Jérôme Bousquié
125 lines
4.1 KiB
Markdown
125 lines
4.1 KiB
Markdown
# Lights, Shadows & Emissive
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Examples covering **lighting**: shadow mapping, isolated light types, and
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emissive materials.
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| Example | Run command | What it shows |
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|---------|-------------|---------------|
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| `shadow` | `cargo run -p wsg-lib --example shadow` | Shadow mapping in isolation (directional light, 4 objects on a floor) |
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| `shadow_test` | `cargo run -p wsg-lib --example shadow_test` | Dedicated shadow test: one directional caster, cube on a ground slab, PCF-softened |
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| `spot_test` | `cargo run -p wsg-lib --example spot_test` | Isolated spot light: directed beam, penumbra, attenuation |
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| `emissive` | `cargo run -p wsg-lib --example emissive` | Emissive materials (increasing intensities 0 → 4.0) |
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> All commands run from the repo root.
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---
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## `shadow` — Shadow Mapping
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Four objects (cube, sphere, cone, cylinder) on a floor, lit by a directional
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light that casts shadows. Shadow quality is controlled by `ShadowConfig`
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(map size, anti-acne bias).
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```sh
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cargo run -p wsg-lib --example shadow
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```
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### Keys
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| Key | Action |
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|-----|--------|
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| Drag (LMB) | Orbit camera |
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| Wheel | Zoom |
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| `R` | Reset camera |
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| `1` | Front view |
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| `2` | Side view |
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| `3` | **Top view** (see shadow shapes clearly) |
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| `L` | Change light direction (3 presets) |
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### What to observe
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- The cube rotates slowly → its shadow moves on the floor.
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- The sphere has a smooth shadow/light transition (soft terminator).
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- The cone produces a distinct triangular shadow.
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- In top view (`3`), you see the exact shape of projected shadows.
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- Shadow map size (1024 default) determines resolution: modify
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`SHADOW_MAP_SIZE` at the top of the file to test 256 (pixelated) or 2048 (sharp).
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---
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## `shadow_test` — Dedicated Shadow Mapping Test
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A single **directional** light is configured as the shadow caster
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(`Scene::set_shadow_caster(Some(0))`). The cube sits on a large thin ground
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slab, so its silhouette is projected as a crisp PCF-softened shadow. With a
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small ambient term the shadow is clearly visible and the light/shadow
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directions are easy to read:
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1. the **blocker** (cube) casts a directional shadow that stretches along the
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ground opposite the light direction — the light sits at the camera's
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front-right and low-ish, so the shadow runs clearly across the ground to
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the left of the cube,
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2. the shadow edge is **softened** by 3×3 PCF (no hard jagged border),
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3. the lit faces are bright while the shadowed ground stays near-ambient,
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proving the depth comparison is applied per-pixel.
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```sh
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cargo run -p wsg-lib --example shadow_test
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```
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---
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## `spot_test` — Isolated Spot Light
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**Only** a spot light is on (the default directional light is removed via
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`clear_lights()`) and the ambient is deliberately **very low**. The rotating
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cube therefore appears nearly black except where the spot's cone reaches it —
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you clearly see:
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1. a **directed beam** (not an omni halo like the point light),
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2. a **smoothed edge** (penumbra) at the cone's limit,
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3. the lighting that **follows the cube** as it rotates (the cone is fixed in
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world space).
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```sh
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cargo run -p wsg-lib --example spot_test
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```
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---
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## `emissive` — Emissive Materials
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Five spheres in a row with increasing emissive intensities:
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| Sphere | Color | Intensity | Effect |
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|--------|-------|-----------|--------|
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| 1 | Gray | 0.0 | No glow (reference) |
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| 2 | Orange | 0.5 | Slight glow |
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| 3 | Yellow | 1.0 | Visible glow |
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| 4 | Green | 2.0 | HDR glow (beyond 1.0) |
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| 5 | Blue | 4.0 | Intense glow (saturation) |
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With HDR, intensities > 1.0 produce a true "glow" (values exceed [0,1] in
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linear space). Without HDR, they would be clamped to white.
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```sh
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cargo run -p wsg-lib --example emissive
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```
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### Keys
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| Key | Action |
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|-----|--------|
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| Drag (LMB) | Orbit camera |
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| Wheel | Zoom |
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| `R` | Reset camera |
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| `E` / `Q` | Exposure ×1.3 / ÷1.3 |
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| `0` | Reset exposure |
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| `C` | **Cycle emissive multiplier** (1× → 2× → 0.5× → …) |
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### What to observe
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- Sphere 1 (intensity 0) is simply lit by the directional light.
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- Spheres 2-5 glow with their own light, independent of scene lighting.
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- `C` doubles or halves all intensities simultaneously (to see the HDR effect).
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