How to increase touch area control points on mobile device ( not increase display size of control points ) in fabricjs? - html5-canvas

Question

How to increase touch area of control points on mobile device with FabricJS? Because on mobile they are too small for smooth interactive with. But not change size of control points ( for nice view ).
Here is my code:
How to increase interactive of control points = view control points size x 2 ?
var canvasObject = document.getElementById("editorCanvas");
// set canvas equal size with div
$(canvasObject).width($("#canvasContainer").width());
$(canvasObject).height($("#canvasContainer").height());
var canvas = new fabric.Canvas('editorCanvas', {
backgroundColor: 'white',
selectionLineWidth: 2,
width: $("#canvasContainer").width(),
height: $("#canvasContainer").height()
});
// test customize control points
var rect = new fabric.Rect({
left: 30,
top: 30,
fill: 'red',
width: 150,
height: 150
});
canvas.add(rect);
rect.set({
transparentCorners: false,
cornerColor: 'white',
cornerStrokeColor: 'rgba(14,19,24,.15)',
borderColor: 'rgba(41,198,203,1)',
selectionLineWidth: 8,
cornerSize: 12,
cornerStyle: 'circle',
});
#canvasContainer {
width: 100%;
height: 100vh;
background-color: gray;
}
<script src="https://code.jquery.com/jquery-3.3.1.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.3.2/fabric.js"></script>
<div id="canvasContainer">
<canvas id="editorCanvas"></canvas>
</div>
Please show me the way to resolve this problem.
By the way: ( on mobile device ) is there any way to allow drag object only object is selected before?
Thank you very much!

Answer 1

You need to override _setCornerCoords method of object and change the value of cornerHypotenuse.
DEMO
var canvasObject = document.getElementById("editorCanvas");
// set canvas equal size with div
$(canvasObject).width($("#canvasContainer").width());
$(canvasObject).height($("#canvasContainer").height());
var canvas = new fabric.Canvas('editorCanvas', {
backgroundColor: 'white',
selectionLineWidth: 2,
width: $("#canvasContainer").width(),
height: $("#canvasContainer").height()
});
// test customize control points
var rect = new fabric.Rect({
left: 30,
top: 30,
fill: 'red',
width: 150,
height: 150
});
canvas.add(rect);
rect.set({
transparentCorners: false,
cornerColor: 'white',
cornerStrokeColor: 'rgba(14,19,24,.15)',
borderColor: 'rgba(41,198,203,1)',
selectionLineWidth: 8,
cornerSize: 5,
cornerStyle: 'circle'
});
rect._setCornerCoords = function() {
var coords = this.oCoords,
newTheta = fabric.util.degreesToRadians(45 - this.angle),
cornerHypotenuse = this.cornerSize * 2 * 0.707106,
cosHalfOffset = cornerHypotenuse * fabric.util.cos(newTheta),
sinHalfOffset = cornerHypotenuse * fabric.util.sin(newTheta),
x, y;
for (var point in coords) {
x = coords[point].x;
y = coords[point].y;
coords[point].corner = {
tl: {
x: x - sinHalfOffset,
y: y - cosHalfOffset
},
tr: {
x: x + cosHalfOffset,
y: y - sinHalfOffset
},
bl: {
x: x - cosHalfOffset,
y: y + sinHalfOffset
},
br: {
x: x + sinHalfOffset,
y: y + cosHalfOffset
}
};
}
}
#canvasContainer {
width: 100%;
height: 100vh;
background-color: gray;
}
<script src="https://code.jquery.com/jquery-3.3.1.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.3.2/fabric.js"></script>
<div id="canvasContainer">
<canvas id="editorCanvas"></canvas>
</div>