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Fluid simulation · gemma-4-26b-a4b-it

Create a real-time fluid simulation on a full-screen canvas where dragging the mouse pushes swirling colored dye through the fluid.

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user

Create a real-time fluid simulation on a full-screen canvas where dragging the mouse pushes swirling colored dye through the fluid.

assistant
thinking
The user wants a real-time fluid simulation in a single `index.html` file.
It should be a full-screen canvas.
Interactivity: Dragging the mouse should push swirling colored dye.
Constraints:
- Single file `index.html`.
- CSS in `<style>`, JS in `<script>`.
- No external resources (no CDNs, no network requests).
- Fully sandboxed.

Plan:
1.  Implement a stable fluid simulation algorithm. Jos Stam's "Stable Fluids" is the classic choice for this.
2.  The simulation involves:
    - Velocity field (u, v).
    - Density field (dye).
    - Advection, Diffusion, Pressure projection (to ensure incompressibility).
3.  Use WebGL for performance if possible, as a CPU-based fluid simulation might be too slow for a full-screen real-time experience in JS. However, a single-file implementation with WebGL shaders can be complex but very efficient.
4.  Given the "single file" and "no external resources" constraint, WebGL is the way to go for high performance.

Let's refine the WebGL approach:
- Two-pass rendering for simulation (ping-pong textures).
- Shaders for:
    - Advection.
    - Divergence calculation.
    - Pressure calculation (Jacobi iteration).
    - Gradient subtraction (to get velocity).
    - Density advection.
    - Splatting (adding velocity/dye from mouse).
    - Rendering (displaying the result).

Implementation details:
- `index.html` structure.
- `<style>` for full-screen canvas.
- `<script>` for WebGL logic.

Wait, writing a full WebGL fluid sim from scratch in one go might be error-prone if I don't have a template. But I can definitely do it.

Algorithm steps (Jos Stam style in WebGL):
1.  `advect`: Move velocity and density along the velocity field.
2.  `divergence`: Compute divergence of the velocity field.
3.  `pressure`: Solve Poisson equation for pressure (Jacobi iteration).
4.  `gradient subtraction`: Subtract pressure gradient from velocity to make it mass-conserving.
5.  `splat`: Add impulse to velocity and density.
6.  `render`: Draw density to screen.

Let's get to coding.

```html <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Fluid Simulation</title> <style> body, html { margin: 0; padding: 0; width: 100%; height: 100%; overflow: hidden; background-color: #000; } canvas { display: block; width: 100vw; height: 100vh; } </style> </head> <body> <canvas id="canvas"></canvas> <script> /** * Real-time Fluid Simulation * Based on Jos Stam's "Stable Fluids" * Implemented in WebGL for performance. */ const canvas = document.getElementById('canvas'); const gl = canvas.getContext('webgl') || canvas.getContext('experimental-webgl'); if (!gl) { alert('WebGL not supported'); } // --- Shader Sources --- const baseVertexShader = ` precision highp float; attribute vec2 aPosition; varying vec2 vUv; void main() { vUv = aPosition * 0.5 + 0.5; gl_Position = vec4(aPosition, 0.0, 1.0); } `; const displayShader = ` precision highp float; varying vec2 vUv; uniform sampler2D uTexture; void main() { vec4 color = texture2D(uTexture, vUv); gl_FragColor = vec4(color.rgb, 1.0); } `; const splatShader = ` precision highp float; varying vec2 vUv; uniform sampler2D uTarget; uniform float uAspect; uniform vec2 uPoint; uniform vec3 uColor; uniform float uRadius; void main() { vec2 p = vUv - uPoint; p.x *= uAspect; float mask = exp(-dot(p, p) / uRadius); vec4 base = texture2D(uTarget, vUv); gl_FragColor = vec4(base.rgb + mask * uColor, base.a); } `; const advectShader = ` precision highp float; varying vec2 vUv; uniform sampler2D uVelocity; uniform sampler2D uSource; uniform float uDt; uniform float uDissipation; uniform vec2 uTexelSize; void main() { vec2 coord = vUv - uDt * texture2D(uVelocity, vUv).xy * uTexelSize; gl_FragColor = uDissipation * texture2D(uSource, coord); } `; const divergenceShader = ` precision highp float; varying vec2 vUv; uniform sampler2D uVelocity; uniform vec2 uTexelSize; void main() { float L = texture2D(uVelocity, vUv - vec2(uTexelSize.x, 0.0)).x; float R = texture2D(uVelocity, vUv + vec2(uTexelSize.x, 0.0)).x; float T = texture2D(uVelocity, vUv + vec2(0.0, uTexelSize.y)).y; float B = texture2D(uVelocity, vUv - vec2(0.0, uTexelSize.y)).y; float div = 0.5 * (R - L + T - B); gl_FragColor = vec4(div, 0.0, 0.0, 1.0); } `; const pressureShader = ` precision highp float; varying vec2 vUv; uniform sampler2D uPressure; uniform sampler2D uDivergence; uniform vec2 uTexelSize; void main() { float L = texture2D(uPressure, vUv - vec2(uTexelSize.x, 0.0)).x; float R = texture2D(uPressure, vUv + vec2(uTexelSize.x, 0.0)).x; float T = texture2D(uPressure, vUv + vec2(0.0, uTexelSize.y)).x; float B = texture2D(uPressure, vUv - vec2(0.0, uTexelSize.y)).x; float div = texture2D(uDivergence, vUv).x; float p = (L + R + B + T - div) * 0.25; gl_FragColor = vec4(p, 0.0, 0.0, 1.0); } `; const gradientSubtractShader = ` precision highp float; varying vec2 vUv; uniform sampler2D uPressure; uniform sampler2D uVelocity; uniform vec2 uTexelSize; void main() { float L = texture2D(uPressure, vUv - vec2(uTexelSize.x, 0.0)).x; float R = texture2D(uPressure, vUv + vec2(uTexelSize.x, 0.0)).x; float T = texture2D(uPressure, vUv + vec2(0.0, uTexelSize.y)).x; float B = texture2D(uPressure, vUv - vec2(0.0, uTexelSize.y)).x; vec2 velocity = texture2D(uVelocity, vUv).xy; velocity -= vec2(R - L, T - B) * 0.5; gl_FragColor = vec4(velocity, 0.0, 1.0); } `; // --- WebGL Helper Functions --- function createShader(gl, type, source) { const shader = gl.createShader(type); gl.shaderSource(shader, source); gl.compileShader(shader); if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) { console.error(gl.getShaderInfoLog(shader)); gl.deleteShader(shader); return null; } return shader; } function createProgram(gl, vsSource, fsSource) { const vs = createShader(gl, gl.VERTEX_SHADER, vsSource); const fs = createShader(gl, gl.FRAGMENT_SHADER, fsSource); const program = gl.createProgram(); gl.attachShader(program, vs); gl.attachShader(program, fs); gl.linkProgram(program); if (!gl.getProgramParameter(program, gl.LINK_STATUS)) { console.error(gl.getProgramInfoLog(program)); return null; } return program; } // --- Simulation State --- const config = { SIM_RESOLUTION: 128, DYE_RESOLUTION: 512, DENSITY_DISSIPATION: 0.98, VELOCITY_DISSIPATION: 0.99, PRESSURE_ITERATIONS: 20, SPLAT_RADIUS: 0.005, }; let width, height; let density, velocity, pressure, divergence; let programs = {}; let quadBuffer; function createFBO(w, h) { const texture = gl.createTexture(); gl.bindTexture(gl.TEXTURE_2D, texture); gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, w, h, 0, gl.RGBA, gl.UNSIGNED_BYTE, null); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE); const fbo = gl.createFramebuffer(); gl.bindFramebuffer(gl.FRAMEBUFFER, fbo); gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0); return { texture, fbo, width: w, height: h, // Double buffering ping: { texture: gl.createTexture(), fbo: gl.createFramebuffer() }, pong: { texture: gl.createTexture(), fbo: gl.createFramebuffer() } }; } function createDoubleFBO(w, h) { const fbo1 = createFBO(w, h); const fbo2 = createFBO(w, h); return { get read() { return fbo1; }, get write() { return fbo2; }, swap() { const tmp = fbo1; fbo1 = fbo2; fbo2 = tmp; } }; // Actually, let's simplify. We need two buffers for ping-pong. } // Refined FBO class for ping-pong class PingPongFBO { constructor(w, h) { this.w = w; this.h = h; this.textures = [this._createTexture(w, h), this._createTexture(w, h)]; this.fbos = [this._createFBO(w, h, this.textures[0]), this._createFBO(w, h, this.textures[1])]; this.readIdx = 0; } _createTexture(w, h) { const tex = gl.createTexture(); gl.bindTexture(gl.TEXTURE_2D, tex); gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, w, h, 0, gl.RGBA, gl.UNSIGNED_BYTE, null); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE); gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE); return tex; } _createFBO(w, h, tex) { const fbo = gl.createFramebuffer(); gl.bindFramebuffer(gl.FRAMEBUFFER, fbo); gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, tex, 0); return fbo; } get read() { return { texture: this.textures[this.readIdx], fbo: this.fbos[this.readIdx], w: this.w, h: this.h }; } get write() { return { texture: this.textures[1 - this.readIdx], fbo: this.fbos[1 - this.readIdx], w: this.w, h: this.h }; } swap() { this.readIdx = 1 - this.readIdx; } } // --- Initialization --- function init() { width = canvas.width = window.innerWidth; height = canvas.height = window.innerHeight; // Programs programs.splat = createProgram(gl, baseVertexShader, splatShader); programs.advect = createProgram(gl, baseVertexShader, advectShader); programs.divergence = createProgram(gl, baseVertexShader, divergenceShader); programs.pressure = createProgram(gl, baseVertexShader, pressureShader); programs.gradientSubtract = createProgram(gl, baseVertexShader, gradientSubtractShader); programs.display = createProgram(gl, baseVertexShader, displayShader); // Buffers quadBuffer = gl.createBuffer(); gl.bindBuffer(gl.ARRAY_BUFFER, quadBuffer); gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1, -1, 1, -1, -1, 1, 1, 1]), gl.STATIC_DRAW); // Simulation Buffers density = new PingPongFBO(config.DYE_RESOLUTION, config.DYE_RESOLUTION); velocity = new PingPongFBO(config.SIM_RESOLUTION, config.SIM_RESOLUTION); pressure = new PingPongFBO(config.SIM_RESOLUTION, config.SIM_RESOLUTION); divergence = new PingPongFBO(config.SIM_RESOLUTION, config.SIM_RESOLUTION); } // --- Interaction --- let pointer = { x: 0, y: 0, dx: 0, dy: 0, moved: false, pressed: false }; window.addEventListener('mousedown', () => pointer.pressed = true); window.addEventListener('mouseup', () => pointer.pressed = false); window.addEventListener('mousemove', (e) => { pointer.dx = (e.clientX - pointer.x) * 5.0; pointer.dy = (e.clientY - pointer.y) * 5.0; pointer.x = e.clientX; pointer.y = e.clientY; pointer.moved = true; }); // Touch support window.addEventListener('touchstart', (e) => { pointer.pressed = true; pointer.x = e.touches[0].clientX; pointer.y = e.touches[0].clientY; }, { passive: false }); window.addEventListener('touchend', () => pointer.pressed = false); window.addEventListener('touchmove', (e) => { pointer.dx = (e.touches[0].clientX - pointer.x) * 5.0; pointer.dy = (e.clientY - pointer.y) * 5.0; pointer.x = e.touches[0].clientX; pointer.y = e.touches[0].clientY; pointer.moved = true; e.preventDefault(); }, { passive: false }); // --- Simulation Loop --- function update() { gl.viewport(0, 0, config.SIM_RESOLUTION, config.SIM_RESOLUTION); // 1. Advection (Velocity) gl.useProgram(programs.advect); gl.uniform2f(gl.getUniformLocation(programs.advect, 'uTexelSize'), 1 / config.SIM_RESOLUTION, 1 / config.SIM_RESOLUTION); gl.uniform1f(gl.getUniformLocation(programs.advect, 'uDt'), 0.016); gl.uniform1f(gl.getUniformLocation(programs.advect, 'uDissipation'), config.VELOCITY_DISSIPATION); gl.uniform1i(gl.getUniformLocation(programs.advect, 'uVelocity'), 0); gl.uniform1i(gl.getUniformLocation(programs.advect, 'uSource'), 0); gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, velocity.read.texture); gl.bindFramebuffer(gl.FRAMEBUFFER, velocity.write.fbo); const posLoc = gl.getAttribLocation(programs.advect, 'aPosition'); gl.enableVertexAttribArray(posLoc); gl.bindBuffer(gl.ARRAY_BUFFER, quadBuffer); gl.vertexAttribPointer(posLoc, 2, gl.FLOAT, false, 0, 0); gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); velocity.swap(); // 2. Advection (Density) gl.viewport(0, 0, config.DYE_RESOLUTION, config.DYE_RESOLUTION); gl.useProgram(programs.advect); gl.uniform2f(gl.getUniformLocation(programs.advect, 'uTexelSize'), 1 / config.DYE_RESOLUTION, 1 / config.DYE_RESOLUTION); gl.uniform1f(gl.getUniformLocation(programs.advect, 'uDt'), 0.016); gl.uniform1f(gl.getUniformLocation(programs.advect, 'uDissipation'), config.DENSITY_DISSIPATION); gl.uniform1i(gl.getUniformLocation(programs.advect, 'uVelocity'), 0); gl.uniform1i(gl.getUniformLocation(programs.advect, 'uSource'), 1); gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, velocity.read.texture); gl.activeTexture(gl.TEXTURE1); gl.bindTexture(gl.TEXTURE_2D, density.read.texture); gl.bindFramebuffer(gl.FRAMEBUFFER, density.write.fbo); gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); density.swap(); // 3. Splat (Input) if (pointer.moved || pointer.pressed) { // Splat Velocity gl.viewport(0, 0, config.SIM_RESOLUTION, config.SIM_RESOLUTION); gl.useProgram(programs.splat); gl.uniform1f(gl.getUniformLocation(programs.splat, 'uAspect'), config.SIM_RESOLUTION / config.SIM_RESOLUTION); gl.uniform2f(gl.getUniformLocation(programs.splat, 'uPoint'), pointer.x / width, 1.0 - pointer.y / height); gl.uniform3f(gl.getUniformLocation(programs.splat, 'uColor'), pointer.dx, -pointer.dy, 0.0); gl.uniform1f(gl.getUniformLocation(programs.splat, 'uRadius'), config.SPLAT_RADIUS); gl.uniform1i(gl.getUniformLocation(programs.splat, 'uTarget'), 0); gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, velocity.read.texture); gl.bindFramebuffer(gl.FRAMEBUFFER, velocity.write.fbo); gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); velocity.swap(); // Splat Density gl.viewport(0, 0, config.DYE_RESOLUTION, config.DYE_RESOLUTION); gl.uniform2f(gl.getUniformLocation(programs.splat, 'uPoint'), pointer.x / width, 1.0 - pointer.y / height); // Pick color based on movement/position or just random/swirly const r = Math.sin(Date.now() * 0.001) * 0.5 + 0.5; const g = Math.sin(Date.now() * 0.0013) * 0.5 + 0.5; const b = Math.sin(Date.now() * 0.0017) * 0.5 + 0.5; gl.uniform3f(gl.getUniformLocation(programs.splat, 'uColor'), r, g, b); gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, density.read.texture); gl.bindFramebuffer(gl.FRAMEBUFFER, density.write.fbo); gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); density.swap(); pointer.moved = false; } // 4. Projection (Pressure / Divergence / Gradient Subtract) // 4.1 Divergence gl.viewport(0, 0, config.SIM_RESOLUTION, config.SIM_RESOLUTION); gl.useProgram(programs.divergence); gl.uniform2f(gl.getUniformLocation(programs.divergence, 'uTexelSize'), 1 / config.SIM_RESOLUTION, 1 / config.SIM_RESOLUTION); gl.uniform1i(gl.getUniformLocation(programs.divergence, 'uVelocity'), 0); gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, velocity.read.texture); gl.bindFramebuffer(gl.FRAMEBUFFER, divergence.write.fbo); gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); divergence.swap(); // 4.2 Pressure Jacobi Iterations gl.useProgram(programs.pressure); gl.uniform2f(gl.getUniformLocation(programs.pressure, 'uTexelSize'), 1 / config.SIM_RESOLUTION, 1 / config.SIM_RESOLUTION); gl.uniform1i(gl.getUniformLocation(programs.pressure, 'uDivergence'), 1); gl.activeTexture(gl.TEXTURE1); gl.bindTexture(gl.TEXTURE_2D, divergence.read.texture); for (let i = 0; i < config.PRESSURE_ITERATIONS; i++) { gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, pressure.read.texture); gl.bindFramebuffer(gl.FRAMEBUFFER, pressure.write.fbo); gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); pressure.swap(); } // 4.3 Gradient Subtract gl.useProgram(programs.gradientSubtract); gl.uniform2f(gl.getUniformLocation(programs.gradientSubtract, 'uTexelSize'), 1 / config.SIM_RESOLUTION, 1 / config.SIM_RESOLUTION); gl.uniform1i(gl.getUniformLocation(programs.gradientSubtract, 'uPressure'), 0); gl.uniform1i(gl.getUniformLocation(programs.gradientSubtract, 'uVelocity'), 1); gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, pressure.read.texture); gl.activeTexture(gl.TEXTURE1); gl.bindTexture(gl.TEXTURE_2D, velocity.read.texture); gl.bindFramebuffer(gl.FRAMEBUFFER, velocity.write.fbo); gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); velocity.swap(); // 5. Render to screen gl.viewport(0, 0, width, height); gl.useProgram(programs.display); gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, density.read.texture); gl.bindFramebuffer(gl.FRAMEBUFFER, null); gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4); requestAnimationFrame(update); } window.addEventListener('resize', () => { width = canvas.width = window.innerWidth; height = canvas.height = window.innerHeight; // In a more robust implementation, we would resize textures here // For simplicity, we'll just keep the simulation scale. }); init(); update(); </script> </body> </html> ``` index.html present.

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modelgemma-4-26b-a4b-it
vendorGoogle
harnesspi-agent
generated2026-07-22

METRICS

runtime—
tokens in50
tokens out6.2k
cached1.3k
cost / run$0.0021