refactor(topics): 멀티 에이전트용 지식 재편 — _Common(공통 기본기) + Domain_* 구조
에이전트 8종(대화형/프로그래머 C·S/디자이너/설계자/기획자/QA/PD/PM)에게 [공통 기본 능력 + 롤별 Specialty] 2층으로 지식을 주입하기 위한 재분류. 문서 내용·포맷은 무수정, 폴더 이동만 (6,372개 문서 수 보존 확인). - Topic_Programming → Domain_Programming (내부 구조 보존) - Topic_Graphic → Domain_Design - Topic_Business → Domain_Product - Topic_General → Domain_General - _Common 신설: Math(구 Topic_Math_Specialty), Reasoning(구 General/From_Thinking & Reasoning), Reasoning_Creativity(구 General/From_창의성), Communication(Poetic_Blog_Writing + From_writing) - 타 도메인의 From_* 폴더는 유지 (출처 표기일 뿐, 이미 도메인에 맞게 분류된 문서) - 빈 폴더 정리 (memory/procedures) - 에이전트→폴더 매핑은 workspace의 .astra/agent-knowledge-map.json (9개 에이전트) Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Antigravity Agent
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---
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id: html-canvas
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title: "HTML Canvas"
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category: "Frontend"
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status: "draft"
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verification_status: "conceptual"
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canonical_id: ""
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aliases: ["canvas element", "HTML5 Canvas", "<canvas>", "2d context", "getContext"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.90
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created_at: 2026-06-23
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updated_at: 2026-06-23
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review_reason: ""
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merge_history: []
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tags: ["html", "web", "frontend", "canvas", "graphics", "html5", "w3schools"]
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raw_sources: ["https://www.w3schools.com/html/html5_canvas.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[HTML Canvas]]
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## 🎯 한 줄 통찰 (One-line insight)
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The HTML `<canvas>` element is an empty container for graphics; all actual drawing — lines, shapes, text, gradients, images — is done at runtime with JavaScript via a 2D drawing context. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **`<canvas>` is just a container** — it has no drawing ability of its own; JavaScript draws into it. [S1]
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- **It can draw** paths, boxes, circles, text, and images, and is supported by all major browsers. [S1]
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- **Always set `id`, `width`, and `height`** — the `id` lets scripts reference it; `width`/`height` set its drawable size. A border style makes the otherwise invisible canvas visible. [S1]
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- **The 2D context is the drawing surface** — obtain it with `canvas.getContext("2d")`; all drawing methods (`moveTo`, `lineTo`, `arc`, `fillText`, etc.) are called on that context object. [S1]
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- **Gradients** — created with `createLinearGradient(...)` or `createRadialGradient(...)`, then color stops are added and the gradient is assigned to `fillStyle`. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Setup pattern** — `getElementById` → `getContext("2d")` → draw. [S1]
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- **Path/line pattern** — `moveTo(x,y)` then `lineTo(x,y)` then `stroke()`. [S1]
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- **Circle pattern** — `beginPath()` → `arc(x,y,r,0,2*Math.PI)` → `stroke()`. [S1]
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- **Text pattern** — set `font`, then `fillText(...)` (filled) or `strokeText(...)` (outline). [S1]
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- **Gradient fill pattern** — create gradient → `addColorStop()` → assign to `fillStyle` → `fillRect(...)`. [S1]
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- **Image pattern** — `drawImage(img, x, y)` paints an existing image element. [S1]
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## 📖 세부 내용 (Details)
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**What is HTML Canvas?** The HTML `<canvas>` element is used to draw graphics, on the fly, via JavaScript. The `<canvas>` element is only a container for graphics — you must use JavaScript to actually draw. Canvas can draw paths, boxes, circles, text, and add images, and it works in all major browsers. [S1]
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**The Canvas element** — a canvas is a rectangular area on an HTML page, specified with the `<canvas>` element. Always specify an `id` (to refer to it in a script) and a `width` and `height` (to define its size). To add a border, use the `style` attribute: [S1]
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```html
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<canvas id="myCanvas" width="200" height="100" style="border:1px solid #000000;">
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</canvas>
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```
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**Draw a Line** — [S1]
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```html
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<script>
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var c = document.getElementById("myCanvas");
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var ctx = c.getContext("2d");
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ctx.moveTo(0, 0);
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ctx.lineTo(200, 100);
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ctx.stroke();
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</script>
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```
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**Draw a Circle** — [S1]
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```html
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<script>
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var c = document.getElementById("myCanvas");
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var ctx = c.getContext("2d");
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ctx.beginPath();
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ctx.arc(95, 50, 40, 0, 2 * Math.PI);
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ctx.stroke();
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</script>
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```
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**Draw Text** — set the font and use `fillText(text, x, y)`: [S1]
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```html
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<script>
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var c = document.getElementById("myCanvas");
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var ctx = c.getContext("2d");
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ctx.font = "30px Arial";
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ctx.fillText("Hello World", 10, 50);
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</script>
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```
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**Stroke Text** — set the font and use `strokeText(text, x, y)` for outlined text: [S1]
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```html
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<script>
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var c = document.getElementById("myCanvas");
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var ctx = c.getContext("2d");
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ctx.font = "30px Arial";
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ctx.strokeText("Hello World", 10, 50);
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</script>
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```
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**Draw Linear Gradient** — gradients can fill rectangles, circles, lines, text, etc. Create a linear gradient, add color stops, set it as the fill style, and fill a rectangle: [S1]
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```html
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<script>
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var c = document.getElementById("myCanvas");
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var ctx = c.getContext("2d");
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// Create gradient
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var grd = ctx.createLinearGradient(0, 0, 200, 0);
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grd.addColorStop(0, "red");
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grd.addColorStop(1, "white");
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// Fill with gradient
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ctx.fillStyle = grd;
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ctx.fillRect(10, 10, 150, 80);
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</script>
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```
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**Draw Radial Gradient** — [S1]
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```html
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<script>
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var c = document.getElementById("myCanvas");
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var ctx = c.getContext("2d");
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// Create gradient
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var grd = ctx.createRadialGradient(75, 50, 5, 90, 60, 100);
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grd.addColorStop(0, "red");
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grd.addColorStop(1, "white");
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// Fill with gradient
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ctx.fillStyle = grd;
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ctx.fillRect(10, 10, 150, 80);
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</script>
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```
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**Draw Image** — use `drawImage(image, x, y)` to paint an existing image element onto the canvas: [S1]
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```html
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<script>
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var c = document.getElementById("myCanvas");
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var ctx = c.getContext("2d");
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var img = document.getElementById("scream");
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ctx.drawImage(img, 10, 10);
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</script>
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```
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## 🛠️ 적용 사례 (Applied in summary)
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The examples above are the canonical applied uses: drawing a diagonal line, a circle, filled and outlined text, linear and radial gradient-filled rectangles, and painting an existing image into the canvas. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Canvas setup + draw a line (HTML + JavaScript):
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```html
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<canvas id="myCanvas" width="200" height="100" style="border:1px solid #000000;"></canvas>
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<script>
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var c = document.getElementById("myCanvas");
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var ctx = c.getContext("2d");
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ctx.moveTo(0, 0);
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ctx.lineTo(200, 100);
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ctx.stroke();
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</script>
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```
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Circle (JavaScript):
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```javascript
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ctx.beginPath();
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ctx.arc(95, 50, 40, 0, 2 * Math.PI);
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ctx.stroke();
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```
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Linear gradient fill (JavaScript):
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```javascript
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var grd = ctx.createLinearGradient(0, 0, 200, 0);
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grd.addColorStop(0, "red");
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grd.addColorStop(1, "white");
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ctx.fillStyle = grd;
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ctx.fillRect(10, 10, 150, 80);
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```
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## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
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The source frames Canvas in contrast to SVG: SVG describes 2D graphics in XML, while Canvas draws 2D graphics on the fly with JavaScript. In Canvas, once a graphic is drawn it is "forgotten" by the browser (immediate-mode, pixel/bitmap output), whereas in SVG each drawn shape is remembered as an object and re-rendered on change (retained-mode). Canvas is resolution dependent, has no built-in event handlers, has poor text rendering, but can save the result as a .png/.jpg image and is well suited to graphic-intensive games. See [[HTML SVG]] for the complementary trade-offs. [S1]
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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No contradictions found in the source. Note the immediate-mode nature: Canvas does not retain a scene graph, so anything that must be interactive or re-rendered on data change has to be redrawn manually by your script. [S1]
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## ✅ 검증 상태 및 신뢰도
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- **상태:** draft
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- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
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- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
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- **신뢰 점수:** 0.90
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- **중복 검사 결과:** 신규 생성 (New discovery)
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## 🔗 지식 그래프 (Knowledge Graph)
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- **상위/루트:** [[HTML Tutorial]]
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- **관련 개념:** [[HTML SVG]], [[HTML Graphics]], [[HTML Media]], [[HTML5]]
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- **참조 맥락:** Referenced when rendering dynamic, script-driven, pixel-based graphics such as charts, visualizations, or games.
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## 📚 출처 (Sources)
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- [S1] W3Schools — HTML Canvas — https://www.w3schools.com/html/html5_canvas.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "HTML Canvas" page (Astra wiki-curation, P-Reinforce v3.1 format).
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