--- stepsCompleted: [ "step-01-init", "step-02-context", "step-03-starter", "step-04-decisions", "step-05-patterns", "step-06-structure", "step-07-validation", "step-08-complete" ] inputDocuments: - "_bmad-output/planning-artifacts/prd.md" - "_bmad-output/planning-artifacts/research/technical-WebGL-SVG-layered-rendering-research-2026-03-12.md" - "_bmad-output/project-context.md" workflowType: "architecture" project_name: "Fantasy-Map-Generator" user_name: "Azgaar" date: "2026-03-12" status: "complete" lastStep: 8 completedAt: "2026-03-12" --- # Architecture Decision Document — Fantasy-Map-Generator WebGL Layer Framework **Project:** Fantasy-Map-Generator **Author:** Azgaar (via Winston/Architect) **Date:** 2026-03-12 **Status:** Complete — Ready for Implementation --- ## 1. Project Context Analysis ### 1.1 Scope Summary This architecture addresses a **brownfield, isolated subsystem replacement** in FMG's rendering pipeline. The surface area is: - **New:** `WebGL2LayerFramework` TypeScript class (`src/modules/webgl-layer-framework.ts`) - **Refactored:** `src/renderers/draw-relief-icons.ts` — migrated to use the framework instead of ad-hoc context management - **Added:** Unit tests (`src/modules/webgl-layer-framework.test.ts`) - **Unchanged:** All 32 SVG layers, D3 data pipeline, `public/modules/` legacy JS, globe renderer, SVG export ### 1.2 Functional Requirements Coverage | FR Category | Count | Architectural Component | | ------------------------------------ | ----- | ----------------------------------------------------------------- | | Framework Core (FR1–FR4) | 4 | `WebGL2LayerFramework` class | | Coordinate Sync (FR5–FR7) | 3 | `syncTransform()` method + orthographic camera | | Layer Lifecycle (FR8–FR11) | 4 | `setVisible()`, `ResizeObserver`, `dispose()` | | Relief Rendering (FR12–FR17) | 6 | `draw-relief-icons.ts` refactored | | Compatibility & Fallback (FR18–FR19) | 2 | `detectWebGL2()` guard in framework init | | Interaction (FR20–FR21) | 2 | `pointer-events: none` on canvas; existing Layers panel unchanged | | Developer API (FR22–FR24) | 3 | `register(config)` public method | | Testability (FR25–FR27) | 3 | Pure functions / injectable dependencies | **Total: 27 FRs — all addressed.** ### 1.3 Non-Functional Constraints Shaping Architecture | NFR | Architectural Impact | | ----------------------------------------------- | ------------------------------------------------------------------------------------------- | | NFR-P6: No GPU teardown on hide | `setVisible(false)` must set `mesh.visible = false` only — NOT call `dispose()` | | NFR-C3: Max 2 WebGL contexts (1 globe + 1 map) | Single `THREE.WebGLRenderer` shared across all registered layers | | NFR-M3: Global Module Pattern | `window.WebGL2LayerFramework = new WebGL2LayerFrameworkClass()` at module bottom | | NFR-B1/B2: Bundle size ≤ 50KB gzip increase | Three.js already present; named imports only (`import { WebGLRenderer, ... } from 'three'`) | | NFR-M5: ≥ 80% Vitest coverage on framework core | Pure coordinate functions and registration API must be injected/mockable | ### 1.4 Critical Brownfield Constraints Discovered in Codebase | Constraint | Detail | Architectural Response | | --------------------------------- | ------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------ | | Existing WebGL relief renderer | `draw-relief-icons.ts` already has a working Three.js renderer | Framework wraps/extends it — not replace from scratch | | `undrawRelief` tears down GPU | Current implementation disposes renderer on hide — violates NFR-P6 | Framework `setVisible(false)` replaces teardown pattern | | Canvas placement is wrong | Currently `insertAdjacentElement("afterend", map)` — canvas sits above all SVG layers | Framework uses positioned wrapper; MVP uses z-index above SVG (see Decision 3) | | Globals `viewX`, `viewY`, `scale` | Coordinate sync uses raw window globals | Framework abstracts to `syncTransform()` callable function; tests inject mock values | | `#map { position: absolute }` | SVG has no positioned parent container | Framework wraps SVG in `#map-container` on init | --- ## 2. Technology Stack No new dependencies are introduced. The framework uses only technologies already in the project: | Technology | Version | Role in This Feature | | ---------- | -------- | ----------------------------------------------------------- | | TypeScript | ^5.9.3 | Framework implementation language | | Three.js | ^0.183.2 | WebGL renderer, orthographic camera, scene management | | Vite | ^7.3.1 | Bundling (tree-shaking Three.js named imports) | | Vitest | ^4.0.18 | Unit tests for coordinate sync and framework API | | D3 | ^7.9.0 | Source of zoom transform values (`viewX`, `viewY`, `scale`) | **Three.js imports used (tree-shaken):** ```typescript import { WebGLRenderer, Scene, OrthographicCamera, BufferGeometry, BufferAttribute, Mesh, MeshBasicMaterial, TextureLoader, SRGBColorSpace, LinearMipmapLinearFilter, LinearFilter, DoubleSide } from "three"; ``` --- ## 3. Core Architectural Decisions ### Decision 1: Single Shared WebGL Context via `WebGL2LayerFramework` **Decision:** A new `WebGL2LayerFrameworkClass` TypeScript module manages a single `THREE.WebGLRenderer` instance shared by all registered WebGL layers. It replaces `draw-relief-icons.ts`'s module-level renderer with a centralized framework. **Rationale:** - Browser WebGL context limit (8–16 per page) requires minimizing context creation - The globe renderer already holds context #1; the map framework holds context #2 — this is the budget maximum (NFR-C3) - A single `THREE.Scene` with `renderOrder` per layer handles draw ordering within the shared context - The existing `draw-relief-icons.ts` will be refactored to register with this framework instead of managing its own renderer **Alternatives rejected:** - One canvas per layer: would exceed context limit at 3+ WebGL layers - Raw WebGL2 without Three.js: Three.js already present; adds no bundle cost; handles context loss/restore, shader compilation, VBO management ### Decision 2: Layer Registration API **Decision:** The framework exposes a `register(config: WebGLLayerConfig)` method. Callers provide an `id`, `anchorLayerId` (SVG element ID for z-position reference), `renderOrder` (Three.js scene draw order), `setup(scene)` callback, and `dispose()` callback. The framework manages canvas lifecycle; layer-specific GPU resource creation happens in `setup`. ```typescript interface WebGLLayerConfig { id: string; anchorLayerId: string; // e.g. "terrain" — SVG whose DOM position sets z-index renderOrder: number; // Three.js renderOrder for objects in this layer setup: (scene: THREE.Scene) => void; // called once after WebGL2 context confirmed dispose: (scene: THREE.Scene) => void; // called on framework.unregister(id) } ``` **What the framework manages:** - Canvas element creation, sizing, positioning - `THREE.WebGLRenderer` + `THREE.Scene` initialization - Z-index derivation from anchor SVG layer DOM position - Visibility toggle (`visible = false/true` on registered `THREE.Object3D` groups) - Canvas resize via `ResizeObserver` - D3 zoom/pan → orthographic camera sync **What each layer module manages:** - Creating `THREE.Mesh` / `BufferGeometry` / textures in `setup(scene)` - Clearing and rebuilding geometry when data changes (called by `drawRelief` equivalent) - Cleaning up GPU objects in `dispose(scene)` ### Decision 3: Canvas Z-Index Positioning — MVP vs. Phase 2 **MVP Decision:** The canvas is inserted as a sibling to `#map` in `#map-container` (a new `position: relative` wrapper div). The z-index is computed from the anchor SVG layer's page position in the DOM stack. **Known limitation:** Because all 32 SVG layers are inside `#map` (a single SVG element), CSS z-index cannot interleave the canvas between SVG layer groups. In MVP, the canvas renders **above the entire SVG** (higher z-index than `#map`). SVG layers that should visually overlay terrain icons (religion fills, borders, labels) will appear underneath the canvas. **Why this is acceptable for MVP:** - The visual impact is limited: relief icons appear in terrain cells (mountains, forests), while labels/burg icons appear in civilized cells — overlap is uncommon in practice - The current codebase ALREADY exhibits this same behavior (`draw-relief-icons.ts` places canvas after `#map` in DOM order with no z-index) - `pointer-events: none` preserves all interaction; the UX regression is purely visual **Phase 2 fix — DOM-Split Architecture:** ``` #map-container (position: relative) ├── svg#map-back (layers 1–11, z-index: 1) ├── canvas#terrainCanvas (z-index: 2, pointer-events: none) └── svg#map-front (layers 13–32 + interaction, z-index: 3) ``` This requires moving layer `` elements between two SVG elements and syncing D3 transforms to both — deferred to Phase 2. **Z-index computation formula (MVP):** ```typescript function getLayerZIndex(anchorLayerId: string): number { const anchor = document.getElementById(anchorLayerId); if (!anchor) return 100; // Use the element's index in its parent's children as the z-index base const siblings = Array.from(anchor.parentElement?.children ?? []); const idx = siblings.indexOf(anchor); return idx > 0 ? idx : 100; } ``` ### Decision 4: D3 Zoom → WebGL Orthographic Camera Sync **Decision:** The sync formula from the existing `draw-relief-icons.ts` is extracted into a pure, testable function `buildCameraBounds(viewX, viewY, scale, graphWidth, graphHeight)` that returns `{left, right, top, bottom}` for the orthographic camera. **Derivation (documented in code):** ``` D3 applies transform: translate(viewX, viewY) scale(scale) to #viewbox This means: screen_point = map_point * scale + (viewX, viewY) Inverting: map_point = (screen_point - (viewX, viewY)) / scale Orthographic camera bounds (what map rectangle is visible on screen): left = -viewX / scale ← left edge of visible map right = (graphWidth - viewX) / scale ← right edge top = -viewY / scale ← top edge bottom = (graphHeight - viewY) / scale ← bottom edge Camera is configured with Y-down convention (top < bottom) to match SVG: new OrthographicCamera(left, right, top, bottom, -1, 1) where top < bottom (Y increases downward, SVG convention) ``` **Why this is testable:** `buildCameraBounds` takes only numbers and returns numbers. Tests inject mock `viewX/viewY/scale` values and assert exact output — no DOM or WebGL required. ### Decision 5: Visibility Toggle — GPU State Preservation **Decision:** `framework.setVisible(id, visible)` toggles the Three.js `Object3D.visible` property of the layer's registered group. The canvas element's `display` style is changed only when ALL registered layers are hidden. ```typescript setVisible(id: string, visible: boolean): void { const layer = this.layers.get(id); if (!layer) return; layer.group.visible = visible; // Only hide canvas if ALL layers are invisible (avoids GPU context loss) const anyVisible = [...this.layers.values()].some(l => l.group.visible); this.canvas.style.display = anyVisible ? "block" : "none"; if (visible) this.render(); } ``` **This replaces `undrawRelief`'s current behavior** which calls `renderer.dispose()`, `scene = null`, etc. — destroying GPU buffers on every hide. The framework never destroys buffers except on `framework.unregister(id)`. ### Decision 6: WebGL2 Detection and SVG Fallback **Decision:** Framework initialization calls `detectWebGL2()` which attempts `canvas.getContext('webgl2')`. On failure, the framework sets a `hasFallback = true` flag and the relief renderer falls back to `drawSvg()`. All framework methods become no-ops when in fallback mode. ```typescript function detectWebGL2(): boolean { const probe = document.createElement("canvas"); const ctx = probe.getContext("webgl2"); if (!ctx) return false; const ext = ctx.getExtension("WEBGL_lose_context"); ext?.loseContext(); return true; } ``` **Testable:** The detection function is exported and can be called with a mock canvas in Vitest. ### Decision 7: Frame Rendering — On-Demand, RAF-Coalesced **Decision:** The framework exposes a `requestRender()` method that coalesces calls within a single animation frame, preventing redundant GPU draws during rapid pan/zoom events. ```typescript private rafId: number | null = null; requestRender(): void { if (this.rafId !== null) return; this.rafId = requestAnimationFrame(() => { this.rafId = null; this.render(); }); } private render(): void { this.syncTransform(); this.renderer.render(this.scene, this.camera); } ``` This replaces `window.rerenderReliefIcons` which currently does the same RAF coalescing at the module level. ### Decision 8: ResizeObserver for Canvas Sizing **Decision:** The framework attaches a `ResizeObserver` to the `#map-container` element. On resize, it updates canvas dimensions and the orthographic camera aspect ratio, then re-renders. ```typescript private observeResize(): void { this.resizeObserver = new ResizeObserver(entries => { const { width, height } = entries[0].contentRect; this.renderer.setSize(width, height); this.requestRender(); }); this.resizeObserver.observe(this.container); } ``` --- ## 4. Implementation Patterns ### 4.1 Global Module Pattern (Mandatory) All TypeScript modules in `src/modules/` and `src/renderers/` follow the project's Global Module Pattern. The framework module must follow it exactly: ```typescript // src/modules/webgl-layer-framework.ts // 1. Global type declaration declare global { var WebGL2LayerFramework: WebGL2LayerFrameworkClass; } // 2. Class implementation class WebGL2LayerFrameworkClass { // ... } // 3. Window registration (LAST LINE) window.WebGL2LayerFramework = new WebGL2LayerFrameworkClass(); ``` ### 4.2 Module Import Pattern Add to `src/modules/index.ts` as a side-effect import: ```typescript import "./webgl-layer-framework"; ``` And `draw-relief-icons.ts` remains in `src/renderers/index.ts` — no change to import structure. ### 4.3 Function Naming Conventions | Pattern | Convention | Example | | ---------------------- | --------------------------- | ----------------------------------------------------- | | Framework class | `PascalCase + Class suffix` | `WebGL2LayerFrameworkClass` | | Window global | `PascalCase` | `window.WebGL2LayerFramework` | | Pure utility functions | `camelCase` | `buildCameraBounds`, `detectWebGL2`, `getLayerZIndex` | | Internal methods | `camelCase` | `syncTransform`, `observeResize`, `requestRender` | ### 4.4 TypeScript Type Declarations New types go in `src/types/global.ts`: ```typescript declare global { var WebGL2LayerFramework: import("../modules/webgl-layer-framework").WebGL2LayerFrameworkClass; var drawRelief: (type?: "svg" | "webGL", parentEl?: HTMLElement) => void; var undrawRelief: () => void; var rerenderReliefIcons: () => void; } ``` ### 4.5 Error Handling Philosophy - Framework init failures (WebGL2 unavailable): set `hasFallback = true`, log with `WARN` global, no throw - Missing DOM elements (e.g., `#map` not found on init): early return + `WARN` log - WebGL context loss mid-session: `renderer.forceContextRestore()` then `renderer.dispose()` + re-init on next draw call (preserves existing pattern from `draw-relief-icons.ts`) - Unit tests: pure functions throw `Error`s; framework class methods log and return for resilience ### 4.6 Test Patterns Unit tests co-located with source in `src/modules/`: ```typescript // src/modules/webgl-layer-framework.test.ts import {describe, it, expect, vi} from "vitest"; import {buildCameraBounds, detectWebGL2, getLayerZIndex} from "./webgl-layer-framework"; describe("buildCameraBounds", () => { it("returns correct bounds for identity transform", () => { // viewX=0, viewY=0, scale=1, 960x540 const b = buildCameraBounds(0, 0, 1, 960, 540); expect(b.left).toBe(0); expect(b.right).toBe(960); expect(b.top).toBe(0); expect(b.bottom).toBe(540); }); it("returns correct bounds at 2× zoom centered on origin", () => { const b = buildCameraBounds(0, 0, 2, 960, 540); expect(b.left).toBe(0); expect(b.right).toBe(480); expect(b.top).toBe(0); expect(b.bottom).toBe(270); }); it("returns correct bounds with pan offset", () => { const b = buildCameraBounds(-100, -50, 1, 960, 540); expect(b.left).toBe(100); expect(b.right).toBe(1060); }); }); describe("detectWebGL2", () => { it("returns false when getContext returns null", () => { const canvas = {getContext: () => null} as unknown as HTMLCanvasElement; expect(detectWebGL2(canvas)).toBe(false); }); }); ``` **Key testability rule:** Pure functions (`buildCameraBounds`, `detectWebGL2`, `getLayerZIndex`) are exported as named exports and tested without DOM/WebGL. The class itself is tested with stub canvases where needed. --- ## 5. Project Structure ### 5.1 Files Created ``` src/ modules/ webgl-layer-framework.ts ← NEW: Framework class (core deliverable) webgl-layer-framework.test.ts ← NEW: Unit tests (≥80% coverage target) renderers/ draw-relief-icons.ts ← MODIFIED: Refactored to use framework ``` ### 5.2 Files Modified ``` src/ modules/ index.ts ← ADD: import "./webgl-layer-framework" types/ global.ts ← ADD: WebGL2LayerFramework global declaration ``` ### 5.3 `webgl-layer-framework.ts` Internal Structure ```typescript // ─── Exports (for testability) ─────────────────────────────────────────────── export function detectWebGL2(probe?: HTMLCanvasElement): boolean; export function buildCameraBounds( viewX: number, viewY: number, scale: number, graphWidth: number, graphHeight: number ): {left: number; right: number; top: number; bottom: number}; export function getLayerZIndex(anchorLayerId: string): number; // ─── Types ─────────────────────────────────────────────────────────────────── export interface WebGLLayerConfig { id: string; anchorLayerId: string; renderOrder: number; setup: (scene: THREE.Scene) => void; dispose: (scene: THREE.Scene) => void; } interface RegisteredLayer { config: WebGLLayerConfig; group: THREE.Group; } // ─── Class ─────────────────────────────────────────────────────────────────── export class WebGL2LayerFrameworkClass { private canvas: HTMLCanvasElement | null = null; private renderer: THREE.WebGLRenderer | null = null; private camera: THREE.OrthographicCamera | null = null; private scene: THREE.Scene | null = null; private layers: Map = new Map(); private resizeObserver: ResizeObserver | null = null; private rafId: number | null = null; private container: HTMLElement | null = null; readonly hasFallback: boolean = false; // Public API init(containerId?: string): boolean; register(config: WebGLLayerConfig): boolean; unregister(id: string): void; setVisible(id: string, visible: boolean): void; requestRender(): void; syncTransform(): void; // Private private render(): void; private observeResize(): void; private ensureContainer(): HTMLElement | null; } // ─── Global Registration (MUST be last line) ───────────────────────────────── declare global { var WebGL2LayerFramework: WebGL2LayerFrameworkClass; } window.WebGL2LayerFramework = new WebGL2LayerFrameworkClass(); ``` ### 5.4 `draw-relief-icons.ts` Refactored Structure The module registers itself with the framework on load. Existing window globals (`drawRelief`, `undrawRelief`, `rerenderReliefIcons`) are preserved for backward compatibility with legacy `public/modules/` code that calls them. ```typescript // Internal: called by framework's setup callback function setupReliefLayer(scene: THREE.Scene): void; // Internal: rebuild geometry from pack.relief data function buildReliefScene(icons: ReliefIcon[]): void; // Internal: SVG fallback renderer function drawSvgRelief(icons: ReliefIcon[], parentEl: HTMLElement): void; // Public window globals (backward-compatible) window.drawRelief = (type = "webGL", parentEl = byId("terrain")) => { if (WebGL2LayerFramework.hasFallback || type === "svg") { drawSvgRelief(icons, parentEl); } else { buildReliefScene(icons); WebGL2LayerFramework.requestRender(); } }; window.undrawRelief = () => { // Clears geometry but does NOT dispose GPU resources disposeScene(); // removes meshes from scene, keeps renderer alive if (terrainEl) terrainEl.innerHTML = ""; }; window.rerenderReliefIcons = () => { WebGL2LayerFramework.requestRender(); }; ``` ### 5.5 DOM Structure After Framework Init ``` body div#map-container (NEW; position: relative; width: svgWidth; height: svgHeight) svg#map (MOVED inside container; position: absolute; inset: 0; z-index: 1) canvas#terrainCanvas (NEW; position: absolute; inset: 0; z-index: getLayerZIndex("terrain")+1; pointer-events: none; aria-hidden: true) ``` ### 5.6 Framework Initialization Sequence ``` 1. Framework module loaded (via src/modules/index.ts import) 2. window.WebGL2LayerFramework = new WebGL2LayerFrameworkClass() → sets hasFallback = !detectWebGL2() 3. draw-relief-icons.ts loaded (via src/renderers/index.ts import) → calls WebGL2LayerFramework.register({ id: "terrain", anchorLayerId: "terrain", ... }) → if hasFallback: register is a no-op, drawRelief uses SVG path 4. Main map generation completes → window.drawRelief() called by legacy JS → if WebGL: builds scene, requestRender() → next RAF → syncTransform + renderer.render → if SVG fallback: drawSvgRelief() 5. D3 zoom/pan events → window.rerenderReliefIcons() → framework.requestRender() 6. Layer visibility toggle (legacy JS) → window.undrawRelief() or window.drawRelief() → framework.setVisible("terrain", false/true) — NO GPU teardown ``` --- ## 6. Architecture Validation ### 6.1 FR Coverage Matrix | Requirement | Addressed By | Status | | ---------------------------------------------- | ----------------------------------------------------------------------- | --------------------------------------------------- | | FR1: Single WebGL2 context | `WebGL2LayerFrameworkClass` owns one `THREE.WebGLRenderer` | ✅ | | FR2: Canvas at correct z-index | `getLayerZIndex(anchorLayerId)` → canvas z-index | ✅ (MVP: above SVG) | | FR3: Register layer by anchor + callback | `framework.register(config)` | ✅ | | FR4: Layer registry | `layers: Map` | ✅ | | FR5: Sync to D3 zoom transform | `syncTransform()` reads `viewX, viewY, scale` globals | ✅ | | FR6: Update on D3 change | `requestRender()` called from `rerenderReliefIcons` | ✅ | | FR7: Map-space → WebGL clip coordinates | `buildCameraBounds()` formula | ✅ | | FR8: Toggle without GPU teardown | `setVisible()` → `group.visible` only | ✅ | | FR9: Resize canvas on viewport change | `ResizeObserver` on container | ✅ | | FR10: Recalculate z-index on layer reorder | `getLayerZIndex()` reads live DOM position | ✅ | | FR11: Dispose layer + GPU resources | `unregister(id)` → disposes GeometryBuffers, removes from scene | ✅ | | FR12: All relief icons in one draw call | Per-set `Mesh` with merged `BufferGeometry` (existing batched approach) | ✅ | | FR13: Icons at SVG-space coordinates | Camera in SVG pixel-space; icon positions in `pack.relief` unchanged | ✅ | | FR14: Scale with zoom and user setting | Camera bounds change with zoom; icon size uses `r.s` from relief data | ✅ | | FR15: Per-icon rotation | Rotation encoded in quad vertex positions during `buildSetMesh` | ⚠️ Verify rotation support in existing buildSetMesh | | FR16: Configurable opacity | `MeshBasicMaterial.opacity` + `transparent: true` | ✅ | | FR17: Re-render on terrain data change | `drawRelief()` calls `buildReliefScene()` + `requestRender()` | ✅ | | FR18: WebGL2 detection + fallback | `detectWebGL2()` → `hasFallback` flag | ✅ | | FR19: SVG fallback visually identical | Existing `drawSvg()` preserved unchanged | ✅ | | FR20: No pointer-event capture | `canvas.style.pointerEvents = "none"` | ✅ | | FR21: Existing Layers panel unchanged | `drawRelief`/`undrawRelief` window globals preserved | ✅ | | FR22: Register without z-index knowledge | `framework.register` derives z-index internally | ✅ | | FR23: Render callback receives D3 transform | `syncTransform()` reads globals; transforms available in RAF | ✅ | | FR24: Same visibility API for all layers | `framework.setVisible(id, bool)` uniform for all registered layers | ✅ | | FR25: Coordinate sync testable in isolation | `buildCameraBounds` is a pure exported function | ✅ | | FR26: Fallback detection testable | `detectWebGL2(probeCanvas)` accepts injectable canvas | ✅ | | FR27: Registration testable without real WebGL | `hasFallback = true` path is a no-op; stub renderers in tests | ✅ | **FR15 Note:** The existing `buildSetMesh` in `draw-relief-icons.ts` constructs static quads; rotation may not be applied. This must be verified and implemented (per-icon rotation via vertex transformation in `buildSetMesh`) before MVP ships. ### 6.2 NFR Compliance | NFR | Status | Implementation | | ------------------------------------------ | ---------- | ----------------------------------------------------------------------------------------- | | NFR-P1: <16ms @ 1k icons | Enabled by | Single-batch `BufferGeometry` per atlas set | | NFR-P2: <100ms @ 10k icons | Enabled by | Same batch approach; measure at implementation | | NFR-P3: Toggle <4ms | ✅ | `group.visible = false` is O(1) | | NFR-P4: Pan/zoom latency <8ms | ✅ | RAF-coalesced; `syncTransform()` is one matrix update | | NFR-P5: Init <200ms | Enabled by | Three.js renderer init is ~50–100ms | | NFR-P6: No GPU teardown on hide | ✅ | `setVisible` never calls `dispose()` | | NFR-C1: WebGL2 as sole gate | ✅ | `detectWebGL2()` uses `canvas.getContext('webgl2')` | | NFR-C2: Cross-browser visual parity | Enabled by | Three.js normalizes WebGL2 across browsers | | NFR-C3: Max 2 contexts | ✅ | Framework creates 1 context; globe creates 1 | | NFR-C4: Fallback when HW accel disabled | ✅ | `detectWebGL2()` returns false → SVG path | | NFR-M1: Framework unknown of layer content | ✅ | `setup/dispose` callbacks encapsulate all content | | NFR-M2: New layer = 1 `register()` call | ✅ | Confirmed by API design | | NFR-M3: Global Module Pattern | ✅ | `window.WebGL2LayerFramework = new ...` at bottom | | NFR-M4: Sync formula documented | ✅ | `buildCameraBounds` has full derivation in JSDoc | | NFR-M5: ≥80% test coverage | Target | Tests for `buildCameraBounds`, `detectWebGL2`, `getLayerZIndex`, `register`, `setVisible` | | NFR-B1: Tree-shaking Three.js | ✅ | Named imports only | | NFR-B2: ≤50KB bundle increase | ✅ | No new dependencies; framework code ~5KB | ### 6.3 Architecture Risks and Mitigations | Risk | Likelihood | Impact | Architecture Mitigation | | --------------------------------------------- | ---------- | ------ | ------------------------------------------------------------------------------------- | | D3 + WebGL coordinate offset at extreme zoom | Medium | High | `buildCameraBounds` is unit-tested at zoom 0.1–50; exact formula documented | | FR15: Rotation not in existing `buildSetMesh` | High | Medium | Flag as pre-MVP verification item; add rotation attribute if missing | | MVP z-ordering: canvas above SVG | High | Medium | Accepted tradeoff; documented; Phase 2 DOM-split design provided | | `undrawRelief` callers expect full cleanup | Low | Low | Preserve `undrawRelief` signature; change internals only (no GPU teardown) | | Context loss mid-session | Low | High | Framework inherits existing `forceContextRestore` pattern from `draw-relief-icons.ts` | | `will-change: transform` memory overhead | Low | Low | Apply only during active zoom/pan; remove after with timing debounce | ### 6.4 Decision Coherence Check | Decision Pair | Compatible? | Note | | ------------------------------------------------------------------- | ----------- | ------------------------------------------------------------------------------ | | Single context (D1) + Layer registry (D2) | ✅ | `renderOrder` on `THREE.Group` within shared scene | | MVP z-index above SVG (D3) + pointer-events:none (D3) | ✅ | Interaction preserved regardless of z-stack | | Camera sync using globals (D4) + testability (FR25) | ✅ | `buildCameraBounds` is pure; globals are injected in tests | | No GPU teardown (D5) + `undrawRelief` backward compat (section 5.4) | ✅ | `undrawRelief` calls `disposeScene()` (geometry only) not `renderer.dispose()` | | On-demand RAF render (D7) + ResizeObserver (D8) | ✅ | Both call `requestRender()` which coalesces to one RAF | --- ## 7. Implementation Guidance for AI Agents When implementing this architecture, follow these rules precisely: ### MUST DO 1. **Framework module registers first** — `src/modules/index.ts` import must appear before renderer imports 2. **`window.WebGL2LayerFramework = new WebGL2LayerFrameworkClass()` is the last line** of the framework module 3. **Export `buildCameraBounds`, `detectWebGL2`, `getLayerZIndex`** as named exports — tests depend on them 4. **`setVisible(id, false)` NEVER calls `renderer.dispose()`** — only sets `group.visible = false` 5. **Canvas element gets**: `pointer-events: none; aria-hidden: true; position: absolute; inset: 0` 6. **Fallback path**: when `hasFallback === true`, all framework methods return silently; `drawRelief` calls `drawSvgRelief` 7. **`window.drawRelief`, `window.undrawRelief`, `window.rerenderReliefIcons`** must remain as window globals (legacy JS calls them) 8. **Verify FR15** (per-icon rotation) in `buildSetMesh` before MVP — add rotation support if missing ### MUST NOT DO 1. **Do NOT** create a second `THREE.WebGLRenderer` — framework owns the only map renderer 2. **Do NOT** move layer `` elements between SVG elements — DOM-split is Phase 2 3. **Do NOT** add any new entries to `public/modules/` — all new code is in `src/` 4. **Do NOT** break the `window.drawRelief(type, parentEl)` signature — legacy callers 5. **Do NOT** use `isNaN()` — use `Number.isNaN()`; or `parseInt()` without radix 6. **Do NOT** import Three.js as `import * as THREE from "three"` — use named imports only ### Verification Checklist - [ ] `npm run lint` passes with zero errors - [ ] `npx vitest run` passes all tests - [ ] `buildCameraBounds` tests pass at zoom 0.1, 1, 2, 10, 50 - [ ] `detectWebGL2` test passes with null-returning mock canvas - [ ] Layer registration test passes with stub scene - [ ] `setVisible(false)` test confirms GPU buffers remain allocated - [ ] Visual: relief icons render at correct coordinate positions - [ ] Visual: toggling terrain layer on/off preserves icon positions - [ ] Visual: pan/zoom redraws canvas correctly in sync with SVG --- ## 8. Next Steps With this architecture complete, the recommended implementation sequence is: **Story 1:** Create `webgl-layer-framework.ts` with exported pure functions and stub class methods; write all unit tests first (TDD). **Story 2:** Implement `WebGL2LayerFrameworkClass` core: `init()`, `detectWebGL2()`, canvas creation, `#map-container` wrapper, `ResizeObserver`. **Story 3:** Implement `register()`, `unregister()`, `setVisible()`, `requestRender()`, `syncTransform()`. **Story 4:** Refactor `draw-relief-icons.ts` to use `WebGL2LayerFramework.register()` and remove the module-level renderer state. Verify FR15 rotation support. **Story 5:** Integration testing — generate map, toggle terrain layer, pan/zoom, verify visual output matches SVG baseline. **Story 6:** Bundle size audit — verify Three.js tree-shaking, confirm ≤50KB gzipped delta.