I need to enable touch zoom/panning on a FabricJS canvas. There are libraries that will allow this behavior on an image (see pinch-zoom-canvas) or via mouse-click events (see this Fiddle) but I can't seem to get the 'touch:gesture' events hooked up properly.
I've built the library with gestures enabled (so this FabricJS demo works locally for me), but I don't know where to start with combining the gestures with the working fiddle.
I tried variations of code like this:
canvas.on({
'touch:gesture': function() {
var text = document.createTextNode(' Gesture ');
info.insertBefore(text, info.firstChild);
// Handle zoom only if 2 fingers are touching the screen
if (event.e.touches && event.e.touches.length == 2) {
// Get event point
var point = new fabric.Point(event.self.x, event.self.y);
// Remember canvas scale at gesture start
if (event.self.state == "start") {
zoomStartScale = self.canvas.getZoom();
}
// Calculate delta from start scale
var delta = zoomStartScale * event.self.scale;
// Zoom to pinch point
self.canvas.zoomToPoint(point, delta);
}
},
'touch:drag': function(e) {
panning = true;
var text = document.createTextNode(' Dragging ');
info.insertBefore(text, info.firstChild);
if (panning && e && e.e) {
debugger;
var units = 10;
var delta = new fabric.Point(e.e.movementX, e.e.movementY);
canvas.relativePan(delta);
}
panning = false;
},
'touch:longpress': function() {
var text = document.createTextNode(' Longpress ');
info.insertBefore(text, info.firstChild);
}
});
But nothing happens when I test on iPhone/iPad.
The pinch to zoom was a stupid mistake, I hadn't included the event in the function parameter. The code below is working for pinch/zoom and tap/drag.
canvas.on({
'touch:gesture': function(e) {
if (e.e.touches && e.e.touches.length == 2) {
pausePanning = true;
var point = new fabric.Point(e.self.x, e.self.y);
if (e.self.state == "start") {
zoomStartScale = self.canvas.getZoom();
}
var delta = zoomStartScale * e.self.scale;
self.canvas.zoomToPoint(point, delta);
pausePanning = false;
}
},
'object:selected': function() {
pausePanning = true;
},
'selection:cleared': function() {
pausePanning = false;
},
'touch:drag': function(e) {
if (pausePanning == false && undefined != e.e.layerX && undefined != e.e.layerY) {
currentX = e.e.layerX;
currentY = e.e.layerY;
xChange = currentX - lastX;
yChange = currentY - lastY;
if( (Math.abs(currentX - lastX) <= 50) && (Math.abs(currentY - lastY) <= 50)) {
var delta = new fabric.Point(xChange, yChange);
canvas.relativePan(delta);
}
lastX = e.e.layerX;
lastY = e.e.layerY;
}
}
});
The absolute ~50px if/then statement is to avoid drags far away from the last point causing the canvas to jump. Also paused the panning to be able to move object independently. Pinch/zoom code was found in a github issues thread.