }
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seconds days
secondsToday
val angle = secondsInDay.map(angleFunc)
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val angle = secondsInDay.map(angleFunc)val light = secondsInDay.map(lightFunc)
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https://www.youtube.com/watch?v=5g7DvNEs6K8&feature=youtu.be
Preview
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val rotate = keys
a ↓shift ↓ a ↑ shift ↑pgup ↓ pgup ↑keys
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val rotate = keys.filter(_ == PAGEUP)
a ↓shift ↓ a ↑ shift ↑pgup ↓ pgup ↑keys
pgup ↓ pgup ↑filter
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val rotate = keys.filter(_ == PAGEUP) .map(_.down)
a ↓shift ↓ a ↑ shift ↑pgup ↓ pgup ↑keys
pgup ↓ pgup ↑filter
true falsemap
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if (rotate()) viewAngle += 1
true falsemap
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Signals
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Reactives arediscrete
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Signals are continuous
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trait Signal[T]extends Reactive[T] { def apply(): T}
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val rotate = keys.filter(_ == PAGEUP) .map(_.down) .signal(false)
true falsemap
signal
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val rotate: Signal[Boolean] = keys.filter(_ == PAGEUP) .map(_.down) .signal(false)
true falsemap
signal
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val rotate: Signal[Boolean]val ticks: Reactive[Long]
ticks
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val rotate: Signal[Boolean]val ticks: Reactive[Long]
ticks
rotate
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val rotate: Signal[Boolean]val ticks: Reactive[Long]val viewAngle: Signal[Double] =
ticks
rotate
viewAngle
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List(1, 2, 3).scanLeft(0)(_ + _)
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List(1, 2, 3).scanLeft(0)(_ + _)
→ List(0, 1, 3, 6)
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def scanLeft[S](z: S)(f: (S, T) => S) : List[S]
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def scanLeft[S](z: S)(f: (S, T) => S) : List[S]
def scanPast[S](z: S)(f: (S, T) => S) : Signal[S]
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val rotate: Signal[Boolean]val ticks: Reactive[Long]val viewAngle: Signal[Double] = ticks.scanPast(0.0)
ticks
rotate
viewAngle
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val rotate: Signal[Boolean]val ticks: Reactive[Long]val viewAngle: Signal[Double] = ticks.scanPast(0.0) { (a, _) => if (rotate()) a + 1 else a }
ticks
rotate
viewAngle
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val velocity = ticks.scanPast(0.0) { (v, _) => }val viewAngle =
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val velocity = ticks.scanPast(0.0) { (v, _) => if (rotate()) v + 1 }val viewAngle =
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val velocity = ticks.scanPast(0.0) { (v, _) => if (rotate()) v + 1 else v – 0.5 }val viewAngle =
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val velocity = ticks.scanPast(0.0) { (v, _) => if (rotate()) v + 1 else v – 0.5 }val viewAngle = velocity.scanPast(0.0)(_ + _)
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Higher-orderreactive values
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(T => S) => (List[S] => List[T])
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(T => S) => (List[S] => List[T])
Reactive[Reactive[S]]
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val mids = mouse .filter(_.button == MIDDLE)
mids ↓ ↓ ↓↑ ↑ ↑
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val mids = mouse .filter(_.button == MIDDLE)val up = mids.filter(!_.down)val down = mids.filter(_.down)
mids ↓ ↓ ↓
up
down ↓ ↓ ↓
↑ ↑ ↑
↑ ↑ ↑
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val mids = mouse .filter(_.button == MIDDLE)val up = mids.filter(!_.down)val down = mids.filter(_.down)val drags = down .map(_ => mouse)
up
down ↓ ↓ ↓
↑ ↑ ↑
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val mids = mouse .filter(_.button == MIDDLE)val up = mids.filter(!_.down)val down = mids.filter(_.down)val drags = down .map(_ => mouse)
up
down ↓ ↓ ↓
↑ ↑ ↑
Reactive[Reactive[MouseEvent]]
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val mids = mouse .filter(_.button == MIDDLE)val up = mids.filter(!_.down)val down = mids.filter(_.down)val drags = down .map(_ => mouse)
up
down ↓ ↓ ↓
↑ ↑ ↑
drags
drags
up ↑ ↑ ↑
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val mids = mouse .filter(_.button == MIDDLE)val up = mids.filter(!_.down)val down = mids.filter(_.down)val drags = down .map(_ => mouse.until(up))
down ↓ ↓ ↓
mouse.until(up)
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val mids = mouse .filter(_.button == MIDDLE)val up = mids.filter(!_.down)val down = mids.filter(_.down)val drags = down .map(_ => mouse.until(up))
down ↓ ↓ ↓
up ↑ ↑ ↑
drags
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val drags = down .map(_ => mouse.until(up)) .map(_.map(_.xy))
drags
1, 12, 3
3, 5
4, 6
6, 9
9, 9
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val drags = down .map(_ => mouse.until(up)) .map(_.map(_.xy)) .map(_.diffPast(_.xy - _.xy))
drags
0, 01, 2
1, 2
0, 0
2, 3
0, 0
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val drags = down .map(_ => mouse.until(up)) .map(_.map(_.xy)) .map(_.diffPast(_.xy - _.xy)) .concat()
drags 0, 0 1, 2 1, 2 0, 0 2, 3 0, 0
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val drags = down .map(_ => mouse.until(up)) .map(_.map(_.xy)) .map(_.diffPast(_.xy - _.xy)) .concat()val pos = drags.scanPast((0, 0))(_ + _)
drags 0, 0 1, 2 1, 2 0, 0 2, 3 0, 0
pos 0, 0 1, 2 2, 4 2, 4 4, 7 4, 7
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http://youtu.be/RsMSZ7OH2fo
Preview
However, a lot of object allocations lead to GC issues.
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Reactive mutators
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class Matrix { def apply(x: Int, y: Int): Double def update(x: Int, y: Int, v: Double)}
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val screenMat: Signal[Matrix] = (projMat zip viewMat)(_ * _)val invScreenMat = screenMat.map(_.inverse)
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Reactive[immutable.Matrix[T]]
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val screenMat: Signal[Matrix] = (projMat zip viewMat)(_ * _)val invScreenMat = screenMat.map(_.inverse)
(4*4*8 + 16 + 16)*4*100 = 64 kb/s
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val screenMat = Mutable(new Matrix)(projMat, viewMat).mutate(screenMat) { (p, v) => screenMat().assignMul(p, v)}val invScreenMat = Mutable(new Matrix)screenMat.mutate(invScreenMat) { m => invScreenMat().assignInv(m)}
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Reactive collections
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http://youtu.be/ebbrAHNsexc
Preview
How do we model that a character is selected?
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val selected: Reactive[Set[Character]]
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val selected: ReactSet[Character]
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trait ReactSet[T]extends ReactContainer[T] { def apply(x: T): Boolean}
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trait ReactContainer[T] { def inserts: Reactive[T] def removes: Reactive[T]}
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A reactive collectionis a pair
of reactive values
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val selected = new ReactHashSet[Character]
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val selected = new ReactHashSet[Character]val decorations = selected .map(c => (c, decoFor(c)))
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class ReactContainer[T] { self => def inserts: Reactive[T] def removes: Reactive[T]
def map[S](f: T => S) = new ReactContainer[S] { def inserts: Reactive[T] = self.inserts.map(f) def removes: Reactive[T] = self.removes.map(f) }}
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val selected = new ReactHashSet[Character]val decorations = selected .map(c => (c, decoFor(c))) .to[ReactHashMap]
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val selected = new ReactHashSet[Character]val decorations = selected .map(c => (c, decoFor(c))) .to[ReactHashMap]
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val selected = new ReactHashSet[Character]val decorations = selected .map(c => (c, decoFor(c))) .to[ReactHashMap]
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val selected = new ReactHashSet[Character]val decorations = selected .map(c => (c, decoFor(c))) .to[ReactHashMap]
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val selected = new ReactHashSet[Character]val decorations = selected .map(c => (c, decoFor(c))) .react.to[ReactHashMap]
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val selected = new ReactHashSet[Character]val decorations = selected .map(c => (c, decoFor(c))) .react.to[ReactHashMap]
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val selected = new ReactHashSet[Character]val decorations = selected .map(c => (c, decoFor(c))) .react.to[ReactHashMap]
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val selected = new ReactHashSet[Character]val decorations = selected .map(c => (c, decoFor(c))) .react.to[ReactHashMap]
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• reactive mutators• reactive collections• @specialized• Scala Macros• shipping computations to the GPU
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http://storm-enroute.com/macrogl/
MacroGL
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https://www.youtube.com/watch?v=UHCeXdxkx70
GC Preview
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Is Scala Ready?
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YES!
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Thank you!
