javascript - 沿 HTML Canvas 中的一条线设置动画点

Question

<分区>

Answer 1

为此，您需要像这样计算Waypoints example - jsfiddle , 在您的情况下，您有一条曲线并计算 Waypoints 这有点棘手，但并非不可能

1. 计算航点见this answer
2. Waypoints 数组循环中的动画点

这是一个只有一行的小例子，你可以添加你的颜色或线条

jsfiddle

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;

var cBez1=[{x:30,y: 0},{x:60,y:320},{x:150,y:320},{x:600,y:330}];


drawBez(cBez1);

var cPoints=findCBezPoints(cBez1);
setInterval(timeanim, 1);
var indexi =0;
var opr = -1;

function timeanim()
{
	//reset view
	ctx.clearRect(0, 0, cw, ch);
	drawBez(cBez1);
	//draw dot
    ctx.fillStyle='red';
    ctx.beginPath();
    ctx.arc(cPoints[indexi].x,cPoints[indexi].y,4,0,Math.PI*2);
    ctx.fill();
    
  if(indexi + opr > cPoints.length-2 ||  indexi + opr < 0){
  	opr *= -1;
  }
  indexi += opr;
}




function findCBezPoints(b){
  var startPt=b[0];
  var controlPt1=b[1];
  var controlPt2=b[2];
  var endPt=b[3];
  var pts=[b[0]];
  var lastPt=b[0];
  var tests=5000;
  for(var t=0;t<=tests;t++){
    // calc another point along the curve
    var pt=getCubicBezierXYatT(b[0],b[1],b[2],b[3], t/tests);
    // add the pt if it's not already in the pts[] array
    var dx=pt.x-lastPt.x;
    var dy=pt.y-lastPt.y;
    var d=Math.sqrt(dx*dx+dy*dy);
    var dInt=parseInt(d);
    if(dInt>0 || t==tests){
      lastPt=pt;
      pts.push(pt);
    }
  }
  return(pts);
}

// Given the 4 control points on a Bezier curve 
// Get x,y at interval T along the curve (0<=T<=1)
// The curve starts when T==0 and ends when T==1
function getCubicBezierXYatT(startPt, controlPt1, controlPt2, endPt, T) {
  var x = CubicN(T, startPt.x, controlPt1.x, controlPt2.x, endPt.x);
  var y = CubicN(T, startPt.y, controlPt1.y, controlPt2.y, endPt.y);
  return ({
    x: x,
    y: y
  });
}

// cubic helper formula
function CubicN(T, a, b, c, d) {
  var t2 = T * T;
  var t3 = t2 * T;
  return a + (-a * 3 + T * (3 * a - a * T)) * T + (3 * b + T * (-6 * b + b * 3 * T)) * T + (c * 3 - c * 3 * T) * t2 + d * t3;
}

function drawPlots(pts){
  ctx.fillStyle='red';
  // don't draw the last dot b/ its radius will display past the curve
  for(var i=0;i<pts.length-1;i++){
    ctx.beginPath();
    ctx.arc(pts[i].x,pts[i].y,1,0,Math.PI*2);
    ctx.fill();
  }
}

function drawBez(b){
  ctx.lineWidth=2;
  ctx.beginPath();
  ctx.moveTo(b[0].x,b[0].y);
  ctx.bezierCurveTo(b[1].x,b[1].y, b[2].x,b[2].y, b[3].x,b[3].y);
  ctx.stroke();
}

  <canvas id="canvas" width=700 height=600></canvas>