我有一个 Canvas ,我可以绘制东西,我想做的是在单击按钮时动态生成新 Canvas 。我定义了一个生成函数,但它不起作用
这是脚本
//<![CDATA[
window.addEventListener('load', function () {
// get the canvas element and its context
var canvas = document.getElementById('sketchpad');
var context = canvas.getContext('2d');
// create a drawer which tracks touch movements
var drawer = {
isDrawing: false,
touchstart: function (coors) {
context.beginPath();
context.moveTo(coors.x, coors.y);
this.isDrawing = true;
},
touchmove: function (coors) {
if (this.isDrawing) {
context.lineTo(coors.x, coors.y);
context.stroke();
}
},
touchend: function (coors) {
if (this.isDrawing) {
this.touchmove(coors);
this.isDrawing = false;
}
}
};
// create a function to pass touch events and coordinates to drawer
function draw(event) {
var type = null;
// map mouse events to touch events
switch(event.type){
case "mousedown":
event.touches = [];
event.touches[0] = {
pageX: event.pageX,
pageY: event.pageY
};
type = "touchstart";
break;
case "mousemove":
event.touches = [];
event.touches[0] = {
pageX: event.pageX,
pageY: event.pageY
};
type = "touchmove";
break;
case "mouseup":
event.touches = [];
event.touches[0] = {
pageX: event.pageX,
pageY: event.pageY
};
type = "touchend";
break;
}
// touchend clear the touches[0], so we need to use changedTouches[0]
var coors;
if(event.type === "touchend") {
coors = {
x: event.changedTouches[0].pageX,
y: event.changedTouches[0].pageY
};
}
else {
// get the touch coordinates
coors = {
x: event.touches[0].pageX,
y: event.touches[0].pageY
};
}
type = type || event.type
// pass the coordinates to the appropriate handler
drawer[type](coors);
}
// detect touch capabilities
var touchAvailable = ('createTouch' in document) || ('ontouchstart' in window);
// attach the touchstart, touchmove, touchend event listeners.
if(touchAvailable){
canvas.addEventListener('touchstart', draw, false);
canvas.addEventListener('touchmove', draw, false);
canvas.addEventListener('touchend', draw, false);
}
// attach the mousedown, mousemove, mouseup event listeners.
else {
canvas.addEventListener('mousedown', draw, false);
canvas.addEventListener('mousemove', draw, false);
canvas.addEventListener('mouseup', draw, false);
}
// prevent elastic scrolling
document.body.addEventListener('touchmove', function (event) {
event.preventDefault();
}, false); // end body.onTouchMove
}, false); // end window.onLoad
function generate(){
var newCanvas = document.createElement('canvas');
newCanvas.width = 400;
newCanvas.height = 400;
document.getElementById('container').appendChild(newCanvas);
ctx = newCanvas.getContext('2d');
}
//]]>
这里是 jsfiddle http://jsfiddle.net/regeme/WVUwn/ ps:绘图未显示在 jsfiddle 上,但它可以在我的本地主机上运行,我完全不知道它,无论如何我需要的是生成函数,我做到了,但我认为我错过了一些东西.. 有任何想法吗?谢谢..
最佳答案
下面是我编写的用于动态创建 Canvas 的函数。
如果 Canvas 已存在(相同 ID),则返回该 Canvas 。
pixelRatio
参数可以默认为 1。它用于在 Retina 显示屏上设置正确的尺寸(因此对于配备 Retina 的 iPhone,该值将为 2)
function createLayer(sizeW, sizeH, pixelRatio, id, zIndex) {
// *** An id must be given.
if (typeof id === undefined) {
return false;
}
// *** If z-index is less than zero we'll make it a buffer image.
isBuffer = (zIndex < 0) ? true : false;
// *** If the canvas exist, clean it and just return that.
var element = document.getElementById(id);
if (element !== null) {
return element;
}
// *** If no zIndex is passed in then default to 0.
if (typeof zIndex === undefined || zIndex < 0) {
zIndex = 0;
}
var canvas = document.createElement('canvas');
canvas.width = sizeW;
canvas.height = sizeH;
canvas.id = id;
canvas.style.width = sizeW*pixelRatio + "px";
canvas.style.height = sizeH*pixelRatio + "px";
canvas.style.position = "absolute";
canvas.style.zIndex = zIndex;
if (!isBuffer) {
var body = document.getElementsByTagName("body")[0];
body.appendChild(canvas);
}
return canvas;
}
关于javascript - 在javascript中动态生成新 Canvas ,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18202795/