FabricJS 触摸平移/缩放整个画布

我需要在 FabricJS 画布上启用触摸缩放/平移。有些库允许在图像上执行此行为（请参阅捏缩放画布 https://github.com/vash15/pinch-zoom-canvas）或通过鼠标单击事件（参见这个小提琴 http://jsfiddle.net/gncabrera/hkee5L6d/5/）但我似乎无法正确连接“触摸：手势”事件。

我已经构建了启用手势的库（所以这个 FabricJS http://fabricjs.com/touch-events演示对我来说在本地工作），但我不知道从哪里开始将手势与工作小提琴结合起来。

我尝试了这样的代码变体：

    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);
        }
    });

但是当我在 iPhone/iPad 上测试时没有任何反应。

捏合缩放是一个愚蠢的错误，我没有将该事件包含在函数参数中。下面的代码适用于捏合/缩放和点击/拖动。

    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;
            }
        }
    });

绝对约 50px if/then 语句是为了避免拖动远离最后一个点导致画布跳跃。还暂停平移以便能够独立移动对象。捏合/缩放代码被发现于github问题线程 https://github.com/kangax/fabric.js/issues/2658.