android - 在 Ionic App 中通过手指(触摸)裁剪图像

Question

我正在开发基于 ionic 的应用程序。我的 ionic 应用程序版本是 1.2.4。我想在我的应用程序中裁剪功能。我想通过 Touch 裁剪不规则形状的图像。所以任何人都有 Create touch cropper 所以请帮助我。

为了更清楚，看下面的gif我想要什么。

过去 2 天，我在谷歌上搜索解决方案，发现可以轻松进行简单裁剪或正方形或矩形裁剪，但无法通过触摸获取裁剪图像。

如果有人做过，请向我推荐正确的方向。

Answer 1

指针事件在移动设备中不起作用，因此这是经过一些修改后可在 Ionic 应用程序或任何跨平台应用程序中完全工作的代码。

 setTimeout(example,0); // ensures that the run us after parsing
   function example(){
   const ctx = canvas.getContext("2d");
   var w = canvas.width;
   var h = canvas.height;
   var cw = w / 2;  // center
   var ch = h / 2;

   var selectLayer = CImageCtx(w,h); // creates a canvas
   var selectedContent = CImageCtx(w,h); // the selected content
   document.getElementById("exampleEle").appendChild(selectedContent);
   var image = new Image;  // the image
   //image.src = "img/temp.png";
   image.src ="https://upload.wikimedia.org/wikipedia/commons/thumb/e/e9/Official_portrait_of_Barack_Obama.jpg/220px-Official_portrait_of_Barack_Obama.jpg";
   // updates the masked result
   function updateSelected(){
     var ctx = selectedContent.ctx;
     ctx.drawImage(image,0,0);
     ctx.globalCompositeOperation = "destination-in";
     ctx.drawImage(selectLayer,0,0);
     ctx.globalCompositeOperation = "source-over";
   }
   function update(){
       // if mouse down then
       if(touch.but){
         // clear the mask if on the right image
         if(touch.oldBut === false && touch.x > 256){
            selectLayer.ctx.clearRect(0,0,w,h);
            touch.but = false;
         }else{
            // draw the red
            selectLayer.ctx.fillStyle = "red";
            fillCircle(touch.x, touch.y, 20, selectLayer.ctx);
         }
         // update the masked result
         updateSelected();
       }
       // clear the canvas
       ctx.clearRect(0,0,w,h);
       // draw the image
       ctx.drawImage(image,0,0);
       // then draw the marking layer over it with comp overlay
       ctx.globalCompositeOperation = "overlay";
       ctx.drawImage(selectLayer,0,0);
       ctx.globalCompositeOperation = "source-over";

       touch.oldBut = touch.but;
       requestAnimationFrame(update);
   }
   requestAnimationFrame(update);
 }
 //#############################################################################
 // helper functions not part of the answer
 //#############################################################################
 const touch  = {
   x : 0, y : 0, but : false,
   events(e){
     console.log("e.type",e);
     const m = touch;
     const bounds = canvas.getBoundingClientRect();
     var rect = e.target.getBoundingClientRect();
     if(e.targetTouches) {
       X   =   parseInt(e.targetTouches[0].pageX - rect.left);
       Y   =   parseInt(e.targetTouches[0].pageY - rect.top);
     }
     m.x = X;
     m.y = Y;
     m.but = e.type === "touchstart" ? true : e.type === "touchend" ? false : m.but;
   }
 };
 (["start","end","move"]).forEach(name => document.addEventListener("touch" + name,touch.events));
 const CImage = (w = 128, h = w) => (c = document.createElement("canvas"),c.width = w,c.height = h, c);
 const CImageCtx = (w = 128, h = w) => (c = CImage(w,h), c.ctx = c.getContext("2d"), c);
 const fillCircle = (l,y=ctx,r=ctx,c=ctx) =>{if(l.p1){c=y; r=leng(l);y=l.p1.y;l=l.p1.x }else if(l.x){c=r;r=y;y=l.y;l=l.x}c.beginPath(); c.arc(l,y,r,0,Math.PI*2); c.fill()}

对于 View ，您必须添加这 3 行 html。

  <div id="exampleEle">

  <canvas id="canvas" width=256 height=256></canvas>
  </div>