réorg doc

lib/examples/cameras/README.md

@@ -0,0 +1,52 @@
+# 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).