FabricJS触摸平移/缩放整个画布 [英] FabricJS Touch Pan/Zoom Entire Canvas

问题描述

我需要在FabricJS画布上启用触摸缩放/平移。有一些库可以在图像上执行此操作（请参见 pinch-zoom-canvas ）或通过鼠标单击事件（请参见此小提琴），但我似乎无法得到正确的'touch：gesture'事件。

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.

我已经建立了启用手势的库（因此此FabricJS 演示在本地适用于我），但我不知道从哪里开始将手势与工作提琴结合起来。

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.

我尝试了以下代码变体：

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);
        }
    });

但是当我在iPhone / iPad上测试时什么也没发生。

But nothing happens when I test on iPhone/iPad.

推荐答案

缩放是一个愚蠢的错误，我没有在函数参数中包含该事件。下面的代码适用于捏/缩放和点击/拖动。

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;
            }
        }
    });

if / then语句的绝对〜50px是为了避免拖动距离导致画布的最后一点很远跳。也暂停了摇摄以能够独立移动对象。在 github问题线程中找到了捏/缩放代码。

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.

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