[英]JavaScript: HTML5 and sliding a ball up the page
对于HTML5和臭名昭着的Canvas元素,我是一个新手 。 目前,我在我的网页上绘制了一个蓝色的球,点击了画布元素后,球滑到一个位置(Y),我将其传递给drawCircle函数。 我想将球滑到 Y位置,而球则跳到Y位置。
这是我到目前为止的代码:
var context, canvas;
var x = 100;
var y = 200;
var dx = 5;
var dy = .02;
function drawCircle(move) {
if(move) {
x = move.x
y = move.y
}
canvas = document.getElementById('myCanvas');
context = canvas.getContext('2d')
context.clearRect(0,0,canvas.width, canvas.height);
context.beginPath()
context.fillStyle = "#0000ff";
context.arc(x, y, 20, 0, Math.PI*2, true);
context.closePath();
context.fill();
// if(x < 0 || x > canvas.width) dx=-dx;
// if(y < 0 || y > canvas.height) dy =- dy;
if(move) {
y+=dy
}
// x+=dx
// y+=dy
}
window.onload = function(e){
// setInterval(drawCircle, 10)
drawCircle()
canvas.onclick = function(){
var move = {
x: 100,
y: 100
}
drawCircle(move)
}
}
JSFiddle: http : //jsfiddle.net/Uam8z/1/
您可以像建议的代码一样使用setInterval
函数,这就是我做的方式..
var context, canvas;
var x = 100;
var y = 200;
var dx = 5;
var dy = 5; //0.02 makes it move v. slowly!
function drawCircle(move) {
if(move) {
x = move.x
y = move.y
}
context.clearRect(0,0,canvas.width, canvas.height);
context.beginPath()
context.fillStyle = "#0000ff";
context.arc(x, y, 20, 0, Math.PI*2, true);
context.closePath();
context.fill();
}
window.onload = function(e){
canvas = document.getElementById('myCanvas');
context = canvas.getContext('2d');
drawCircle()
var interval;
canvas.onclick = function(){
if(interval) //don't run if already doing so..
return;
var end_move = {
x: 100,
y: 100
};
var interval = setInterval(function(){
if(x === end_move.x && y === end_move.y){
//stop animation case..
clearInterval(interval);
interval = undefined;
} else {
var newX;
if(Math.abs(x - end_move.x) < dx){
newX = x;
} else {
newX = (x > end_move.x) ? x-dx : x+dx;
}
var newY;
if(Math.abs(y - end_move.y) < dy){
newY = y;
} else {
newY = (y > end_move.y) ? y-dy : y+dy;
}
drawCircle({
x: newX,
y: newY
});
}
}, 10);
}
}
代码设置了一个end_position
,其中球应该结束。 然后它设置一个间隔以在每次迭代时将其移动相同的距离,当它接近所需位置时,它通过将位置设置为所需位置来确保间隔终止。
您不需要继续定义画布并设置上下文。 这会处理向上滑动:
var context, canvas, target;
var x = 100;
var y = 200;
var dx = 5;
var dy = 2; //.2 is pretty slow
function drawCircle() {
// sliding up
if (y > target) {
y -= dy;
}
context.clearRect(0, 0, canvas.width, canvas.height);
context.beginPath()
context.fillStyle = "#0000ff";
context.arc(x, y, 20, 0, Math.PI * 2, true);
context.fill();
context.closePath();
}
window.onload = function () {
// get canvas, and context once
canvas = document.getElementById('myCanvas');
context = canvas.getContext('2d');
// set target y position
canvas.onclick = function (e) {
target = e.clientY;
}
// 30fps
setInterval(drawCircle, (1000 / 30));
}
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