docs: case04 Readme.html 新增交互式轨道示意图

使用 HTML5 Canvas + JavaScript 绘制椭圆轨道图，
支持滑块调整偏心率 e（0~0.85），实时更新：
- 椭圆形状变化
- a/b/c 参数标注
- 近日点/远日点数值
- 速度矢量方向
- 底部信息面板

examples/case04/Readme.html

@@ -116,8 +116,69 @@ MathJax = {
     padding: 8px 0;
   }
 
+  .diagram-wrap {
+    background: #0d1117;
+    border: 1px solid var(--border);
+    border-radius: 8px;
+    padding: 16px;
+    margin: 16px 0;
+    text-align: center;
+  }
+  .diagram-wrap canvas {
+    display: block;
+    margin: 0 auto;
+    max-width: 100%;
+    height: auto;
+  }
+  .diagram-controls {
+    display: flex;
+    flex-wrap: wrap;
+    align-items: center;
+    justify-content: center;
+    gap: 16px;
+    margin-top: 12px;
+  }
+  .diagram-controls label {
+    font-size: 0.85rem;
+    color: var(--text-dim);
+  }
+  .diagram-controls input[type="range"] {
+    width: 200px;
+    accent-color: var(--accent);
+  }
+  .diagram-controls .val {
+    font-size: 0.9rem;
+    font-weight: 500;
+    color: var(--teal);
+    min-width: 48px;
+    display: inline-block;
+    text-align: center;
+  }
+  .diagram-info {
+    display: flex;
+    flex-wrap: wrap;
+    justify-content: center;
+    gap: 20px;
+    margin-top: 10px;
+    font-size: 0.82rem;
+    color: var(--text-dim);
+  }
+  .diagram-info span {
+    display: inline-flex;
+    align-items: center;
+    gap: 4px;
+  }
+  .diagram-info .dot {
+    display: inline-block;
+    width: 10px;
+    height: 10px;
+    border-radius: 50%;
+    margin-right: 2px;
+  }
+
   @media (max-width: 640px) {
     body { padding: 16px; }
+    .diagram-controls { flex-direction: column; gap: 8px; }
   }
 </style>
 </head>
@@ -175,7 +236,20 @@ MathJax = {
 
 <h2>三、轨道力学</h2>
 
-<h3>3.1 偏心率定义</h3>
+<h3>3.1 交互式轨道示意图</h3>
+
+<p>拖动下方滑块改变偏心率 $e$，观察轨道形状的变化和参数标注：</p>
+
+<div class="diagram-wrap">
+  <canvas id="orbitCanvas" width="760" height="400"></canvas>
+  <div class="diagram-controls">
+    <label>偏心率 e = <span class="val" id="eDisplay">0.50</span></label>
+    <input type="range" id="eSlider" min="0" max="85" value="50">
+  </div>
+  <div class="diagram-info" id="diagramInfo"></div>
+</div>
+
+<h3>3.2 偏心率定义</h3>
 
 <div class="highlight-eq">
   <p>偏心率 $e$ 描述椭圆轨道偏离正圆的程度：</p>
@@ -193,7 +267,7 @@ MathJax = {
   <tr><td>$e &gt; 1$</td><td>双曲线</td><td>飞越轨道，速度超过逃逸速度</td></tr>
 </table>
 
-<h3>3.2 半长轴与半短轴的关系</h3>
+<h3>3.3 半长轴与半短轴的关系</h3>
 
 <div class="highlight-eq">
   <div class="formula-block">
@@ -202,7 +276,7 @@ MathJax = {
   <p>当 $e \ll 1$ 时，$b \approx a\left(1 - \dfrac{e^2}{2}\right)$，椭圆度非常微小。</p>
 </div>
 
-<h3>3.3 近日点与远日点</h3>
+<h3>3.4 近日点与远日点</h3>
 
 <div class="highlight-eq">
   <p>近日点（距太阳最近）和远日点（距太阳最远）的距离分别为：</p>
@@ -216,7 +290,7 @@ MathJax = {
   </div>
 </div>
 
-<h3>3.4 开普勒三大定律</h3>
+<h3>3.5 开普勒三大定律</h3>
 
 <ol>
   <li><strong>椭圆定律</strong>：行星轨道是椭圆，太阳位于椭圆的一个焦点上。</li>
@@ -290,5 +364,229 @@ MathJax = {
 </ul>
 
 </div>
+
+<script>
+(function() {
+  var canvas = document.getElementById('orbitCanvas');
+  var ctx = canvas.getContext('2d');
+  var slider = document.getElementById('eSlider');
+  var eDisplay = document.getElementById('eDisplay');
+  var infoDiv = document.getElementById('diagramInfo');
+
+  var W = 760, H = 400;
+  var cx = 380, cy = 200;
+
+  // 实际绘图区域半径
+  var A = 140;
+
+  function draw(e) {
+    ctx.clearRect(0, 0, W, H);
+
+    var b = A * Math.sqrt(1 - e * e);
+    var f = e * A;
+
+    // 长轴辅助线
+    ctx.beginPath();
+    ctx.moveTo(cx - A - 20, cy);
+    ctx.lineTo(cx + A + 20, cy);
+    ctx.strokeStyle = '#30363d';
+    ctx.lineWidth = 0.5;
+    ctx.setLineDash([4, 3]);
+    ctx.stroke();
+    ctx.setLineDash([]);
+
+    // 椭圆轨道
+    ctx.beginPath();
+    ctx.ellipse(cx - f, cy, A, b, 0, 0, Math.PI * 2);
+    ctx.strokeStyle = '#58a6ff';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+
+    // 半长轴 a（标注线）
+    var aY = cy + 28;
+    ctx.beginPath();
+    ctx.moveTo(cx - f, aY);
+    ctx.lineTo(cx - f + A, aY);
+    ctx.strokeStyle = '#c9d1d9';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+    // 箭头
+    ctx.beginPath();
+    ctx.moveTo(cx - f + 6, aY - 4);
+    ctx.lineTo(cx - f, aY);
+    ctx.lineTo(cx - f + 6, aY + 4);
+    ctx.strokeStyle = '#c9d1d9';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+    ctx.beginPath();
+    ctx.moveTo(cx - f + A - 6, aY - 4);
+    ctx.lineTo(cx - f + A, aY);
+    ctx.lineTo(cx - f + A - 6, aY + 4);
+    ctx.strokeStyle = '#c9d1d9';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+    ctx.fillStyle = '#c9d1d9';
+    ctx.font = '13px "Segoe UI", Arial, sans-serif';
+    ctx.textAlign = 'center';
+    ctx.textBaseline = 'top';
+    ctx.fillText('a = ' + A.toFixed(0), cx - f + A/2, aY + 6);
+
+    // 偏心距 c = ea 标注
+    var cY = cy - b - 20;
+    ctx.beginPath();
+    ctx.moveTo(cx - f, cY);
+    ctx.lineTo(cx, cY);
+    ctx.strokeStyle = '#d29922';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+    ctx.beginPath();
+    ctx.moveTo(cx - f + 5, cY - 4);
+    ctx.lineTo(cx - f, cY);
+    ctx.lineTo(cx - f + 5, cY + 4);
+    ctx.strokeStyle = '#d29922';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+    ctx.beginPath();
+    ctx.moveTo(cx - 5, cY - 4);
+    ctx.lineTo(cx, cY);
+    ctx.lineTo(cx - 5, cY + 4);
+    ctx.strokeStyle = '#d29922';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+    ctx.fillStyle = '#d29922';
+    ctx.font = '13px "Segoe UI", Arial, sans-serif';
+    ctx.textAlign = 'center';
+    ctx.textBaseline = 'bottom';
+    ctx.fillText('c = ea = ' + f.toFixed(1), cx - f/2, cY - 4);
+
+    // 半短轴 b 标注
+    var bX = cx - f + A + 18;
+    ctx.beginPath();
+    ctx.moveTo(bX, cy);
+    ctx.lineTo(bX, cy - b);
+    ctx.strokeStyle = '#3fb950';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+    ctx.beginPath();
+    ctx.moveTo(bX - 4, cy - 6);
+    ctx.lineTo(bX, cy);
+    ctx.lineTo(bX + 4, cy - 6);
+    ctx.strokeStyle = '#3fb950';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+    ctx.beginPath();
+    ctx.moveTo(bX - 4, cy - b + 6);
+    ctx.lineTo(bX, cy - b);
+    ctx.lineTo(bX + 4, cy - b + 6);
+    ctx.strokeStyle = '#3fb950';
+    ctx.lineWidth = 1.5;
+    ctx.stroke();
+    ctx.fillStyle = '#3fb950';
+    ctx.font = '13px "Segoe UI", Arial, sans-serif';
+    ctx.textAlign = 'left';
+    ctx.textBaseline = 'middle';
+    ctx.fillText('b = ' + b.toFixed(1), bX + 8, cy - b/2);
+
+    // 太阳（焦点）
+    ctx.beginPath();
+    ctx.arc(cx, cy, 7, 0, Math.PI * 2);
+    ctx.fillStyle = '#d29922';
+    ctx.fill();
+    ctx.strokeStyle = '#f0883e';
+    ctx.lineWidth = 1;
+    ctx.stroke();
+    ctx.fillStyle = '#f0f6fc';
+    ctx.font = '13px "Segoe UI", Arial, sans-serif';
+    ctx.textAlign = 'center';
+    ctx.textBaseline = 'bottom';
+    ctx.fillText('太阳（焦点）', cx, cy - 12);
+
+    // 近日点标注
+    var periX = cx - f - A;
+    ctx.fillStyle = '#58a6ff';
+    ctx.beginPath();
+    ctx.arc(periX, cy, 4, 0, Math.PI * 2);
+    ctx.fill();
+    ctx.fillStyle = '#8b949e';
+    ctx.font = '12px "Segoe UI", Arial, sans-serif';
+    ctx.textAlign = 'center';
+    ctx.textBaseline = 'top';
+    ctx.fillText('近日点 r = a(1-e) = ' + (A * (1 - e)).toFixed(1), periX, cy + 12);
+
+    // 远日点标注
+    var apX = cx - f + A;
+    ctx.fillStyle = '#58a6ff';
+    ctx.beginPath();
+    ctx.arc(apX, cy, 4, 0, Math.PI * 2);
+    ctx.fill();
+    ctx.fillStyle = '#8b949e';
+    ctx.font = '12px "Segoe UI", Arial, sans-serif';
+    ctx.textAlign = 'center';
+    ctx.textBaseline = 'top';
+    ctx.fillText('远日点 r = a(1+e) = ' + (A * (1 + e)).toFixed(1), apX, cy + 12);
+
+    // 地球（轨道上的点）
+    var angle = 0.4;
+    var ex = cx - f + A * Math.cos(angle);
+    var ey = cy - b * Math.sin(angle);
+    ctx.beginPath();
+    ctx.arc(ex, ey, 5, 0, Math.PI * 2);
+    ctx.fillStyle = '#58a6ff';
+    ctx.fill();
+    ctx.strokeStyle = '#1f6feb';
+    ctx.lineWidth = 1;
+    ctx.stroke();
+    ctx.fillStyle = '#58a6ff';
+    ctx.font = '12px "Segoe UI", Arial, sans-serif';
+    ctx.textAlign = 'left';
+    ctx.textBaseline = 'bottom';
+    ctx.fillText('地球', ex + 8, ey);
+
+    // 速度矢量
+    var vlen = 32;
+    var vx = -A * Math.sin(angle) * 0.7;
+    var vy = b * Math.cos(angle) * 0.7;
+    var vl = Math.sqrt(vx*vx + vy*vy);
+    if (vl > 0) {
+      vx = vx / vl * vlen;
+      vy = vy / vl * vlen;
+    }
+    ctx.beginPath();
+    ctx.moveTo(ex, ey);
+    ctx.lineTo(ex + vx, ey + vy);
+    ctx.strokeStyle = '#3fb950';
+    ctx.lineWidth = 2;
+    ctx.stroke();
+    ctx.beginPath();
+    var tipX = ex + vx, tipY = ey + vy;
+    var a1 = 0.3;
+    ctx.moveTo(tipX, tipY);
+    ctx.lineTo(tipX - vx * a1 + vy * a1 * 0.5, tipY - vy * a1 - vx * a1 * 0.5);
+    ctx.lineTo(tipX - vx * a1 - vy * a1 * 0.5, tipY - vy * a1 + vx * a1 * 0.5);
+    ctx.closePath();
+    ctx.fillStyle = '#3fb950';
+    ctx.fill();
+
+    // 信息面板
+    var roundE = Math.round(e * 10000) / 10000;
+    infoDiv.innerHTML =
+      '<span><span class="dot" style="background:#58a6ff"></span>椭圆轨道 e = ' + roundE.toFixed(4) + '</span>' +
+      '<span><span class="dot" style="background:#d29922"></span>偏心距 c = ' + f.toFixed(1) + '</span>' +
+      '<span><span class="dot" style="background:#3fb950"></span>b/a = ' + (b / A).toFixed(4) + '</span>' +
+      '<span>近日点 ' + (A * (1 - e)).toFixed(1) + ' / 远日点 ' + (A * (1 + e)).toFixed(1) + '</span>';
+  }
+
+  function update() {
+    var val = parseInt(slider.value);
+    var e = val / 100;
+    eDisplay.textContent = e.toFixed(2);
+    draw(e);
+  }
+
+  slider.addEventListener('input', update);
+  update();
+})();
+</script>
+
 </body>
 </html>