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Rumah > Soal Jawab > teks badan
迷茫2017-04-11 11:48:23
<p class="view">
<p class="box" id="bb">
<canvas id="cas" ></canvas>
</p>
</p>
var canvas = document.getElementById("cas"), ctx = canvas.getContext("2d");
var x1, y1, a = 30, timeout, totimes = 100, distance = 30;
var saveDot = [];
var canvasBox = document.getElementById("bb");
canvas.width = canvasBox.clientWidth;
canvas.height = canvasBox.clientHeight;
var img = new Image();
img.src = "pic1.JPG";
img.onload = function () {
var w = canvas.height*img.width/img.height;
ctx.drawImage(img, (canvas.width-w)/2, 0, w, canvas.height);
// var box = document.querySelector('.box');
// box.style.backgroundImage='pic2.JPG';
tapClip()
};
function getClipArea(e, hastouch){
var x = hastouch ? e.targetTouches[0].pageX : e.clientX;
var y = hastouch ? e.targetTouches[0].pageY : e.clientY;
var ndom = canvas;
while(ndom.tagName!=="BODY"){
x -= ndom.offsetLeft;
y -= ndom.offsetTop;
ndom = ndom.parentNode;
}
return {
x: x,
y: y
}
}
//通过修改globalCompositeOperation来达到擦除的效果
function tapClip() {
var hastouch = "ontouchstart" in window ? true : false,
tapstart = hastouch ? "touchstart" : "mousedown",
tapmove = hastouch ? "touchmove" : "mousemove",
tapend = hastouch ? "touchend" : "mouseup";
var area;
var x2,y2;
ctx.lineCap = "round";
ctx.lineJoin = "round";
ctx.lineWidth = a * 2;
ctx.globalCompositeOperation = "destination-out";
window.addEventListener(tapstart, function (e) {
clearTimeout(timeout);
e.preventDefault();
area = getClipArea(e, hastouch);
x1 = area.x;
y1 = area.y;
drawLine(x1, y1);
this.addEventListener(tapmove, tapmoveHandler);
this.addEventListener(tapend, function () {
this.removeEventListener(tapmove, tapmoveHandler);
//检测擦除状态
timeout = setTimeout(function () {
var imgData = ctx.getImageData(0, 0, canvas.width, canvas.height);
var dd = 0;
for (var x = 0; x < imgData.width; x += distance) {
for (var y = 0; y < imgData.height; y += distance) {
var i = (y * imgData.width + x) * 4;
if (imgData.data[i + 3] > 0) { dd++ }
}
}
if (dd / (imgData.width * imgData.height / (distance * distance)) < 0.4) {
canvas.className = "noOp";
}
}, totimes)
});
function tapmoveHandler(e) {
clearTimeout(timeout);
e.preventDefault();
area = getClipArea(e, hastouch);
x2 = area.x;
y2 = area.y;
drawLine(x1, y1, x2, y2);
x1 = x2;
y1 = y2;
}
})
}
function drawLine(x1, y1, x2, y2){
// ctx.save();
// if(arguments.length==2){
// saveDot = [[x1, y1]];
// ctx.beginPath();
// ctx.arc(x1, y1, a, 0, 2 * Math.PI);
// ctx.fill();
// }else {
// saveDot.push([x2,y2]);
// if(saveDot.length >= 3){
// ctx.beginPath();
// ctx.moveTo(saveDot[0][0], saveDot[0][1]);
// ctx.quadraticCurveTo(saveDot[1][0], saveDot[1][1], saveDot[2][0], saveDot[2][1]);
// ctx.stroke();
// saveDot = [saveDot.pop()];
// }
// }
// ctx.restore();
ctx.save();
ctx.beginPath();
if(arguments.length==2){
ctx.arc(x1, y1, a, 0, 2 * Math.PI);
ctx.fill();
}else {
ctx.moveTo(x1, y1);
ctx.lineTo(x2, y2);
ctx.stroke();
}
ctx.restore();
}
//使用clip来达到擦除效果
function otherClip() {
var hastouch = "ontouchstart" in window ? true : false,
tapstart = hastouch ? "touchstart" : "mousedown",
tapmove = hastouch ? "touchmove" : "mousemove",
tapend = hastouch ? "touchend" : "mouseup";
var area;
canvas.addEventListener(tapstart, function (e) {
clearTimeout(timeout);
e.preventDefault();
area = getClipArea(e, hastouch);
x1 = area.x;
y1 = area.y;
ctx.save();
ctx.beginPath();
ctx.arc(x1, y1, a, 0, 2 * Math.PI);
ctx.clip();
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.restore();
canvas.addEventListener(tapmove, tapmoveHandler);
canvas.addEventListener(tapend, function () {
canvas.removeEventListener(tapmove, tapmoveHandler);
timeout = setTimeout(function () {
var imgData = ctx.getImageData(0, 0, canvas.width, canvas.height);
var dd = 0;
for (var x = 0; x < imgData.width; x += distance) {
for (var y = 0; y < imgData.height; y += distance) {
var i = (y * imgData.width + x) * 4;
if (imgData.data[i + 3] > 0) {
dd++
}
}
}
if (dd / (imgData.width * imgData.height / (distance * distance)) < 0.4) {
canvas.className = "noOp";
}
}, totimes)
});
function tapmoveHandler(e) {
e.preventDefault();
area = getClipArea(e, hastouch);
x2 = area.x;
y2 = area.y;
var asin = a * Math.sin(Math.atan((y2 - y1) / (x2 - x1)));
var acos = a * Math.cos(Math.atan((y2 - y1) / (x2 - x1)));
var x3 = x1 + asin;
var y3 = y1 - acos;
var x4 = x1 - asin;
var y4 = y1 + acos;
var x5 = x2 + asin;
var y5 = y2 - acos;
var x6 = x2 - asin;
var y6 = y2 + acos;
ctx.save();
ctx.beginPath();
ctx.arc(x2, y2, a, 0, 2 * Math.PI);
ctx.clip();
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.restore();
ctx.save();
ctx.beginPath();
ctx.moveTo(x3, y3);
ctx.lineTo(x5, y5);
ctx.lineTo(x6, y6);
ctx.lineTo(x4, y4);
ctx.closePath();
ctx.clip();
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.restore();
x1 = x2;
y1 = y2;
}
})
}