# Cameras & Camera-Driven Rendering

Examples where the **camera** drives what gets rendered.

| Example | Run command | What it shows |
|---------|-------------|---------------|
| `culling` | `cargo run -p wsg-lib --example culling` | GPU-driven frustum culling: a 15×15 grid of cubes, off-frustum objects skipped |

> All commands run from the repo root.

The frustum is defined by the camera's view-projection matrix, so frustum
culling is inherently a camera concept: move the camera and the set of drawn
objects changes — with **zero CPU cost** (the GPU decides in a compute pass).

---

## `culling` — GPU Frustum Culling

A grid of **15×15 = 225 cubes** is placed on a large floor. The GPU-driven
culling (compute shader) determines which cubes are visible in the camera
frustum and zeros their indirect draw args — **zero CPU cost**.

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

### Keys

| Key | Action |
|-----|--------|
| Drag (LMB) | Orbit camera (look around) |
| Wheel | Zoom in/out |
| `R` | Reset (top view) |
| `1` | Front view (cubes behind are culled) |
| `2` | Side view |
| `3` | **Top view** (see the full grid) |

### What to observe

- In top view (`3`): the entire grid is visible.
- Orbit to 90°: cubes behind the camera **are not drawn** (culled).
- Zoom very close: only cubes near the near plane are rendered.
- Cubes rotate slowly (staggered phases) → culling is dynamic (a cube can
  enter/leave the frustum during a frame).

> **Note**: culling is enabled via `AppBuilder::with_culling(true)`. Changing
> it to `false` in the source disables culling (all cubes are always drawn,
> even off-screen).
>
> The GPU-driven pipeline (compute matrices → culling → indirect draws) is
> documented in [`docs/tech/ARCHI_CPU_GPU.md`](../../docs/tech/ARCHI_CPU_GPU.md)
> and [`docs/user/gpu-driven.md`](../../docs/user/gpu-driven.md).