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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

HTML

              
                <canvas id="canvas"></canvas>
<div class="parameters">
  <div class="row">
    <div class="col-md-5 form-group">
      <div class="input-group">
        <span class="input-group-addon">a</span>
        <input id="eqn-a" type="number" class="form-control" value="-7">
      </div>
    </div>
    <div class="col-md-5 form-group">
      <div class="input-group">
        <span class="input-group-addon">b</span>
        <input id="eqn-b" type="number" class="form-control" value=0>
      </div>
    </div>
  </div>
  <div class="row">
    <div class="col-md-5 form-group">
      <div class="input-group">
        <span class="input-group-addon">p</span>
        <input id="eqn-p" type="number" class="form-control" value="67">
      </div>
    </div>
  </div>
  <div class="row">
    <div class="col-md-10 form-group">
      <p id="eqn"></p>
      <p id="addition"></p>
    </div>
  </div>
  <div class="row">
    <div class="col-md-10 form-group">
      <p id="instructions"></p>
    </div>
  </div>
  <div class="row">
    <div class="col-md-10 form-group">
      <button id="btn-plot" class="btn btn-primary">1. Plot</button>
      <button id="btn-add" class="btn" disabled>2. Add</button>
      <button id="btn-reset" class="btn btn-danger">Reset</button>
    </div>
  </div>
<!-- <div id="points-to-add" style="display:none">
    <div class="row">
      <div class="col-md-5 form-group">
        <div class="input-group">
          <span class="input-group-addon">x1</span>
          <input id="x1" type="number" class="form-control">
        </div>
      </div>
      <div class="col-md-5 form-group">
        <div class="input-group">
          <span class="input-group-addon">y1</span>
          <input id="y1" type="number" class="form-control">
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-md-5 form-group">
        <div class="input-group">
          <span class="input-group-addon">x2</span>
          <input id="x2" type="number" class="form-control">
        </div>
      </div>
      <div class="col-md-5 form-group">
        <div class="input-group">
          <span class="input-group-addon">y2</span>
          <input id="y2" type="number" class="form-control">
        </div>
      </div>
    </div>
    <div class="row">
      <div class="col-md-5 form-group">
        <button id="btn-add" class="btn btn-primary">Add</button>
      </div>
    </div>
  </div> -->
</div>
<div class="tooltip">(88, 88)</div>
              
            
!

CSS

              
                #canvas {
  border: solid 1px #ccc;
  margin: 10px;
}
.parameters {
  position: absolute;
  left: 440px;
  top: 10px;
}
.tooltip {
  position: absolute;
  z-index: 2;
  border-radius: 2px;
  background: #0069dc;
  color: #fff;
  padding: 2px 4px;
  opacity: 0;
  transition: opacity 0.2s;
}
              
            
!

JS

              
                const WIDTH = 400;
const HEIGHT = 400;
const canvas = document.getElementById("canvas");
canvas.width = WIDTH;
canvas.height = HEIGHT;
paper.setup(canvas);
const tooltip = document.querySelector(".tooltip");

let mode = 0; // 0: select; 1: add; 2: result
const instructions = [
  "Enter values of a, b, p and click Plot",
  "Select two points on the plot and click Add",
  "Click Reset to start over"
];
function mod(n, m) {
  return ((n % m) + m) % m;
}
class ECFF {
  constructor(a, b, p) {
    this.p = p;
    this.a = a;
    this.b = b;
    
    this.selected = [];
  }
  f(x) {
    return mod(Math.pow(x, 3) + this.a*x + this.b, this.p);
  }
  _inverse(x) {
    for(let i=1; i<this.p; i++) {
      if(mod(i*x, this.p) == 1)
        return i;
    }
    throw new Error(`inv(${x}) mod ${this.p} does not exist`);
  }
  _plotPoint(x, y, fillColor, radius, hover, onClick) {
    const point = new paper.Path.Circle(
      new paper.Point(x*WIDTH/this.p, HEIGHT-y*HEIGHT/this.p),
      radius
    );
    point.fillColor = fillColor;
    point.data.x = x;
    point.data.y = y;
    if(hover) {
      point.onMouseEnter = () => {
        if(!hover())
          return;
        tooltip.style.left = point.position.x + "px";
        tooltip.style.top = (point.position.y - 20) + "px";
        tooltip.innerHTML = `${x}, ${y}`;
        tooltip.style.opacity = 1;
        tooltip.setAttribute("data-id", point.id);
      };
      point.onMouseLeave = () => {
        if(!hover())
          return;
        tooltip.style.opacity = 0;
      };
    }
    if(onClick) {
      point.onClick = () => onClick(point, x, y);
    }
  }
  plotField() {
    for(let x=0; x<this.p; x++) {
      for(let y=0; y<this.p; y++) {
        if(mod(y*y, this.p) == this.f(x)) {
          this._plotPoint(
            x, y, "#999999", 4,
            () => mode == 1,
            (point, x, y) => {
              if(mode != 1)
                return;
              if(this.selected.length==2)
                return;
              this.selected.push({
                x: x,
                y: y
              });
              point.fillColor = "red";
            }
          );
        }
      }
    }
    return true;
  }
  add() {
    if(this.selected.length<2) {
      alert("Please select two points first");
      return;
    }
    const x1 = this.selected[0].x;
    const y1 = this.selected[0].y;
    const x2 = this.selected[1].x;
    const y2 = this.selected[1].y;
    const slope = mod((y2-y1) * this._inverse(x2-x1), this.p);
    let path = new paper.Path();
    path.strokeColor = "red";
    let py = null;
    let ppy = null
    console.log(slope)
    for(let x=0; x<this.p; x++) {
      let y = mod(slope*x - slope*x1 + y1, this.p);
      console.log(x, y);
      if(py!==null && ppy != null && y - py != py - ppy) {
        path = new paper.Path();
        path.strokeColor = "red";
        ppy = null;
        py = null;
        console.log("BRK")
      }
      ppy = py;
      py = y;
      const point = new paper.Point(x*WIDTH/this.p, HEIGHT-y*HEIGHT/this.p);
      path.add(point);
      if(mod(y*y, this.p) == this.f(x)) {
        this._plotPoint(
          x, y, "red", 6,
          () => mode == 2
        );
      }
    }
    const x3 = mod(slope*slope - x1 - x2, this.p);
    const y3 = mod(slope * (x1 - x3) - y1, this.p);
    this._plotPoint(
      x3, y3, "green", 6,
      () => mode == 2
    );
    return [
      this.selected[0],
      this.selected[1],
      {x: x3, y: y3}
    ];
  }
  clear() {
    paper.project.clear();
  }
}
let ecff;
const btnPlot = document.getElementById("btn-plot");
const btnAdd = document.getElementById("btn-add");
const btnReset = document.getElementById("btn-reset");
const pInstr = document.getElementById("instructions");
const pEqn = document.getElementById("eqn");
const pAddition = document.getElementById("addition");

pInstr.innerHTML = instructions[mode];

function toggleBtn(btn, enabled) {
  if(!enabled) {
    btn.className = btn.className.replace("btn-primary", "");
    btn.setAttribute("disabled", "disabled");
  } else {
    btn.className = btn.className + " btn-primary";
    btn.removeAttribute("disabled");
  }
}
btnPlot.addEventListener("click", e => {
  const a = parseInt(document.getElementById("eqn-a").value);
  const b = parseInt(document.getElementById("eqn-b").value);
  const p = parseInt(document.getElementById("eqn-p").value);
  ecff = new ECFF(a, b, p);
  if(ecff.plotField()) {
    toggleBtn(btnPlot, false);
    toggleBtn(btnAdd, true);
    mode = 1;
    pInstr.innerHTML = instructions[mode];
    pEqn.innerHTML = "y^2 = x^3" +
      (a ? " + " + a + "x" : "") +
      (b ? " + " + b : "") +
       " mod " + p;
  }
}, false);
btnAdd.addEventListener("click", e => {
  const points = ecff.add();
  if(points) {
    toggleBtn(btnAdd, false);
    toggleBtn(btnReset, true);
    mode = 2;
    pInstr.innerHTML = instructions[mode];
    pAddition.innerHTML = `P1(${points[0].x}, ${points[0].y}) + P2(${points[1].x}, ${points[1].y}) = P3(${points[2].x}, ${points[2].y})`;
  }
}, false);
btnReset.addEventListener("click", e => {
  ecff.clear();
  ecff = null;
  toggleBtn(btnPlot, true);
  toggleBtn(btnAdd, false);
  mode = 1;
  pInstr.innerHTML = instructions[mode];
  pAddition.innerHTML = "";
}, false);

              
            
!
999px

Console