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5/gemini-3.5-flash #18

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19f5810
Fix density accumulation. Add tanh getDensity helper in display shade…
jayf0x Jun 4, 2026
0049c0e
Add density saturation shader tests. Verify tanh helper presence and …
jayf0x Jun 4, 2026
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24 changes: 15 additions & 9 deletions src/core/shaders.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -168,26 +168,32 @@ export const displayShader = /* glsl */ `
uniform int uAlgorithm;
uniform int uEnableAlpha;

float getDensity(vec2 uv) {
float raw = max(texture2D(uTexture, uv).r, 0.0);
float e2 = exp(2.0 * min(raw, 10.0));
return (e2 - 1.0) / (e2 + 1.0);
}

void main () {
float obs = texture2D(uObstacle, vUv).r;
// Smooth fade: density falls off over the blurred obstacle boundary zone
// rather than cutting off at a hard step, eliminating the jagged fringe.
float density = max(texture2D(uTexture, vUv).r, 0.0) * (1.0 - obs);
float density = getDensity(vUv) * (1.0 - obs);
float coverage = texture2D(uCoverage, vUv).r;

// 8-tap Sobel normal — computes gradient via 3×3 kernel (no centre sample needed).
// texelSize = 1/displayRes; density FBO is at simScale (0.5×), so s=6 display px
// ≈ 3 sim texels per axis. The Sobel kernel properly averages the gradient in
// every direction — no 4-tap cross bias that creates 45° circuit-board artefacts.
float sx = texelSize.x * 6.0, sy = texelSize.y * 6.0;
float d00 = max(texture2D(uTexture, vUv + vec2(-sx, -sy)).r, 0.0);
float d10 = max(texture2D(uTexture, vUv + vec2(0.0, -sy)).r, 0.0);
float d20 = max(texture2D(uTexture, vUv + vec2( sx, -sy)).r, 0.0);
float d01 = max(texture2D(uTexture, vUv + vec2(-sx, 0.0)).r, 0.0);
float d21 = max(texture2D(uTexture, vUv + vec2( sx, 0.0)).r, 0.0);
float d02 = max(texture2D(uTexture, vUv + vec2(-sx, sy)).r, 0.0);
float d12 = max(texture2D(uTexture, vUv + vec2(0.0, sy)).r, 0.0);
float d22 = max(texture2D(uTexture, vUv + vec2( sx, sy)).r, 0.0);
float d00 = getDensity(vUv + vec2(-sx, -sy));
float d10 = getDensity(vUv + vec2(0.0, -sy));
float d20 = getDensity(vUv + vec2( sx, -sy));
float d01 = getDensity(vUv + vec2(-sx, 0.0));
float d21 = getDensity(vUv + vec2( sx, 0.0));
float d02 = getDensity(vUv + vec2(-sx, sy));
float d12 = getDensity(vUv + vec2(0.0, sy));
float d22 = getDensity(vUv + vec2( sx, sy));
float gx = (d20 + 2.0*d21 + d22) - (d00 + 2.0*d01 + d02);
float gy = (d02 + 2.0*d12 + d22) - (d00 + 2.0*d10 + d20);

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41 changes: 23 additions & 18 deletions src/core/wgsl-shaders.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@
// render-to-texture round-trips consistent (no Y flip in simulation FBOs).
// Source textures are uploaded WITHOUT flipY so their row 0 (visual top)
// also lands at uv.y=0.
const SHARED_VS_STRUCT = /* wgsl */`
const SHARED_VS_STRUCT = /* wgsl */ `
struct VSOut {
@builtin(position) pos : vec4f,
@location(0) uv : vec2f,
Expand All @@ -24,7 +24,7 @@ struct VSOut {

// ─── Advection ───────────────────────────────────────────────────────────────

export const advectionWGSL = /* wgsl */`
export const advectionWGSL = /* wgsl */ `
${SHARED_VS_STRUCT}

struct U {
Expand Down Expand Up @@ -60,7 +60,7 @@ struct U {

// ─── Divergence ──────────────────────────────────────────────────────────────

export const divergenceWGSL = /* wgsl */`
export const divergenceWGSL = /* wgsl */ `
${SHARED_VS_STRUCT}

struct U { texelSize: vec2f, _pad: vec2f }
Expand Down Expand Up @@ -91,7 +91,7 @@ struct U { texelSize: vec2f, _pad: vec2f }

// ─── Pressure ────────────────────────────────────────────────────────────────

export const pressureWGSL = /* wgsl */`
export const pressureWGSL = /* wgsl */ `
${SHARED_VS_STRUCT}

struct U { texelSize: vec2f, _pad: vec2f }
Expand Down Expand Up @@ -125,7 +125,7 @@ struct U { texelSize: vec2f, _pad: vec2f }

// ─── Gradient subtract ───────────────────────────────────────────────────────

export const gradientSubtractWGSL = /* wgsl */`
export const gradientSubtractWGSL = /* wgsl */ `
${SHARED_VS_STRUCT}

struct U { texelSize: vec2f, _pad: vec2f }
Expand Down Expand Up @@ -160,7 +160,7 @@ struct U { texelSize: vec2f, _pad: vec2f }

// ─── Splat ───────────────────────────────────────────────────────────────────

export const splatWGSL = /* wgsl */`
export const splatWGSL = /* wgsl */ `
${SHARED_VS_STRUCT}

// texelSize occupies bytes 0-7 for the shared vertex stage; aspectRatio/radius fill the rest.
Expand Down Expand Up @@ -197,7 +197,7 @@ struct U {

// ─── Curl ────────────────────────────────────────────────────────────────────

export const curlWGSL = /* wgsl */`
export const curlWGSL = /* wgsl */ `
${SHARED_VS_STRUCT}

struct U { texelSize: vec2f, _pad: vec2f }
Expand Down Expand Up @@ -227,7 +227,7 @@ struct U { texelSize: vec2f, _pad: vec2f }

// ─── Vorticity ───────────────────────────────────────────────────────────────

export const vorticityWGSL = /* wgsl */`
export const vorticityWGSL = /* wgsl */ `
${SHARED_VS_STRUCT}

struct U {
Expand Down Expand Up @@ -278,7 +278,7 @@ struct U {
// 56 algorithm i32
// 60 enableAlpha i32 (1 = premultiplied alpha output, 0 = opaque)

export const displayWGSL = /* wgsl */`
export const displayWGSL = /* wgsl */ `
${SHARED_VS_STRUCT}

struct U {
Expand All @@ -300,6 +300,11 @@ struct U {
@group(0) @binding(5) var uCov : texture_2d<f32>;
@group(0) @binding(6) var uVel : texture_2d<f32>;

fn getDensity(uv: vec2f) -> f32 {
let raw = max(textureSample(uTex, samp, uv).r, 0.0);
return tanh(raw);
}

@vertex fn vs(@location(0) a: vec2f) -> VSOut {
var o: VSOut;
o.uv = vec2f(a.x * 0.5 + 0.5, 0.5 - a.y * 0.5);
Expand All @@ -313,19 +318,19 @@ struct U {

@fragment fn fs(i: VSOut) -> @location(0) vec4f {
let obs = textureSample(uObs, samp, i.uv).r;
let density = max(textureSample(uTex, samp, i.uv).r, 0.0) * (1.0 - obs);
let density = getDensity(i.uv) * (1.0 - obs);
let cov = textureSample(uCov, samp, i.uv).r;

let sx = u.texelSize.x * 6.0;
let sy = u.texelSize.y * 6.0;
let d00 = max(textureSample(uTex, samp, i.uv + vec2f(-sx, -sy)).r, 0.0);
let d10 = max(textureSample(uTex, samp, i.uv + vec2f(0.0, -sy)).r, 0.0);
let d20 = max(textureSample(uTex, samp, i.uv + vec2f( sx, -sy)).r, 0.0);
let d01 = max(textureSample(uTex, samp, i.uv + vec2f(-sx, 0.0)).r, 0.0);
let d21 = max(textureSample(uTex, samp, i.uv + vec2f( sx, 0.0)).r, 0.0);
let d02 = max(textureSample(uTex, samp, i.uv + vec2f(-sx, sy)).r, 0.0);
let d12 = max(textureSample(uTex, samp, i.uv + vec2f(0.0, sy)).r, 0.0);
let d22 = max(textureSample(uTex, samp, i.uv + vec2f( sx, sy)).r, 0.0);
let d00 = getDensity(i.uv + vec2f(-sx, -sy));
let d10 = getDensity(i.uv + vec2f(0.0, -sy));
let d20 = getDensity(i.uv + vec2f( sx, -sy));
let d01 = getDensity(i.uv + vec2f(-sx, 0.0));
let d21 = getDensity(i.uv + vec2f( sx, 0.0));
let d02 = getDensity(i.uv + vec2f(-sx, sy));
let d12 = getDensity(i.uv + vec2f(0.0, sy));
let d22 = getDensity(i.uv + vec2f( sx, sy));
let gx = (d20 + 2.0*d21 + d22) - (d00 + 2.0*d01 + d02);
let gy = (d02 + 2.0*d12 + d22) - (d00 + 2.0*d10 + d20);

Expand Down
65 changes: 65 additions & 0 deletions tests/core/shaders.test.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,65 @@
import { describe, expect, it } from 'vitest';

import { displayShader } from '../../src/core/shaders.ts';
import { displayWGSL } from '../../src/core/wgsl-shaders.ts';

describe('displayShader density saturation', () => {
it('GLSL displayShader contains getDensity helper', () => {
expect(displayShader).toContain('getDensity');
});

it('GLSL getDensity uses tanh-equivalent soft saturation', () => {
// The implementation uses (e2-1)/(e2+1) which equals tanh(raw).
// Verify the shader does NOT use the old unbounded max(..., 0.0) directly
// for the main density or Sobel samples.
const lines = displayShader.split('\n');
const mainDensityLine = lines.find((l) => l.includes('float density') && l.includes('1.0 - obs'));
expect(mainDensityLine).toContain('getDensity');
});

it('WGSL displayWGSL contains getDensity helper', () => {
expect(displayWGSL).toContain('getDensity');
});

it('WGSL getDensity uses tanh', () => {
expect(displayWGSL).toContain('tanh(');
});

it('WGSL main density line uses getDensity', () => {
const lines = displayWGSL.split('\n');
const mainDensityLine = lines.find((l) => l.includes('let density') && l.includes('1.0 - obs'));
expect(mainDensityLine).toContain('getDensity');
});
});

describe('getDensity saturation behaviour (JS simulation)', () => {
// Verify the tanh-like formula used in GLSL: (e^2x - 1) / (e^2x + 1)
const glslGetDensity = (raw) => {
const r = Math.max(raw, 0.0);
const e2 = Math.exp(2.0 * Math.min(r, 10.0));
return (e2 - 1.0) / (e2 + 1.0);
};

it('maps 0 to 0', () => {
expect(glslGetDensity(0)).toBeCloseTo(0, 5);
});

it('maps 1 to < 1', () => {
expect(glslGetDensity(1)).toBeLessThan(1.0);
});

it('maps values > 1 to < 1 (prevents glow saturation)', () => {
expect(glslGetDensity(2.0)).toBeLessThan(1.0);
expect(glslGetDensity(5.0)).toBeLessThan(1.0);
expect(glslGetDensity(100.0)).toBeLessThan(1.0);
});

it('is monotonically increasing', () => {
expect(glslGetDensity(0.5)).toBeLessThan(glslGetDensity(1.0));
expect(glslGetDensity(1.0)).toBeLessThan(glslGetDensity(2.0));
});

it('clamps negative raw values to 0', () => {
expect(glslGetDensity(-1.0)).toBeCloseTo(0, 5);
});
});
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