Flow-field particles · gemma-4-26b-a4b-it

The user wants a full-screen flow-field particle animation using `p5.js`.
The animation should:
- Use `p5.min.js` (provided locally).
- Animate at least 2,000 particles.
- Use Perlin noise for the vector field.
- Particles should follow locally coherent directions.
- Leave fading trails.
- Vary colors over time.
- Evolve the field gradually.
- Recycle particles at boundaries.
- Provide Pause/Resume and Restart buttons.
- Fit the viewport (1200x800).
- Be contained in `index.html`.

Plan:
1. Check if `p5.min.js` exists in the current directory.
2. Write the `index.html` file with CSS, HTML structure (canvas + controls), and JavaScript logic.
3. Implement the particle class and flow field logic in JS.
4. Use `p5.js` in global mode for simplicity.
5. Verify with the `browser` tool.

Let's start by checking the directory.

`p5.min.js` is present.

Now I will write the `index.html`.

Detailed implementation plan:
- HTML:
    - Container for the canvas.
    - Control overlay with buttons (Pause/Resume, Restart).
- CSS:
    - Full screen, hide overflow.
    - Style buttons to be semi-transparent and overlaying the top or bottom.
- JS:
    - `Particle` class:
        - `pos`, `vel`, `acc`, `maxSpeed`.
        - `update()`: apply acceleration, update position, check boundaries.
        - `follow(field)`: update acceleration based on field.
        - `show()`: draw the particle.
    - `FlowField` logic:
        - Use `noise()` to generate vectors.
        - A 2D grid of vectors.
        - `field.get(x, y)` returns the vector.
        - `field.update()` evolves the noise.
    - `setup()`:
        - Create canvas, resize to window.
        - Initialize particles.
        - Create UI elements.
    - `draw()`:
        - Fading effect: draw a semi-transparent rectangle over the canvas instead of clear background.
        - Update and draw particles.
    - Controls:
        - `isPaused` flag.
        - `restart()` function.

Refined plan for `draw()`:
To achieve fading trails, instead of `background(0)`, I'll draw a semi-transparent rectangle: `fill(0, alpha); rect(0, 0, width, height);`.

Refined plan for evolving field:
I can use a `time` variable that increments and is used as an offset in the `noise()` function.

Wait, the prompt says "Evolve the field gradually so the pattern changes instead of repeating a short recorded sequence".
I'll use `noise(x * scale, y * scale, time * noiseScale)`.

Let's write the code.

Wait, I tried to write to an empty path. I should specify `index.html`.
Also, I noticed a small mistake in my `draw()` logic: `p.show(drawingContext)` is not how you typically use p5 functions inside a class if you want to use the global p5 instance. If I'm using global mode, I can just use `stroke()` and `point()` directly inside the class methods, and they will refer to the global `p5` instance.

Let me rewrite the `index.html` properly.
I'll use `colorMode(HSB)` and ensure the `draw` function works correctly.
I will also make sure to use `stroke` and `point` from the global p5.

Actually, I'll use `p.show()` and inside it use `stroke()` and `point()`.

One thing to consider: `p5.min.js` is available.

Let's refine the `index.html` content.

Now I will run the application using the `browser` tool to verify it.