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index.html
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<html>
<head>
<title>draw</title>
<style>
body{margin: 0px; background-color: #D4D4D4;}
</style>
</head>
<body>
<canvas></canvas>
<div id="tool"></div>
</body>
<script>
var lastPoints = [];
var canvas = document.getElementsByTagName('canvas');
canvas.style.backgroundColor = "#FFF";
canvas.height = window.innerHeight - 100; //默认=300
canvas.width = window.innerWidth; //默认=150
canvas.onmousedown = startDraw;
canvas.onmouseup = stopDraw;
canvas.ontouchstart = startDraw;
canvas.ontouchstop = stopDraw;
canvas.ontouchmove = drawMouse; // 绑定ontouchmove，不绑定onmousemove
var context = canvas.getContext("2d"); //二维绘图上下文
context.lineCap = "round";
context.lineJoin = "round";
setColor();
setLineWidth();
function setColor(color) {
color = color || "rgb(0, 0, 0)";
context.strokeStyle = context.fillStyle = color;
}
function setLineWidth(size) {
size = size || 2;
context.lineWidth = size;
}
function startDraw(e) {
if (e.touches) {
e.preventDefault();
// Touch event
for (var i = 0; i < e.touches.length; i++) {
lastPoints[i] = getCoords(e.touches[i]);
}
}
else {
// Mouse event
lastPoints[0] = getCoords(e);
canvas.onmousemove = drawMouse;
}
context.beginPath();
return false;
}
function drawMouse(e) {
if (e.touches) {
e.preventDefault();
e.stopPropagation();
for (var i = 0; i < e.touches.length; i++) {
var p = getCoords(e.touches[i]);
lastPoints[i] = drawLine(lastPoints[i], p);
}
}
else {
var p = getCoords(e);
lastPoints[0] = drawLine(lastPoints[0], p);
}
context.stroke();
context.closePath();
context.beginPath();
return false;
}
function stopDraw(e) {
// 点击一下的时候画一个点
if (e.touches) {
e.preventDefault();
e.stopPropagation();
for (var i = 0; i < e.touches.length; i++) {
var p = getCoords(e.touches[i]);
if(lastPoints[i].x == p.x && lastPoints[i].y == p.y)
lastPoints[i] = drawDot(p);
}
}
else {
var p = getCoords(e);
if(lastPoints[0].x == p.x && lastPoints[0].y == p.y)
lastPoints[0] = drawDot(p);
canvas.onmousemove = null;
}
context.fill();
context.closePath();
return false;
}
function getCoords(e) {
if (e.offsetX) {
// Works in Chrome / Safari (except on iPad/iPhone)
return { x: e.offsetX, y: e.offsetY };
}
else if (e.layerX) {
// Works in Firefox
return { x: e.layerX, y: e.layerY };
}
else {
// Works in Safari on iPad/iPhone
return { x: e.pageX - canvas.offsetLeft, y: e.pageY - canvas.offsetTop };
}
}
// Draw a line on the canvas from (s)tart to (e)nd
function drawLine(s, e) {
if (s && e) {
context.moveTo(s.x, s.y);
context.lineTo(e.x, e.y);
}
return e;
}
function drawDot(p) {
context.arc(p.x, p.y, context.lineWidth/2, 0, Math.PI*2, true);
return p;
}
function clearAll() {
context.clearRect(0, 0, canvas.width, canvas.height);
}
function saveCanvas() {
var imgSrc = canvas.toDataURL();
var oImgElement = document.createElement("img");
oImgElement.src = imgSrc;
oImgElement.width = 100;
oImgElement.style.margin = "10px 8px";
oImgElement.style.backgroundColor = "#FFF";
document.body.appendChild(oImgElement);
}
</script>
</html>