如何解决Fabric JS-反复裁剪无法保持先前的位置
FabricJS在重复（多次）裁剪图像时遇到了一些问题。我设法通过在图像上绘制一个矩形，然后将其推入fabricjs组来裁剪它。然后我将clipPath反转以显示裁剪后的图像。 
我对另一部分重复该过程以多次裁剪。但以某种方式无法保持先前的裁剪位置。因此，先前裁切的图像将从原始位置移动。我尝试使用克隆，但仍然无法保持该位置。 
这里是jsFiddle：https://jsfiddle.net/advcha/xy7h8u40/14/或代码：
<!DOCTYPE html>
<html lang='en'>
<head>
<meta charset='UTF-8'>
<title>Fabricjs Crop Background Image</title>
<script src='https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js'></script>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.6.6/fabric.min.js"></script>
<style>
body {
background-color:#ccc;
}
</style>
<script type="text/javascript">
$(document).ready(function() {
var lastSelectedPicture = null;
var isInsertingCropRectangle = false;
canvas = new fabric.Canvas('c',{
selection: true,preserveObjectStacking: true,});
var crop_rect,isDown,origX,origY,mask,target;
var done = false;
var scaleX = 1.0;
var scaleY = 1.0;
var maskArray = [];
var counter = 0;
var src = "https://upload.wikimedia.org/wikipedia/commons/4/44/LampFlowchart.png";
fabric.Image.fromURL(src,function(img) {
img.selectable = true;
img.id = 'target';
scaleX = canvas.width / img.width;
scaleY = canvas.height / img.height;
img.set({
originX: 'left',originY: 'top',scaleX: scaleX,scaleY: scaleY,});
canvas.add(img);
});
canvas.on('object:added',function(e) {
target = null;
mask = null;
canvas.forEachObject(function(obj) {
//console.log(obj.get('id'));
var id = obj.get('id');
if (id === 'target') {
target = obj;
//target.dirty = true;
canvas.setActiveObject(obj);
}
/*if (id === 'mask') {*/
if (id.includes('mask')) {
mask = obj;
counter++;
}
});
});
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;
done = false;
});
document.getElementById("invert_crop").addEventListener("click",function() {
if (target !== null && mask !== null) {
target.setCoords();
// Re-scale mask
mask = rescaleMask(target,mask);
mask.setCoords();
mask.set({opacity: 1.0});
//maskArray.push(mask);
var maskCloned;
mask.clone(function(cloned) {
maskCloned = cloned;
});
maskArray.push(maskCloned);
console.log(maskArray);
var g = new fabric.Group(maskArray);
g.inverted = true;
target.clipPath = g;
target.dirty=true;
canvas.setActiveObject(target);
canvas.bringToFront(target);
target.selectable = true;
canvas.remove(mask);
canvas.renderAll();
}
});
//////////////////////////////////////////////////////////
// RE-SCALE MASK FOR CROPPING
//////////////////////////////////////////////////////////
function rescaleMask(target,ori_mask){
ori_mask.scaleX = 1;
ori_mask.scaleY = 1;
ori_mask.scaleX/=target.scaleX;
ori_mask.scaleY/=target.scaleY;
var targetCenterX = target.width * target.scaleX / 2;
var targetCenterY = target.height * target.scaleY / 2;
var maskOverlapX = ori_mask.left - target.left;
var maskOverlapY = ori_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;
}
ori_mask.left = centerBasedX;
ori_mask.top = centerBasedY;
ori_mask.originX = 'left';
ori_mask.originY = 'top';
ori_mask.setCoords();
ori_mask.dirty=true;
canvas.renderAll();
//var newMask = mask;
return(ori_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_'+counter,});
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>
</head>
<body>
<div>
<canvas style="-moz-user-select: none; cursor: crosshair;" width="500" height="500" id="c"></canvas>
</div>
<div>
<button id="mask">Mask</button>
<button id="invert_crop">Invert Crop</button>
</div>
</body>
</html>
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