## 2. What option 12 shows

- **Two stages.** A 256×224 pixel scene is drawn first. A WebGL shader then runs a small program for every screen pixel, rebuilding how a tube TV would show it.
- **Four presets:**

| Preset | Glass | Mask | Signal |
|---|---|---|---|
| Home TV | Strongly curved | Slot mask | Blurry composite, colour bleed, noise |
| Arcade monitor | Mild curve | Shadow mask (dot triads) | Clean RGB (red-green-blue) feed |
| Pro monitor | Nearly flat | Aperture grille (vertical stripes) | Sharpest scanlines |
| Raw pixels | None | None | Emulator default |

- **Test pattern.** Switch to it and check two things. The colour bars show the mask tint most clearly. The row of 1-pixel black-and-white stripes smears into grey on "Home TV" (tick composite bleed).

## 3. Less obvious details

- **Bright lines get fatter.** The scanline width depends on brightness: the beam spreads on bright pixels. That's why white text on a CRT looks bold and dark gaps shrink. Look at the white bot vs the dark bricks.
- **The mask darkens the whole image.** Each screen pixel lights only one of red, green or blue phosphor, which throws away about two-thirds of the light. The shader boosts brightness to compensate, just as real TVs ran hotter.
- **Pixel art was designed for this.** Artists relied on the blur to merge dithering into smooth shades. Composite bleed turned checker patterns into new colours and even fake transparency. Raw pixels show dithering as harsh dots it was never meant to look like.
- **The rolling dark band** in "Signal noise" is hum bar: mains electricity leaking into the picture. The occasional horizontal line shift is sync jitter.
- **Glass glare:** a faint top-left reflection plus corner darkening (vignette) sells the feeling of a curved tube.

## Examples

**Three phosphor masks (zoomed)**
```
aperture grille     slot mask          shadow mask
R G B R G B        R G B R G B        R G B R G B
R G B R G B        R G B ─ ─ ─          G B R G B R
R G B R G B        ─ ─ ─ R G B        R G B R G B
(continuous)       (staggered gaps)   (offset dot rows)
```

**Shader pipeline, per screen pixel**
```
screen pixel → bend by curvature → outside? draw bezel
            → sample source row (sharp + soft mix)
            → composite bleed (blur colour, keep brightness)
            → scanline beam (width grows with brightness)
            → + bloom (blurred bright areas)
            → × phosphor mask → vignette + glare → noise/hum
```

**Scanline beam profile**
```
dark pixel:   ▁▂█▂▁   narrow beam, visible gap
bright pixel: ▂▅███▅▂ wide beam, gap nearly closes
```