TwoD rendering + Simulation — dogfood gaps · novolis-lab

Orthographic 2D lives in `Novolis.Rendering.TwoD` (+ `Backends.TwoD.Silk`). Simulation stays BCL `Vector3` / `Quaternion` on the XZ plane (Y = 0). Do not add Vector2, suffix-3 types, or TwoD types to Math or Physics.

Dogfood apps (new)

App	Stack	Purpose
`labs/rendering/SilkTwoDHello`	Rendering.TwoD + Silk	Collision, platforms, HUD, menus — no Simulation
`labs/PlatformerTwoD`	Simulation.Kinematics + World + Rendering.TwoD	Same tile demo as `PlatformerHop`, planar XZ via `PlanarAgent`
`labs/RtsLiteTwoD`	Shared RTS sim + Rendering.TwoD	Top-down orthographic RTS (Raylib `RtsLite` = pseudo-3D + PNG billboards)

Run:

dotnet run --project labs/rendering/SilkTwoDHello
dotnet run --project labs/PlatformerTwoD
dotnet run --project labs/RtsLiteTwoD

Raylib (3D-style)	TwoD (orthographic)
`PlatformerHop`	`PlatformerTwoD`
`RtsLite`	`RtsLiteTwoD`

Shared helpers: labs/shared/Novolis.Lab.TwoD (DenseGridPlatforms, OrthoPanCamera).

Side-view vs planar XZ

Convention	Horizontal	Vertical	Depth
Raylib `PlatformerHop`	`Vector3.X`	`Vector3.Y`	`Z ≈ 0`
Simulation + TwoD	`Vector3.X`	`Vector3.Z`	`Y = 0`

Bridge at the app layer only (no Simulation → Rendering package reference):

// Side-view position (Raylib) → planar (Simulation / TwoD)
static Vector3 SideToPlanar(Vector3 side) => new(side.X, 0f, side.Y);

PlanarHopPlayer uses PlanarAgent.Move + SideLevel grid where grid row y maps to world Z.

Simulation: what exists vs gaps

Already aligned (XZ, BCL)

Package	API	Role for 2D
`Novolis.Simulation.Kinematics`	`PlanarAgent.Move`	Grid + optional BVH sweep on XZ
`Novolis.Simulation.World`	`PlanarOccupancy`	Circle vs `DenseGrid<byte>`
`Novolis.Simulation.View`	`ViewPose`, orbit/free rigs	3D cameras — not orthographic 2D

Gaps (no new Math/Physics types)

No side-view camera in Simulation.View — ViewPose targets perspective 3D. Orthographic 2D uses TwoDViewport in Rendering at compose time. Optional future: document-only “side rig” recipe in dogfood, not a new Simulation type.
Duplicate collision paths — PlanarOccupancy (Simulation) vs TwoDCollisionWorld (Rendering). Apps should pick one per game: PlatformerTwoD uses Simulation for motion; SilkTwoDHello uses Rendering collision only.
No Simulation → TwoD scene builder — tile grids are app-wired (AddPlatform per cell). A shared dogfood helper (not a platform package) could emit platforms from DenseGrid<byte> if more 2D apps appear.
ViewPose bridge — still app-only for path tracing (simulation-viewpose-to-rendering-bridge); irrelevant for orthographic TwoD.
NeuralRacing / headless sims — no visualization; 2D would be a new app if needed.
RtsLite / top-down — RtsLiteTwoD dogfoods orthographic RTS; PNG billboards still Raylib-only in RtsLite.
Assets — no committed PNGs under lab for SilkTwoDPngLoader; polygon/HUD dogfood works without art.

Explicit non-goals

Vector2, Vector3d, or planar types in Math/Physics
Novolis.Simulation.* referencing Novolis.Rendering.*
Quaternion helpers for 2D (Y-axis spin only if ever needed — use BCL Quaternion in apps)

Avalonia hosts

Package `Novolis.Avalonia.Rendering` (novolis-avalonia):

Control	Renders
`TwoDSceneControl`	`TwoDScene` via OpenGL (`SilkTwoDRenderer`)
`Rgba32FrameControl`	CPU `Rgba32` frames (`IFramePresenter`) — path trace preview

Sample: novolis-lab/labs/avalonia/RenderingAvalonia. PackageReference Novolis.Avalonia.Rendering (no cross-repo ProjectReference).

Dropped: TerraFX

Low-level GPU interop (VMA, D3D12) was considered and not adopted — Novolis stays on Silk.NET for Vulkan/OpenGL presenters.

Rendering gaps (for follow-up)

Raylib TwoD backend — not planned; Silk-only host for Rendering.TwoD
Procedural / solid-color sprites without PNG — today use TwoDStaticPolygon or register a 1×1 texture
PlatformerHop axis — migrating the Raylib app would require coordinate remap or a documented side-view profile

TwoD rendering + Simulation — dogfood gaps