如何解决如何使用画布和 JavaScript 使雪花形状旋转到其中心?
我正在尝试创建一个脚本,该脚本使用雪花形状来模拟下雪,该形状在下落时以中心旋转。
问题在于尝试 ctx.rotate() 会旋转画布中心的所有雪花,而不是将每个单独的雪花旋转到其中心。 代码。
(function() {
window.requestAnimationFrame = requestAnimationFrame;
})();
var flakes = [],c = document.getElementById('canvas'),ctx = c.getContext("2d"),flakeCount = 100
c.width = window.innerWidth;
c.height = window.innerHeight;
init();
function init() {
for (var i = 0; i < flakeCount; i++) {
var x = Math.floor(Math.random() * canvas.width),y = Math.floor(Math.random() * canvas.height),speed = (Math.random() * 1) + 0.5
img = draw();
flakes.push({
img: img,velY: speed,velX: 0,x: x,y: y,color: getRandomColor()
});
}
snow();
}
function snow() {
ctx.clearRect(0,canvas.width,canvas.height);
for (var i = 0; i < flakeCount; i++) {
var flake = flakes[i]
flake.y += flake.velY;
flake.x += flake.velX+getRand(0.1,0.3);
if (flake.y >= canvas.height || flake.y <= 0) {
reset(flake);
}
if (flake.x >= canvas.width || flake.x <= 0) {
reset(flake);
}
ctx.filter = flake.color;
ctx.drawImage(flake.img,flake.x,flake.y)
}
requestAnimationFrame(snow);
};
function reset(flake) {
flake.x = Math.floor(Math.random() * canvas.width);
flake.y = 0;
flake.speed = (Math.random() * 1) + 0.5;
flake.velY = flake.speed;
flake.velX = 0;
flake.color = getRandomColor()
}
function draw() {
let c = document.createElement('canvas');
var canvas = c;
c.width = window.innerWidth;
c.height = window.innerHeight;
if (canvas.getContext) {
var context = canvas.getContext('2d');
var width = canvas.width;
var height = canvas.height;
context.lineWidth = 20;
context.lineCap = 'round';
context.fillStyle = "rgba(255,255,0.0)";
context.strokeStyle = "#FFFFFF";
context.fillRect(0,width,height);
context.scale(0.1,0.1)
context.translate(width/2,height/2);
for(var count = 0; count < 6; count++) {
context.save();
drawSegment(context,100,40);
drawSegment(context,80);
drawSegment(context,0);
context.restore();
context.rotate(Math.PI/3);
}
}
return canvas;
}
function drawSegment(context,segmentLength,branchLength) {
context.beginPath();
context.moveTo(0,0);
context.lineTo(segmentLength,0);
context.stroke();
context.translate(segmentLength,0);
if (branchLength > 0) {
drawBranch(context,branchLength,1);
drawBranch(context,-1);
}
}
function drawBranch(context,direction) {
context.save();
context.rotate(direction*Math.PI/3);
context.moveTo(0,0);
context.lineTo(branchLength,0);
context.stroke();
context.restore();
}
在下面的JSFiddle中你可以找到代码 https://jsfiddle.net/hkz3nyfL/7/
(你会注意到顶部的形状看起来是破碎的,我不知道为什么会这样,这是因为屏幕太小了)
提前致谢
解决方法
运行给定代码时,我的浏览器 (Edge) 偶尔会抱怨违规 - requestAnimationFrames 之间似乎需要太多的 JS 运行时 - 我认为这意味着它无法跟上正常的 60fps。
GPU 使用率介于 98% 和 100% 之间。问题是在 100 个画布上完成了太多工作,将它们绘制到每个帧的主画布上。
改用 img 元素而不是每个雪花的画布,但仍使用问题中给出的画布技术绘制它们,并使用 CSS 动画为每个雪花制作动画,没有标记违规,GPU 使用率约为 30%。>
注意:还有一个问题是给定的代码在 Safari 上没有正常运行。这是由于使用了画布过滤器,因此在替换每个动画周期后使用新颜色重新绘制 img。
现在开始回答问题!
由于处理使用率高,所以不追求画布旋转路线,所以坚持使用 img 路线,可以通过向关键帧添加旋转(30度)等来旋转每个雪花。 GPU 使用率上升到 40% 到 50% 之间,但没有标记违规。顺便说一句,Firefox 上的 GPU 使用率始终高于 Windows 10 笔记本电脑上的 Edge。
这是一个使用 imgs 而不是画布的片段。初始条件需要一些整理,我们注意到雪花是固定大小的。对于响应式解决方案,它们的大小可能应与视口最小尺寸成比例。每个雪花都有固定的旋转次数,如果需要更改,最好在 JS 中计算关键帧以获得更通用的解决方案。
ffmpeg -fflags nobuffer \
-rtsp_transport udp \
-i rtsp://<source>/ \
-vsync 0 \
-copyts \
-vcodec copy \
-movflags frag_keyframe+empty_moov \
-an \
-hls_flags delete_segments \
-f segment \
-segment_list_flags live \
-segment_time 1 \
-segment_list_size 5 \
-segment_format mpegts \
-segment_list streaming.m3u8 \
-segment_list_type m3u8 \
-segment_list_entry_prefix ./ \
%d.ts \
-q:v 10 -vf fps=1 output_%03d.jpg
function loaded() {
const flakeCount = 100;
const flakesEl = document.getElementById('flakes');
const imgc = document.getElementById('canvas'); // work space on which to draw a snowflake of random color
// FF seemed to require that this is done rather than just innerWidth which was smaller than 100vw
const width = Math.max(document.documentElement.clientWidth,window.innerWidth || 0);
const height= Math.max(document.documentElement.clientHeight,window.innerHeight || 0);
init();
function init() {
for (var i = 0; i < flakeCount; i++) {
let flakeEl = document.createElement('img');
flakeEl.addEventListener('webkitAnimationEnd',animationEnd);
flakeEl.addEventListener('animationend',animationEnd);
flakeEl.style.animationDuration = ((Math.random() * 1) + 0.5) * 10 + 's';
flakeEl.style.left = Math.floor(Math.random() * width) + 'px';
flakeEl.style.top = '-100px';
flakeEl.classList.add('descend');
flakeEl.classList.remove('descend1');
draw(flakeEl);
flakesEl.appendChild(flakeEl);
}
}
function animationEnd(event) {
reset(event.target);
}
function reset(flakeEl) {
flakeEl.style.top = '-100px';
flakeEl.style.left = Math.floor(Math.random() * width) + 'px';
flakeEl.style.animationDuration = ((Math.random() * 1) + 0.5) * 10 + 's';
flakeEl.style.animationDelay = '0s';
draw(flakeEl);
flakeEl.classList.toggle('descend');
flakeEl.classList.toggle('descend1');
}
function getRandomColor() {
let color = `invert(${getRand(40,50)}%) sepia(${getRand(30,100)}%) hue-rotate(${getRand(-360,360)}deg) saturate(${getRand(10,50)})`;
// Safari does not support canvas fill filter so we just use a normal rgb for this test
return 'rgb('+getRand(0,255)+','+getRand(0,255)+')';
}
function getRand(min,max) {
return Math.random() * (max - min) + min;
}
function draw(flakeEl) {
imgc.width = 650; // enough spaace to get a whole snowflake in
imgc.height = imgc.width;
var imgctx = imgc.getContext('2d');
var width = imgc.width;
var height = imgc.height;
imgctx.clearRect(0,width,height);
imgctx.lineWidth = 20;
imgctx.lineCap = 'round';
imgctx.fillStyle = "rgba(255,255,0.0)";
imgctx.strokeStyle = getRandomColor();
imgctx.fillRect(0,height);
imgctx.translate(width/2,height/2);
for(var count = 0; count < 6; count++) {
imgctx.save();
drawSegment(imgctx,100,40);
drawSegment(imgctx,80);
drawSegment(imgctx,0);
imgctx.restore();
imgctx.rotate(Math.PI/3);
}
flakeEl.src = imgc.toDataURL();
}
function drawSegment(context,segmentLength,branchLength) {
context.beginPath();
context.moveTo(0,0);
context.lineTo(segmentLength,0);
context.stroke();
context.translate(segmentLength,0);
if (branchLength > 0) {
drawBranch(context,branchLength,1);
drawBranch(context,-1);
}
}
function drawBranch(context,direction) {
context.save();
context.rotate(direction*Math.PI/3);
context.moveTo(0,0);
context.lineTo(branchLength,0);
context.stroke();
context.restore();
}
}
window.onload = loaded;
*{
margin: 0;
padding: 0;
box-sizing: border-box;
}
html,body{
height: 100vh;
width: 100vw;
roverflow: hidden;
}
#flakes {
position: relative;
overflow: hidden;
width: 100%;
height: 100%;
}
#canvas {
visibility: hidden;
position: absolute;
top: 0;
left: 0;
}
img {
position: absolute;
animation-name: descend1;
animation-iteration-count: 1;
animation-timing-function: linear;
width: 100px;
height: 100px;
}
.descend {
animation-name: descend;
}
.descend1 {
animation-name: descend1;
}
@keyframes descend {
0% {
transform: translateY(0) rotate(0deg);
}
16.66% {
transform: translateY(calc(16.66vh + 16.66px)) rotate(30deg);
}
33.32% {
transform: translateY(calc(33.32vh + 33.32px)) rotate(0deg);
}
49.98% {
transform: translateY(calc(49.98vh + 49.98px)) rotate(-30deg);
}
66.64% {
transform: translateY(calc(66.64vh + 66.64px)) rotate(0deg);
}
83.30% {
transform: translateY(calc(83.30vh + 83.30px)) rotate(30deg);
}
100% {
transform: translateY(calc(100vh + 100px)) rotate(0deg);
}
}
@keyframes descend1 {
0% {
transform: translateY(0) rotate(0deg);
}
16.66% {
transform: translateY(calc(16.66vh + 16.66px)) rotate(30deg);
}
33.32% {
transform: translateY(calc(33.32vh + 33.32px)) rotate(0deg);
}
49.98% {
transform: translateY(calc(49.98vh + 49.98px)) rotate(-30deg);
}
66.64% {
transform: translateY(calc(66.64vh + 66.64px)) rotate(0deg);
}
83.30% {
transform: translateY(calc(83.30vh + 83.30px)) rotate(30deg);
}
100% {
transform: translateY(calc(100vh + 100px)) rotate(0deg);
}
}
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