Fabric JS 2.4.1 如何使用 clipPath 裁剪缩放比例小于或大于 1:1 的图像

Question

我一直在努力找出在调整目标图像的大小后计算遮罩矩形的位置和大小时我做错了什么。

以下是来自 fabric JS 的文档：

剪辑路径：fabric.Object 一个 fabricObject，它没有描边，用它们的形状定义一个剪裁区域。填充为黑色 clipPath 对象在对象渲染后被使用，上下文被放置在对象 cacheCanvas 的中心。如果您希望 clipPath 的 0,0 与对象中心对齐，请使用 clipPath。originX/Y 到 'center' 类型： fabric.Object 资源： fabric.js，第 12991 行

当图像未调整大小（缩放 1:1 X 和 Y）时，我的代码可以完美运行。在名为 rescaleMask 的代码函数中，我尝试将遮罩定位到零中心 X 和 Y，当我运行我的数学在一张方格纸上手动显示时是正确的。显然，有一块我没有意识到会导致定位以不同的方式关闭，具体取决于执行裁剪的象限。这里有相当多的代码，但重要的是掩码是动态创建的而不是硬编码的。问题一定出在 rescaleMask 函数中，因此希望可以忽略其余代码。

我创建了一个带有编号方块的测试图像图表，我将通过单击蒙版按钮裁剪它，用鼠标左键在其中一个框周围绘制一个矩形，然后单击裁剪按钮。在创建遮罩和裁剪之前调整图像大小时会出现此问题。

这是测试图片：

这是一个 jsfiddle fabric Creating rect with a mouse dynamic js 2.4.1 sent as fix #4

<canvas id="c" width="500" height="500" style="border:1px solid #ccc"></canvas>
<button id="mask">Mask</button>
<button id="crop">Crop</button>

JS

var lastSelectedPicture = null;
var isInsertingCropRectangle = false;
var canvas = new fabric.Canvas('c', {
  selection: true,
  preserveObjectStacking: true,
  height: 700,
  width: 800
});

var crop_rect, isDown, origX, origY, mask, target;
var done = false;

var src = "https://stealth-apsvaw.streamhoster.com/fabric_js_2_4_1_crop_test/graph_paper_540.png";
fabric.Image.fromURL(src, function(img) {
  img.selectable = true;
  img.id = 'target';
  img.top = 30;
  img.left = 30;
  canvas.add(img);
});

canvas.on('object:added', function(e) {
  target = null;
  mask = null;
  canvas.forEachObject(function(obj) {
    //alert(obj.get('id'));
    var id = obj.get('id');
    if (id === 'target') {
      target = obj;
     canvas.setActiveObject(obj);
   }
    if (id === 'mask') {
      //alert(done);
      //alert('mask');
      mask = obj;
    }
  });
});

canvas.on('object:modified', function(e) {
  e.target.setCoords();
  canvas.renderAll();
});

//////////////////////////////////////////////////////////
// MASK
//////////////////////////////////////////////////////////
document.getElementById("mask").addEventListener("click", function() {
  isInsertingCropRectangle = true;
    canvas.discardActiveObject();
    lastSelectedPicture.selectable = false;
    lastSelectedPicture.setCoords();
    lastSelectedPicture.dirty = true;
    canvas.renderAll();
    canvas.discardActiveObject();
    isInsertingCropRectangle = true;
});

//////////////////////////////////////////////////////////
// CROP
//////////////////////////////////////////////////////////
document.getElementById("crop").addEventListener("click", function() {
  if (target !== null && mask !== null) {
    target.setCoords();
    // Re-scale mask
    mask = rescaleMask(target, mask);
    mask.setCoords();

    // Do the crop
    target.clipPath = mask;

    target.dirty=true;
    canvas.setActiveObject(target);
    canvas.bringToFront(target);
    target.selectable = true;
    canvas.remove(mask);
    canvas.renderAll();
    console.log(target);
  }
});

//////////////////////////////////////////////////////////
// RE-SCALE MASK FOR CROPPING
// P R O B L E M  I N  T H I S  F U N C T I O N
//////////////////////////////////////////////////////////
function rescaleMask(target, mask){
  mask.scaleX = 1;
  mask.scaleY = 1;
  var targetCenterX = target.width * target.scaleX / 2;
  var targetCenterY = target.height * target.scaleY / 2;
  var maskOverlapX = mask.left - target.left;
  var maskOverlapY = mask.top - target.top;
  var centerBasedX = maskOverlapX - targetCenterX;
  var centerBasedY = maskOverlapY - targetCenterY;

  if( maskOverlapX >= targetCenterX){
    centerBasedX = maskOverlapX - targetCenterX;
  }
  else{
    centerBasedX = -(targetCenterX) + maskOverlapX;
  }

  if( maskOverlapY >= targetCenterY){
    centerBasedY = maskOverlapY - targetCenterY;
  }
  else{
    centerBasedY = -(targetCenterY) + maskOverlapY;
  }

  console.log('targetleft = '+target.left);
  console.log('targettop = '+target.top);
  console.log('targetCenterX = '+targetCenterX);
  console.log('targetCenterY = '+targetCenterY);
  console.log('maskleft = '+mask.left);
  console.log('masktop = '+mask.top);
  console.log('maskOverlapX = '+maskOverlapX);
  console.log('maskOverlapY = '+maskOverlapY);
  console.log('centerBasedX = '+centerBasedX);
  console.log('centerBasedY = '+centerBasedY);

  mask.left = centerBasedX;
  mask.top = centerBasedY;
  mask.originX = 'left';
  mask.originY = 'top';

  mask.setCoords();
  mask.dirty=true;
  canvas.renderAll();



  //var newMask = mask;
  return(mask);
}

canvas.on('mouse:down', function(o) {
  if( isInsertingCropRectangle == true ){
    console.log('mouse down done = '+done);
    if (done) {
      canvas.renderAll();
      return;
    }
    isDown = true;
    var pointer = canvas.getPointer(o.e);
    origX = pointer.x;
    origY = pointer.y;
    crop_rect = new fabric.Rect({
      left: origX,
      top: origY,
      width: pointer.x - origX,
      height: pointer.y - origY,
      opacity: .3,
      transparentCorners: false,
      selectable: true,
      id: 'mask'
    });
    canvas.add(crop_rect);
    canvas.renderAll();
  }
  else{

  }
});

canvas.on('mouse:move', function(o) {
  if( isInsertingCropRectangle == true ){
    console.log('mouse move done = '+done);
    if (done) {
      canvas.renderAll();
      return;
    }
    if (!isDown) return;
    var pointer = canvas.getPointer(o.e);

    if (origX > pointer.x) {
      crop_rect.set({
        left: Math.abs(pointer.x)
      });
    }
    if (origY > pointer.y) {
      crop_rect.set({
        top: Math.abs(pointer.y)
      });
    }

    crop_rect.set({
      width: Math.abs(origX - pointer.x)
    });
    crop_rect.set({
      height: Math.abs(origY - pointer.y)
    });


    crop_rect.setCoords();
    canvas.renderAll();
  }
  else{

  }
});

canvas.on('mouse:up', function(o) {
  if( isInsertingCropRectangle == true ){
    console.log('mouse up done = '+done);
    if (done) {
      canvas.renderAll();
      return;
    }
    isDown = false;

    crop_rect.set({
      selectable: true
    });
    done = true;
  }
  else{

  }
});

  canvas.on('selection:created', function(event) {
    console.log("canvas.on('selection:created'");
    selectionChanged(event);
  });

  canvas.on('selection:updated', function(event) {
    console.log("canvas.on('selection:updated'");
    selectionChanged(event);
  });

  function selectionChanged(event){
    console.log("selectionChanged");
    console.log("selectionChanged type = "+event.target.type);
    switch(event.target.type) {
      case 'textbox':
        break;
      case 'image':
        lastSelectedPicture = event.target;
        break;
      case 'rect':
        break;
      case 'group':
        break;
      default:
        break;
    }

  }

Answer 1

你需要考虑掩码的 target.scaleX 和 target.scaleY。

var lastSelectedPicture = null;
var isInsertingCropRectangle = false;
canvas = new fabric.Canvas('c', {
  selection: true,
  preserveObjectStacking: true,
  height: 700,
  width: 800
});

var crop_rect, isDown, origX, origY, mask, target;
var done = false;

var src = "https://stealth-apsvaw.streamhoster.com/fabric_js_2_4_1_crop_test/graph_paper_540.png";
fabric.Image.fromURL(src, function(img) {
  img.selectable = true;
  img.id = 'target';
  img.top = 30;
  img.left = 30;
  canvas.add(img);
});

canvas.on('object:added', function(e) {
  target = null;
  mask = null;
  canvas.forEachObject(function(obj) {
    //alert(obj.get('id'));
    var id = obj.get('id');
    if (id === 'target') {
      target = obj;
    canvas.setActiveObject(obj);
   }
    if (id === 'mask') {
      //alert(done);
      //alert('mask');
      mask = obj;
    }
  });
});

canvas.on('object:modified', function(e) {
  e.target.setCoords();
  canvas.renderAll();
});

//////////////////////////////////////////////////////////
// MASK
//////////////////////////////////////////////////////////
document.getElementById("mask").addEventListener("click", function() {
 isInsertingCropRectangle = true;
  canvas.discardActiveObject();
  lastSelectedPicture.selectable = false;
  lastSelectedPicture.setCoords();
  lastSelectedPicture.dirty = true;
  canvas.renderAll();
  canvas.discardActiveObject();
  isInsertingCropRectangle = true;
});

//////////////////////////////////////////////////////////
// CROP
//////////////////////////////////////////////////////////
document.getElementById("crop").addEventListener("click", function() {
  if (target !== null && mask !== null) {
    target.setCoords();
  // Re-scale mask
    mask = rescaleMask(target, mask);
    mask.setCoords();
    
    // Do the crop
    target.clipPath = mask;
    
    target.dirty=true;
    canvas.setActiveObject(target);
    canvas.bringToFront(target);
    target.selectable = true;
    canvas.remove(mask);
    canvas.renderAll();
    console.log(target);
  }
});

//////////////////////////////////////////////////////////
// RE-SCALE MASK FOR CROPPING
// P R O B L E M  I N  T H I S  F U N C T I O N
//////////////////////////////////////////////////////////
function rescaleMask(target, mask){
  mask.scaleX = 1;
  mask.scaleY = 1;

  mask.scaleX/=target.scaleX;
  mask.scaleY/=target.scaleY;
 
  var targetCenterX = target.width * target.scaleX / 2;
 var targetCenterY = target.height * target.scaleY / 2;

  var maskOverlapX = mask.left  - target.left;
  var maskOverlapY = mask.top - target.top;
 var centerBasedX = maskOverlapX - targetCenterX;
 var centerBasedY = maskOverlapY - targetCenterY;

  if( maskOverlapX >= targetCenterX){
   centerBasedX = (maskOverlapX - targetCenterX)/target.scaleX;
  }
  else{
 
   centerBasedX = (-(targetCenterX) + maskOverlapX)/target.scaleX;
  }

  if( maskOverlapY >= targetCenterY){
   centerBasedY = (maskOverlapY - targetCenterY)/target.scaleY;
  }
  else{
   centerBasedY = (-(targetCenterY) + maskOverlapY)/target.scaleY;
  }
  
 
  
  
  console.log('targetleft = '+target.left);
  console.log('targettop = '+target.top);
  console.log('targetCenterX = '+targetCenterX);
  console.log('targetCenterY = '+targetCenterY);
  console.log('maskleft = '+mask.left);
  console.log('masktop = '+mask.top);
 console.log('maskOverlapX = '+maskOverlapX);
 console.log('maskOverlapY = '+maskOverlapY);
  console.log('centerBasedX = '+centerBasedX);
  console.log('centerBasedY = '+centerBasedY);

  mask.left = centerBasedX;
  mask.top = centerBasedY;
  mask.originX = 'left';
  mask.originY = 'top';
 
  mask.setCoords();
  mask.dirty=true;
  canvas.renderAll();
  
  
  
  //var newMask = mask;
  return(mask);
}

canvas.on('mouse:down', function(o) {
 if( isInsertingCropRectangle == true ){
    console.log('mouse down done = '+done);
    if (done) {
      canvas.renderAll();
      return;
    }
    isDown = true;
    var pointer = canvas.getPointer(o.e);
    origX = pointer.x;
    origY = pointer.y;
    crop_rect = new fabric.Rect({
      left: origX,
      top: origY,
      width: pointer.x - origX,
      height: pointer.y - origY,
      opacity: .3,
      transparentCorners: false,
      selectable: true,
      id: 'mask'
    });
    canvas.add(crop_rect);
    canvas.renderAll();
  }
  else{
  
  }
});

canvas.on('mouse:move', function(o) {
 if( isInsertingCropRectangle == true ){
    console.log('mouse move done = '+done);
    if (done) {
      canvas.renderAll();
      return;
    }
    if (!isDown) return;
    var pointer = canvas.getPointer(o.e);

    if (origX > pointer.x) {
      crop_rect.set({
        left: Math.abs(pointer.x)
      });
    }
    if (origY > pointer.y) {
      crop_rect.set({
        top: Math.abs(pointer.y)
      });
    }

    crop_rect.set({
      width: Math.abs(origX - pointer.x)
    });
    crop_rect.set({
      height: Math.abs(origY - pointer.y)
    });


    crop_rect.setCoords();
    canvas.renderAll();
  }
  else{
  
  }
});

canvas.on('mouse:up', function(o) {
 if( isInsertingCropRectangle == true ){
    console.log('mouse up done = '+done);
    if (done) {
      canvas.renderAll();
      return;
    }
    isDown = false;

    crop_rect.set({
      selectable: true
    });
    done = true;
  }
  else{
  
  }
});

 canvas.on('selection:created', function(event) {
  console.log("canvas.on('selection:created'");
  selectionChanged(event);
 });
 
 canvas.on('selection:updated', function(event) {
  console.log("canvas.on('selection:updated'");
  selectionChanged(event);
 });

 function selectionChanged(event){
  console.log("selectionChanged");
  console.log("selectionChanged type = "+event.target.type);
  switch(event.target.type) {
   case 'textbox':
    break;
   case 'image':
    lastSelectedPicture = event.target;
    break;
   case 'rect':
    break;
   case 'group':
    break;
   default:
    break;
  }
  
 }

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.4.1/fabric.min.js"></script>
<canvas id="c" width="500" height="500" style="border:1px solid #ccc"></canvas>
<button id="mask">Mask</button>
<button id="crop">Crop</button>

Fabric JS 2.4.1 如何使用 clipPath 裁剪缩放比例小于或大于 1:1 的图像

Fabric JS 2.4.1 How to use clipPath to crop image that has been scaled smaller or larger then 1:1 Ratio

image

mask

crop

scale

fabricjs