图像的缩放按钮 - 不知道如何

Question

对于我正在制作的网站，我制作了一张自定义地图，这是一张图片。不过，对于这个网站，我需要使这个图像可缩放，并在特定的“框”内拖动。

我用 JS 在“item”中获得了图像，这使得图像可以滚动和拖动。我使用的图像很大，因为它需要放大/缩小。

代码：

var dragItem = document.querySelector("#item");
var container = document.querySelector("#container");

var active = false;
var currentX;
var currentY;
var initialX;
var initialY;
var xOffset = 0;
var yOffset = 0;

container.addEventListener("touchstart", dragStart, false);
container.addEventListener("touchend", dragEnd, false);
container.addEventListener("touchmove", drag, false);

container.addEventListener("mousedown", dragStart, false);
container.addEventListener("mouseup", dragEnd, false);
container.addEventListener("mousemove", drag, false);

function dragStart(e) {
  if (e.type === "touchstart") {
    initialX = e.touches[0].clientX - xOffset;
    initialY = e.touches[0].clientY - yOffset;
  } else {
    initialX = e.clientX - xOffset;
    initialY = e.clientY - yOffset;
  }

  if (e.target === dragItem) {
    active = true;
  }
}

function dragEnd(e) {
  initialX = currentX;
  initialY = currentY;

  active = false;
}

function drag(e) {
  if (active) {

    e.preventDefault();

    if (e.type === "touchmove") {
      currentX = e.touches[0].clientX - initialX;
      currentY = e.touches[0].clientY - initialY;
    } else {
      currentX = e.clientX - initialX;
      currentY = e.clientY - initialY;
    }

    xOffset = currentX;
    yOffset = currentY;

    setTranslate(currentX, currentY, dragItem);
  }
}

function setTranslate(xPos, yPos, el) {
  el.style.transform = "translate3d(" + xPos + "px, " + yPos + "px, 0)";
}

#container {
  width: 9109px;
  height: 5963px;
  background-color: #3ab0c9;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  touch-action: none;
}

#item {
  width: 9109px;
  height: 5963px;
  background-image: url("map.png");
  touch-action: none;
  user-select: none;
}

#item:hover {
  cursor: pointer;
  border-width: 20px;
}

<div id="outerContainer">
  <div id="container">
    <div id="item">

    </div>
  </div>
</div>

我只需要创建缩放按钮，但我不知道怎么做！有人能帮我吗？我只是无法让它工作......

Answer 1

您应该使用canvas 元素来绘制图像。 下面的代码将是构建 HTML5 画布缩放和平移工具的良好开端。

请参阅HTML5 Canvas Zoom and Pan Image 以获取以下代码的工作示例。

<canvas></canvas>

    var canvas = document.getElementsByTagName('canvas')[0];
    canvas.width = 800;
canvas.height = 600;

    var gkhead = new Image;

    window.onload = function(){     

            var ctx = canvas.getContext('2d');
            trackTransforms(ctx);

    function redraw(){

          // Clear the entire canvas
          var p1 = ctx.transformedPoint(0,0);
          var p2 = ctx.transformedPoint(canvas.width,canvas.height);
          ctx.clearRect(p1.x,p1.y,p2.x-p1.x,p2.y-p1.y);

          ctx.save();
          ctx.setTransform(1,0,0,1,0,0);
          ctx.clearRect(0,0,canvas.width,canvas.height);
          ctx.restore();

          ctx.drawImage(gkhead,0,0);

        }
        redraw();

      var lastX=canvas.width/2, lastY=canvas.height/2;

      var dragStart,dragged;

      canvas.addEventListener('mousedown',function(evt){
          document.body.style.mozUserSelect = document.body.style.webkitUserSelect = document.body.style.userSelect = 'none';
          lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
          lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
          dragStart = ctx.transformedPoint(lastX,lastY);
          dragged = false;
      },false);

      canvas.addEventListener('mousemove',function(evt){
          lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
          lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
          dragged = true;
          if (dragStart){
            var pt = ctx.transformedPoint(lastX,lastY);
            ctx.translate(pt.x-dragStart.x,pt.y-dragStart.y);
            redraw();
                }
      },false);

      canvas.addEventListener('mouseup',function(evt){
          dragStart = null;
          if (!dragged) zoom(evt.shiftKey ? -1 : 1 );
      },false);

      var scaleFactor = 1.1;

      var zoom = function(clicks){
          var pt = ctx.transformedPoint(lastX,lastY);
          ctx.translate(pt.x,pt.y);
          var factor = Math.pow(scaleFactor,clicks);
          ctx.scale(factor,factor);
          ctx.translate(-pt.x,-pt.y);
          redraw();
      }

      var handleScroll = function(evt){
          var delta = evt.wheelDelta ? evt.wheelDelta/40 : evt.detail ? -evt.detail : 0;
          if (delta) zoom(delta);
          return evt.preventDefault() && false;
      };

      canvas.addEventListener('DOMMouseScroll',handleScroll,false);
      canvas.addEventListener('mousewheel',handleScroll,false);
    };

    gkhead.src = 'http://phrogz.net/tmp/gkhead.jpg';

    // Adds ctx.getTransform() - returns an SVGMatrix
    // Adds ctx.transformedPoint(x,y) - returns an SVGPoint
    function trackTransforms(ctx){
      var svg = document.createElementNS("http://www.w3.org/2000/svg",'svg');
      var xform = svg.createSVGMatrix();
      ctx.getTransform = function(){ return xform; };

      var savedTransforms = [];
      var save = ctx.save;
      ctx.save = function(){
          savedTransforms.push(xform.translate(0,0));
          return save.call(ctx);
      };

      var restore = ctx.restore;
      ctx.restore = function(){
        xform = savedTransforms.pop();
        return restore.call(ctx);
              };

      var scale = ctx.scale;
      ctx.scale = function(sx,sy){
        xform = xform.scaleNonUniform(sx,sy);
        return scale.call(ctx,sx,sy);
              };

      var rotate = ctx.rotate;
      ctx.rotate = function(radians){
          xform = xform.rotate(radians*180/Math.PI);
          return rotate.call(ctx,radians);
      };

      var translate = ctx.translate;
      ctx.translate = function(dx,dy){
          xform = xform.translate(dx,dy);
          return translate.call(ctx,dx,dy);
      };

      var transform = ctx.transform;
      ctx.transform = function(a,b,c,d,e,f){
          var m2 = svg.createSVGMatrix();
          m2.a=a; m2.b=b; m2.c=c; m2.d=d; m2.e=e; m2.f=f;
          xform = xform.multiply(m2);
          return transform.call(ctx,a,b,c,d,e,f);
      };

      var setTransform = ctx.setTransform;
      ctx.setTransform = function(a,b,c,d,e,f){
          xform.a = a;
          xform.b = b;
          xform.c = c;
          xform.d = d;
          xform.e = e;
          xform.f = f;
          return setTransform.call(ctx,a,b,c,d,e,f);
      };

      var pt  = svg.createSVGPoint();
      ctx.transformedPoint = function(x,y){
          pt.x=x; pt.y=y;
          return pt.matrixTransform(xform.inverse());
      }
    }