Buffer Update

<!--
  说明：二百个顶点连成一条波浪线，每帧改写顶点位置并重新上传，形成流动效果
  核心逻辑：Buffer.write 覆盖整段顶点数据，Model 的拓扑设为 line-strip
  依赖：@luma.gl/core 9.4.2、webgl、shadertools、engine · jsDelivr CDN（UMD）
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>缓冲区数据更新</title>
<style>
  html,body{height:100%;margin:0;background:#0d1117}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif;color:#e6e8ec}
  .bar{flex:0 0 auto;padding:8px 12px;background:#161b22;border-bottom:1px solid #252c36;
       display:flex;gap:12px;align-items:center;font-size:12px;color:#8b93a1;flex-wrap:wrap}
  .bar b{color:#58a6ff;font-weight:600}
  .bar input[type=range]{width:120px;accent-color:#4f9ef8}
  .bar button{font:inherit;font-size:12px;padding:4px 10px;border-radius:5px;cursor:pointer;
       border:1px solid #303845;background:#1d2531;color:#c8d2e0}
  .bar button:hover{background:#253040}
  .bar .sp{flex:1 1 auto}
  .wrap{position:relative;flex:1 1 auto;min-height:0;display:flex}
  #cv{flex:1 1 auto;min-height:0;width:100%;display:block}
  #err{position:absolute;left:0;right:0;top:0;padding:16px;color:#ff9d85;
       font:12px/1.7 ui-monospace,Consolas,monospace;white-space:pre-wrap;display:none}
</style>
</head>
<body>
<div class="bar">
  <span>顶点 <b id="n">200</b></span>
  <span>上传 <b id="cnt">0</b> 次</span>
  <label>振幅 <input type="range" id="amp" min="0.1" max="0.6" step="0.02" value="0.35"></label>
  <label>频率 <input type="range" id="freq" min="2" max="12" step="0.5" value="6"></label>
  <button id="pause">暂停</button>
  <span class="sp"></span>
  <span>line-strip · 每帧整体覆盖缓冲区</span>
</div>
<div class="wrap">
  <canvas id="cv"></canvas>
  <div id="err"></div>
</div>

<script src="https://cdn.jsdelivr.net/npm/@luma.gl/core@9.4.2/dist/dist.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/@luma.gl/webgl@9.4.2/dist/dist.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/@luma.gl/shadertools@9.4.2/dist/dist.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/@luma.gl/engine@9.4.2/dist/dist.min.js"></script>
<script>
(function () {
  'use strict';

  var cv = document.getElementById('cv');
  var errBox = document.getElementById('err');

  function fail(msg) {
    errBox.style.display = 'block';
    errBox.textContent = '运行失败：' + msg;
  }

  if (!window.luma || !luma.Model || !luma.AnimationLoop) {
    fail('luma.gl 未加载成功，请检查能否访问 cdn.jsdelivr.net');
    return;
  }

  var COUNT = 200;
  var amp = 0.35;
  var freq = 6;
  var running = true;
  var uploads = 0;

  var data = new Float32Array(COUNT * 3);

  function fillBuffer(t) {
    for (var i = 0; i < COUNT; i++) {
      var x = (i / (COUNT - 1)) * 2 - 1;
      var y = Math.sin(x * freq + t * 1.6) * amp * (1 - 0.35 * Math.abs(x));
      data[i * 3] = x * 0.92;
      data[i * 3 + 1] = y;
      data[i * 3 + 2] = 0;
    }
  }

  fillBuffer(0);
  document.getElementById('n').textContent = COUNT;

  luma.luma.createDevice({
    type: 'webgl',
    adapters: [luma.webgl2Adapter],
    createCanvasContext: {
      canvas: cv,
      useDevicePixels: Math.min(window.devicePixelRatio, 2),
      autoResize: true
    }
  }).then(function (device) {
    var posBuffer = device.createBuffer({
      data: data,
      usage: luma.Buffer.VERTEX | luma.Buffer.COPY_DST
    });

    var model = new luma.Model(device, {
      id: 'wave',
      topology: 'line-strip',
      vertexCount: COUNT,
      attributes: { positions: posBuffer },
      bufferLayout: [
        { name: 'positions', stepMode: 'vertex', format: 'float32x3' }
      ],
      vs: [
        '#version 300 es',
        'in vec3 positions;',
        'void main() {',
        '  gl_Position = vec4(positions, 1.0);',
        '}'
      ].join('\n'),
      fs: [
        '#version 300 es',
        'precision highp float;',
        'out vec4 fragColor;',
        'void main() {',
        '  fragColor = vec4(0.42, 0.85, 0.98, 1.0);',
        '}'
      ].join('\n')
    });

    var start = performance.now();
    var cntEl = document.getElementById('cnt');

    var loop = new luma.AnimationLoop({
      device: device,
      onRender: function (props) {
        var pass = props.device.beginRenderPass({ clearColor: [0.04, 0.06, 0.09, 1] });

        if (running) {
          fillBuffer((performance.now() - start) / 1000);
          posBuffer.write(data);
          uploads++;
        }

        model.draw(pass);
        pass.end();

        if (uploads % 10 === 0) cntEl.textContent = uploads;
      },
      onError: function (e) { fail(e.message); }
    });

    loop.start();

    document.getElementById('amp').addEventListener('input', function () {
      amp = Number(this.value);
    });
    document.getElementById('freq').addEventListener('input', function () {
      freq = Number(this.value);
    });

    var pauseBtn = document.getElementById('pause');
    pauseBtn.addEventListener('click', function () {
      running = !running;
      pauseBtn.textContent = running ? '暂停' : '继续';
    });
  }).catch(function (e) {
    fail(e && e.message ? e.message : String(e));
  });
})();
</script>
</body>
</html>