我正在尝试实现在Canvas上绘制arcTo线的动画。例如,对于一条直线,动画将如下所示
c = canvas.getContext("2d");
width = window.innerWidth;
height = window.innerHeight;
complete = false
var percent = 1
function drawEdge(x1, y1, x2, y2, color){
c.beginPath();
c.lineWidth = 10;
c.strokeStyle = color;
c.moveTo(x1, y1);
c.lineTo(x2, y2);
c.stroke();
c.closePath();
}
function getPosition(x1, y1, x2, y2, percentageBetweenPoints){
let xPosition = x1 + (x2 - x1) * (percentageBetweenPoints / 100);
let yPosition = y1 + (y2 - y1) * (percentageBetweenPoints / 100);
const position = {
x: xPosition,
y: yPosition,
}
return position
}
function drawLine(){
if (!complete){
requestAnimationFrame(drawLine);
}
if (percent >= 100){
complete = true;
percent = 100;
} else{
percent = percent + 1;
}
position = getPosition(300,300,1000,300,percent);
c.clearRect(0, 0 , width, height);
drawEdge(300,300,position.x,position.y, "black");
}
drawLine()
这将创建在屏幕上绘制线条的动画。但是,我无法对arcTo线执行相同的操作。有什么办法可以实现?
答案 0 :(得分:1)
您正在寻找类似的东西吗?
let ctx = canvas.getContext('2d');
ctx.textAlign = "center";
ctx.textBaseline = "middle";
ctx.font = 'bold 18px Arial';
requestAnimationFrame(draw);
function draw(t) {
t = t % 5e3 / 5e3;
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.beginPath();
ctx.arc(canvas.width/2, canvas.height/2, 50, 0, t * 2 * Math.PI);
ctx.stroke();
ctx.fillText((t*100).toFixed(0), canvas.width/2, canvas.height/2);
requestAnimationFrame(draw);
}
<canvas id=canvas></canvas>
答案 1 :(得分:0)
有两种方法可以做到这一点
计算每个线段的起点,终点和长度,起点,终点角度,方向(CW或CCW)以及每个弧段的中心。基本上重复所有使None
成为有用的渲染函数的数学和逻辑(大约50行代码)。
使用arcTo
并使用长划线和长空格。随着时间的推移,使用ctx.lineDash
来移动破折号,使线条的长度逐渐增加(请参见演示)。破折号偏移值是相反的,从最大长度开始,到零为止。
注意,此方法存在一个问题。您不知道行的长度,因此您不知道完成行将花费多长时间。您可以进行估算。要知道行的长度,您必须进行所有计算(大约)
由于第二种方法最容易实现并且满足大多数需求,因此我将演示该方法。
不用多说了,它为ctx.lineDashOffset
创建的路径设置了动画
附带的好处是它将使使用ctx.arcTo
ctx.stroke
requestAnimationFrame(mainLoop);
// Line is defined in unit space.
// Origin is at center of canvas, -1,-1 top left, 1, 1 bottom right
// Unit box is square and will be scaled to fit the canvas size.
// Note I did not use ctx.setTransform to better highlight what is scaled and what is not.
const ctx = canvas.getContext("2d");
var w, h, w2, h2; // canvas size and half size
var linePos; // current dash offset
var scale; // canvas scale
const LINE_WIDTH = 0.05; // in units
const LINE_STYLE = "#000"; // black
const LINE_SPEED = 1; // in units per second
const MAX_LINE_LENGTH = 9; // in units approx
const RADIUS = 0.08; //Arc radius in units
const SHAPE = [[0.4, 0.2], [0.8, 0.2], [0.5, 0.5], [0.95, 0.95], [0.0, 0.5], [-0.95, 0.95], [-0.5, 0.5], [-0.8, 0.2], [-0.2, 0.2], [-0.2, -0.2], [-0.8, -0.2], [-0.5, -0.5], [-0.95, -0.95], [0.0, -0.5], [0.95,-0.95], [0.5, -0.5], [0.8, -0.2], [0.2, -0.2], [0.2, 0.2], [0.6, 0.2], [0.8, 0.2]];
function sizeCanvas() {
w2 = (w = canvas.width = innerWidth) / 2;
h2 = (h = canvas.height = innerHeight) / 2;
scale = Math.min(w2, h2);
resetLine();
}
function addToPath(shape) {
var p1, p2;
for (p2 of shape) {
!p2.length ?
ctx.closePath() :
(p1 ? ctx.arcTo(p1[0] * scale + w2, p1[1] * scale + h2, p2[0] * scale + w2, p2[1] * scale + h2, RADIUS * scale) :
ctx.lineTo(p2[0] * scale + w2, p2[1] * scale + h2)
);
p1 = p2;
}
}
function resetLine() {
ctx.setLineDash([MAX_LINE_LENGTH * scale, MAX_LINE_LENGTH * scale]);
linePos = MAX_LINE_LENGTH * scale;
ctx.lineWidth = LINE_WIDTH * scale;
ctx.lineJoin = ctx.lineCap = "round";
}
function mainLoop() {
if (w !== innerWidth || h !== innerHeight) { sizeCanvas() }
else { ctx.clearRect(0, 0, w, h) }
ctx.beginPath();
addToPath(SHAPE);
ctx.lineDashOffset = (linePos -= LINE_SPEED * scale * (1 / 60));
ctx.stroke();
if (linePos <= 0) { resetLine() }
requestAnimationFrame(mainLoop);
}
body {
padding: 0px,
margin: 0px;
}
canvas {
position: absolute;
top: 0px;
left: 0px;
}