let slv;

let elv;

​

function setup() {

  createCanvas(400, 400);

  pts = [

    createVector(20,20),

    createVector(50,200),

    createVector(350,200),

    createVector(380,380),

  ];  

  slv = pts[0];

  elv = pts[3];

  noStroke();

}

​

function draw() {

  background(220);

  let steps = 100;

  beginShape(TRIANGLE_STRIP);  

  for (let i = 0; i <= steps; i++) {    

    let tc = i / steps;

    let col = lerpColor(color("#0000FF"), color("#FF00FF"), tc);

    fill(col); 

    stroke(col);

    let cbp = createVector(

      bezierPoint(pts[0].x, pts[1].x, pts[2].x, pts[3].x, tc),

      bezierPoint(pts[0].y, pts[1].y, pts[2].y, pts[3].y, tc)

    );    

    let clp = p5.Vector.lerp(slv, elv, tc);

    vertex(cbp.x, cbp.y);

    vertex(clp.x, clp.y);

  }  

  endShape();

}

​