# WSG — Detailed Documentation

> Technical content from the main README: status, architecture, API reference, workflows, roadmap.

## Status

| Area | State |
|------|-------|
| Manual workflow (`Context` + `Renderer` + `PipelineCache`) | ✅ Working (advanced — fine-grained control) |
| `App` / `AppBuilder` / `AppHandler` event-loop facade | ✅ Working — window, events, frame presentation, automatic scene rendering |
| `Scene` resource/entity registry | ✅ Working — auto-rendered in one batched pass (`App::render_scene`) |
| GPU-driven two-pass pipeline (Compute → indirect draw) | ✅ Working (Phase 3) — `render_scene` + shadow pass 100% indirect; opt-in frustum culling |
| 3D infrastructure (uniform bind groups, MVP + camera) | ✅ Working — per-frame camera + per-entity world matrices in shared uniforms |
| Shadows (shadow mapping) | ✅ Working — directional/spot, slope-scaled bias, PCF 3×3 |
| HDR + Tone Mapping | ✅ Working — offscreen Rgba16Float, ACES/Reinhard, opt-in |
| LOD (Level of Detail) | ✅ Working — quadric decimation, hysteresis, multi-level buffer |
| Mesh module (primitives + import) | ✅ Working — feature-gated primitives, OBJ parser |
| Bloom | ✅ Working — threshold + separable blur + composite, HDR required |
| Fog | ✅ Working — 3 modes (linear, exp, exp²), runtime switchable |
| MSAA | ✅ Working — 4× multisample, resolve pass |
| DoF | ✅ Working — CoC + disc blur, focus presets |
| PBR (metallic/roughness + normal maps) | ✅ Working — Cook-Torrance, GGX, IBL, derivative tangent |

Note: `standard_shader.wgsl` (Phong + PBR, with an explicit **unlit** mode) is the **single** shader the library ships. Flat 2D drawing is its unlit variant (`Renderer::set_unlit(true)`).

## Architecture

### Layer model

- **Manager layer (`Context`)** — owns the GPU hardware lifecycle (Instance → Surface → Adapter → Device → Queue). Created once at startup; `configure()` sets up the swapchain, `Frame` wraps each frame's surface texture + view.
- **Executor layer (`Renderer`)** — binds a `Material` pipeline + `Mesh` buffers into a RenderPass and submits. `render_scene` batches all entities into one encoder + one submit per frame.
- **Supporting pieces** — `PipelineCache` (shader → compiled RenderPipeline, `Arc`-shared), `Material`, `Geometry`/`Mesh`/`Vertex`, `Scene` (string-ID registry), `Camera`/`Transform`.

### GPU-driven pipeline (Phase 3)

A Compute Pass derives each entity's world matrix and fills per-entity indirect draw arguments (with opt-in frustum culling), then the main and shadow render passes issue one indirect draw per active slot.

Spec: [docs/tech/ARCHI_CPU_GPU.md](docs/tech/ARCHI_CPU_GPU.md) · User guide: [docs/user/gpu-driven.md](docs/user/gpu-driven.md)

### Module layout

```
lib/src/
├── lib.rs              # crate root, re-exports
├── prelude.rs          # glob re-exports
├── app.rs              # App + AppBuilder
├── handler.rs          # AppHandler trait
├── camera.rs           # Camera, CameraController
├── input.rs            # InputState
├── lights.rs           # Lights, Light, LightType, directional_light, …
├── core/
│   ├── context.rs      # GPU lifecycle (Instance/Surface/Adapter/Device/Queue)
│   ├── renderer.rs     # RenderPass execution, shadow pass, HDR/TM pass
│   ├── frame.rs        # Per-frame RAII (surface texture + view)
│   ├── geometry.rs     # Geometry (positions/normals/UVs/indices) + BBox
│   ├── transform.rs    # Transform (translation/rotation/scale)
│   ├── frustum.rs      # Frustum (6 planes, sphere/box culling)
│   ├── lod.rs          # LOD decimation (quadric edge collapse)
│   ├── shadow.rs       # ShadowConfig (map size, bias, PCF)
│   ├── hdr.rs          # ToneMapper enum (Aces/Reinhard)
│   ├── bloom.rs        # BloomConfig + BloomPipeline
│   ├── msaa.rs         # MsaaConfig
│   ├── fog.rs          # FogConfig + FogMode
│   └── dof.rs          # DoFConfig + DoFPipeline
├── mesh/
│   ├── mod.rs          # Re-exports flat
│   ├── primitives/     # 6 feature-gated generators
│   └── import/         # OBJ parser + glTF stub
├── pipeline/           # PipelineCache (shader → RenderPipeline)
├── resources/          # Mesh, Material, Texture, Uniform, Vertex
├── scene/              # Scene (registry), Entity
└── utils/              # Conf constants, WsgError
```

## Quick reference (types)

| Concept | Type | Responsibility |
|---------|------|---------------|
| App / AppBuilder | Facade | Window + event loop + frame + auto scene render |
| AppHandler | Trait | `setup()` / `update()` / `render()` callbacks |
| Scene | Struct | Registry: shaders, materials, meshes, entities, lights, camera |
| Context | Struct | GPU hardware (Instance, Surface, Adapter, Device, Queue) |
| Renderer | Struct | RenderPass execution (scene, shadow, HDR/TM, bloom, DoF) |
| PipelineCache | Struct | Shader → compiled RenderPipeline cache |
| Material | Struct | Shader ID + texture + pipeline + PBR params |
| Geometry | Struct | CPU vertex data (positions/normals/UVs/colors/indices) |
| Mesh / Vertex | Struct | GPU geometry / interleaved upload tuple |
| Frame | Struct | Per-frame RAII (surface texture + view) |
| Camera / Transform | Struct | Camera math + per-entity transform |
| CameraController | Struct | Orbital camera (orbit/zoom/reset/apply_to) |
| InputState | Struct | Unified keyboard/mouse (pressed/held/released, delta, scroll) |
| Texture | Struct | GPU image (Rgba8UnormSrgb) + sampler |
| Lights / Light | Struct | Light list (directional/point/spot, MAX=8) + ambient |
| ShadowConfig | Struct | Shadow map size, bias, PCF taps, scene radius |
| ToneMapper | Enum | ACES Filmic / Reinhard |
| BloomConfig | Struct | Threshold, intensity, H/V passes |
| MsaaConfig | Struct | Sample count (1 = disabled) |
| FogConfig | Struct | Mode, near/far, density, color |
| DoFConfig | Struct | Focus distance, aperture, max blur |
| BBox | Struct | Axis-aligned bounding box (min/max) |
| Frustum | Struct | 6 planes, sphere/box culling |

## Declarative workflow (recommended)

```rust
use wsg_lib::prelude::*;
use wsg_lib::app::AppBuilder;
use wsg_lib::utils::WsgError;

struct MyScene;

impl AppHandler for MyScene {
    fn setup(&mut self, app: &mut wsg_lib::App) {
        app.scene
            .register_shader("standard", wsg_lib::utils::STANDARD_SHADER_PATH)
            .unwrap();
        app.scene.add_material_shader("mat", "standard").unwrap();
        app.scene.create_mesh("cube", cube(1.0), Some("mat")).unwrap();
        app.scene.add_entity("my_cube", "cube").unwrap();
    }
    fn update(&mut self, app: &mut wsg_lib::App) {
        // your per-frame logic
    }
    // render() default: app.render_scene(frame.view()) — auto-draws everything
}

#[pollster::main]
async fn main() -> Result<(), WsgError> {
    let app = AppBuilder::new().title("WSG").build().await?;
    app.run(MyScene);
    Ok(())
}
```

> `Scene` methods return `Result<_, String>` — typed-error unification is on the roadmap.

## Manual workflow (advanced)

Bypass the `App` facade and drive `Context`, `Renderer` and `PipelineCache` yourself:

```rust
use std::sync::Arc;
use winit::event_loop::EventLoop;
use winit::window::WindowBuilder;
use wsg_lib::core::{Context, Frame, Renderer};
use wsg_lib::pipeline::PipelineCache;
use wsg_lib::resources::{Geometry, Material, Mesh};
use wsg_lib::utils;

fn main() {
    let event_loop = EventLoop::new().unwrap();
    let window = Arc::new(WindowBuilder::new().build(&event_loop).unwrap());
    let context = pollster::block_on(Context::new(window.clone())).expect("GPU init");
    let format = context.configure(&context.adapter, 800, 600).expect("surface config");

    let mut renderer = Renderer::new(&context, format, 800, 600);
    let mut cache = PipelineCache::new(Arc::new(context.device.clone()));
    cache.register_shader("standard", utils::STANDARD_SHADER_PATH).unwrap();

    let material = Material::new(renderer.format(), "standard", &mut cache);
    let geometry = Geometry::new(vec![-0.5f32, 0.5, 0.0, 0.5, 0.5, 0.0, 0.5, -0.5, 0.0, -0.5, -0.5, 0.0])
        .with_indices(vec![0, 1, 2, 0, 2, 3]);
    let mesh = Mesh::from_geometry(renderer.device(), Arc::new(geometry), None);

    event_loop.run(|event, elwt| {
        match event {
            winit::event::Event::AboutToWait => window.request_redraw(),
            winit::event::Event::WindowEvent { event: winit::event::WindowEvent::RedrawRequested, .. } => {
                if let Some(frame) = Frame::try_new(&context.surface) {
                    renderer.render(frame.view(), &mesh, &material);
                    renderer.present(frame);
                }
            }
            winit::event::Event::WindowEvent { event: winit::event::WindowEvent::CloseRequested, .. } => elwt.exit(),
            _ => {}
        }
    }).unwrap();
}
```

## Features

| Feature | Default | Provides |
|---------|---------|----------|
| `prim-cube` | ✅ | `cube(size)` |
| `prim-plane` | ✅ | `plane(w, d, seg_x, seg_z)` |
| `prim-sphere` | ✅ | `uv_sphere(…)`, `icosphere(…)` |
| `prim-cylinder` | ✅ | `cylinder(…)` |
| `prim-cone` | ✅ | `cone(…)` |
| `prim-torus` | ✅ | `torus(…)` |
| `all-prims` | ✅ (default) | All 6 primitives |
| `import-obj` | ⬜ | `load_obj(path)`, `parse_obj(str)` |
| `import-gltf` | ⬜ | `load_gltf(path)` (stub) |

## Design principle: opt-in = zero cost

| Feature | How to enable | If NOT enabled |
|---------|--------------|----------------|
| Shadows | `scene.set_shadow_caster(Some(idx))` | No shadow map, no depth pass, no PCF |
| HDR + TM | `AppBuilder::with_hdr(ToneMapper::Aces)` | No offscreen texture, no TM pass |
| Bloom | `AppBuilder::with_bloom(BloomConfig::…)` | No bloom textures, no passes |
| MSAA | `AppBuilder::with_msaa(MsaaConfig { sample_count: 4 })` | Single sample, no resolve |
| Fog | `AppBuilder::with_fog(FogConfig::…)` | No fog uniforms |
| DoF | `AppBuilder::with_dof(DoFConfig::…)` | No CoC/blur textures |
| GPU-driven culling | `AppBuilder::with_gpu_driven(true)` | No compute pipeline, no indirect buffers |
| LOD | `scene.create_mesh_with_lod(…, levels)` | Single-level mesh |
| Primitives | Cargo feature `prim-*` | Not compiled |
| File import | Cargo feature `import-*` | Not compiled |

## Roadmap

| Phase | Status |
|-------|--------|
| 1 — Foundations (window, render loop, Context) | ✅ |
| 2 — 3D infrastructure (Geometry, Mesh, Material, Pipeline) | ✅ |
| 3 — GPU-driven (compute pass, indirect draws, culling) | ✅ |
| 4 — Advanced rendering (shadows, HDR/TM, lights) | ✅ |
| 5 — Polish (LOD, camera controller, input, demo) | ✅ |
| 6 — Post-MVP (bloom, PBR, fog, DoF, MSAA, cascaded shadows, SSAO) | 🔄 |

## Documentation

| Where | What |
|-------|------|
| [docs/user/](docs/user/README.md) | User guide |
| [docs/tech/](docs/tech/ARCHI_APP.md) | Internal architecture |
| [docs/ROADMAP.md](docs/ROADMAP.md) | Roadmap |
| [docs/PLAN.md](docs/PLAN.md) | Recipe book (step history) |
| `cargo doc -p wsg-lib --no-deps` | API reference (rustdoc) |