docs: add README and CLAUDE.md, use Pico dropdown for image picker

- README: API docs, usage example, dev tool instructions
- CLAUDE.md: architecture notes on Hono JSX, Pico CSS, implementation details
- Image picker now uses Pico's <details> dropdown pattern

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,148 @@
+# tiny-sprites
+
+See [README.md](./README.md) for the API and usage documentation.
+
+## Architecture
+
+### Hono JSX (not React)
+
+This project uses Hono's JSX implementation, not React. Key differences:
+
+- **Server-side**: `hono/jsx` for the Sprite component (renders to HTML strings)
+- **Client-side**: `hono/jsx/dom` for the dev tool UI (renders to DOM)
+- **No hooks**: The Sprite component is pure server-side JSX with zero client JavaScript. No `useState`, no `useEffect`. The dev tool uses vanilla JS with a simple mutable `state` object and manual DOM updates via `render()` calls.
+
+### Dev Tool Styling
+
+The dev tool uses [Pico CSS](https://picocss.com) for styling:
+
+- Classless styling - semantic HTML gets styled automatically
+- `<details class="dropdown">` for the image picker (native open/close, no JS needed)
+- CSS variables like `var(--pico-primary-background)` for theming
+
+### Interesting Implementation Details
+
+**CSS Variables in @keyframes**: Instead of generating unique keyframes per sprite, we define one global keyframe that uses CSS custom properties:
+
+```css
+@keyframes sprite {
+  from { background-position: var(--x) var(--y) }
+  to { background-position: var(--ex) var(--y) }
+}
+```
+
+Each sprite just sets `--x`, `--y`, `--ex` as inline styles. This avoids `dangerouslySetInnerHTML` entirely.
+
+**Frame Detection Algorithm**: The analyzer (`src/dev/analyze.ts`) scans pixel columns to find content regions. It requires a minimum 10px gap between regions to count as separate frames - this handles sprites that have internal empty columns within a frame.
+
+**Crop Calculation**: For each frame, we find the bounding box of non-transparent pixels, then union all frames' bounds. This gives a consistent crop that works across all animation frames without the sprite "jumping".
+
+**Canvas Pixel Analysis**: We draw the image to a canvas and use `getImageData()` to read pixel alpha values. The alpha byte is at index `(y * width + x) * 4 + 3` in the flat pixel array.
+
+---
+
+Default to using Bun instead of Node.js.
+
+- Use `bun <file>` instead of `node <file>` or `ts-node <file>`
+- Use `bun test` instead of `jest` or `vitest`
+- Use `bun build <file.html|file.ts|file.css>` instead of `webpack` or `esbuild`
+- Use `bun install` instead of `npm install` or `yarn install` or `pnpm install`
+- Use `bun run <script>` instead of `npm run <script>` or `yarn run <script>` or `pnpm run <script>`
+- Use `bunx <package> <command>` instead of `npx <package> <command>`
+- Bun automatically loads .env, so don't use dotenv.
+
+## APIs
+
+- `Bun.serve()` supports WebSockets, HTTPS, and routes. Don't use `express`.
+- `bun:sqlite` for SQLite. Don't use `better-sqlite3`.
+- `Bun.redis` for Redis. Don't use `ioredis`.
+- `Bun.sql` for Postgres. Don't use `pg` or `postgres.js`.
+- `WebSocket` is built-in. Don't use `ws`.
+- Prefer `Bun.file` over `node:fs`'s readFile/writeFile
+- Bun.$`ls` instead of execa.
+
+## Testing
+
+Use `bun test` to run tests.
+
+```ts#index.test.ts
+import { test, expect } from "bun:test";
+
+test("hello world", () => {
+  expect(1).toBe(1);
+});
+```
+
+## Frontend
+
+Use HTML imports with `Bun.serve()`. Don't use `vite`. HTML imports fully support React, CSS, Tailwind.
+
+Server:
+
+```ts#index.ts
+import index from "./index.html"
+
+Bun.serve({
+  routes: {
+    "/": index,
+    "/api/users/:id": {
+      GET: (req) => {
+        return new Response(JSON.stringify({ id: req.params.id }));
+      },
+    },
+  },
+  // optional websocket support
+  websocket: {
+    open: (ws) => {
+      ws.send("Hello, world!");
+    },
+    message: (ws, message) => {
+      ws.send(message);
+    },
+    close: (ws) => {
+      // handle close
+    }
+  },
+  development: {
+    hmr: true,
+    console: true,
+  }
+})
+```
+
+HTML files can import .tsx, .jsx or .js files directly and Bun's bundler will transpile & bundle automatically. `<link>` tags can point to stylesheets and Bun's CSS bundler will bundle.
+
+```html#index.html
+<html>
+  <body>
+    <h1>Hello, world!</h1>
+    <script type="module" src="./frontend.tsx"></script>
+  </body>
+</html>
+```
+
+With the following `frontend.tsx`:
+
+```tsx#frontend.tsx
+import React from "react";
+import { createRoot } from "react-dom/client";
+
+// import .css files directly and it works
+import './index.css';
+
+const root = createRoot(document.body);
+
+export default function Frontend() {
+  return <h1>Hello, world!</h1>;
+}
+
+root.render(<Frontend />);
+```
+
+Then, run index.ts
+
+```sh
+bun --hot ./index.ts
+```
+
+For more information, read the Bun API docs in `node_modules/bun-types/docs/**.mdx`.

README.md

@@ -0,0 +1,78 @@
+# tiny-sprites
+
+A tiny CSS sprite animation component for Hono JSX. Pure CSS animations with zero runtime JavaScript.
+
+## Installation
+
+```bash
+bun add tiny-sprites
+```
+
+## Usage
+
+```tsx
+import { Sprite, SpriteStyles } from "tiny-sprites"
+
+export default function Page() {
+  return (
+    <html>
+      <head>
+        <SpriteStyles />
+      </head>
+      <body>
+        <Sprite
+          src="/sprites/player.png"
+          frames={4}
+          frameDuration={100}
+          sheetWidth={128}
+          sheetHeight={32}
+        />
+      </body>
+    </html>
+  )
+}
+```
+
+## API
+
+### `<SpriteStyles />`
+
+Renders a global `@keyframes` rule. Include once in your `<head>`.
+
+### `<Sprite />`
+
+Renders an animated sprite.
+
+| Prop | Type | Required | Default | Description |
+|------|------|----------|---------|-------------|
+| `src` | `string` | Yes | | URL to the spritesheet image |
+| `frames` | `number` | Yes | | Number of frames in the animation |
+| `frameDuration` | `number` | Yes | | Duration of each frame in milliseconds |
+| `sheetWidth` | `number` | Yes | | Width of the spritesheet in pixels |
+| `sheetHeight` | `number` | Yes | | Height of the spritesheet in pixels |
+| `crop` | `Crop` | No | | Crop each frame to a smaller region |
+| `scale` | `number` | No | `1` | Scale factor for rendering |
+| `class` | `string` | No | | CSS class name |
+| `style` | `string` | No | | Additional inline styles |
+| `playing` | `boolean` | No | `true` | Whether the animation is playing |
+
+#### Crop
+
+```ts
+type Crop = {
+  x: number      // X offset within each frame
+  y: number      // Y offset within each frame
+  width: number  // Cropped width
+  height: number // Cropped height
+}
+```
+
+## Dev Tool
+
+A dev server is included to help tune sprite animations and auto-detect frame counts and crop bounds.
+
+```bash
+bunx tiny-sprites ./path/to/assets
+```
+
+Then open http://localhost:3000 to select spritesheets and configure animations. The tool generates the `<Sprite>` code for you.

src/dev/app.tsx

@@ -157,49 +157,30 @@ const updatePreview = () => {
 }
 
 const renderImagePicker = (filter = "") => {
-  const container = $("image-picker")
+  const list = $("image-list")
-  if (state.availableImages.length === 0) {
+  const summary = $("image-picker-summary")
-    container.style.display = "none"
+
-    return
+  if (state.availableImages.length === 0) return
-  }
+
+  // Update summary text
+  summary.textContent = state.relativePath || "Select spritesheet..."
 
   const filtered = filter
     ? state.availableImages.filter((p) => p.toLowerCase().includes(filter))
     : state.availableImages
 
-  container.style.display = "block"
+  // Clear existing items (keep the filter input)
-  container.innerHTML = ""
+  list.innerHTML = ""
-
-  const list = document.createElement("div")
-  list.style.maxHeight = "300px"
-  list.style.overflowY = "auto"
-  list.style.background = "var(--pico-card-background-color)"
-  list.style.borderRadius = "var(--pico-border-radius)"
 
   for (const path of filtered) {
-    const item = document.createElement("div")
+    const li = document.createElement("li")
-    item.style.cursor = "pointer"
-    item.style.display = "flex"
-    item.style.flexDirection = "column"
-    item.style.alignItems = "center"
-    item.style.gap = "4px"
-    item.style.padding = "12px"
-    item.style.borderBottom = "1px solid var(--pico-muted-border-color)"
 
-    if (state.relativePath === path) {
+    const link = document.createElement("a")
-      item.style.background = "var(--pico-primary-background)"
+    link.href = "#"
-    }
+    link.style.display = "flex"
-
+    link.style.flexDirection = "column"
-    item.onmouseenter = () => {
+    link.style.alignItems = "center"
-      if (state.relativePath !== path) {
+    link.style.gap = "4px"
-        item.style.background = "var(--pico-secondary-background)"
-      }
-    }
-    item.onmouseleave = () => {
-      if (state.relativePath !== path) {
-        item.style.background = ""
-      }
-    }
 
     const img = document.createElement("img")
     img.src = `/assets/${encodeURIComponent(path).replace(/%2F/g, "/")}`
@@ -208,20 +189,24 @@ const renderImagePicker = (filter = "") => {
     img.style.objectFit = "contain"
     img.style.imageRendering = "pixelated"
 
-    const label = document.createElement("div")
+    const label = document.createElement("span")
     label.style.fontSize = "11px"
     label.style.wordBreak = "break-all"
     label.style.textAlign = "center"
     label.textContent = path
 
-    item.appendChild(img)
+    link.appendChild(img)
-    item.appendChild(label)
+    link.appendChild(label)
-    item.onclick = () => loadImageFromPath(path)
+    link.onclick = (e) => {
+      e.preventDefault()
+      loadImageFromPath(path)
+      // Close dropdown
+      $<HTMLDetailsElement>("image-picker").open = false
+    }
 
-    list.appendChild(item)
+    li.appendChild(link)
+    list.appendChild(li)
   }
-
-  container.appendChild(list)
 }
 
 const fetchImages = async () => {
@@ -238,19 +223,20 @@ const fetchImages = async () => {
 const App = () => (
   <div class="grid">
     <div>
-      <label>
+      <input
-        Filter
+        type="search"
-        <input
+        id="filter"
-          type="text"
+        placeholder="Filter spritesheets..."
-          id="filter"
+        onInput={(e) => {
-          placeholder="Search images..."
+          const filter = (e.target as HTMLInputElement).value.toLowerCase()
-          onInput={(e) => {
+          renderImagePicker(filter)
-            const filter = (e.target as HTMLInputElement).value.toLowerCase()
+        }}
-            renderImagePicker(filter)
+        style={{ marginBottom: "0.5rem" }}
-          }}
+      />
-        />
+      <details class="dropdown" id="image-picker" style={{ marginBottom: "1rem" }}>
-      </label>
+        <summary id="image-picker-summary">Select spritesheet...</summary>
-      <div id="image-picker" style={{ marginBottom: "1rem", display: "none" }}></div>
+        <ul id="image-list" style={{ maxHeight: "400px", overflowY: "auto" }}></ul>
+      </details>
       <div
         id="error-message"
         style={{