2nd/10_Wiki/Topics/Frontend/OffscreenCanvas Safari 제약 사항.md

---
id: wiki-2026-0508-offscreencanvas-safari-제약-사항
title: OffscreenCanvas Safari 제약 사항
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [OffscreenCanvas Safari, Safari OffscreenCanvas Limits, OffscreenCanvas WebKit]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [canvas, safari, webkit, browser-compat, offscreencanvas]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: JavaScript
  framework: Browser
---

# OffscreenCanvas Safari 제약 사항

## 매 한 줄
> **"매 Safari OffscreenCanvas 의 partial support"**. Safari 16.4+ 매 2D context 만 지원, WebGL/WebGPU OffscreenCanvas 는 매 17.0+ 부터 점진. iOS Safari 매 worker context 의 transferControlToOffscreen 동작 차이 + Background tab throttling 매 강함. 2026 기준 Chrome/Firefox 와 매 feature parity 거의 도달, 매 edge case 잔존.

## 매 핵심

### 매 Safari 의 timeline
- Safari **16.4** (2023): OffscreenCanvas 2D context.
- Safari **17.0** (2023): WebGL OffscreenCanvas in worker.
- Safari **18.x** (2025): WebGPU OffscreenCanvas (experimental flag).
- iOS Safari 매 desktop 의 1-2 minor 늦게 따라옴.

### 매 주요 제약
- **Background tab throttling**: 매 worker animation frame 매 1Hz 까지 drop (Chrome/Firefox 보다 강한 throttle).
- **Memory pressure**: iOS 매 background tab 의 OffscreenCanvas 즉시 release — 매 reload 후 lost-context 처리 필요.
- **ImageBitmap transfer**: 매 large bitmap 의 `transferToImageBitmap` 매 occasional jank — Chrome 보다 느림.
- **WebGL2 context loss**: iOS Safari 매 page-hide 즉시 lost.
- **Worker termination**: 매 page navigation 시 Safari 매 worker cleanup 의 timing 차이.

### 매 응용
1. Image processing (Photopea-style) — main thread 차단 회피.
2. Chart rendering (Plotly, Apache ECharts worker mode).
3. Game offscreen rendering.
4. PDF/canvas thumbnail 생성.

## 💻 패턴

### Feature detection (매 graceful fallback)
```ts
function supportsOffscreen2D(): boolean {
  return typeof OffscreenCanvas !== "undefined"
    && typeof new OffscreenCanvas(1, 1).getContext === "function";
}

function supportsOffscreenWebGL(): boolean {
  if (!supportsOffscreen2D()) return false;
  try {
    return !!new OffscreenCanvas(1, 1).getContext("webgl2");
  } catch {
    return false;
  }
}
```

### Safari-safe transferControlToOffscreen
```ts
const canvas = document.querySelector("canvas")!;
let offscreen: OffscreenCanvas | null = null;
let worker: Worker | null = null;

function start() {
  if (!supportsOffscreen2D()) {
    renderOnMainThread(canvas);
    return;
  }
  offscreen = canvas.transferControlToOffscreen();
  worker = new Worker(new URL("./renderer.worker.ts", import.meta.url), { type: "module" });
  worker.postMessage({ type: "init", canvas: offscreen }, [offscreen]);
}
```

### Lost context handling (매 iOS 필수)
```ts
// renderer.worker.ts
self.addEventListener("message", (e) => {
  if (e.data.type === "init") {
    const canvas = e.data.canvas as OffscreenCanvas;
    let gl = canvas.getContext("webgl2");

    canvas.addEventListener?.("webglcontextlost", (ev) => {
      ev.preventDefault();
      console.warn("WebGL context lost (Safari background?)");
    });
    canvas.addEventListener?.("webglcontextrestored", () => {
      gl = canvas.getContext("webgl2");
      reinitScene();
    });
  }
});
```

### Visibility-aware rendering (매 throttle 회피)
```ts
let isVisible = !document.hidden;
document.addEventListener("visibilitychange", () => {
  isVisible = !document.hidden;
  worker?.postMessage({ type: "visibility", visible: isVisible });
});

// In worker:
let raf: number;
function loop() {
  draw();
  raf = self.requestAnimationFrame?.(loop) ?? setTimeout(loop, 16);
}
self.addEventListener("message", (e) => {
  if (e.data.type === "visibility") {
    if (e.data.visible) loop();
    else cancelAnimationFrame?.(raf);
  }
});
```

### ImageBitmap chunked transfer (매 Safari jank 회피)
```ts
async function processInChunks(blob: Blob, chunkSize = 1024) {
  const bitmap = await createImageBitmap(blob);
  for (let y = 0; y < bitmap.height; y += chunkSize) {
    const chunk = await createImageBitmap(bitmap, 0, y, bitmap.width, Math.min(chunkSize, bitmap.height - y));
    worker.postMessage({ type: "chunk", chunk, y }, [chunk]);
    await new Promise(r => setTimeout(r, 0)); // yield to UI
  }
  bitmap.close();
}
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| 2D rendering, modern browser | OffscreenCanvas + worker |
| WebGL on iOS Safari | feature-detect + main-thread fallback |
| Long-running animation | visibilitychange 의 pause |
| Large bitmap | chunked transfer |
| Production, broad support | progressive enhancement, never required |

**기본값**: feature-detect + 매 main-thread fallback path 매 항상 유지.

## 🔗 Graph
- 부모: [[Web-Workers]] · [[Canvas-API]]
- 변형: [[OffscreenCanvas]] · [[ImageBitmap]]
- 응용: [[Image-Processing]] · [[Chart-Rendering]] · [[WebGL]]
- Adjacent: [[Browser-Compatibility]] · [[Safari-Quirks]] · [[WebGPU]]

## 🤖 LLM 활용
**언제**: heavy canvas 작업의 worker 위임 + Safari/iOS target.
**언제 X**: simple animation / 매 main thread 충분.

## ❌ 안티패턴
- **No fallback**: 매 OffscreenCanvas 의 mandatory 가정 — 매 old Safari user crash.
- **Ignore context lost**: 매 iOS background → resume 후 매 black canvas.
- **Throttle 무시**: 매 background tab 의 animation 매 progress 가정 — 매 desync.
- **Sync transferToImageBitmap loop**: 매 매 frame transfer — 매 GC pressure.

## 🧪 검증 / 중복
- Verified (caniuse OffscreenCanvas, WebKit blog 16.4/17.0/18, MDN OffscreenCanvas).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — Safari timeline, throttling/lost-context/chunked-transfer 패턴 |