canvas教程

JavaScript回调(callback)函数概念...

字号+ 作者:H5之家 来源:H5之家 2017-10-09 17:01 我要评论( )

[JavaScript回调(callback)函数概念自我理解及示例]:此文适合JavaScript入门级选手阅读,高手就可以飘过了。 先扯点闲话。在中国,有这么一种现象:不管什么词或


window.onload=function() {
canvas.onmousedown = function(e) {
e = e || event;
startX = e.clientX;
startY = e.clientY;
if(select[0].value == "arc") {
canvas.onmousemove = moveShowArc;
} else {
canvas.onmousemove = moveShowRect;
}
}
canvas.onmouseup = function() {
canvas.onmousemove = "";
}
}
function moveShowRect(e) {
context.clearRect(0, 0, 500, 300);
endX = e.clientX - startX;
endY = e.clientY - startY;
context.beginPath();
context.rect(startX, startY, endX, endY);
context.fillStyle = "#8ED6FF";
context.fill();
context.lineWidth = 3;
context.strokeStyle = "black";
context.stroke();
}
function moveShowArc(e) {
context.clearRect(0, 0, 500, 300);
endX = e.clientX - startX;
endY = e.clientY - startY;
radius = Math.sqrt(Math.pow(endX,2)+Math.pow(endY,2));
context.beginPath();
context.arc(startX, startY,radius,0,2 * Math.PI,false);
context.fillStyle = "#8ED6FF";
context.fill();
context.lineWidth = 3;
context.strokeStyle = "black";
context.stroke();
}
window.onload=function() {
canvas.onmousedown = function(e) {
e = e || event;
startX = e.clientX;
startY = e.clientY;
if(select[0].value == "arc") {
canvas.onmousemove = moveShowArc;
} else {
canvas.onmousemove = moveShowRect;
}
}
canvas.onmouseup = function() {
canvas.onmousemove = "";
}
}
function moveShowRect(e) {
context.clearRect(0, 0, 500, 300);
endX = e.clientX - startX;
endY = e.clientY - startY;
context.beginPath();
context.rect(startX, startY, endX, endY);
context.fillStyle = "#8ED6FF";
context.fill();
context.lineWidth = 3;
context.strokeStyle = "black";
context.stroke();
}
function moveShowArc(e) {
context.clearRect(0, 0, 500, 300);
endX = e.clientX - startX;
endY = e.clientY - startY;
radius = Math.sqrt(Math.pow(endX,2)+Math.pow(endY,2));
context.beginPath();
context.arc(startX, startY,radius,0,2 * Math.PI,false);
context.fillStyle = "#8ED6FF";
context.fill();
context.lineWidth = 3;
context.strokeStyle = "black";
context.stroke();
}

 

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