Align object to canvas in fabricjs

Question

I'm trying to implement object alignment (i.e Top - Bottom - Left - Right - CenterH - CenterV) my code is working great but i don't know how to handle the alignment if the object is rotated (with the code provided part of the object disappear when the angle is different than 0, I want to know how to calculate the min left offset to be able to still see the whole rotated object). My code below.

var canvas = new fabric.Canvas('a');
canvas.add(new fabric.Rect({
  left: 50,
  top: 50,
  height: 50,
  width: 50,
  fill: 'red'
}));
canvas.add(new fabric.Rect({
  angle: 76,
  left: 180,
  top: 50,
  height: 50,
  width: 50,
  fill: 'green'
}));
canvas.add(new fabric.Rect({
  left: 90,
  top: 130,
  height: 50,
  width: 50,
  fill: 'blue'
}));

canvas.renderAll();

$('.alignment').click(function() {
  var cur_value = $(this).attr('data-action');
  var activeObj = canvas.getActiveObject() || canvas.getActiveGroup();
  if (cur_value != '' && activeObj) {
    process_align(cur_value, activeObj);
    activeObj.setCoords();
    canvas.renderAll();
  } else {
    alert('Please select a item');
    return false;
  }
});

/* Align the selected object */
function process_align(val, activeObj) {
  switch (val) {

    case 'left':
      activeObj.set({
        left: 0
      });
      break;
    case 'right':
      activeObj.set({
        left: canvas.width - (activeObj.width * activeObj.scaleX)
      });
      break;
    case 'top':
      activeObj.set({
        top: 0
      });
      break;
    case 'bottom':
      activeObj.set({
        top: canvas.height - (activeObj.height * activeObj.scaleY)
      });
      break;
    case 'centerH':
      activeObj.set({
        left: (canvas.width / 2) - ((activeObj.width * activeObj.scaleX) / 2)
      });
      break;
    case 'centerV':
      activeObj.set({
        top: (canvas.height / 2) - ((activeObj.height * activeObj.scaleY) / 2)
      });
      break;
  }
}

canvas {
  border: 2px solid black;
}

<script
  src="https://code.jquery.com/jquery-2.2.4.min.js"
  integrity="sha256-BbhdlvQf/xTY9gja0Dq3HiwQF8LaCRTXxZKRutelT44="
  crossorigin="anonymous"></script>
<script type='text/javascript' src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.19/fabric.js"></script>
<button class="alignment" data-action="left">Align Left</button>
<button class="alignment" data-action="centerH">Align CenterH</button>
<button class="alignment" data-action="centerV">Align CenterV</button>
<button class="alignment" data-action="right">Align Right</button>
<button class="alignment" data-action="top">Align Top</button>
<button class="alignment" data-action="bottom">Align Bottom</button>
<canvas id="a" width="400" height="200"></canvas>

How can i update the code to be able to align rotated object as well? (check the alignment on the green rect)

Answer 1

So as @HelderSepulveda suggested I used aCoords to dynamically calculate the coordinates, I'll paste the working code below in case anyone needs it.

var canvas = new fabric.Canvas('a');
canvas.add(new fabric.Rect({
  left: 50,
  top: 50,
  height: 50,
  width: 50,
  fill: 'red'
}));
canvas.add(new fabric.Rect({
  angle: 76,
  left: 180,
  top: 50,
  height: 50,
  width: 50,
  fill: 'green'
}));
canvas.add(new fabric.Rect({
  left: 90,
  top: 130,
  height: 50,
  width: 50,
  fill: 'blue'
}));

canvas.renderAll();

$('.alignment').click(function() {
  var cur_value = $(this).attr('data-action');
  var activeObj = canvas.getActiveObject() || canvas.getActiveGroup();
  if (cur_value != '' && activeObj) {
    process_align(cur_value, activeObj);
    activeObj.setCoords();
    canvas.renderAll();
  } else {
    alert('Please select a item');
    return false;
  }
});

/* Align the selected object */
function process_align(val, activeObj) {
  switch (val) {

    case 'left':
      var left;
      if(activeObj.angle <= 90) {
        left = activeObj.aCoords.tl.x - activeObj.aCoords.bl.x;
      }
      if(activeObj.angle > 90 && activeObj.angle <= 180) {
        left = activeObj.aCoords.tl.x - activeObj.aCoords.br.x;
      }
      if(activeObj.angle > 180 && activeObj.angle <= 270) {
        left = activeObj.aCoords.tl.x - activeObj.aCoords.tr.x;
      }
      if(activeObj.angle > 270) {
        left = 0;
      }
      activeObj.set({
        left: left
      });
      break;
    case 'right':
      var left;
      if(activeObj.angle <= 90) {
        left = activeObj.aCoords.tl.x + (canvas.width - activeObj.aCoords.tr.x);
      }
      if(activeObj.angle > 90 && activeObj.angle <= 180) {
        left = canvas.width;
      }
      if(activeObj.angle > 180 && activeObj.angle <= 270) {
        left = activeObj.aCoords.tl.x + (canvas.width - activeObj.aCoords.bl.x);
      }
      if(activeObj.angle > 270) {
        left = activeObj.aCoords.tl.x + (canvas.width - activeObj.aCoords.br.x);
      }
      activeObj.set({
        left: left
      });
      break;
    case 'top':
      var top;
      if(activeObj.angle <= 90) {
        top = 0;
      }
      if(activeObj.angle > 90 && activeObj.angle <= 180) {
        top = activeObj.aCoords.tl.y - activeObj.aCoords.bl.y;
      }
      if(activeObj.angle > 180 && activeObj.angle <= 270) {
        top = activeObj.aCoords.tl.y - activeObj.aCoords.br.y;
      }
      if(activeObj.angle > 270) {
        top = activeObj.aCoords.tl.y - activeObj.aCoords.tr.y;
      }
      activeObj.set({
        top: top
      });
      break;
    case 'bottom':
      var top;
      if(activeObj.angle <= 90) {
        top = activeObj.aCoords.tl.y + (canvas.height - activeObj.aCoords.br.y);
      }
      if(activeObj.angle > 90 && activeObj.angle <= 180) {
        top = activeObj.aCoords.tl.y + (canvas.height - activeObj.aCoords.tr.y);
      }
      if(activeObj.angle > 180 && activeObj.angle <= 270) {
        top = canvas.height;
      }
      if(activeObj.angle > 270) {
        top = activeObj.aCoords.tl.y + (canvas.height - activeObj.aCoords.bl.y);
      }
      activeObj.set({
        top: top
      });
      break;
    case 'centerH':
      activeObj.viewportCenterH();
      break;
    case 'centerV':
      activeObj.viewportCenterV();
      break;
  }
}

canvas {
  border: 2px solid black;
}

<script
  src="https://code.jquery.com/jquery-2.2.4.min.js"
  integrity="sha256-BbhdlvQf/xTY9gja0Dq3HiwQF8LaCRTXxZKRutelT44="
  crossorigin="anonymous"></script>
<script type='text/javascript' src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.19/fabric.js"></script>
<button class="alignment" data-action="left">Align Left</button>
<button class="alignment" data-action="centerH">Align CenterH</button>
<button class="alignment" data-action="centerV">Align CenterV</button>
<button class="alignment" data-action="right">Align Right</button>
<button class="alignment" data-action="top">Align Top</button>
<button class="alignment" data-action="bottom">Align Bottom</button>
<canvas id="a" width="400" height="200"></canvas>

Answer 2

Take a look at this approach, the animate has a nice abort option that I'm using to stop if any of the corner points exceeds the boundaries of the canvas, I just tested on chrome and to simplify removed the center aligns, you can add that later if you need.

function move(obj, prop, value) {
    obj.saveState();
    obj.animate(prop, value, {
        duration: 1000,
        onChange: canvas.renderAll.bind(canvas),
        onComplete: canvas.renderAll.bind(canvas),
        easing: fabric.util.ease["easeOutQuad"],
        abort: function () {
            obj.setCoords();
            for (const prop in obj.aCoords) {
                point = obj.aCoords[prop]
                if (point.x <= 0 || point.x >= canvas.width ||
                    point.y <= 0 || point.y >= canvas.height) {
                    obj.left = obj._stateProperties.left;
                    obj.top = obj._stateProperties.top;
                    return true
                }
            }
            obj.saveState();
        }
    });
}

function process_align(val, obj) {
    switch (val) {
        case 'left':
            move(obj, 'left', 1);
            break;
        case 'right':
            move(obj, 'left', canvas.width - 1);
            break;
        case 'top':
            move(obj, 'top', 1);
            break;
        case 'bottom':
            move(obj, 'top', canvas.height - 1);
            break;
    }
}

var canvas = new fabric.Canvas('a');
canvas.stateful = true;
canvas.add(new fabric.Rect({ left: 50, top: 50, height: 50, width: 50, fill: 'red' }));
canvas.add(new fabric.Rect({ angle: 76, left: 240, top: 50, height: 50, width: 50, fill: 'green' }));
canvas.add(new fabric.Rect({ left: 120, top: 100, height: 50, width: 50, fill: 'blue' }));
canvas.renderAll();

$('.alignment').click(function () {
    var cur_value = $(this).attr('data-action');
    var activeObj = canvas.getActiveObject() || canvas.getActiveGroup();
    if (cur_value != '' && activeObj) {
        process_align(cur_value, activeObj);
        activeObj.setCoords();
        canvas.renderAll();
    } else {
        alert('Please select a item');
        return false;
    }
});

canvas {
  border: 2px solid black;
}

<script src="https://code.jquery.com/jquery-2.2.4.min.js" integrity="sha256-BbhdlvQf/xTY9gja0Dq3HiwQF8LaCRTXxZKRutelT44=" crossorigin="anonymous"></script>
<script type='text/javascript' src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.19/fabric.js"></script>

<button class="alignment" data-action="left">Align Left</button>
<button class="alignment" data-action="right">Align Right</button>
<button class="alignment" data-action="top">Align Top</button>
<button class="alignment" data-action="bottom">Align Bottom</button>
<canvas id="a" width="400" height="160"></canvas>

And there are a few animation easings you can pick from:
http://fabricjs.com/animation-easing