feat(render): Add RGB565 raster path and ESP32-P4 PPA backend

.github/workflows/esp32p4.yml

@@ -0,0 +1,53 @@
+name: ESP32-P4 backend
+
+on:
+  pull_request:
+    paths:
+      - ".github/workflows/esp32p4.yml"
+      - "engine/core/**"
+      - "engine/backends/esp32p4-ppa/**"
+      - "hosts/esp32p4/**"
+  push:
+    branches: [main]
+    paths:
+      - ".github/workflows/esp32p4.yml"
+      - "engine/core/**"
+      - "engine/backends/esp32p4-ppa/**"
+      - "hosts/esp32p4/**"
+  workflow_dispatch: {}
+
+permissions:
+  contents: read
+
+jobs:
+  rust:
+    name: Rust renderer
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: dtolnay/rust-toolchain@stable
+
+      - name: Test RGB565 core rasterizer
+        run: cargo test --locked --manifest-path engine/core/Cargo.toml
+
+      - name: Test ESP32-P4 DrawList backend
+        run: cargo test --locked --manifest-path engine/backends/esp32p4-ppa/Cargo.toml --features std
+
+      - name: Check ESP-IDF Rust adapter
+        run: cargo check --locked --manifest-path engine/backends/esp32p4-ppa/Cargo.toml --features esp-idf
+
+  esp-idf:
+    name: ESP-IDF release/v6.0
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build ESP32-P4 component smoke app
+        uses: espressif/esp-idf-ci-action@v1
+        with:
+          esp_idf_version: release-v6.0
+          target: esp32p4
+          path: hosts/esp32p4/examples/ppa-smoke

contracts/spec/spec.ts

@@ -496,10 +496,11 @@ export const ENUMS = {
 // ---------------------------------------------------------------------------
 // Values MUST equal rust-psp's TexturePixelFormat (sceGuTexMode arg), as used
 // by the dreamcart runtime — verified against rust-psp/psp/src/sys/gu.rs
-// (Psm4444 = 2, Psm8888 = 3) and runtime/src/gfx3d.rs psm_for(). v1 supports
-// only these two (4444 for baked corner/shadow alpha sprites, 8888 for images).
+// (Psm5650 = 0, Psm4444 = 2, Psm8888 = 3) and runtime/src/gfx3d.rs
+// psm_for().
 
 export const PSM = {
+  PSM_5650: 0, // RGB 565, 16-bit (B5:G6:R5 bit order)
   PSM_4444: 2, // RGBA 4444, 16-bit
   PSM_8888: 3, // RGBA 8888, 32-bit
   PSM_T8: 5, //   CLUT8: one palette index/px + a 256 x u32 ABGR palette

docs/DESIGN.md

@@ -60,6 +60,11 @@ artifacts: `$JOB_TMP/map-*.json`).
   PSP bin wraps it with QuickJS + sceGu; `wasm32-unknown-unknown` build wraps
   it with a deterministic software rasterizer used by BOTH the browser dev
   host and headless Bun goldens. One layout engine everywhere.
+- **ESP32-P4 stays 16-bit**: `engine/backends/esp32p4-ppa/` consumes the same
+  DrawList into an opaque RGB565 target. It maps flat fills, A8 coverage
+  blending, and compatible PSM 5650 texture transforms to the PPA, then
+  preserves ordering with the core RGB565 rasterizer for unsupported ops.
+  It never allocates a full-frame RGB888/ARGB8888 intermediate.
 - **Native animation**: tweens/springs tick in Rust per vblank with **fixed
   dt = 1/60 s** (frame content is a pure function of frame index — this is
   what makes byte-exact goldens possible **[R]**). JS only declares motion.

docs/STRUCTURE.md

@@ -9,6 +9,7 @@ directory; nothing else gets a top-level name.
 pocketjs/
 ├─ engine/       Cores: the Rust simulation cores
 │  ├─ core/       pocketjs-core — retained UI tree, taffy layout, raster (standalone crate)
+│  ├─ backends/    platform render backends (ESP32-P4 PPA is a standalone no_std crate)
 │  ├─ wasm/       core compiled to wasm32 for web/sim hosts (standalone crate)
 │  ├─ pocket3d/   the 3D core family (bsp, cook, gu, vita) + desktop examples
 │  ├─ crates/     non-3D engine crates: pocket-mod, pocket-ui-wgpu, pocket-vrm, pocket-widget
@@ -18,6 +19,7 @@ pocketjs/
 ├─ hosts/        Surfaces: every embedding of the cores
 │  ├─ psp/        QuickJS + rust-psp EBOOT host
 │  ├─ vita/       Vita host
+│  ├─ esp32p4/    reusable ESP-IDF PPA adapter + component smoke build
 │  ├─ web/        browser dev host (wasm core)
 │  └─ sim/        deterministic headless simulation host (docs/DETERMINISM.md)
 ├─ framework/    Guest: @pocketjs/framework
@@ -60,7 +62,7 @@ New things go where the axis says — never invent a top-level directory:
 - **npm surface is frozen**: `@pocketjs/framework/*` export *keys* never
   change; the `exports`/`files` maps in package.json absorb internal moves.
 - **Cargo stays non-workspace where toolchains demand it**: `engine/core`,
-  `engine/wasm`, `hosts/psp`, `hosts/vita`, and the gu/vita 3D crates each
-  stand alone with their own lockfiles. `engine/Cargo.toml` is the one
-  desktop workspace.
+  `engine/wasm`, `engine/backends/esp32p4-ppa`, `hosts/psp`, `hosts/vita`,
+  and the gu/vita 3D crates each stand alone with their own lockfiles.
+  `engine/Cargo.toml` is the one desktop workspace.
 - **Moves are `git mv`** — history stays traceable.

engine/Cargo.toml

@@ -2,8 +2,9 @@
 # (docs/RUNTIMES.md: these are the Cores plus their desktop surfaces).
 #
 # Deliberately EXCLUDED and standalone (each with its own Cargo.lock):
-#   core/, wasm/          — cargo-psp needs hosts/psp to consume core as a
-#                           lone standalone crate (see core/Cargo.toml)
+#   core/, wasm/, backends/esp32p4-ppa/
+#                        — cargo-psp and ESP-IDF need to consume these as
+#                           lone standalone crates (see their Cargo.toml)
 #   pocket3d/crates/pocket3d-gu, gu-demo — PSP-only (cargo-psp toolchain)
 #   pocket3d/crates/pocket3d-vita        — Vita-only (vitasdk toolchain)
 [workspace]
@@ -21,6 +22,7 @@ members = [
     "pocket3d/examples/uihost",
 ]
 exclude = [
+    "backends/esp32p4-ppa",
     "core",
     "wasm",
     "pocket3d/crates/pocket3d-gu",

engine/backends/esp32p4-ppa/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "pocketjs-esp32p4-ppa"
+version = "0.1.0"
+edition = "2021"
+license = "MIT"
+publish = false
+
+[dependencies]
+pocketjs-core = { path = "../../core" }
+
+[dev-dependencies]
+pocketjs-core = { path = "../../core", features = ["std"] }
+
+[features]
+default = []
+esp-idf = []
+std = ["pocketjs-core/std"]
+
+[workspace]

engine/backends/esp32p4-ppa/README.md

@@ -0,0 +1,42 @@
+# PocketJS ESP32-P4 PPA backend
+
+This `no_std` crate interprets PocketJS DrawLists directly into an RGB565
+surface. It accelerates operations that map exactly to the ESP32-P4 Pixel
+Processing Accelerator and preserves DrawList order with an RGB565 software
+fallback for everything else.
+
+The default crate deliberately does not depend on ESP-IDF or a board support
+package. Hosts can implement `PpaOps` for another driver or test double.
+Enabling the `esp-idf` feature exposes the concrete `EspIdfPpaOps`
+implementation, backed by the reusable ESP-IDF component under
+[`hosts/esp32p4`](../../../hosts/esp32p4/README.md). Board-specific display
+presentation remains in the BSP.
+
+Accelerated paths:
+
+- opaque and translucent flat rectangles (`FILL` or A8 `BLEND`);
+- antialiased font runs (`A8` coverage composed once, then `BLEND`);
+- single-color alpha textures such as PocketJS rounded-corner masks (`A8`
+  `BLEND`);
+- opaque PSM 5650 texture quads (`SRM`) when scaling semantics are compatible.
+
+Gradients, arbitrary triangles, textured triangles, and unsupported texture
+formats fall back to `pocketjs_core::raster::render_scaled_rgb565_over`.
+No full-frame RGB888 or ARGB8888 surface is allocated.
+
+## Test
+
+Run the portable renderer and pixel-parity tests on the host:
+
+```sh
+cargo test --locked --manifest-path engine/backends/esp32p4-ppa/Cargo.toml \
+  --features std
+```
+
+Compile-check the Rust side of the ESP-IDF adapter without linking an IDF
+application:
+
+```sh
+cargo check --locked --manifest-path engine/backends/esp32p4-ppa/Cargo.toml \
+  --features esp-idf
+```