为什么我的小应用程序不能在智能手机上绘制？

Question

我有这段代码，可以在 android 智能手机平板电脑上绘图。我使用触摸事件。对于桌面事件，它可以工作，在桌面浏览器上，它也可以工作。在代码中，我注释掉了桌面代码，只留下 android 智能手机和平板电脑的代码。有什么想法吗？

这是HTML：

<div id="canvas">Click to draw<br/></div>

这里是 JavaScript:


(function() {
    // Creates a new canvas element and appends it as a child
    // to the parent element, and returns the reference to
    // the newly created canvas element


    function createCanvas(parent, width, height) {
        var canvas = {};
        canvas.node = document.createElement('canvas');
        canvas.context = canvas.node.getContext('2d');
        canvas.node.width = width || 100;
        canvas.node.height = height || 100;
        parent.appendChild(canvas.node);
        return canvas;
    }

    function init(container, width, height, fillColor) {
        var canvas = createCanvas(container, width, height);
        var ctx = canvas.context;
        // define a custom fillCircle method
        ctx.fillCircle = function(x, y, radius, fillColor) {
            this.fillStyle = fillColor;
            this.beginPath();
            this.moveTo(x, y);
            this.arc(x, y, radius, 0, Math.PI * 2, false);
            this.fill();
        };
        ctx.clearTo = function(fillColor) {
            ctx.fillStyle = fillColor;
            ctx.fillRect(0, 0, width, height);
        };
        ctx.clearTo(fillColor || "#ddd");

        // bind mouse events
        /*canvas.node.onmousemove = function(e) {
            if (!canvas.isDrawing) {
               return;
            }
            var x = e.pageX - this.offsetLeft;
            var y = e.pageY - this.offsetTop;
            var radius = 5; // or whatever
            var fillColor = '#ff0000';
            ctx.fillCircle(x, y, radius, fillColor);
        };
        canvas.node.onmousedown = function(e) {
            canvas.isDrawing = true;
        };
        canvas.node.onmouseup = function(e) {
            canvas.isDrawing = false;
        };
        */
        // bind touch events
        canvas.node.ontouchmove = function(e) {
            if (!canvas.isDrawing) {
               return;
            }
            var x = e.pageX - this.offsetLeft;
            var y = e.pageY - this.offsetTop;
            var radius = 5; // or whatever
            var fillColor = '#ff0000';
            ctx.fillCircle(x, y, radius, fillColor);
        };
        canvas.node.ontouchstart = function(e) {
            canvas.isDrawing = true;
        };
        canvas.node.ontouchend = function(e) {
            canvas.isDrawing = false;
        };
    }

    var container = document.getElementById('canvas');
    init(container, 200, 200, '#ddd');

})();

Link 到代码：https://codepen.io/sp2012/pen/gOmGZGV

Answer 1

应该是因为你的x和y提取

   var x = e.pageX - this.offsetLeft;
   var y = e.pageY - this.offsetTop;

检查 this documentation 是否有 canvas 个触摸事件

我认为您应该访问 e.touches 数组来提取 pageX 和 pageY 信息。

这里有一个 link where I made some changes to make it work for mobile. But it's just a hack :) . Also go through this link 有类似的问题。

为什么我的小应用程序不能在智能手机上绘制？

Why my small app does not draw on smartphones?

javascript

canvas