# Review Paint

> Audit the D2D paint pipeline for per-frame waste — allocations, recomputation, redundant API calls at 120-240fps

- Skill: `majiayu000/review-paint` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds add majiayu000/review-paint`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/review-paint/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: DevOps & Infra
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/review-paint

---

Enter planning mode. Deep-audit the D2D paint pipeline for anything that wastes cycles per frame — from per-frame allocations to redundant D2D API calls. Use maximum parallelism — spawn explore agents for independent subsystems.

## Context

The overlay renders at 120-240fps via Direct2D 1.1. At these frame rates, per-frame waste compounds fast: a 5μs allocation ×30/frame ×240fps = 36ms/s of pure garbage. The AHK runtime allocates objects on the heap — every `Buffer()`, `Array()`, `Object()`, and `Map()` lookup is a real cost.

This review covers the **D2D rendering pipeline** — from pre-render through `BeginDraw` to `EndDraw`, including the 8-layer compositor stack, effect chains, and resource management. It does NOT cover:
- Shader compilation or D3D11 interop (use `review-d3d` for that)
- Window data / store operations (use `review-latency` Path 1)
- Keyboard hook latency (use `review-latency` Path 2 preamble)

**Post-#177 architecture note:** The compositor is an 8-layer stack: DWM backdrop → background image → shader layers 1-N → background image (configurable order) → mouse effect → selection effect → hover effect → window list + text. Shader layers render to independent D3D11 intermediate textures, composited via `DrawImage` with premultiplied alpha srcOver blending. PushLayer/PopLayer is eliminated for shader opacity (baked into HLSL via `AT_PostProcess`). However, `PushAxisAlignedClip`/`PopLayer` is still used for BG-shader-as-selection clipping (rounded rect clip to selection row). The pre-render phase (`FX_PreRenderShaderLayers`, `FX_PreRenderMouseEffect`, `FX_PreRenderSelectionEffect`) runs D3D11 dispatches BEFORE `BeginDraw` — this is part of the paint-path cost even though it's outside the D2D draw calls.

## What to Look For

### 1. Per-Frame Allocations (Highest Priority)

Any `Buffer()`, `[]` array literal, `{}` object literal, or `Map()` creation inside a function called every frame.

**The fix pattern is established** (from `ahk-patterns.md`):
```ahk
; WRONG — allocates every call
MyHotFunc() {
    buf := Buffer(72)
    NumPut("float", x, buf, 0)
    DllCall(..., "Ptr", buf, ...)
}

; CORRECT — static buffer, repopulated (ONLY if not reachable during STA pump)
MyHotFunc() {
    static buf := Buffer(72)
    NumPut("float", x, buf, 0)
    DllCall(..., "Ptr", buf, ...)
}
```

Scan for: `Buffer(`, `Array(`, literal `[`, literal `{` inside any function reachable from the paint path.

**Exceptions**:
- Buffers whose size varies per call cannot be made static. Flag them but note the constraint.
- Buffers in functions reachable during STA pump reentrancy MUST NOT be static — COM calls (DrawText, DrawBitmap, FillRoundedRectangle, EndDraw, DwmFlush) pump the STA message loop and can re-enter the same function through timer/callback dispatch, corrupting the shared buffer. `Critical "On"` does NOT prevent this. See `ahk-patterns.md` Hot Path Resource Rules.

### 2. Redundant D2D API Calls

D2D operations that produce the same result every frame:
- Setting the same effect property to the same value (e.g., blur radius that hasn't changed)
- Creating/releasing resources that could be cached (brushes, geometries, layers)
- `SetTransform` / `GetTransform` pairs that could be avoided
- Effect chain `SetInput` / `GetOutput` calls that don't change between frames

### 3. Cacheable Computation

Values computed every frame that only change on config change, resize, or state transition:
- Layout math (positions, rects) recomputed on every paint when overlay size hasn't changed
- Color conversions (hex → ARGB) done per-frame instead of on config load
- Gradient stop arrays rebuilt identically every frame
- Shadow/glow parameters recomputed from config values that haven't changed

### 4. Map Lookup Overhead

`gFX_GPU["effectName"]` string-keyed Map lookups on the hot path. Each lookup hashes the string and walks the bucket. When the same key is accessed multiple times per frame, cache it in a local variable.

### 5. Unnecessary DrawImage / DrawBitmap Calls

- Drawing layers with zero opacity (should early-exit)
- Drawing effects whose inputs haven't changed (could cache output bitmap like `gui_bgimage.ahk` does)
- Drawing off-screen content that will be fully occluded by later layers

### 6. PushLayer / PopLayer / PushAxisAlignedClip Overhead

Phase 5b eliminated PushLayer/PopLayer for shader opacity (now baked into HLSL premultiplied alpha). However, `PushAxisAlignedClip` + `PopLayer` is still used for BG-shader-as-selection and BG-shader-as-hover (clipping background shaders to the selection/hover row rounded rect). Check:
- Can the clip be avoided when the shader already respects `selRect` bounds via cbuffer?
- Are clips applied when the selection shader isn't using BG-as-selection mode (wasted clip/pop)?
- Is clip setup per-frame even when selection hasn't moved?

### 7. Any other detected optimizations. 

## Files to Audit

Primary (called every frame):
- `src/gui/gui_paint.ahk` — main paint orchestrator (`_GUI_PaintOverlay`)
- `src/gui/gui_effects.ahk` — 8-layer compositor: `FX_PreRenderShaderLayers`, `FX_DrawShaderLayers`, `FX_PreRenderMouseEffect`, `FX_DrawMouseEffect`, `FX_PreRenderSelectionEffect`, `FX_DrawSelectionEffect`, `FX_PreRenderHoverEffect`, `FX_DrawHoverEffect`, `FX_DrawSoftRect`, inner shadow chains
- `src/gui/gui_bgimage.ahk` — background image layer
- `src/gui/gui_animation.ahk` — animation tick + frame pacing

Supporting (called from paint path):
- `src/gui/gui_gdip.ahk` — D2D resource management, bitmap creation, cached brushes
- `src/gui/gui_math.ahk` — layout calculations
- `src/gui/d2d_shader.ahk` — `Shader_GetBitmap` returns intermediate textures for DrawImage (D3D11 dispatch internals are out of scope — use `review-d3d`)

Init/config (not per-frame, but relevant for cache invalidation):
- `src/gui/gui_effects.ahk` — `FX_Init()`, shader layer registration, effect disposal
- `src/shared/config_registry.ahk` — which values feed into paint-path computations

## Explore Strategy

Split by subsystem (run in parallel):

- **Paint orchestrator agent**: `gui_paint.ahk` — trace `_GUI_PaintOverlay` from pre-render through `BeginDraw` to `EndDraw`. Map every function call, every Buffer allocation, every D2D API call. Include the pre-render phase (shader/mouse/selection pre-render calls happen before BeginDraw but are per-frame cost). Count per-frame frequency.
- **Effects agent**: `gui_effects.ahk` — the 8-layer compositor. For each layer: pre-render cost, draw cost, allocations, recomputed invariants. Key functions: `FX_PreRenderShaderLayers` (loops N shader layers, calls Shader_PreRender each), `FX_DrawShaderLayers` (loops N layers, DrawImage each), `FX_PreRenderMouseEffect` (compute dispatch + adaptive FPS skip), `FX_PreRenderSelectionEffect`/`FX_PreRenderHoverEffect` (selection/hover shader dispatch), `FX_DrawSelectionEffect`/`FX_DrawHoverEffect` (clip + DrawImage), `FX_DrawSoftRect` (inner shadow chains). Note: mouse effect has QPC-based adaptive framerate skip — check if similar skip logic would benefit background shader layers.
- **Resource agent**: `gui_gdip.ahk`, `gui_math.ahk`, `gui_animation.ahk` — resource caching effectiveness, layout recomputation, animation state updates.

### Tools

- `query_function.ps1 <func>` — extract function bodies without loading full files
- `query_interface.ps1 <file>` — public API surface of paint path files
- `query_timers.ps1` — find animation/repaint timers and their frequencies
- `query_global_ownership.ps1 <global>` — trace who writes paint-path globals

## Assessment Format

Surface **everything** — do not auto-exclude findings based on estimated size. At 240fps, a 2μs saving ×240 = 480μs/s. That matters.

For each finding:

| Finding | File:Lines | Per-Call Cost | Calls/Frame | Per-Frame Cost | Complexity | Fix |
|---------|-----------|--------------|-------------|----------------|------------|-----|
| `FX_LayerParams` allocates 72B Buffer | `gui_effects.ahk:123` | ~3μs | 4 | ~12μs | One-line static | `static buf := Buffer(72)` |

**Columns:**
- **Per-Call Cost**: Estimated cost of one invocation (allocation + computation)
- **Calls/Frame**: How many times this runs per frame (trace the paint path, don't guess)
- **Per-Frame Cost**: Per-Call × Calls/Frame — the actual per-frame waste
- **Complexity**: One-line, small refactor, medium refactor, architectural
- **Fix**: Concrete fix description

**Do not filter.** A 1μs saving ×30/frame is 30μs/frame = 7.2ms/s at 240fps. List everything, ordered by per-frame cost (highest first).

## Validation

After explore agents report back, **validate every finding yourself**:

1. **Trace the call path**: Confirm the function is actually called per-frame by tracing from `_GUI_PaintOverlay` → ... → the function. Don't flag init-time code as per-frame.
2. **Check for existing optimization**: This codebase has been through optimization passes. Some functions already use `static` buffers, cached brushes, or early-exits. Verify the waste still exists.
3. **Verify mutability**: Before suggesting `static`, confirm the buffer content actually changes between calls (otherwise it could be a one-time init). If content is frame-invariant, the fix might be "compute once, cache" rather than "static buffer."
4. **Check AHK semantics**: `static` in AHK v2 persists across calls to the same function. `Critical "On"` prevents timer/hotkey interruption but does NOT prevent STA pump reentrancy — any D2D/COM draw call can dispatch callbacks that re-enter the same function, corrupting the static buffer. Only use `static` when the buffer is fully consumed before any COM/D2D call, or when the function is provably unreachable from STA pump paths.
5. **Preserve Float() on GPU buffers**: Never remove `Float()` wrappers from `NumPut("float", ...)` calls that feed D2D/D3D geometry buffers (rects, points, ellipses, viewports). These ensure IEEE 754 bit patterns — AHK v2 integer-to-float coercion in NumPut is not guaranteed safe. Removing them is not an optimization.
6. **Distinguish from shader path**: If a finding is in `d2d_shader.ahk` and relates to D3D11 operations (texture creation, SRV binding, shader dispatch), it's out of scope. Only flag the D2D-side draw call.

## Plan Format

**Section 1 — Per-Frame Allocations:**

| Finding | File:Lines | Per-Call Cost | Calls/Frame | Per-Frame Cost | Complexity | Fix |
|---------|-----------|--------------|-------------|----------------|------------|-----|

**Section 2 — Redundant D2D API Calls:**

| Finding | File:Lines | Per-Call Cost | Calls/Frame | Per-Frame Cost | Complexity | Fix |
|---------|-----------|--------------|-------------|----------------|------------|-----|

**Section 3 — Cacheable Computation:**

| Finding | File:Lines | Per-Call Cost | Calls/Frame | Per-Frame Cost | Complexity | Fix |
|---------|-----------|--------------|-------------|----------------|------------|-----|

**Section 4 — Map Lookups & Misc:**

| Finding | File:Lines | Per-Call Cost | Calls/Frame | Per-Frame Cost | Complexity | Fix |
|---------|-----------|--------------|-------------|----------------|------------|-----|

Order within each section by per-frame cost (highest first).

Ignore any existing plans — create a fresh one.