固定缩放

2024年01月19日
柏拉文
越努力，越幸运
一、认识

二、实现

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>缩放模块</title>
    <style>
      .container {
        width: 800px;
        height: 800px;
        position: relative;
        background-color: #f0f0f0;
      }
      .draggable {
        cursor: grab;
        width: 100px;
        height: 100px;
        position: absolute;
        user-select: none;
        touch-action: none;
        background-color: #3498db;
      }
    </style>
  </head>
  <body>
    <div class="container">
      <div class="draggable"></div>
    </div>
    <script>
      const container = document.querySelector('.container');
      const draggable = document.querySelector('.draggable');

      draggable.style.transformOrigin = `${draggable.offsetWidth / 2}px ${
        draggable.offsetHeight / 2
      }px`;

      let isDragging = false;
      let scale = 1;
      const maxScale = 5;
      const minScale = 0.5;
      const scaleFactor = 0.1;

      const translateXY = {
        x: 0,
        y: 0
      };

      const wheelInvoker = e => {
        wheelInvoker?.value?.(e);
      };

      function getRelativeOfElPosition(e, el) {
        const normalizedE = e.type.startsWith('mouse') ? e : e.targetTouches[0];
        const rect = el.getBoundingClientRect();
        let x = normalizedE.pageX - rect.left - window.scrollX;
        let y = normalizedE.pageY - rect.top - window.scrollY;
        return [x, y];
      }

      function onScale(e) {
        e.preventDefault();
        if (!e.wheelDelta) {
          return;
        }

        let [x, y] = getRelativeOfElPosition(e, draggable);
        x = x - translateXY.x;
        y = y - translateXY.y;

        const moveX = (x / scale) * scaleFactor;
        const moveY = (y / scale) * scaleFactor;

        if (e.wheelDelta > 0) {
          translateXY.x -= scale >= maxScale ? 0 : moveX;
          translateXY.y -= scale >= maxScale ? 0 : moveY;
          scale += scaleFactor;
        } else {
          translateXY.x += scale <= minScale ? 0 : moveX;
          translateXY.y += scale <= minScale ? 0 : moveY;
          scale -= scaleFactor;
        }

        scale = Math.min(maxScale, Math.max(scale, minScale));

        draggable.style.transform = `scale(${scale},${scale})`;
      }

      function run() {
        document.addEventListener('mousewheel', wheelInvoker, {
          passive: false
        });
        wheelInvoker.value = onScale;
      }

      run();
    </script>
  </body>
</html>
一、认识​

二、实现​

一、认识

二、实现
