feat(P4B.T4): WhiteboardCanvas — pen/eraser drawing engine

2026-05-16 20:27:09 +02:00
parent 2243c646ac
commit be6f5b9c6f
1 changed files with 142 additions and 0 deletions
@@ -0,0 +1,142 @@
+import { useEffect, useRef, useState } from 'react';
+
+import type { WhiteboardStroke } from '@chat-app/shared/chat';
+
+export type WhiteboardTool = 'pen' | 'eraser';
+export type WhiteboardColor = '#000000' | '#ef4444' | '#3b82f6' | '#22c55e' | '#facc15' | '#a855f7';
+export type WhiteboardWidth = 2 | 4 | 8;
+
+export interface WhiteboardStrokePayload {
+  tool: WhiteboardTool;
+  color: WhiteboardColor;
+  width: WhiteboardWidth;
+  // [x, y, t-ms-since-stroke-start]
+  points: Array<[number, number, number]>;
+}
+
+interface Props {
+  strokes: WhiteboardStroke[];
+  tool: WhiteboardTool;
+  color: WhiteboardColor;
+  width: WhiteboardWidth;
+  onStroke: (payload: WhiteboardStrokePayload) => void;
+  logicalWidth?: number;
+  logicalHeight?: number;
+}
+
+const DEFAULT_LOGICAL_W = 1280;
+const DEFAULT_LOGICAL_H = 720;
+
+export function WhiteboardCanvas({
+  strokes,
+  tool,
+  color,
+  width,
+  onStroke,
+  logicalWidth = DEFAULT_LOGICAL_W,
+  logicalHeight = DEFAULT_LOGICAL_H,
+}: Props) {
+  const canvasRef = useRef<HTMLCanvasElement | null>(null);
+  const draftRef = useRef<WhiteboardStrokePayload | null>(null);
+  const strokeStartRef = useRef<number>(0);
+  const [, forceTick] = useState(0);
+
+  useEffect(() => {
+    const cv = canvasRef.current;
+    if (!cv) return;
+    cv.width = logicalWidth;
+    cv.height = logicalHeight;
+    const ctx = cv.getContext('2d');
+    if (!ctx) return;
+    ctx.fillStyle = '#ffffff';
+    ctx.fillRect(0, 0, cv.width, cv.height);
+    for (const s of strokes) {
+      const payload = s.strokeJson as Partial<WhiteboardStrokePayload> | null;
+      if (payload) renderStroke(ctx, payload);
+    }
+    if (draftRef.current) renderStroke(ctx, draftRef.current);
+  });
+
+  function canvasPoint(e: React.PointerEvent<HTMLCanvasElement>): [number, number] {
+    const cv = canvasRef.current!;
+    const rect = cv.getBoundingClientRect();
+    const scaleX = cv.width / rect.width;
+    const scaleY = cv.height / rect.height;
+    return [(e.clientX - rect.left) * scaleX, (e.clientY - rect.top) * scaleY];
+  }
+
+  const handlePointerDown = (e: React.PointerEvent<HTMLCanvasElement>) => {
+    const cv = canvasRef.current;
+    if (!cv) return;
+    cv.setPointerCapture(e.pointerId);
+    const [x, y] = canvasPoint(e);
+    strokeStartRef.current = Date.now();
+    draftRef.current = {
+      tool,
+      color,
+      width,
+      points: [[x, y, 0]],
+    };
+    forceTick((n) => n + 1);
+  };
+
+  const handlePointerMove = (e: React.PointerEvent<HTMLCanvasElement>) => {
+    if (!draftRef.current) return;
+    const [x, y] = canvasPoint(e);
+    draftRef.current.points.push([x, y, Date.now() - strokeStartRef.current]);
+    forceTick((n) => n + 1);
+  };
+
+  const handlePointerUp = (e: React.PointerEvent<HTMLCanvasElement>) => {
+    const cv = canvasRef.current;
+    if (cv && cv.hasPointerCapture(e.pointerId)) cv.releasePointerCapture(e.pointerId);
+    const draft = draftRef.current;
+    draftRef.current = null;
+    if (!draft) return;
+    if (draft.points.length < 2) {
+      forceTick((n) => n + 1);
+      return;
+    }
+    onStroke(draft);
+    forceTick((n) => n + 1);
+  };
+
+  return (
+    <canvas
+      ref={canvasRef}
+      onPointerDown={handlePointerDown}
+      onPointerMove={handlePointerMove}
+      onPointerUp={handlePointerUp}
+      onPointerLeave={handlePointerUp}
+      className="block max-h-full max-w-full cursor-crosshair touch-none rounded-lg border border-line/40 bg-white shadow-2xl"
+      style={{ aspectRatio: logicalWidth + ' / ' + logicalHeight, width: '100%' }}
+    />
+  );
+}
+
+function renderStroke(
+  ctx: CanvasRenderingContext2D,
+  s: Partial<WhiteboardStrokePayload>,
+): void {
+  const points = Array.isArray(s.points) ? s.points : null;
+  if (!points || points.length < 1) return;
+
+  ctx.save();
+  ctx.lineCap = 'round';
+  ctx.lineJoin = 'round';
+  ctx.lineWidth = typeof s.width === 'number' ? s.width : 4;
+  if (s.tool === 'eraser') {
+    ctx.strokeStyle = '#ffffff';
+    ctx.lineWidth = Math.max(8, (typeof s.width === 'number' ? s.width : 4) * 4);
+  } else {
+    ctx.strokeStyle = typeof s.color === 'string' ? s.color : '#000000';
+  }
+
+  ctx.beginPath();
+  ctx.moveTo(points[0]![0], points[0]![1]);
+  for (let i = 1; i < points.length; i++) {
+    ctx.lineTo(points[i]![0], points[i]![1]);
+  }
+  ctx.stroke();
+  ctx.restore();
+}