Crafter.Graphics/README.md

# Crafter.Graphics

Vulkan + WebGPU graphics library built around C++20 modules and
bindless heaps. Provides window management, ray tracing, and a
compute-shader-driven UI on a single, opinionated stack. Native
builds use Vulkan with `VK_EXT_descriptor_heap`; `wasm32-*` builds
target the browser via WebGPU and a DOM window backend.

## Backends

Backends are chosen at build time by the target triple:

| Target              | Window                 | Renderer            | Shaders |
|---------------------|------------------------|---------------------|---------|
| native Linux        | Wayland                | Vulkan (heap-bound) | GLSL → SPIR-V |
| native Windows      | Win32                  | Vulkan (heap-bound) | GLSL → SPIR-V |
| `wasm32-*` (any)    | DOM (canvas + JS env)  | WebGPU              | WGSL (loaded at runtime) |

The two backends share the same C++ surface for the high-level pieces
(`UIRenderer`, `Mesh`, `RenderingElement3D`, `RTPass`, item structs,
`FontAtlas`, `Image2D`, `ComputeShader`). Backend-typed pieces
(`*Vulkan` vs `*WebGPU`) live behind `#ifdef CRAFTER_GRAPHICS_WINDOW_DOM`.
Vulkan ray tracing is hardware (`VK_KHR_ray_tracing_pipeline`); WebGPU
ray tracing is a library-built software path (BVH + traceRay in a
compute pipeline composed from user-supplied WGSL stages). The WebGPU
path supports triangle and AABB (procedural, `VK_GEOMETRY_TYPE_AABBS_KHR`)
geometry, closest-hit / miss / any-hit / intersection shaders — see
[examples/RTVolume](examples/RTVolume/README.md) for procedural spheres
shaded through an intersection shader with an any-hit cut-out.

> **Native RT status:** reading an acceleration structure through
> `VK_EXT_descriptor_heap` aborts with `VK_ERROR_DEVICE_LOST` on NVIDIA
> driver `610.43.02` — a driver-side fault in the brand-new descriptor-heap
> acceleration-structure path, not an engine bug (the setup is correct and
> validation-clean; images/buffers through the same heap work). The engine
> **works around it transparently** (issue #15): on the NVIDIA driver only,
> `VulkanShader` rewrites the compiled SPIR-V so heap AS reads become a
> TLAS-device-address + `OpConvertUToAccelerationStructureKHR` path (which
> reads no descriptor), and `RTPass` supplies the address as push data.
> Shaders and example code are unchanged, and it's a single fenced block
> gated on `Device::workaroundDescriptorHeapAS`, removable once a fixed
> driver ships. See
> [examples/VulkanTriangle/README.md](examples/VulkanTriangle/README.md)
> for the full investigation. WebGPU RT is unaffected.

> **Native RT limitation — dynamic `descriptor_heap` indexing in hit
> shaders:** on the same NVIDIA driver, indexing a `descriptor_heap`
> array with a **runtime (non-constant)** index inside a ray-tracing
> **hit** shader also device-losts (`VK_ERROR_DEVICE_LOST`), for plain
> SSBO **and** sampled-image descriptors. A **constant / spec-constant**
> index is fine (that's why [Sponza](examples/Sponza/README.md)'s
> closest-hit reads `albedo[albedoSlot]` through a spec constant), and
> the identical dynamic pattern works in fragment shaders (the UI
> renderer indexes `uiTextures[]` by per-item runtime slots) — so this
> is **RT-stage-specific**, not a general heap problem. Unlike the
> AS-read fault above this **cannot** be worked around transparently:
> sampled images have no device-address escape hatch the way an
> acceleration structure does (`OpConvertUToAccelerationStructureKHR`).
> The recommended pattern for bindless per-mesh geometry/material is to
> **bind one resource and index *within* it dynamically** rather than
> selecting a descriptor dynamically: pack geometry into a single SSBO
> (or reach it via `buffer_reference`) at a spec-constant slot and index
> by element offset, and put materials in one `texture2DArray` indexed
> by layer. Dynamic addressing *inside* a bound resource is ordinary
> memory/layer addressing and is unaffected; only dynamic selection of a
> *descriptor* faults. This is exactly what the WebGPU path already does
> (bucketed texture arrays + a single buffer). Full investigation and
> GLSL in [examples/Sponza/README.md](examples/Sponza/README.md) (issue
> #23). WebGPU RT is unaffected.

## What's in here

- **Window** — Wayland, Win32, and DOM backends, swapchain ring / canvas
  framing, input events. Pick a backend at build time via the target
  triple. The DOM backend routes every dynamic symbol through
  [additional/dom-env.js](additional/dom-env.js) and
  [additional/dom-webgpu.js](additional/dom-webgpu.js).
- **Device** *(Vulkan only)* — single-instance bring-up targeting
  `VK_EXT_descriptor_heap`; pipelines are created with
  `VK_PIPELINE_CREATE_2_DESCRIPTOR_HEAP_BIT_EXT` so there are no
  descriptor-set layouts and push constants travel via
  `vkCmdPushDataEXT`.
- **DescriptorHeapVulkan / DescriptorHeapWebGPU** — bindless slot
  allocators. Vulkan side allocates image/buffer/sampler slots in a
  `VK_EXT_descriptor_heap`; WebGPU side resolves slots to JS-side
  handle-table cookies that the dispatch bridge binds per pass.
- **VulkanBuffer\<T, Mapped\> / WebGPUBuffer\<T\>** — typed buffer.
  Vulkan variant has optional host mapping and a `FlushDevice` that
  issues the right host-write barrier; WebGPU variant goes through
  `queue.writeBuffer` over the JS bridge.
- **ImageVulkan\<Pixel\> / Image2D\<Pixel\> / Image2DArray\<Pixel\>** —
  image + staging buffer with mip-chain support on Vulkan; on WebGPU,
  `rgba8unorm` 2D / 2D-array textures created and written via the
  bridge. Atlas (`r8unorm`, sub-region writes) is a separate path.
- **PipelineRTVulkan / PipelineRTWebGPU / ShaderBindingTableVulkan /
  ShaderBindingTableWebGPU / RTPass** — ray-tracing pipelines. Vulkan
  uses native RT pipelines + SBTs; WebGPU compiles a **wavefront /
  streaming** software tracer — five `@compute` kernels
  (`GENERATE → PREP → TRACE → SHADE → RESOLVE`) sharing one module,
  connected by GPU ray/hit/payload buffers and a GPU-driven indirect
  bounce loop (`dispatchWorkgroupsIndirect`). TRACE carries zero user
  code (traversal + intersection only); user raygen calls
  `rtEmitPrimaryRay`, and closesthit / miss run in SHADE where they
  `rtEmitRay` continuation/shadow rays and `rtAccumulate` radiance. An
  optional Resolve shader tonemaps the linear accumulator. See
  [WAVEFRONT-DESIGN.md](WAVEFRONT-DESIGN.md).
- **ComputeShader / WebGPUComputeShader** — Tier 1 wrapper used by the
  UI system. Vulkan loads a `.spv` and dispatches with
  `vkCmdPushDataEXT`; WebGPU loads a user-supplied `.wgsl` blob at
  runtime via `wgpuLoadCustomShader`. Use it directly for any custom
  compute.
- **UI** — three-tier UI system; see below. The standard shaders ship
  as four `.spv` blobs on native and four WGSL strings baked into the
  WebGPU dispatcher.
- **FontAtlas** — single-channel SDF atlas (1024×1024, 32pt base,
  shelf-packed, lazy `Ensure` per codepoint, dirty-flush via `Update`).
  Backend-agnostic.
- **Mesh / RenderingElement3D / Animation** — BLAS/TLAS construction
  and 3D scene plumbing. Vulkan calls `vkCmdBuildAccelerationStructures`;
  WebGPU registers BLAS data (verts, idx, BVH nodes, primRemap, optional
  per-vertex attribs) into global mesh heaps and builds the TLAS in a
  library compute pass.
- **Clipboard / Input / Gamepad / Router / Dom** — input plumbing.
  Gamepad uses libudev+libevdev on Linux and WGI on Windows; the DOM
  backend exposes the host page DOM (`Dom::HtmlElement`) and a router
  for hash-routed wasm apps.

## UI system (three tiers)

The UI is *deliberately* layered to balance no-boilerplate against
no-lock-in:

- **Tier 1 — `ComputeShader`.** Load any `.spv`, dispatch with push
  constants, library inserts inter-dispatch barriers. The escape hatch:
  if the standard shaders don't fit, write your own compute and
  dispatch it next to them.
- **Tier 2 — `UIRenderer` + standard shaders.** Four shipped compute
  shaders (`drawQuads`, `drawCircles`, `drawImages`, `drawText`), POD
  item structs (`QuadItem`, `CircleItem`, `ImageItem`, `GlyphItem`), a
  shared GLSL contract in [shaders/ui-shared.glsl](shaders/ui-shared.glsl),
  and helpers (`RegisterBuffer`, `RegisterImage`, `RegisterSampler`,
  `FillHeader`, `Dispatch*`, `ShapeText`). You build your own per-shader
  SSBOs (manual batching) and call one `Dispatch*` per shader type per
  frame. Item array order = draw order.
- **Tier 3 — stateless presentation functions.** `DrawButton`,
  `DrawCheckbox`, `DrawSlider`, `DrawProgressBar`. Each is a small
  function that *appends* items to your buffers — they don't dispatch.
  Colors come in as small inline `*Colors` aggregates, no library
  `Theme` type. **The source is the customization API**: if a
  component doesn't fit, copy its body and edit it. No virtual hooks,
  no extension points.

What's *not* in the UI: widget tree, layout engine (just a `Rect::SubRect`
carving helper), theming, hit-testing, focus management. State for
interactive components (hover, drag, focus) lives in user-owned POD
structs, not the library.

### UI dispatch model

Standard shaders dispatch one workgroup per 8×8 *screen tile* — each
thread iterates every item in the SSBO in array order, accumulating
into a local `dst`, and stores once. Total cost is `O(W·H·N)`; works
well up to a few hundred items at 1080p. Splitting one buffer into
multiple dispatches doesn't help — the same total work plus barrier
overhead. If you need to render thousands of UI items, you want a
different shader (tile binning, per-item-list resolve), not more
dispatches.

## Build

The repository is built with `crafter-build` (a project-config based
build system; the project description lives in `project.cpp`):

```bash
crafter-build                        # native: Wayland on Linux, Win32 on Windows
crafter-build --target=wasm32-wasip1 # browser: DOM window + WebGPU renderer
crafter-build -r                     # build and run (in an example directory)
```

The build picks the window + renderer pair automatically from the
target triple: any `wasm32-*` triple flips to DOM + WebGPU (no Vulkan
loader linked), everything else stays on the native Vulkan path. Each
example with both backends ships GLSL *and* WGSL copies of its shaders
side-by-side (e.g. [raygen.glsl](examples/Sponza/raygen.glsl) +
[raygen.wgsl](examples/Sponza/raygen.wgsl)); `project.cpp` selects the
right set per target.

## Examples

See [examples/](examples/). Quick map:

- [HelloWindow](examples/HelloWindow/) — minimal native window, no rendering.
- [HelloDom](examples/HelloDom/) — wasm-only smoke test of the DOM
  partition: page-level events, `HtmlElement::CreateInBody`, and
  `Router::PushState`-driven SPA navigation. No GPU work.
- [VulkanTriangle](examples/VulkanTriangle/) — ray-traced triangle on
  both Vulkan and WebGPU. The smallest test of the bindless + RT path
  on each backend.
- [RTStress](examples/RTStress/) — wavefront RT benchmark: an N×N×N grid
  of a cube mesh (instance-count knob `kGrid`, 512 → 8000) shaded with
  primary + shadow rays. Prints a GPU timestamp-query per-pass breakdown
  each second. WebGPU/DOM only.
- [Sponza](examples/Sponza/) — ray-traced Sponza atrium on both
  backends. Exercises `.cmesh` / `.ctex` decompression (GPU
  `VK_EXT_memory_decompression` on Vulkan, CPU on WebGPU) and a
  textured closest-hit. See [its README](examples/Sponza/README.md)
  for asset provenance.
- [HelloUI](examples/HelloUI/) — UI smoke test using all three tiers
  (background quad, slider, progress bar, button with text label,
  cursor-tracking circle).
- [CustomShader](examples/CustomShader/) — Tier 1 demo: a user-authored
  compute shader inverting RGB under a list of item-circles, dispatched
  alongside the standard `drawQuads`. Shipped as both
  [`.comp.glsl`](examples/CustomShader/inverse-circle.comp.glsl) and
  [`.comp.wgsl`](examples/CustomShader/inverse-circle.comp.wgsl).
- [Decompression](examples/Decompression/) — `Crafter::Compression`
  CPU round-trip smoke test (used by the WebGPU asset path).
- [InputSystem](examples/InputSystem/) — keyboard / mouse / gamepad
  event surface check.

## License

LGPL 3.0. See per-file headers and `LICENSE`.