193 lines
6.3 KiB
JavaScript
193 lines
6.3 KiB
JavaScript
/**
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* 文件功能：聊天室雷电特效
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*
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* 使用递归分叉算法叠加云层闪光、主闪电、余辉残影，
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* 在聊天室中模拟更有压迫感的雷暴闪电效果。
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*/
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const LightningEffect = (() => {
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/**
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* 递归绘制闪电路径（分裂算法）
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*
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* @param {CanvasRenderingContext2D} ctx
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* @param {number} x1 起点 x
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* @param {number} y1 起点 y
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* @param {number} x2 终点 x
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* @param {number} y2 终点 y
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* @param {number} depth 当前递归深度（控制分叉层数）
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* @param {number} width 线条宽度
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*/
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function _drawBolt(ctx, x1, y1, x2, y2, depth, width) {
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if (depth <= 0) return;
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// 中点随机偏移（越深层偏移越小，产生流畅感）
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const mx = (x1 + x2) / 2 + (Math.random() - 0.5) * 80 * depth;
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const my = (y1 + y2) / 2 + (Math.random() - 0.5) * 20 * depth;
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const glow = ctx.createLinearGradient(x1, y1, x2, y2);
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glow.addColorStop(0, "rgba(200, 220, 255, 0.9)");
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glow.addColorStop(1, "rgba(150, 180, 255, 0.6)");
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ctx.save();
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ctx.strokeStyle = glow;
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ctx.lineWidth = width;
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ctx.shadowColor = "#aaccff";
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ctx.shadowBlur = 18;
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ctx.beginPath();
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ctx.moveTo(x1, y1);
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ctx.quadraticCurveTo(mx, my, x2, y2);
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ctx.stroke();
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ctx.restore();
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// 递归绘制两段子路径
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_drawBolt(ctx, x1, y1, mx, my, depth - 1, width * 0.65);
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_drawBolt(ctx, mx, my, x2, y2, depth - 1, width * 0.65);
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// 随机在中途分叉一条小支路（50% 概率）
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if (depth > 1 && Math.random() > 0.5) {
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const bx = mx + (Math.random() - 0.5) * 120;
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const by = my + Math.random() * 80 + 40;
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_drawBolt(ctx, mx, my, bx, by, depth - 2, width * 0.4);
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}
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}
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/**
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* 绘制顶部乌云压光层，让闪电更有“雷暴”氛围。
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*
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* @param {HTMLCanvasElement} canvas
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* @param {CanvasRenderingContext2D} ctx
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*/
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function _drawStormGlow(canvas, ctx) {
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const w = canvas.width;
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const h = canvas.height;
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const sky = ctx.createLinearGradient(0, 0, 0, h * 0.8);
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sky.addColorStop(0, "rgba(7, 18, 38, 0.34)");
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sky.addColorStop(0.45, "rgba(15, 23, 42, 0.18)");
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sky.addColorStop(1, "rgba(15, 23, 42, 0)");
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ctx.fillStyle = sky;
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ctx.fillRect(0, 0, w, h);
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for (let i = 0; i < 3; i++) {
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const cloudX = w * (0.12 + Math.random() * 0.76);
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const cloudY = h * (0.05 + Math.random() * 0.22);
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const cloudR = 120 + Math.random() * 160;
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const cloud = ctx.createRadialGradient(cloudX, cloudY, 0, cloudX, cloudY, cloudR);
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cloud.addColorStop(0, "rgba(210, 226, 255, 0.18)");
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cloud.addColorStop(0.38, "rgba(168, 196, 255, 0.1)");
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cloud.addColorStop(1, "rgba(168, 196, 255, 0)");
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ctx.fillStyle = cloud;
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ctx.beginPath();
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ctx.arc(cloudX, cloudY, cloudR, 0, Math.PI * 2);
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ctx.fill();
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}
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}
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/**
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* 渲染一次闪电 + 闪屏效果。
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*
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* @param {HTMLCanvasElement} canvas
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* @param {CanvasRenderingContext2D} ctx
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*/
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function _flash(canvas, ctx) {
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const w = canvas.width;
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const h = canvas.height;
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// 清空画布
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ctx.clearRect(0, 0, w, h);
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// 先铺一层压暗天空，再叠加闪白，让明暗反差更明显。
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_drawStormGlow(canvas, ctx);
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ctx.fillStyle = "rgba(228, 239, 255, 0.46)";
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ctx.fillRect(0, 0, w, h);
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// 绘制 1-3 条主闪电，并给出明显的白色核心线。
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const boltCount = Math.floor(Math.random() * 3) + 1;
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for (let i = 0; i < boltCount; i++) {
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const x1 = w * (0.12 + Math.random() * 0.76);
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const y1 = 0;
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const x2 = x1 + (Math.random() - 0.5) * 360;
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const y2 = h * (0.55 + Math.random() * 0.35);
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const width = 3.6 + Math.random() * 1.8;
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_drawBolt(ctx, x1, y1, x2, y2, 5, width);
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ctx.save();
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ctx.strokeStyle = "rgba(255,255,255,0.92)";
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ctx.lineWidth = Math.max(1.2, width * 0.34);
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ctx.shadowColor = "rgba(255,255,255,0.95)";
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ctx.shadowBlur = 22;
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ctx.beginPath();
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ctx.moveTo(x1, y1);
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ctx.lineTo(x2, y2);
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ctx.stroke();
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ctx.restore();
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}
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// 短促残影：闪电消失后保留一层很淡的余辉，避免“闪一下就没了”。
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setTimeout(() => {
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ctx.clearRect(0, 0, w, h);
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_drawStormGlow(canvas, ctx);
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ctx.fillStyle = "rgba(185, 205, 255, 0.12)";
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ctx.fillRect(0, 0, w, h);
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}, 90);
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setTimeout(() => {
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ctx.clearRect(0, 0, w, h);
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}, 190);
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}
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/**
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* 启动雷电特效
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*
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* @param {HTMLCanvasElement} canvas 全屏 Canvas
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* @param {Function} onEnd 特效结束回调
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*/
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function start(canvas, onEnd) {
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const ctx = canvas.getContext("2d");
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const FLASHES = 9;
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const DURATION = 7600;
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let count = 0;
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let finished = false;
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/**
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* 统一结束特效，避免多次触发 onEnd。
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*/
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function finish() {
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if (finished) {
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return;
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}
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finished = true;
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ctx.clearRect(0, 0, canvas.width, canvas.height);
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onEnd();
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}
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// 间隔不规则触发多次闪电（模拟真实雷电节奏）
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function nextFlash() {
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if (count >= FLASHES) {
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setTimeout(() => {
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finish();
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}, 520);
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return;
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}
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_flash(canvas, ctx);
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count++;
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// 让雷电节奏有“成组爆发”的感觉：有时连续两下，有时间隔更久。
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const delay = Math.random() > 0.65
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? 140 + Math.random() * 140
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: 420 + Math.random() * 520;
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setTimeout(nextFlash, delay);
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}
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// 短暂延迟后开始第一次闪电
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setTimeout(nextFlash, 300);
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// 安全兜底：超时强制结束
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setTimeout(() => {
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finish();
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}, DURATION + 500);
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}
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return { start };
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})();
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