Fluid simulation · qwen3.8-27b
Create a real-time fluid simulation on a full-screen canvas where dragging the mouse pushes swirling colored dye through the fluid.
transcript · 12 messages
Create a real-time fluid simulation on a full-screen canvas where dragging the mouse pushes swirling colored dye through the fluid.
thinking
Need to create a self-contained index.html that includes a fluid simulation. Classic approach: a simplified Stam stable fluids solver on a grid, rendered to a full-screen canvas. Keep the grid reasonably sized (e.g., 128x128) and use bilinear upscaling for rendering. Implement velocity advection/diffusion/pressure (a few Jacobi iterations), vorticity confinement for the swirls, dye advection, and mouse drag adds velocity and colored dye. Use requestAnimationFrame. Let's write the code carefully. Standard implementation: - N grid, field size (N+2)^2 - u, v, dyeR/G/B, prev arrays - addSource, diffuse (skip for velocity, use lightweight viscosity), advect, project, vorticity confinement - Render with ImageData at the grid scale to an offscreen canvas, then drawImage-scaled up with imageSmoothingEnabled=true. Grid N=128 → 130² ≈ 17k cells. Pressure iterations 20 should be fine. 3 dye channels. Should be OK at 60fps. Color: hue cycles based on time/position while dragging. Let's write it.
/tmp/ws/index.html (806 bytes)</parameter> </function> </tool_call>
Successfully wrote 806 bytes to /tmp/ws/index.html
thinking
Wait, I ended up writing a truncated file. The write completed, but it only contains the head/style and it's cut off midway. In fact, I wrote content ending in the middle of the style. The file ends with `</style>` — no wait, I wrote up to `</style>`, but didn't include the canvas, script, or closing tags. I need to rewrite the entire file. Let me write the complete file right now.
I accidentally truncated that write — let me write the complete file:
/tmp/ws/index.html (11591 bytes)Successfully wrote 11591 bytes to /tmp/ws/index.html
thinking
Quick sanity check: run node with a stub? I can extract the script and at least do a syntax check with node. The script uses browser globals, so syntax check only.
Quick syntax check of the embedded script:
{"command":"cd /tmp/ws && node -e \"\nconst html = require('fs').readFileSync('index.html','utf8');\nconst m = html.match(/<script>([\\s\\S]JS syntax OK, file size: 11591 -rw-r--r--. 1 node node 11593 Aug 15 13:52 index.html
thinking
Should I also do a simple headless functional test of the solver logic on Node with the canvas stubbed out? That'd be good. Let me just simulate the solver function on its own and quickly verify that NaNs don't come out.
{"command":"cd /tmp/ws && node -e \"\n// Headless smoke test: stub DOM, run 120 simulated frames, check for NaN\nconst fs = require('fs');\n<anonymous_script>:194 canvas.addEventListener('mousedown', onDown); ^ TypeError: canvas.addEventListener is not a function
thinking
My stub canvas needs addEventListener. Also, the window.addEventListener I stubbed to do nothing isn't capturing the handlers — I'll improve it to store the handlers, and then simulate drag afterwards. Let me redo the stubs.
{"command":"cd /tmp/ws && node -e \"\nconst fs = require('fs');\nconst js = fs.readFileSync('index.html','utf8').match(/<script>([\\s\\S]*?)frames run: 241
thinking
241 frames were executed without any errors (including 60 drag moves). Note: since requestAnimationFrame is being called inside frames, frames increments by 1 for each frame and the initial call. Good. NaN check: since putImageData is a stub, we don't verify the dye values. But no exceptions were thrown. Should be sufficient. Done.
Done. `index.html` is in place at `/tmp/ws/index.html` — fully self-contained (inline CSS + JS, zero external resources), and the embedded script passed a syntax check plus a 240-frame headless smoke test with a simulated drag (no errors). **What it does:** - **Real fluid solver** — a full Jos Stam "Stable Fluids" implementation on a 144×144 grid: semi-Lagrangian advection, diffusion, and a 16-iteration Jacobi pressure projection to keep the velocity field incompressible (so dye genuinely swirls and folds like a real fluid). - **Vorticity confinement** — continuously re-injects small-scale rotation that numerical diffusion would otherwise kill, which is what makes the dye form those tight, curling vortices as you drag. - **Interactive dye** — pressing and dragging stamps colored dye along the stroke path with a Gaussian falloff, and injects momentum in the direction of movement (splats are interpolated along fast strokes so trails stay continuous). Hue drifts as you drag, so a long stroke sweeps through the spectrum. Touch events work too. - **Rendering** — the grid is tone-mapped (soft knee to avoid clipping to white) into an offscreen `ImageData`, then bilinearly upscaled to the full-screen canvas for a smooth look. Dye slowly fades and velocity damps so the scene relaxes back to black. - **Extras** — three seeded splats on load so the screen isn't empty, an idle-press "pulsing blob" behavior, DPR/resize handling, and a fading hint label. Just open the file in a browser and drag.
TAKE IT TO CODE
A single self-contained HTML file — copy it and open in any browser, or reuse the prompt with your own pi-agent run.
RUN
EVALUATION
Fluid sim with colorful dye swirls that responds strongly to drag and wheel, but slowly decays to black when idle.
Vision grade · anthropic/claude-sonnet-5
MEASUREMENTS
Raw readings from the capture, not a verdict — the grade above is the only judgement. Percentages are how much of the screen changed; the measure under-reports sparse motion on a dark background.