user3356048 user3356048 - 4 months ago 62
Javascript Question

fabric.js limit rotation to x degrees with rotation handle

I am using fabric.js and trying to allow rotation for any object on my canvas, not freely 360 degrees, but only 15 degrees at a time, using the rotation handle. I searched really hard but couldn't find an answer so far. Is this possible?

Answer

You can use canvas.on("object:rotating") to interfer with rotation of all objects. I defined a set of valid angles, and then on the rotation event i checked which one to use.

var angles = [0, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, 180, 195, 210, 225, 240, 255, 270, 285, 300, 315, 330, 345, 360];

canvas.on("object:rotating", function(rotEvtData) {
    var targetObj = rotEvtData.target;
    var angle = targetObj.angle % 360;
    for (var i=0; i < angles.length; i++) {
       if (angle <=  angles[i]) {
          targetObj.angle = angles[i];
          break;
       }
    }
  });

var canvas = new fabric.Canvas("c");

var rect = new fabric.Rect({
    left: 100,
    top: 100,
    fill: 'red',
    width: 90,
    height: 90
});

canvas.add(rect);

var angles = [0, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, 180, 195, 210, 225, 240, 255, 270, 285, 300, 315, 330, 345, 360];
canvas.on("object:rotating", function(rotEvtData) {
    var targetObj = rotEvtData.target;
    var angle = targetObj.angle % 360;
    for (var i=0; i < angles.length; i++) {
       if (angle <=  angles[i]) {
          targetObj.angle = angles[i];
          break;
       }
    }
  });
<script src="http://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.5.0/fabric.min.js"></script>
<canvas id="c" width="400" height="400"></canvas>

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