procedural_anim/spider.js

const vec = p5.Vector;

class Leg {
  constructor() {
    this.base = new vec(0, 0);
    this.end = new vec(0, 0);
    this.interPos = new vec(0, 0);
    this.ikJoint = new IKJoint(4, 47);
    this.repositionDist = 90;
    this.moveSpeed = 0.4;
  }

  moveTo(startX, startY, endX, endY) {
    this.base = new vec(startX, startY);
    let target = new vec(endX, endY);

    if (vec.dist(target, this.end) > this.repositionDist) {
      this.end = new vec(endX, endY);
    }
    this.interPos.lerp(this.end, this.moveSpeed);
    this.ikJoint.moveTo(startX, startY, this.interPos.x, this.interPos.y);
  }

  getPoints() {
    return this.ikJoint.points;
  }
}

class IKJoint {
  constructor(numSegments, pointDist) {
    this.origin = new vec(0, 0);
    this.points = [];
    for (let i = 0; i < numSegments + 1; i++) {
      this.points.push(new ConstraintPoint(0, 0, pointDist, 7));
    }
    this.pointDist = pointDist;
    this.iterations = 20;
  }

  moveStart(targetX, targetY) {
    let numPts = this.points.length;
    this.points[0].size = 1;
    this.points[0].follow(targetX, targetY);

    for (let i = 1; i < numPts; i++) {
      let prevPoint = this.points[i - 1];
      this.points[i].follow(prevPoint.pos.x, prevPoint.pos.y, prevPoint.forward);
    }
  }

  moveEnd(targetX, targetY) {
    let numPts = this.points.length;
    this.points[numPts - 1].pos.x = targetX;
    this.points[numPts - 1].pos.y = targetY;

    for (let i = numPts - 2; i >= 0; i--) {
      let prevPoint = this.points[i + 1];
      this.points[i].follow(prevPoint.pos.x, prevPoint.pos.y, null);
    }
  }

  moveTo(origX, origY, targetX, targetY) {
    for (let i = 0; i < this.iterations; i++) {
      this.moveEnd(targetX, targetY);
      this.moveStart(origX, origY);
    }
  }
}

class ConstraintPoint {
  constructor(x, y, size, angleConstraint = 0.2) {
    this.size = size;
    this.pos = new vec(x, y);
    this.forward = new vec(0, 0);
    this.angleConstraint = angleConstraint;
  }

  getRel(angleOffset, dist) {
    let dir = vec.rotate(this.forward, angleOffset);
    dir.setMag(dist);
    return vec.add(this.pos, dir);
  }

  follow(targetX, targetY, parentForward = null) {
    let target = new vec(targetX, targetY);
    let targetForward = vec.sub(target, this.pos);
    let targetAngle = targetForward.heading();

    if (parentForward) {
      let parentAngle = parentForward.heading();
      let diff = targetAngle - parentAngle;

      while (diff < -PI) diff += TWO_PI;
      while (diff > PI) diff -= TWO_PI;

      let maxAngle = this.angleConstraint;
      diff = constrain(diff, -maxAngle, maxAngle);

      targetAngle = parentAngle + diff;
    }

    this.forward = p5.Vector.fromAngle(targetAngle);

    let dir = p5.Vector.mult(this.forward, -this.size);
    this.pos = vec.add(target, dir);
  }
}

function drawPoints(points, sizes, turnSegments = 10) {
  beginShape();

  let numPoints = points.length;
  let head = points[0];
  let tail = points[numPoints - 1];

  for (let angle = -HALF_PI; angle <= HALF_PI; angle += PI / turnSegments) {
    let p = head.getRel(angle, sizes[0]);
    curveVertex(p.x, p.y);
  }

  for (let i = 1; i < numPoints - 1; i++) {
    let p = points[i].getRel(HALF_PI, sizes[i]);
    curveVertex(p.x, p.y);
  }

  for (let angle = HALF_PI; angle <= HALF_PI + PI; angle += PI / turnSegments) {
    let p = tail.getRel(angle, sizes[numPoints - 1]);
    curveVertex(p.x, p.y);
  }

  for (let i = numPoints - 2; i >= 1; i--) {
    let p = points[i].getRel(-HALF_PI, sizes[i]);
    curveVertex(p.x, p.y);
  }
  endShape(CLOSE);
}

let numPoints = 0;
const bodySizes = [18, 22, 25, 22, 14, 30, 35, 40, 35, 30]; 
const legSizes = [6, 5, 4, 3, 2, 2, 1, 1, 1]; 

const bodyPoints = [];
const legs = [];
let mouseInter = new vec(0, 0);

function setup() {
  createCanvas(displayWidth, displayHeight);
  numPoints = bodySizes.length;
  
  for (let i = 0; i < numPoints; i++) {
    let pt = new ConstraintPoint(400, 400, 15);
    bodyPoints.push(pt);
  }
  
  for (let i = 0; i < 8; i++) {
    legs.push(new Leg());
  }
}

function draw() {
  background(180);

  mouseInter.lerp(new vec(mouseX, mouseY), 0.05);
  let time = millis();

  bodyPoints[0].follow(mouseInter.x, mouseInter.y);

  for (let i = 1; i < numPoints; i++) {
    let prevPoint = bodyPoints[i - 1];
    bodyPoints[i].follow(prevPoint.pos.x, prevPoint.pos.y, prevPoint.forward);
  }

  let legAngles = [
    -PI / 3, PI / 3,
    -PI / 1.8, PI / 1.8,
    -PI * 0.7, PI * 0.7,
    -PI * 0.85, PI * 0.85
  ];
  
  let legAttachmentIndices = [1, 1, 2, 2, 3, 3, 4, 4];

  for (let i = 0; i < 8; i++) {
    let baseJoint = bodyPoints[legAttachmentIndices[i]];
    let bodyRadius = bodySizes[legAttachmentIndices[i]];
    
    let basePos = baseJoint.getRel(legAngles[i], bodyRadius * 0.6);
    
    let reach = 120; 
    let endPos = baseJoint.getRel(legAngles[i], reach);

    legs[i].moveTo(basePos.x, basePos.y, endPos.x, endPos.y);
  }

  fill(30);
  stroke(10);
  strokeWeight(1);

  for (let i = 0; i < 8; i++) {
    drawPoints(legs[i].getPoints(), legSizes);
  }

  let currentBodySizes = [...bodySizes];
  let breathSpeed = time * 0.005;

  for (let i = 0; i < numPoints; i++) {
    if (i > 4) {
      let breathExpansion = sin(breathSpeed - i * 0.2) * 2.5;
      currentBodySizes[i] += breathExpansion;
    }
  }

  drawPoints(bodyPoints, currentBodySizes);

  let eye1 = bodyPoints[0].getRel(PI / 5, 12);
  let eye2 = bodyPoints[0].getRel(-PI / 5, 12);
  let eye3 = bodyPoints[0].getRel(PI / 2.5, 15);
  let eye4 = bodyPoints[0].getRel(-PI / 2.5, 15);
  
  fill(220, 20, 20);
  noStroke();
  circle(eye1.x, eye1.y, 8);
  circle(eye2.x, eye2.y, 8);
  circle(eye3.x, eye3.y, 4);
  circle(eye4.x, eye4.y, 4);
}