wsg/AGENTS.md

WSG - WGPU Simple Graphics Library

Project Type

Rust workspace (2024 edition) wrapping wgpu for simple 3D drawing operations.

Workspace Structure

Cargo.toml          # workspace root — no dependencies here
lib/Cargo.toml      # wsg-lib crate: wgpu 30.0.0, winit 0.30
examples/Cargo.toml # depends on wsg-lib via path reference
lib/lib.rs          # lib entry point
lib/context.rs      # Context type (aggregates wgpu objects: Instance, Surface, Adapter, Device, Queue)
lib/renderer.rs     # renderer implementation
examples/src/main.rs # example binary

Key convention: wsg-lib is referenced from examples/ via relative path (path = "../lib"). Do not publish this to crates.io as-is — it uses a local path dependency.

Essential Commands

Action	Command
Build everything	cargo build --workspace
Run examples	cargo run -p examples
Test	cargo test --workspace
Check	cargo check --workspace
Format	cargo fmt --all

No custom scripts or linting tooling beyond standard Cargo conventions.

Architecture Overview

The library's purpose is to abstract the five core wgpu objects into a single Context:

• Instance — GPU backend selection (Vulkan/Metal/DX12)
• Surface — window rendering surface (via winit)
• Adapter — physical/logical GPU device
• Device — buffer/texture/pipeline creation
• Queue — command submission

WGPU doesn't have a native "Context" object — this type groups them together for a simpler user API. See README.md for the French documentation of each component.

Gotchas

• Rust 2024 edition is used. Ensure your Rust toolchain supports it (rustup update).
• wgpu 30.0.0 is pinned in lib/Cargo.toml. The comment says "check the latest version" — verify compatibility before upgrading.
• No feature flags, no dev-dependencies, no tests yet. Adding any requires updating both Cargo.toml files if the dependency spans crates.
• The workspace has no [workspace.dependencies] section. Dependencies are declared per-crate rather than centrally.
• WGSL select argument order (cost us a day): select(reject, accept, cond) returns the second arg when cond is true — the reverse of HLSL's select(trueVal, falseVal, cond). In shaders/gpu_driven.wgsl the cull pass must stay select(0u, u32(flags.z), visible) (visible ⇒ full count, culled ⇒ 0). Swapped args silently zero the counts of every visible entity → black window. See the GOTCHA comment at the top of that shader.
• LOD UV blending: never fold integer-tile jumps, freeze seam twins instead (cost us a day, 2026-09-23): a UV seam is two copies of the same 3-D point on integer-apart UVs (u=0/u=1 columns) — it is NOT a mesh edge, so the decimation must record the weld's refused pairs and freeze those twins (any edge touching one is excluded from the PQ). A co-facial edge spanning a whole tile (cone apex v=1 ↔ base v=0) is a legit chart span — the chart is bilinear, so the UVs blend linearly (fold the integer jump to zero and the apex UV smears down the cone side). And the attribute-aware weld refuses a Δ of exactly 0.5 (ambiguous: seam at its widest vs legit half-tile jump — the cone's u=1 column vs the cap-disc chart sits exactly there). See the comments in geometry.rs (welded, Collapse::collapse_edge) and the cone/seam regression tests.

lean-ctx

Prefer lean-ctx MCP tools over native equivalents for token savings. Full rules: @LEAN-CTX.md