# llimphi-cpu

> The GPU-less rasterizer of [llimphi](../README.md).

Records draw calls into a `Escena` —the same eight `vello::Scene` methods that
`llimphi-compositor` uses, with identical signatures— and renders them with
`vello_cpu` into a `Pixmap`, which is then blitted to any framebuffer honoring
its stride and channel order.

`no_std + alloc` by birth: the end consumer is wawa's bare-metal kernel, where
there is no wgpu, no winit, and no `std`. This is W1 of
[`PLAN-LLIMPHI.md`](../../../03_ukupacha/wawa/PLAN-LLIMPHI.md).

## Why it exists

`vello::Scene` is an **encoded buffer** for the GPU to devour in one go;
`vello_cpu::RenderContext` is **imperative and stateful**. They don't plug into
each other. `Escena` bridges the gap by recording each call as an `Orden`, and
`Pintor` replays them, setting the state each one declares.

Recording is not a detour: it is what makes `append` possible —composing a child
scene inside the parent— without which the compositor cannot reuse the subtrees
it cached.

## Parts

- `escena` — the recorder. `Escena`, `Orden`, `Forma`.
- `pintor` — replays the scene against `vello_cpu`, yielding a `Pixmap`.
- `lienzo` — blits the `Pixmap` to the framebuffer (`stride`, BGRA/RGBA).

## What it does NOT do

**Text.** Shaping lives in `llimphi-text`, still tied to `std` and to system
fonts — that is W2 of the plan, the most expensive phase, and mixing it in here
would bog down both.

## Deps

- `vello_cpu` (`default-features = false`, `u8_pipeline`)
- `fearless_simd` (`force_support_fallback`)

## The two profiles — and why they are not interchangeable

```bash
cargo test -p llimphi-cpu                    # std (default), Linux
cargo check -p llimphi-cpu --target x86_64-wawa \
  --no-default-features --features libm \
  -Z build-std=core,alloc                    # bare-metal, wawa
```

`vello_common` imports `peniko::kurbo::common::FloatFuncs`, and kurbo **only
defines that trait when its `std` feature is off**. So this crate's profile must
match kurbo's in the same build. Since `vello` declares `peniko` with
`default-features = true`, any build where vello and vello_cpu coexist has kurbo
**with** std — and asking for `libm` there fails with "no `FloatFuncs` in
`common`".

Hence `std` is the default (the only coherent profile across the workspace), and
`libm` is requested explicitly for wawa, where no vello unifies anything. Under
`libm` the SIMD level is scalar: `Level::new()` uses `is_x86_feature_detected!`,
which does not exist without an OS. That it suffices is not a consolation — the
W0 spike measured it at 909-5,000 fps at 480x400.