试图在画布中动画形状，它会出现，但不会移动
试图在画布中动画形状，它会出现，但不会移动
提问于 2016-04-23 19:24:30
我试着在画布中用lineTo制作多边形动画。它出现了，但不动。我试着遵循物体的方法，但它似乎什么也没做。
帮助?
<!doctype html>
<html>
<head>
<style>
canvas {
border: 1px solid black;
}
</style>
<script>
"use strict";
var canvas;
var ctx;
var timer;
var shapes;
var x;
var y;
function degreesToRadians(degrees) {
return (degrees*Math.PI)/180;
}
//to rotate stuff, not currently in use
function rotateStuff() {
roTimer = setInterval(ctx.rotate(degreesToRadians(60)),100);
}
//constructor for Shape object, not currently in use
function Shape() {
//this.x = canvas.width/2 + Math.random()*10-5;
//this.y = canvas.height/2 + Math.random()*10-5;
this.r = Math.random()*20-5;
this.vx = Math.random()*10-5;
this.vy = Math.random()*10-5;
var colors = ['red','green','orange','purple','blue','aqua','pink','gold'];
this.color = colors[Math.floor(Math.random()*colors.length)];
}
//pushes the shapes to an array, not currently in use
function makeShapes() {
shapes = [];
for (var i = 0; i<2; i++){
shapes.push(new Shape());
}
}
//fills and resets background
function fillBackground() {
ctx.globalCompositeOperation = 'source-over';
ctx.fillStyle = 'rgba(0,0,0,0.3)';
ctx.fillRect(0,0,canvas.width,canvas.height);
ctx.globalCompositeOperation = 'lighter';
}
//draws the shape
function drawShapes(r, p, m) {
//canvas, x position, y position, radius, number of points, fraction of radius for inset
fillBackground();
x = 350;
y = 350;
r = Math.random()*20-5;
//for (var i = 0; i < shapes.length; i++) {
//var s = shapes[i];
ctx.save();
ctx.beginPath();
ctx.translate(x, y);
ctx.moveTo(0,0-r);
//}
for (var i2 = 0; i2 < p; i2++) {
ctx.rotate(Math.PI / p);
ctx.lineTo(0, 0 - (r*m));
ctx.rotate(Math.PI / p);
ctx.lineTo(0, 0 - r);
}
ctx.fillStyle = "yellow";
ctx.fill();
var vx = Math.random()*10-5;
var vy = Math.random()*10-5;
x += vx;
y += vy;
r -=8
ctx.restore();
}
//}
window.onload = function() {
canvas = document.getElementById('animCanvas');
ctx = canvas.getContext('2d');
//makeShapes();
//console.log(shapes);
timer = setInterval(drawShapes(40, 5, 0.5), 100);
//timer2 = setInterval(makeShapes, 4500);
}
</script>
</head>
<body>
<canvas width='700' height='700' id='animCanvas'></canvas>
</body>
</html>回答 1
Stack Overflow用户
回答已采纳
发布于 2016-04-23 20:34:35
编码提示：将您的代码分离为独立的任务。这种分离使您可以将编码重点集中在更简单的任务上。一旦您正确地运行了该任务，您就可以转移到另一个任务上，而不必担心以前的任务已经中断。
这里是您的“旋转星星”项目的任务
1. Draw a star and
2. Rotate that star using animation.*..。以及他们的描述
drawShapes()在指定的[x,y]位置在指定的currentAngle处绘制一颗恒星
animate()运行一个动画循环：
Clears the canvas.
Fills the background.
Draws the star (or many stars) with `drawShapes`.
Changes the `currentAngle` rotation for the next loop.
Requests another animation loop.关于旋转
旋转你的形状是一个简单的两个步骤的过程：
1. Move to the shape's centerpoint: `.translate(centerX,centerY)'
2. Rotate the canvas to the currently desired angle: `rotate(currentAngle)`由于translate和rotate不是自动撤消的，所以您必须在转换之后“清理”。一个简单的方法是这样做：context.setTransform(1,0,0,1,0,0)。这将内部转换矩阵设置为默认状态(==fully未转换)。
所以你的轮换过程变成：
1. Move to the shape's centerpoint: `.translate(centerX,centerY)'
2. Rotate the canvas to the currently desired angle: `.rotate(currentAngle)`
3. Reset the canvas: `.setTransform(1,0,0,1,0,0)`这里有注释的代码和演示：
var canvas;
var ctx;
canvas = document.getElementById('animCanvas');
ctx = canvas.getContext('2d');
var cw=canvas.width;
var ch=canvas.height;
var shapes=[];
var star1={ x:50, y:100, r:40, currentAngle:0, p:5, m:.5, fill:'yellow',angleChange:Math.PI/60}
var star2={ x:150, y:100, r:25, currentAngle:0, p:55, m:5, fill:'blue',angleChange:-Math.PI/360}
var star3={ x:250, y:100, r:25, currentAngle:0, p:15, m:3, fill:'red',angleChange:Math.PI/120}
requestAnimationFrame(animate);
function drawShapes(star) {
ctx.save();
// translate to the star's centerpoint
ctx.translate(star.x,star.y);
// rotate to the current angle
ctx.rotate(star.currentAngle)
// draw the star
ctx.beginPath();
ctx.moveTo(0,0-star.r);
for (var i2 = 0; i2 < star.p; i2++) {
ctx.rotate(Math.PI / star.p);
ctx.lineTo(0, 0 - (star.r*star.m));
ctx.rotate(Math.PI / star.p);
ctx.lineTo(0, 0 - star.r);
}
ctx.fillStyle =star.fill;
ctx.fill();
ctx.restore();
}
function fillBackground() {
ctx.globalCompositeOperation = 'source-over';
ctx.fillStyle = 'rgba(0,0,0,0.3)';
ctx.fillRect(0,0,canvas.width,canvas.height);
ctx.globalCompositeOperation = 'lighter';
}
function animate(time){
// clear the canvas
ctx.clearRect(0,0,cw,ch);
// fill the background
fillBackground();
// draw the stars
// If you put star1,star2,star3 in a stars[] array then
// you could simply the following demo code by looping
// through the array
//
// draw the star1
drawShapes(star1);
// increase star1's current rotation angle
star1.currentAngle+=star1.angleChange;
// draw the star2
drawShapes(star2);
// increase star2's current rotation angle
star2.currentAngle+=star2.angleChange;
// draw the star3
drawShapes(star3);
// increase star3's current rotation angle
star3.currentAngle+=star2.angleChange;
// request another animation loop
requestAnimationFrame(animate);
}<canvas width='700' height='700' id='animCanvas'></canvas> </body>
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/36815379
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