Function rescale

internal/driver/html/common.js:42–69

(s, u)

  // Change the scaling for the svg to s, keeping the point denoted
  // by u (in svg coordinates]) fixed at the same screen location.
  function rescale(s, u) {
    // Limit to a good range.
    if (s < 0.2) s = 0.2;
    if (s > 10.0) s = 10.0;

    currentScale = s;

    // svg.viewBox defines the visible portion of the user coordinate
    // system.  So to magnify by s, divide the visible portion by s,
    // which will then be stretched to fit the viewport.
    const vb = svg.viewBox;
    const w1 = vb.baseVal.width;
    const w2 = initWidth / s;
    const h1 = vb.baseVal.height;
    const h2 = initHeight / s;
    vb.baseVal.width = w2;
    vb.baseVal.height = h2;

    // We also want to adjust vb.baseVal.x so that u.x remains at same
    // screen X coordinate.  In other words, want to change it from x1 to x2
    // so that:
    //     (u.x - x1) / w1 = (u.x - x2) / w2
    // Simplifying that, we get
    //     (u.x - x1) * (w2 / w1) = u.x - x2
    //     x2 = u.x - (u.x - x1) * (w2 / w1)
    vb.baseVal.x = u.x - (u.x - vb.baseVal.x) * (w2 / w1);
    vb.baseVal.y = u.y - (u.y - vb.baseVal.y) * (h2 / h1);
  }

  function handleWheel(e) {
    if (e.deltaY == 0) return;