现在,当用户旋转鼠标滚轮时,会生成一些形状(我只包括了三角形,因为它们都是以相同的方式生成的)。我想在逐渐消失的形状后面留下痕迹。我环顾四周并尝试了几种不同的方法,但似乎无法使它们中的任何一种起作用。这是代码:
<html>
<head>
<script>
var canvas;
var context;
var triangles = [];
var timer;
function init() {
canvas = document.getElementById('canvas');
context = canvas.getContext("2d");
resizeCanvas();
window.addEventListener('resize', resizeCanvas, false);
window.addEventListener('orientationchange', resizeCanvas, false);
canvas.onwheel = function(event) {
handleClick(event.clientX, event.clientY);
};
var timer = setInterval(resizeCanvas, 30);
}
function Triangle(x,y,triangleColor) {
this.x = x;
this.y = y;
this.triangleColor = triangleColor;
this.vx = Math.random() * 30 - 15;
this.vy = Math.random() * 30 - 15;
this.time = 100;
}
function handleClick(x,y) {
var colors = [[0,170,255], [230,180,125], [50,205,130]];
var triangleColor = colors[Math.floor(Math.random()*colors.length)];
triangles.push(new Triangle(x,y,triangleColor));
for (var i=0; i<triangles.length; i++) {
drawTriangle(triangles[i]);
}
}
function drawTriangle(triangle) {
context.beginPath();
context.moveTo(triangle.x,triangle.y);
context.lineTo(triangle.x+25,triangle.y+25);
context.lineTo(triangle.x+25,triangle.y-25);
var c = triangle.triangleColor
context.fillStyle = 'rgba(' + c[0] + ', ' + c[1] + ', ' + c[2] + ', ' + (triangle.time / 100) + ')';
context.fill();
}
function resizeCanvas() {
canvas.width = window.innerWidth-20;
canvas.height = window.innerHeight-20;
fillBackgroundColor();
for (var i=0; i<triangles.length; i++) {
var t = triangles[i];
drawTriangle(t);
if (t.x + t.vx > canvas.width || t.x + t.vx < 0)
t.vx = -t.vx
if (t.y + t.vy > canvas.height || t.y + t.vy < 0)
t.vy = -t.vy
if (t.time === 0) {
triangles.splice(i,1);
}
t.time -= 1;
t.x += t.vx;
t.y += t.vy;
}
}
function fillBackgroundColor() {
context.fillStyle = "black";
context.fillRect(0,0,canvas.width,canvas.height);
}
window.onload = init;
</script>
</head>
<body>
<canvas id="canvas" width="500" height="500"></canvas>
</body>
</html>
最佳答案
我设法做到这一点的方法是存储对象的过去位置(例如,过去的10个位置,然后从一个位置绘制到下一个位置。
1.将数组pastX和pastY添加到三角形对象。
this.pastX = [];
this.pastY = [];
2.每个刻度线将每个元素再放置1个位置,并首先添加当前位置。
在更新三角形位置之前
for(var k = t.pastX.length; k > 0; k--){
if(k < 10){
t.pastX[k] = pastX[k-1];
t.pastY[k] = pastY[k-1];
}
t.pastX[0] = t.x;
t.pastY[0] = t.y;
这样在它们之间画线(从0到1,从1到2,依此类推);
for(var k = 0; k //画一条线从pastX [k],pastY [k]到pastX [k + 1],pastY [k + 1]
}
希望我能帮到你。