Major progress in introducing arbitrary boundaries! EDT in the house.

This commit is contained in:
2025-12-08 21:14:30 -05:00
parent 45b286b66e
commit 48df951042
8 changed files with 521 additions and 29 deletions

293
edt/edt.go Normal file
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@@ -0,0 +1,293 @@
package edt
import "math"
type Bounds struct {
X int
Y int
}
type Coordinate struct {
X int
Y int
}
/*
Represents a Euclidean Distance Transform of dimensions Dimensions with the transform
stored in D and a lookup in L. The lookup represents the nearest occupied coordinate (x, y)
relative to the current coordinate.
*/
type EDT struct {
Dimensions Bounds //spatial dimensions
D []float64 //distance transform
L []Coordinate //transform lookup
gx []float64 //buffer for our vector function, per row
gy []float64 //buffer for our vector function, per column
}
func NewEDT(dimensions Bounds) *EDT {
edt := &EDT{
Dimensions: dimensions,
}
edt.InitializeD()
return edt
}
func (edt *EDT) InitializeD() {
n := edt.Dimensions.X * edt.Dimensions.Y
if n <= 0 {
return
}
edt.D = make([]float64, n)
edt.L = make([]Coordinate, n)
edt.gx = make([]float64, edt.Dimensions.X)
edt.gy = make([]float64, edt.Dimensions.Y)
for i := range n {
edt.D[i] = math.Inf(+1)
}
}
/*
Reinitializes EDT using occupancy values. Occupancy dimensions must match EDT.
*/
func (edt *EDT) AssignOccupancy(occupancy []bool) {
n := edt.Dimensions.X * edt.Dimensions.Y
if len(occupancy) != n {
return
}
//assign occupancy values
for i := range n {
if occupancy[i] {
edt.D[i] = 0
} else {
edt.D[i] = math.Inf(+1)
}
}
}
/*
EDT must already have been initialized with occupancy assigned
*/
func (edt *EDT) ComputeDistanceTransform() {
if len(edt.D) == 0 {
return
}
//compute edt for each row
for j := range edt.Dimensions.Y {
//prepare our row vector
edt.ConstructGx(j)
//compute distance transform for this row
//rowD, rowL := edt.DistanceTransform1D(edt.gx)
rowD, rowL := edt1D_with_labels(edt.gx)
//update corresponding row
edt.UpdateRow(j, rowD, rowL)
}
//compute edt for each column
for i := range edt.Dimensions.X {
//prepare our column vector
edt.ConstructGy(i)
//compute distance transform for this column
//colD, colL := edt.DistanceTransform1D(edt.gy)
colD, colL := edt1D_with_labels(edt.gy)
//update corresponding column
edt.UpdateCol(i, colD, colL)
}
}
/*Computes EDT and assigns lookup coordinates for given vector g*/
func (edt *EDT) DistanceTransform1D(g []float64) (d []float64, l []int) {
//perform 1d distance transform
n := len(g)
d = make([]float64, n)
l = make([]int, n)
v := make([]int, n)
// envelope sites (seed indices)
z := make([]float64, n+1) // changeover abscissae
k := 0
// top
v[0] = 0
z[0] = math.Inf(-1)
z[1] = math.Inf(+1)
// initialize first valid seed
k = -1
for q := 0; q < n; q++ {
if g[q] == math.Inf(+1) {
continue
}
// push q: pop while it starts before current segment
var s float64
for {
if k < 0 {
k = 0
v[0] = q
z[0] = math.Inf(-1)
z[1] = math.Inf(+1)
break
}
i := v[k]
// intersection s(i,q)
s = ((float64(q*q) + g[q]) - (float64(i*i) + g[i])) / float64(2*(q-i))
if s <= z[k] {
k--
if k < 0 {
continue
} // force a push with -inf
} else {
k++
v[k] = q
z[k] = s
z[k+1] = math.Inf(+1)
break
}
}
}
// evaluate
k = 0
for x := 0; x < n; x++ {
for z[k+1] <= float64(x) {
k++
}
i := v[k]
l[x] = i
dx := float64(x - i)
d[x] = dx*dx + g[i]
}
return d, l
}
func edt1D_with_labels(g []float64) ([]float64, []int) {
n := len(g)
d := make([]float64, n)
l := make([]int, n)
// --- 1. Gather valid seeds ---
type site struct {
i int
gi float64
}
seeds := make([]site, 0, n)
for i := 0; i < n; i++ {
if !math.IsInf(g[i], +1) { // it's a seed
seeds = append(seeds, site{i, g[i]})
}
}
// --- 2. Handle empty case directly ---
if len(seeds) == 0 {
for i := 0; i < n; i++ {
d[i] = math.Inf(+1)
l[i] = -1
}
return d, l
}
// --- 3. Lower-envelope construction (FelzenszwalbHuttenlocher) ---
v := make([]int, len(seeds))
z := make([]float64, len(seeds)+1)
k := 0
v[0] = seeds[0].i
z[0] = math.Inf(-1)
z[1] = math.Inf(+1)
for q := 1; q < len(seeds); q++ {
i := seeds[q].i
gi := seeds[q].gi
for {
j := v[k]
gj := g[j]
s := ((float64(i*i) + gi) - (float64(j*j) + gj)) / float64(2*(i-j))
if s <= z[k] {
k--
if k < 0 {
k = 0
break
}
continue
}
k++
v[k] = i
z[k] = s
z[k+1] = math.Inf(+1)
break
}
}
// --- 4. Evaluate ---
k = 0
for x := 0; x < n; x++ {
for z[k+1] <= float64(x) {
k++
}
i := v[k]
l[x] = i
dx := float64(x - i)
d[x] = dx*dx + g[i]
}
return d, l
}
/*
Prepares row vector (gx) from specified column in D
*/
func (edt *EDT) ConstructGx(col int) {
if col < edt.Dimensions.Y {
//we can be very efficient due to slice referencing
startIdx := col * edt.Dimensions.Y
edt.gx = edt.D[startIdx : startIdx+edt.Dimensions.X]
}
}
/*
Prepares column vector (gy) from specified row in D
*/
func (edt *EDT) ConstructGy(row int) {
if row < edt.Dimensions.X {
for j := range edt.Dimensions.Y {
edt.gy[j] = edt.D[j*edt.Dimensions.X+row]
}
}
}
/*
Writes data and lookup values into EDT row specified by rowidx
*/
func (edt *EDT) UpdateRow(rowidx int, data []float64, lookup []int) {
if rowidx < edt.Dimensions.Y {
startidx := rowidx * edt.Dimensions.X
for i := range edt.Dimensions.X {
edt.D[startidx+i] = data[i]
edt.L[startidx+i].X = lookup[i]
}
}
}
/*
Writes data and lookup values into EDT column specified by colidx
*/
func (edt *EDT) UpdateCol(colidx int, data []float64, lookup []int) {
if colidx < edt.Dimensions.X {
for j := range edt.Dimensions.Y {
edt.D[j*edt.Dimensions.X+colidx] = data[j]
edt.L[j*edt.Dimensions.X+colidx].X = edt.L[lookup[j]*edt.Dimensions.X+colidx].X
edt.L[j*edt.Dimensions.X+colidx].Y = lookup[j]
}
}
}

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@@ -12,6 +12,8 @@ import (
const (
RoundedBottomFlaskWidth = 32 //pixels
RoundedBottomFlaskHeight = 32 //pixels
RBFlaskMaskWidth = 46 //pixels
RBFlaskMaskHeight = 46 //pixels
RoundedBottomFlaskFluidRadius = 9 //pixels: represents spherical portion of the flask where fluid will be contained
RoundedBottomFlaskFluidOriginX = 16 //pixels: x origin of fluid area
RoundedBottomFlaskFluidOriginY = 20 //pixels: y origin of fluid area
@@ -23,26 +25,37 @@ const (
type RoundedBottomFlask struct {
MappedEntityBase
fluid *fluid.Fluid //our physical representation of the fluid
fluidbuff *ebiten.Image //predraw for the fluid
fluidbuffS *ebiten.Image //predraw for the fluid, static
fluidbuffD *ebiten.Image //predraw for the fluid, dynamic
fluidcellbuff *ebiten.Image //persistent fluid sprite, we redraw this everywhere we want to represent fluid
flaskbase *ebiten.Image //flask background (container)
flaskhighlight *ebiten.Image //flask foreground (glassware highlights)
fieldscale gamedata.Vector //used for transforming from fluid-space to sprite-space
flaskboundarymask *ebiten.Image //flask boundary mask
fieldscaleStatic gamedata.Vector //used for transforming from fluid-space to sprite-space: static
fieldscaleDyanmic gamedata.Vector //used for transforming from fluid-space to sprite-space: dynamic
angle float64
//fluid color business
fluidcolor color.RGBA //premultiplied fluid color, as set by external sources
fluidcolorF []float32 //for caching of individual color values, we compute rarely
//boundary
boundaryinitialized bool
container *fluid.Boundary
}
func NewRoundedBottomFlask() *RoundedBottomFlask {
flask := &RoundedBottomFlask{
fluidbuff: ebiten.NewImage(RoundedBottomFlaskFluidRadius*2, RoundedBottomFlaskFluidRadius*2),
fluidbuffS: ebiten.NewImage(RoundedBottomFlaskFluidRadius*2, RoundedBottomFlaskFluidRadius*2),
fluidbuffD: ebiten.NewImage(RBFlaskMaskWidth, RBFlaskMaskHeight),
fluidcellbuff: ebiten.NewImage(1, 1),
flaskbase: ebiten.NewImageFromImage(resources.ImageBank[resources.RoundedBottomFlaskBase]),
flaskhighlight: ebiten.NewImageFromImage(resources.ImageBank[resources.RoundedBottomFlaskHighlights]),
flaskboundarymask: ebiten.NewImageFromImage(resources.ImageBank[resources.RoundedBottomFlaskBoundaryMap46]),
//flaskboundarymask: ebiten.NewImageFromImage(resources.ImageBank[resources.RoundedBottomFlaskBoundaryMap]),
angle: 0,
fluidcolorF: make([]float32, 4), //one field each for R,G,B,A
boundaryinitialized: false,
}
flask.Initialize()
return flask
@@ -66,17 +79,23 @@ func (flask *RoundedBottomFlask) Initialize() {
flask.fluid.Initialize()
flask.fluid.Block = false //rounded flask, not a rect volume
//compute fieldscale using newly created fluid
flask.fieldscale = gamedata.Vector{
//compute fieldscales using newly created fluid
flask.fieldscaleStatic = gamedata.Vector{
X: RoundedBottomFlaskFluidRadius * 2 / float64(flask.fluid.Field.Nx-1),
Y: RoundedBottomFlaskFluidRadius * 2 / float64(flask.fluid.Field.Ny-1),
}
flask.fieldscaleDyanmic = gamedata.Vector{
X: RBFlaskMaskWidth / float64(flask.fluid.Field.Nx-2),
Y: RBFlaskMaskHeight / float64(flask.fluid.Field.Ny-2),
}
//setup default fluid color
flask.SetFluidColor(color.RGBA{R: 0x0, G: 0x0, B: 0xff, A: 0xff})
}
func (flask *RoundedBottomFlask) Update() {
if flask.paused {
return
}
@@ -91,7 +110,11 @@ func (flask *RoundedBottomFlask) Draw() {
flask.Sprite.DrawImage(flask.flaskbase, nil)
//render fluid
flask.RenderFluid()
if flask.boundaryinitialized {
flask.RenderFluidDynamic()
} else {
flask.RenderFluidStatic()
}
//render flask foreground
flask.Sprite.DrawImage(flask.flaskhighlight, nil)
@@ -107,8 +130,10 @@ func (flask *RoundedBottomFlask) GetAngle() float64 {
return flask.angle
}
func (flask *RoundedBottomFlask) RenderFluid() {
flask.fluidbuff.Clear()
func (flask *RoundedBottomFlask) RenderFluidDynamic() {
flask.fluidbuffD.Clear()
//flask.fluidbuffD.Fill(color.White)
//vector.StrokeRect(flask.fluidbuffD, 0, 0, 46, 46, 1, color.White, true)
//construct fluid buffer from fluid simulation
for i := range flask.fluid.Field.Nx {
@@ -125,17 +150,56 @@ func (flask *RoundedBottomFlask) RenderFluid() {
celldensity = 1
}*/
ox := float64(i) * flask.fieldscale.X
oy := float64(j) * flask.fieldscale.Y
ox := float64(i) * flask.fieldscaleDyanmic.X
oy := float64(j) * flask.fieldscaleDyanmic.Y
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(-.5, -.5)
op.GeoM.Scale(flask.fieldscale.X, flask.fieldscale.Y)
op.GeoM.Scale(flask.fieldscaleDyanmic.X, flask.fieldscaleDyanmic.Y)
op.GeoM.Translate(ox, oy)
op.ColorScale.ScaleAlpha(celldensity)
op.ColorScale.Scale(flask.fluidcolorF[0], flask.fluidcolorF[1], flask.fluidcolorF[2], flask.fluidcolorF[3])
// op.ColorM.Scale(0, 0, 1, 1)
//flask.Sprite.DrawImage(flask.fluidcellbuff, op)
flask.fluidbuff.DrawImage(flask.fluidcellbuff, op)
flask.fluidbuffD.DrawImage(flask.fluidcellbuff, op)
}
}
//transform buffer for our flask space
s := float64(RoundedBottomFlaskWidth) / RBFlaskMaskWidth * 67. / 104
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(-RBFlaskMaskWidth/2, -RBFlaskMaskHeight/2)
op.GeoM.Scale(s, -s*1.15)
op.GeoM.Translate(RoundedBottomFlaskWidth/2, RoundedBottomFlaskHeight/2+2)
//op.GeoM.Translate(RoundedBottomFlaskFluidOriginX, RoundedBottomFlaskFluidOriginY)
flask.Sprite.DrawImage(flask.fluidbuffD, op)
}
func (flask *RoundedBottomFlask) RenderFluidStatic() {
flask.fluidbuffS.Clear()
//construct fluid buffer from fluid simulation
for i := range flask.fluid.Field.Nx {
for j := range flask.fluid.Field.Ny {
idx := i*flask.fluid.Field.Ny + j
if flask.fluid.Field.CellType[idx] != fluid.CellTypeFluid {
continue
}
celldensity := flask.fluid.ParticleDensity[idx] / flask.fluid.ParticleRestDensity
/*if celldensity > 0.8 {
celldensity = 1
}*/
ox := float64(i) * flask.fieldscaleStatic.X
oy := float64(j) * flask.fieldscaleStatic.Y
op := &ebiten.DrawImageOptions{}
op.GeoM.Translate(-.5, -.5)
op.GeoM.Scale(flask.fieldscaleStatic.X, flask.fieldscaleStatic.Y)
op.GeoM.Translate(ox, oy)
op.ColorScale.ScaleAlpha(celldensity)
op.ColorScale.Scale(flask.fluidcolorF[0], flask.fluidcolorF[1], flask.fluidcolorF[2], flask.fluidcolorF[3])
flask.fluidbuffS.DrawImage(flask.fluidcellbuff, op)
}
}
@@ -145,7 +209,7 @@ func (flask *RoundedBottomFlask) RenderFluid() {
op.GeoM.Translate(-RoundedBottomFlaskFluidRadius, -RoundedBottomFlaskFluidRadius)
op.GeoM.Scale(1, -1)
op.GeoM.Translate(RoundedBottomFlaskFluidOriginX, RoundedBottomFlaskFluidOriginY)
flask.Sprite.DrawImage(flask.fluidbuff, op)
flask.Sprite.DrawImage(flask.fluidbuffS, op)
}
func (flask *RoundedBottomFlask) SetFluidColor(c color.RGBA) {
@@ -155,3 +219,47 @@ func (flask *RoundedBottomFlask) SetFluidColor(c color.RGBA) {
flask.fluidcolorF[2] = float32(flask.fluidcolor.B) / float32(flask.fluidcolor.A)
flask.fluidcolorF[3] = float32(flask.fluidcolor.A) / 0xff
}
func (flask *RoundedBottomFlask) InitializeBoundary() {
//prepare the dimensions of our boundary map
dimensions := fluid.BoundaryDimensions{
X: RBFlaskMaskWidth,
Y: RBFlaskMaskHeight,
}
//instantiate the boundary structure
flask.container = fluid.NewBoundary(dimensions)
//load pixel data from boundary
var pixels []byte = make([]byte, dimensions.X*dimensions.Y*4)
flask.flaskboundarymask.ReadPixels(pixels)
//populate our boundary map based on the pixel data
for i := 0; i < len(pixels); i += 4 {
cellidx := i / 4
boundary := pixels[i] == 0
flask.container.Cells[cellidx] = !boundary
}
//apply to fluid simulation
flask.fluid.SetBoundary(flask.container)
flask.boundaryinitialized = true
}
// set new boundary mask and reinitialize associated data, including computing and
// passing that into the associated fluid simulation
func (flask *RoundedBottomFlask) SetBoundaryMap(img *ebiten.Image) {
flask.flaskboundarymask = img
flask.InitializeBoundary()
}
func (flask *RoundedBottomFlask) ToggleBoundaryMask() {
if flask.boundaryinitialized {
flask.fluid.SetBoundary(nil)
flask.boundaryinitialized = false
} else {
flask.InitializeBoundary()
flask.boundaryinitialized = true
}
}

19
fluid/boundary.go Normal file
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@@ -0,0 +1,19 @@
package fluid
type BoundaryDimensions struct {
X int
Y int
}
type Boundary struct {
Dimensions BoundaryDimensions
Cells []bool
}
func NewBoundary(dimensions BoundaryDimensions) *Boundary {
b := &Boundary{
Dimensions: dimensions,
Cells: make([]bool, dimensions.X*dimensions.Y),
}
return b
}

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@@ -4,6 +4,7 @@
package fluid
import (
"fluids/edt"
"fluids/utils"
"math"
)
@@ -41,6 +42,9 @@ type Fluid struct {
flipPicRatio float32
numSubSteps int //number of simulation substeps
Block bool //rectangular or circular field container
//for arbitrary boundaries
edt *edt.EDT
}
func NewFluid(dimensions FieldVector, spacing float32) *Fluid {
@@ -52,6 +56,7 @@ func NewFluid(dimensions FieldVector, spacing float32) *Fluid {
flipPicRatio: FluidDefaultFlipPicRatio,
numSubSteps: FluidDefaultSubSteps,
Block: true,
edt: nil,
}
f.Initialize()
@@ -268,6 +273,11 @@ func (f *Fluid) HandleParticleCollisions() {
minDist2 := minDist * minDist
*/
if f.edt != nil {
f.HandleBoundaryCollisions()
return
}
if f.Block {
minX := f.Field.H + f.particleRadius
maxX := float32(f.Field.Nx-1)*f.Field.H - f.particleRadius
@@ -651,3 +661,53 @@ func (f *Fluid) SolveIncompressibility() {
func (f *Fluid) ToggleShape() {
f.Block = !f.Block
}
func (f *Fluid) SetBoundary(b *Boundary) {
if b != nil {
dim := edt.Bounds{
X: b.Dimensions.X,
Y: b.Dimensions.Y,
}
f.edt = edt.NewEDT(dim)
f.edt.AssignOccupancy(b.Cells)
f.edt.ComputeDistanceTransform()
} else {
f.edt = nil
}
}
// we perform our boundary resolution on particles according to our defined fluid boundary
func (f *Fluid) HandleBoundaryCollisions() {
//grid spacing within our distance field
dx := f.Field.Dimensions.X / float32(f.edt.Dimensions.X)
dy := f.Field.Dimensions.Y / float32(f.edt.Dimensions.Y)
//find cell of distance field for which particles belong, check if it's in bounds
for i := range f.Particles {
p := &f.Particles[i]
xi := utils.Clamp(int(math.Floor(float64(p.Position.X/dx))), 0, f.edt.Dimensions.X-1)
yi := utils.Clamp(int(math.Floor(float64(p.Position.Y/dy))), 0, f.edt.Dimensions.Y-1)
cellidx := xi + yi*f.edt.Dimensions.X
//if our current cell isn't a boundary, then we skip
if f.edt.D[cellidx] == 0 {
continue
}
//find where the particle actually belongs
pos := f.edt.L[cellidx]
newx := (float32(pos.X-xi) + f.particleRadius) * dx
newy := (float32(pos.Y-yi) + f.particleRadius) * dy
p.Position.X += newx
p.Position.Y += newy
p.Velocity.X = 0
p.Velocity.Y = 0
}
}

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@@ -335,6 +335,10 @@ func (g *Game) ManageFlaskInputs() {
g.mfangle = g.mfangle + (angle - g.mdangle)
}
if inpututil.IsKeyJustPressed(ebiten.KeyM) {
g.flask.ToggleBoundaryMask()
}
}
func (g *Game) UpdateFlask() {

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@@ -15,6 +15,8 @@ type ImageName string
const (
RoundedBottomFlaskBase ImageName = "RoundedBottomFlaskBase"
RoundedBottomFlaskHighlights ImageName = "RoundedBottomFlaskHighlights"
RoundedBottomFlaskBoundaryMap ImageName = "RoundedBottomFlaskBoundaryMap"
RoundedBottomFlaskBoundaryMap46 ImageName = "RoundedBottomFlaskBoundaryMap46"
)
var (
@@ -23,13 +25,19 @@ var (
//go:embed rounded_bottom_flask_base.png
rounded_bottom_flask_base []byte
//go:embed rounded_bottom_flask_highlights.png
rounded_bottom_flask_highlitsh []byte
rounded_bottom_flask_highlight []byte
//go:embed rounded_bottom_flask_boundary_map.png
rounded_bottom_flask_boundary_map []byte
//go:embed rounded_bottom_flask_boundary_map_46.png
rounded_bottom_flask_boundary_map_46 []byte
)
func LoadImages() {
ImageBank = make(map[ImageName]*ebiten.Image)
ImageBank[RoundedBottomFlaskBase] = LoadImagesFatal(rounded_bottom_flask_base)
ImageBank[RoundedBottomFlaskHighlights] = LoadImagesFatal(rounded_bottom_flask_highlitsh)
ImageBank[RoundedBottomFlaskHighlights] = LoadImagesFatal(rounded_bottom_flask_highlight)
ImageBank[RoundedBottomFlaskBoundaryMap] = LoadImagesFatal(rounded_bottom_flask_boundary_map)
ImageBank[RoundedBottomFlaskBoundaryMap46] = LoadImagesFatal(rounded_bottom_flask_boundary_map_46)
}
func LoadImagesFatal(b []byte) *ebiten.Image {

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