wsg/lib/examples/effects/README.md

# Effects: HDR, Post-process & Showcase

Examples covering **HDR / tone mapping** and **post-process effects**, plus
the full showcase that combines everything.

| Example | Run command | What it shows |
|---------|-------------|---------------|
| `demo` | `cargo run -p wsg-lib --example demo` | **Full showcase**: 6 LOD primitives, 3 lights, shadows, HDR/ACES, bloom, culling, orbital camera |
| `bloom` | `cargo run -p wsg-lib --example bloom` | Post-process bloom (glow around bright areas) |
| `hdr` | `cargo run -p wsg-lib --example hdr` | HDR + tone mapping (ACES) + runtime exposure control |
| `msaa` | `cargo run -p wsg-lib --example msaa` | MSAA 4× (multisample anti-aliasing, smooth edges) |
| `fog` | `cargo run -p wsg-lib --example fog --features "all-prims"` | Distance fog (3 modes: linear, exp, exp²) |
| `dof` | `cargo run -p wsg-lib --example dof --features "all-prims"` | Depth of field (cinematic bokeh, focus presets) |

> All commands run from the repo root. All effects are **opt-in** — a disabled
> effect allocates nothing and executes nothing.

---

## `demo` — Full Showcase

Combines **all** effects: LOD primitives, procedural textures, lights
(directional + point + spot), shadows, HDR/ACES, exposure, emissive, bloom, culling.

```sh
cargo run -p wsg-lib --example demo
```

### Keys

| Key | Action |
|-----|--------|
| Drag (LMB) | Orbit camera |
| Wheel | Zoom |
| `R` | Reset camera |
| `1` / `2` / `3` | Presets: front / side / top |
| `+` / `-` | Exposure ×1.3 / ÷1.3 |
| `0` | Reset exposure |

---

## `bloom` — Post-process Bloom

Two emissive spheres (orange intensity 2.0, blue intensity 3.0) produce a
visible halo. The cube and floor serve as reference (non-emissive).

Bloom is a 4-pass GPU pipeline: threshold → blur H → blur V → composite.

```sh
cargo run -p wsg-lib --example bloom
```

### Keys

| Key | Action |
|-----|--------|
| Drag (LMB) | Orbit camera |
| Wheel | Zoom |
| `R` | Reset camera |
| `+` / `-` | **Bloom threshold** +0.1 / −0.1 |
| `[` / `]` | **Bloom intensity** +0.1 / −0.1 |
| `I` / `O` | **Bloom radius** +0.5 / −0.5 |
| `E` / `Q` | Exposure ×1.3 / ÷1.3 |
| `0` | Reset exposure |

### What to observe

- **Low threshold** (0.0): the entire image "blooms" (very diffuse effect).
- **High threshold** (2.0+): only the bright emissive spheres produce glow.
- **Intensity 0.0**: no visible glow (even though the threshold extracts pixels).
- **Large radius** (10+): the glow spreads over a large area.

---

## `hdr` — HDR + Tone Mapping

Demonstrates HDR rendering with the ACES Filmic curve. Three objects:

- **Cube**: normal lighting (no emissive) — LDR reference.
- **Bright sphere** (emissive 3.0): without HDR, it would be clamped to white.
  With ACES, highlights "roll off" smoothly toward white.
- **Dark sphere** (emissive 0.3): stays dark even at high exposure.

```sh
cargo run -p wsg-lib --example hdr
```

### Keys

| Key | Action |
|-----|--------|
| Drag (LMB) | Orbit camera |
| Wheel | Zoom |
| `R` | Reset camera |
| `E` | **Exposure ×1.3** (brighter) |
| `Q` | **Exposure ÷1.3** (darker) |
| `0` | Reset exposure to 1.0 |

### What to observe

- At exposure 1.0: the bright sphere is white but with detail (ACES rolloff).
- At high exposure (E×E×E): the scene brightens, the bright sphere stays white
  (saturated), but the cube gains detail.
- At low exposure (Q×Q): everything darkens, the bright sphere becomes orange
  (HDR values > 1.0 are compressed).

> **Note**: the tone mapper is compiled into the pipeline at build time. To
> compare ACES vs Reinhard, change `ToneMapper::Aces` → `ToneMapper::Reinhard`
> in the source.

---

## `msaa` — MSAA 4× (Anti-aliasing)

Demonstrates multisample anti-aliasing: object edges (cube, sphere) are smooth
instead of "stair-stepped". The scene contains a cube (sharp edges), a sphere
(curved silhouette), and a small cube near the camera (maximum aliasing).

```sh
cargo run -p wsg-lib --example msaa
```

### Keys

| Key | Action |
|-----|--------|
| Drag (LMB) | Orbit camera |
| Wheel | Zoom |
| `R` | Reset camera |
| `M` | Show sample count |

### To compare with/without MSAA

Remove the `.with_msaa(4)` line in the source and recompile: the scene is
identical, only the edges differ (stair-stepped vs smooth).

> **Note**: MSAA is a build-time setting (multisample texture allocation). It
> works independently of HDR: with HDR, the MSAA texture is `Rgba16Float` and
> resolves into the HDR texture before bloom/TM.

---

## `fog` — Distance Fog

Demonstrates the 3 fog modes: **linear**, **exponential**, **exponential²**.
The scene contains a row of cubes receding into the distance and scattered
spheres on a large floor plane. Fog blends objects toward a background color,
creating the illusion of an infinite world.

```sh
cargo run -p wsg-lib --example fog --features "all-prims"
```

**Keys**: `1` = linear, `2` = exp, `3` = exp², `4` = off, `R` = reset.

> Fog is applied in the main fragment shader (after lighting, before tone
> mapping). It uses the Euclidean distance from the fragment to the camera.

---

## `dof` — Depth of Field (Cinematic Bokeh)

Demonstrates depth of field blur: an object at the focus plane stays sharp
while foreground and background blur according to their distance from the
focus plane. Creates a natural attention effect (cinematic style).

The scene contains 20 cubes in a row along Z (z=3 to z=-25.5) and 5 spheres to
the sides, on a floor plane. Focus presets at 3 m / 8 m / 15 m.

```sh
cargo run -p wsg-lib --example dof --features "all-prims"
```

**Keys**: `1` = cinematic, `2` = subtle, `3` = focus 3 m, `4` = focus 15 m,
`5` = off, `R` = reset.

> DoF operates in linear HDR (after bloom, before tone mapping). Two passes:
> CoC (depth → per-pixel blur radius) then 12-tap disc blur with variable radius.