将图像加载到画布上并放大/缩小并移动它以适应并保存画布上的内容

Posted 2023-03-25

【中文标题】将图像加载到画布上并放大/缩小并移动它以适应并保存画布上的内容

【英文标题】：Loading an image on to a canvas and zooming in/out and move it to fit and save what is on the canvas

【发布时间】：2022-01-02 21:47:06

【问题描述】：

您好，我遇到了一些将图像加载到画布的代码。加载的图像可以移动和放大和缩小。它工作得很好，但我希望能够保存出现在画布中或画布上的图像，如果我以正确的方式得到它？我该怎么办？我希望能够选择一个文件来使用，而不是在代码中指定一个。我以前从来没有用canvas做过任何事情，谢谢

我已经添加了这个新的位来保存它，但我一直收到这个错误，是因为它是从另一个来源加载的吗？

到 html 保存图片

到 javascript

function saveImg() 
var fullQuality = canvas.toDataURL('image/jpeg', 1.0);
console.log(fullQuality);

var canvas = document.getElementsByTagName('canvas')[0];
    canvas.width = 200;
canvas.height = 200;


    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 = 'https://www.uberfantasies.com/img/avatar.png';
    
    // 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());
      
    

        body  background:#eee; margin:1em; text-align:center; 
        canvas  border-radius:25%;display:block; margin:1em auto; background:#fff; border:1px solid #ccc 

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<p>Showing how to use transform methods on the HTML5 Canvas Context to selectively zoom in and out. Drag to pan. Click to zoom at that location. Shift-click to zoom out. Mousewheel up/down over the canvas to zoom in to/out from that location.</p>

<canvas></canvas>
   

【参考方案1】：

要保存画布上可见的任何内容，您可以使用画布元素的toDataURL 属性。

您可以参考this网址参考。

类似这样的：-

var dataURL = canvas.toDataURL("image/jpeg", 1.0);

注意：- dataURL 包含base64格式的图片数据。

【讨论】：

嗨，它给了我 DOMException：无法在“HTMLCanvasElement”上执行“toDataURL”：可能无法导出受污染的画布。

您的问题请参考此网址***.com/questions/22710627/…

您可以将图像的跨域属性设置为匿名。 <img crossorigin="anonymous"></img>