feat: animation: drain

Author: cfoust

pkg/anim/fluid/anim.go

@@ -13,6 +13,7 @@ type Fluid struct {
 	sim     *Simulator
 	start   image.Image
 	current image.Image
+	options []Option
 }
 
 var _ meta.Animation = (*Fluid)(nil)
@@ -21,6 +22,10 @@ const (
 	POSITION_FACTOR = 10
 )
 
+func NewAnimation(options ...Option) *Fluid {
+	return &Fluid{options: options}
+}
+
 func (f *Fluid) Init(start image.Image) {
 	f.start = start
 
@@ -45,6 +50,7 @@ func (f *Fluid) Init(start image.Image) {
 		float64(size.C)*POSITION_FACTOR,
 		float64(size.R)*POSITION_FACTOR,
 		particles,
+		f.options...,
 	)
 }
 

pkg/anim/fluid/module.go

@@ -1,7 +1,28 @@
 package fluid
 
+import "math/rand"
+
 type number = float64
 
+// Option configures a Simulator.
+type Option func(*Simulator)
+
+// WithDrain adds a hole in the bottom and top boundaries at random X
+// positions. Particles that fall through the bottom hole wrap to the top.
+func WithDrain() Option {
+	return func(s *Simulator) {
+		holeWidth := s.width / 4
+		maxOffset := s.width - holeWidth
+		bottomStart := rand.Float64() * maxOffset
+		topStart := rand.Float64() * maxOffset
+		s.drainEnabled = true
+		s.bottomHoleMinX = bottomStart
+		s.bottomHoleMaxX = bottomStart + holeWidth
+		s.topHoleMinX = topStart
+		s.topHoleMaxX = topStart + holeWidth
+	}
+}
+
 type Simulator struct {
 	width     number
 	height    number
@@ -20,13 +41,24 @@ type Simulator struct {
 	particleListNextIdx []int
 
 	material Material
+
+	// Drain mode: particles in the bottom hole wrap to the top hole
+	drainEnabled   bool
+	bottomHoleMinX number
+	bottomHoleMaxX number
+	topHoleMinX    number
+	topHoleMaxX    number
 }
 
 func (s *Simulator) Particles() []Particle {
 	return s.particles
 }
 
-func New(width, height number, particles []Particle) *Simulator {
+func New(
+	width, height number,
+	particles []Particle,
+	options ...Option,
+) *Simulator {
 	s := &Simulator{
 		width:          width,
 		height:         height,
@@ -50,5 +82,10 @@ func New(width, height number, particles []Particle) *Simulator {
 	s.particleListNextIdx = make([]int, len(particles))
 
 	s.material = NewMaterial("water", 4, 0.5, 0.5, 40)
+
+	for _, opt := range options {
+		opt(s)
+	}
+
 	return s
 }

pkg/anim/fluid/update.go

@@ -286,10 +286,26 @@ func (s *Simulator) resolveCollisions(dt number) {
 			s.particles[i].X += boundaryMul * (boundaryMaxX - p.X)
 		}
 
-		if p.Y < boundaryMinY {
-			s.particles[i].Y += boundaryMul * (boundaryMinY - p.Y)
-		} else if p.Y > boundaryMaxY {
-			s.particles[i].Y += boundaryMul * (boundaryMaxY - p.Y)
+		inBottomHole := s.drainEnabled &&
+			p.X >= s.bottomHoleMinX &&
+			p.X <= s.bottomHoleMaxX
+
+		if inBottomHole && p.Y > boundaryMaxY {
+			// Map X proportionally from bottom hole to top hole
+			t := (p.X - s.bottomHoleMinX) /
+				(s.bottomHoleMaxX - s.bottomHoleMinX)
+			s.particles[i].X = s.topHoleMinX +
+				t*(s.topHoleMaxX-s.topHoleMinX)
+			s.particles[i].prevX = s.particles[i].X
+			// Wrap to top
+			s.particles[i].Y = boundaryMinY + FLUID_PADDING
+			s.particles[i].prevY = s.particles[i].Y
+		} else {
+			if p.Y < boundaryMinY {
+				s.particles[i].Y += boundaryMul * (boundaryMinY - p.Y)
+			} else if p.Y > boundaryMaxY {
+				s.particles[i].Y += boundaryMul * (boundaryMaxY - p.Y)
+			}
 		}
 	}
 }

pkg/anim/module.go

@@ -40,8 +40,11 @@ func init() {
 	registerAnimation("cy", func() Animation {
 		return &cy.Cyform{}
 	})
+	registerAnimation("drain", func() Animation {
+		return fluid.NewAnimation(fluid.WithDrain())
+	})
 	registerAnimation("fluid", func() Animation {
-		return &fluid.Fluid{}
+		return fluid.NewAnimation()
 	})
 	registerAnimation("perlin", func() Animation {
 		return perlin.New()