# og-gen — per-post OG image generator

Generates a branded 1200×630 social-share image for a blog post, matching the
site's cobalt-blue `#295cff` branding, the `logo-square.png` mark, and the
"terminal / debugging" visual style.

## Usage

```bash
node scripts/og-gen/generate.mjs <post-slug>
```

Reads frontmatter (`title`, `category`, `tags`) from
`src/content/posts/<slug>.md`, fills `template.html`, renders with headless
Chrome, and writes `public/og/<slug>.png`.

The post's frontmatter needs `ogImage: /og/<slug>.png` so the blog serves it
(layout already renders `og:image` + width/height; PostList shows it as a
card thumbnail).

## Customizing the terminal box

Each post shows a "terminal" panel (the red error / green fix lines). Add an
entry keyed by slug in `TERMINALS` inside `generate.mjs`, using these tokens:

```html
<div class="line"><span class="prompt">$</span><span class="cmd">command</span></div>
<div class="line"><span class="prompt">&nbsp;</span><span class="err">error line</span></div>
<div class="line"><span class="prompt">$</span><span class="cmd">fix</span><span class="fix">→ done ✓</span></div>
```

No entry → a generic default terminal.

## Requirements

- Google Chrome at `C:\Program Files\Google\Chrome\Application\chrome.exe`
  (override with `CHROME_PATH` env var).
- Node 20+.

## Notes

- PNG (not JPG) is intentional: for flat UI/terminal art, PNG is smaller and
  sharper than JPG (see commit history).
- The `logo-square.png` referenced lives at `public/logo-square.png`.

---

## v2 pipeline ("one art, four targets") — `render_from_art.mjs`

The consultant-approved redesign replaces the generated terminal panels with **one
zero-text base-art frame per post**, composited into four assets:

| Target | Path | Size |
|---|---|---|
| hero banner | `public/banners/<slug>.webp` (+ `.jpg` fallback from frontmatter) | 1600×900 |
| social card | `public/og/<slug>.jpg` (EN), `public/og/zh-<slug>.jpg` (ZH) | 1200×630 |
| bento/list thumb | `public/og/thumb/<slug>-800.webp` | 800×420 |
| small thumb | `public/og/thumb/<slug>-400.webp` | 400×210 |

The card is `template-v2.2.html` (frosted bento + blueprint grid + full-width evidence
bar) filled from the post's own frontmatter plus `art-meta.json`; the self-fitting
headline script reports `FIT <n>px` through `<title>`, and a render that does not
settle fails instead of shipping a silently-shrunken card.

```bash
# metadata first: art path (default <art-dir>/<slug>.png) + a HAND-WRITTEN evidence line
$EDITOR scripts/og-gen/art-meta.json

node scripts/og-gen/render_from_art.mjs --only <slug>[,<slug>] --out /tmp/og-check
node scripts/og-gen/render_from_art.mjs --all            # writes into public/
```

- `--format jpg` (default) or `png`. **JPEG is the default because it is measured**:
  a composited card renders 558 KB as PNG and lands at **84 KB at mozjpeg q85**
  (256-colour PNG = 240 KB). The default site card already ships as JPG for the
  same reason.
- `evidence` is **required and never derived** — it is editorial text, and inventing
  one from the description is the "invented specificity" failure the blog avoids.
  A missing entry aborts with the slug list.
- `ogTitle_en` / `ogTitle_zh` shorten only the card's headline (the article keeps
  its real title) — the consultant's answer to the English headline-rag problem.
- Reproducibility check: re-rendering the two sample posts produced banners and
  800px thumbs **byte-identical** to the consultant's accepted delivery
  (sha256 16e6a7b0…, f3b29f38…, c4e28291…, 8095ec6c…).
- ⚠ Changing `ogImage` from `.png` to `.jpg` also needs `PostList.astro`'s thumb
  helper updated (`/\.(png|jpe?g)$/`), or the listing derives
  `…-800.webp` from `slug.jpg` and every thumb 404s.