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  { selector: ".site-nav a:nth-of-type(1)", text: "Overview" },
  { selector: ".site-nav a:nth-of-type(2)", text: "Core Math" },
  { selector: ".site-nav a:nth-of-type(3)", text: "Workflow" },
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const indexTranslations = [
  { selector: ".intro-copy .section-label", text: "2D & 3D Motion Tracking Tool" },
  { selector: ".intro-copy h1", html: "MotionLab Tracker<br>Technical Guide" },
  {
    selector: ".intro-copy > p:not(.section-label)",
    text:
      "MotionLab 2D / 3D Workbench is a physics experiment video-tracking tool for high school classrooms and inquiry-based labs. The portable .exe requires no installation — ZNCC auto-tracking, robust 3D fusion, and one-click CSV / Python export included.",
  },
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  {
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    attrs: { "aria-label": "MotionLab 2D and 3D application screenshots" },
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    text: "Single-view tracking with calibration, scale setup, and exported motion data.",
  },
  {
    selector: ".app-shot:not(.app-shot-primary) figcaption span",
    text: "Dual-view XZ / YZ tracking with depth calibration and 3D trajectory output.",
  },
  // Feature strip
  { selector: ".fcard:nth-child(1) h3", text: "ZNCC Auto Track" },
  { selector: ".fcard:nth-child(1) p", text: "ZNCC template matching — robust to lighting changes; single cached frame read for fast continuous tracking." },
  { selector: ".fcard:nth-child(2) h3", text: "Robust 3D Fusion" },
  { selector: ".fcard:nth-child(2) p", text: "Sub-frame sync search, Huber IRLS outlier rejection, SG velocity smoothing, cubic Hermite resampling." },
  { selector: ".fcard:nth-child(3) h3", text: "One-click Export" },
  { selector: ".fcard:nth-child(3) p", text: "Export XYZ data as CSV, 3D plot, four-view image, and a ready-to-run Python analysis script." },
    { selector: "#principles .section-head .section-label", text: "Core Math" },
  { selector: "#principles .section-head h2", text: "Core Calculation Principles" },
  {
    selector: "#principles .split-block:not(.reverse) h3",
    text: "2D Tracker: calibration, coordinates, and derivatives",
  },
  {
    selector: "#principles .split-block:not(.reverse) > div:first-child > p:nth-of-type(1)",
    text:
      "2D tracking treats the video as a calibrated plane. After choosing an origin, axis direction, and known physical length, pixel positions can be converted into real-world coordinates. With the frame rate, position samples can then be transformed into displacement, velocity, and acceleration.",
  },
  {
    selector: "#principles .split-block:not(.reverse) .equation-card:nth-child(1) figcaption",
    html: "A known physical length L and its pixel distance d<sub>px</sub> define the pixel-to-world scale S.",
  },
  {
    selector: "#principles .split-block:not(.reverse) .equation-card:nth-child(2) figcaption",
    text:
      "Pixel coordinates are translated to the selected origin, rotated into the chosen axes, and scaled into physical coordinates.",
  },
  {
    selector: "#principles .split-block:not(.reverse) .equation-card:nth-child(3) figcaption",
    text:
      "Velocity and acceleration are estimated from neighboring frames, so stable tracking points and frame rate matter.",
  },
  {
    selector: "#principles .split-block:not(.reverse) > div:first-child > p:nth-of-type(2)",
    text:
      "The exported data is suited for classroom analysis, graphs, CSV processing, and follow-up fitting. When the tracked point jitters, centroid snap and manual correction reduce frame-to-frame noise.",
  },
  { selector: "#principles .split-block:not(.reverse) .note-panel h4", text: "2D Use Notes" },
  {
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    text: "Use a clear calibration length in the same plane as the motion.",
  },
  {
    selector: "#principles .split-block:not(.reverse) .note-panel li:nth-child(2)",
    text: "Keep the camera still and avoid perspective changes when possible.",
  },
  {
    selector: "#principles .split-block:not(.reverse) .note-panel li:nth-child(3)",
    text: "Export time, x, y, vx, vy, and derived data for graphs or CSV analysis.",
  },
  {
    selector: "#principles .split-block.reverse > div:first-child h3",
    text: "3D Tracker: paired XZ / YZ views",
  },
  {
    selector: "#principles .split-block.reverse > div:first-child > p:nth-of-type(1)",
    text:
      "MotionLab 3D Workbench uses two synchronized views: view A records the XZ plane and view B records the YZ plane. After setting scale, FPS, and matching frames, the two tracks can be fused into X, Y, and Z coordinates.",
  },
  {
    selector: "#principles .split-block.reverse .equation-card:nth-child(1) figcaption",
    text: "Parallax model: the depth of Y affects x_A, and the depth of X affects y_B.",
  },
  {
    selector: "#principles .split-block.reverse .equation-card:nth-child(2) figcaption",
    text: "View B is aligned by scale (s) and offset (b) before fusion: both Y and Z are scaled, Z also offset.",
  },
  {
    selector: "#principles .split-block.reverse .equation-card:nth-child(3) figcaption",
    text: "Z is estimated jointly from both views; Z residual RMS gauges fusion quality.",
  },
  {
    selector: "#principles .split-block.reverse > div:first-child > p:nth-of-type(2)",
    text:
      "α and β are estimated by Huber IRLS across all valid frames; sub-frame sync τ is found by golden-section search. Each frame's X, Y, Z is solved individually using the current depth, then resampled with cubic Hermite splines for smooth curved trajectories.",
  },
  { selector: "#principles .split-block.reverse .note-panel h4", text: "3D Calibration & Use Notes" },
  {
    selector: "#principles .split-block.reverse .note-panel li:nth-child(1)",
    text: "Place the origin near a shared calibration reference visible in both views.",
  },
  {
    selector: "#principles .split-block.reverse .note-panel li:nth-child(2)",
    text: "If view B shoots from +X toward −X, map the horizontal axis to world Y: left = +Y, right = −Y.",
  },
  {
    selector: "#principles .split-block.reverse .note-panel li:nth-child(3)",
    text: "Full 3D mode suits trajectories with clear X, Y, and Z variation; plane mode suits mostly-flat motion.",
  },
  {
    selector: "#principles .split-block.reverse .note-panel li:nth-child(4)",
    text: "Inspect the 3D trajectory and export CSV/Python-ready data after correction.",
  },
  { selector: "#workflow .section-head .section-label", text: "How To Use" },
  { selector: "#workflow .section-head h2", text: "Operating Workflow" },
  { selector: ".workflow-card:nth-child(1) h3", text: "2D Workbench Workflow" },
  {
    selector: ".workflow-card:nth-child(1) li:nth-child(1)",
    text: "Import a video, confirm FPS, and set a clear calibration length.",
  },
  {
    selector: ".workflow-card:nth-child(1) li:nth-child(2)",
    text: "Use the calibration tool to define origin, axes, and the real-world scale.",
  },
  {
    selector: ".workflow-card:nth-child(1) li:nth-child(3)",
    text: "Create a point mass and click the tracked object frame by frame (← → to step, Shift+← → for ±10 frames).",
  },
  {
    selector: ".workflow-card:nth-child(1) li:nth-child(4)",
    text: "Press T to capture a template, R to run continuous auto-tracking, or Shift+click to skip snap on a frame.",
  },
  {
    selector: ".workflow-card:nth-child(1) li:nth-child(5)",
    text: "Use centroid snap or auto tracking when the target is visually stable.",
  },
  {
    selector: ".workflow-card:nth-child(1) li:nth-child(6)",
    text: "Export coordinates, velocity, acceleration, graphs, and CSV data.",
  },
  { selector: ".workflow-card:nth-child(2) h3", text: "3D Workbench Workflow" },
  {
    selector: ".workflow-card:nth-child(2) li:nth-child(1)",
    text: "Load view A for XZ tracking and view B for YZ tracking.",
  },
  {
    selector: ".workflow-card:nth-child(2) li:nth-child(2)",
    text: "Calibrate both views with scale, orientation, and synchronized frame timing.",
  },
  {
    selector: ".workflow-card:nth-child(2) li:nth-child(3)",
    text: "Track the same physical point in both views with matched frames.",
  },
  {
    selector: ".workflow-card:nth-child(2) li:nth-child(4)",
    text: "Run Z correction and check the residual or alignment quality.",
  },
  {
    selector: ".workflow-card:nth-child(2) li:nth-child(5)",
    text: "Inspect the 3D trajectory with the plot controls and switch views as needed.",
  },
  {
    selector: ".workflow-card:nth-child(2) li:nth-child(6)",
    text: "Export the 3D result for CSV, graphing, or Python analysis.",
  },
  // Shortcut strip
  { selector: ".shortcut-label", text: "Common Shortcuts" },
  { selector: ".sc-item:nth-child(1) span", text: "Step frame" },
  { selector: ".sc-item:nth-child(2) span", text: "±10 frames" },
  { selector: ".sc-item:nth-child(3) span", text: "Play / Pause" },
  { selector: ".sc-item:nth-child(4) span", text: "Capture template" },
  { selector: ".sc-item:nth-child(5) span", text: "Auto track" },
  { selector: ".sc-item:nth-child(6) span", text: "Switch view (3D)" },
  { selector: ".sc-item:nth-child(7) span", text: "Run fusion (3D)" },
  { selector: ".sc-item:nth-child(8) span", text: "Export bundle" },
    { selector: "#downloads .section-head .section-label", text: "Downloads" },
  { selector: "#downloads .section-head h2", text: "Downloads And Release Status" },
  {
    selector: "#downloads .section-head p:not(.section-label)",
    text: "Both portable packages are available on GitHub Releases — no installation needed, just download and run.",
  },
  // Download cards
  { selector: ".dl-card:nth-child(1) strong", text: "MotionLab 2D Workbench" },
  { selector: ".dl-card:nth-child(1) .dl-features li:nth-child(1)", text: "ZNCC auto-track · Smart centroid snap v2" },
  { selector: ".dl-card:nth-child(1) .dl-features li:nth-child(2)", text: "Savitzky-Golay velocity / acceleration smoothing" },
  { selector: ".dl-card:nth-child(1) .dl-features li:nth-child(3)", text: "FFT spectrum analysis · CSV / Python export" },
  { selector: ".dl-card:nth-child(1) .dl-features li:nth-child(4)", text: "Windows 10+ · Portable single .exe" },
  { selector: ".dl-card:nth-child(1) .dl-btn span", text: "Download .exe" },
  { selector: ".dl-card:nth-child(2) strong", text: "MotionLab 3D Workbench" },
  { selector: ".dl-card:nth-child(2) .dl-features li:nth-child(1)", text: "Dual-view XZ / YZ fusion · sub-frame sync search" },
  { selector: ".dl-card:nth-child(2) .dl-features li:nth-child(2)", text: "Huber IRLS robust calibration · cubic Hermite resampling" },
  { selector: ".dl-card:nth-child(2) .dl-features li:nth-child(3)", text: "3D trajectory plot · four-view image · Python export" },
  { selector: ".dl-card:nth-child(2) .dl-features li:nth-child(4)", text: "Windows 10+ · Portable single .exe" },
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    selector: ".download-row:nth-child(1) span",
    text: "Complete Electron / JavaScript source, build configuration, and technical documentation under the MIT License.",
  },
  { selector: ".download-row:nth-child(1) .button", text: "View Source Code" },
  { selector: ".download-row:nth-child(2) strong", text: "Demo Videos And Sample Data" },
  {
    selector: ".download-row:nth-child(2) span",
    text: "Sample videos, projects, CSV output, and classroom notes will be published after organization.",
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  { selector: ".download-row:nth-child(2) .button", text: "Pending" },
  { selector: ".references .section-head .section-label", text: "Technical References" },
  { selector: ".references .section-head h2", text: "Technical Reference Sources" },
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    selector: ".references > p",
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      "The technical notes are based on concepts from older Tracker resources and DLTdv8 references. MotionLab reorganizes those ideas into a compact teaching workflow for 2D and 3D video tracking, with references preserved for later expansion.",
  },
  {
    selector: ".reference-list li:nth-child(1) span",
    text: "Open Source Physics / Tracker official documentation and project overview.",
  },
  {
    selector: ".reference-list li:nth-child(2) span",
    text: "Tracker getting-started workflow, including video import, calibration, tracking, and export.",
  },
  {
    selector: ".reference-list li:nth-child(3) span",
    text: "Tracker open-source project and implementation resources under the Open Source Physics framework.",
  },
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    text: "DLTdv8 reference for DLT coefficients, 2D/3D DLT calibration, and multi-view reconstruction.",
  },
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  { selector: ".author-preview h2", text: "Teacher Chang-Yi Jiang" },
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      "A physics educator focused on high-school physics teaching, inquiry-based practice, physics competition mentoring, physics simulations, and MotionLab video-tracking tools for classroom and research use.",
  },
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  { selector: ".footer-copy", text: "© 2026 MotionLab · aiphysicsteacher" },
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  { selector: ".author-summary h1", text: "Teacher Chang-Yi Jiang" },
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      "A physics educator dedicated to high-school physics teaching, inquiry-based practice, science fair mentoring, and physics competitions. MotionLab turns video tracking, data visualization, and physics modeling into classroom-ready tools so students can study motion, mechanics, and 3D trajectory data from real footage.",
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  { selector: ".education-card li:nth-child(2)", text: "M.S., Graduate Institute of Physics, National Changhua University of Education" },
  { selector: ".education-card li:nth-child(3)", text: "Doctoral student, Graduate Institute of Science Education, National Taiwan Normal University" },
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  { selector: ".achievement-item:nth-child(2) span", text: "Third place in Taichung Astronomy and Physics science fair category" },
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  { selector: ".achievement-item:nth-child(4) strong", text: "TYPT" },
  { selector: ".achievement-item:nth-child(4) span", text: "Taiwan Young Physicists' Tournament: 2 gold medals, 3 bronze medals, and 3 individual awards" },
  { selector: ".achievement-item:nth-child(5) strong", text: "4 students" },
  { selector: ".achievement-item:nth-child(5) span", text: "Advanced to the national physics academic ability competition" },
  { selector: ".achievement-item:nth-child(6) strong", text: "4 medals" },
  { selector: ".achievement-item:nth-child(6) span", text: "Inquiry and practice competition: 2 gold medals and 2 bronze medals" },
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  {
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      "MotionLab 2D / 3D Tracker is a video analysis tool designed for physics classes, inquiry-based practice, and science fair research. The project combines older Tracker resources, DLTdv8-related concepts, and classroom workflow needs to support calibration, tracking, graph review, data export, and 3D trajectory analysis.",
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  {
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      "The 2D and 3D portable packages are available on GitHub Releases. The complete MotionLab 3D Workbench source code and build documentation are publicly available under the MIT License.",
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    text: "Chang-Yi Jiang. (2016). The Secrets and Techniques of Swinging. Chinese Physics, 17(2), 25-32.",
  },
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    selector: ".publication-list li:nth-child(2) a",
    text: "Master's thesis: Conceptual Difficulties And Instructional Effects Of Friction",
  },
  {
    selector: ".publication-list li:nth-child(3) a",
    text: "Physics Bimonthly: Revealing The Secrets Of Polarized Light And Color",
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  {
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    text: "Physics Bimonthly column: Physics Inquiry And Practice: Online Simulation",
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  { selector: ".publication-links a:nth-child(2)", text: "Competition Physics Simulations" },
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  { selector: ".author-footer-actions .copy-email", text: "Copy Email" },
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initCopyEmailButtons();

// ===== SCROLL REVEAL =====
function initScrollReveal() {
  if (typeof IntersectionObserver === 'undefined') {
    document.querySelectorAll('[data-reveal]').forEach(el => el.classList.add('revealed'));
    return;
  }
  const observer = new IntersectionObserver((entries) => {
    entries.forEach(entry => {
      if (entry.isIntersecting) {
        entry.target.classList.add('revealed');
        observer.unobserve(entry.target);
      }
    });
  }, { threshold: 0.06, rootMargin: '0px 0px -40px 0px' });
  document.querySelectorAll('[data-reveal]').forEach(el => observer.observe(el));
}
initScrollReveal();

// ===== THEME TOGGLE =====
// Reads system preference on first visit; subsequent visits use localStorage.
// The anti-flash inline script in <head> applies the saved theme before CSS loads.
function initThemeToggle() {
  var btn = document.getElementById('themeToggle');
  if (!btn) return;

  btn.addEventListener('click', function () {
    var html = document.documentElement;
    var isDark = html.getAttribute('data-theme') === 'dark';
    if (isDark) {
      html.removeAttribute('data-theme');
      localStorage.setItem('ml-theme', 'light');
    } else {
      html.setAttribute('data-theme', 'dark');
      localStorage.setItem('ml-theme', 'dark');
    }
  });
}
initThemeToggle();