7GUIs/circle_drawer.html at main · marshallworks/7GUIs · GitHub

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<!DOCTYPE html>
<button id="undo" onmousedown="undo()">Undo</button>
<button id="redo" onmousedown="redo()">Redo</button>
<br />
<canvas id="canvas"
        width="480"
        height="320"
        style="border: 1px solid #000;"
        onmousedown="selectCreate(event)"
        oncontextmenu="return false"
></canvas>
<dialog id="diameter-dialog">
  <label for="diameter">
    Adjust diameter of circle at (<span id="coord"></span>).<br />
    <input type="range" id="diameter" min="10" max="400" value="20" oninput="updateDiameter()" />
  </label>
</dialog>
<script>
const diameterDialog = document.getElementById('diameter-dialog');
const diameterInput = document.getElementById('diameter');
const diameterCoor = document.getElementById('coord');
const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

let actionIndex = -1;
const actions = [];

function coorDistance(a, b) {
  const xDiff = a.x - b.x;
  const yDiff = a.y - b.y;
  return Math.sqrt((xDiff*xDiff) + (yDiff*yDiff));
}

function getCircles() {
  const circlesMap = new Map();
  let selected = '';
  for (let i = 0; i <= actionIndex; ++i) {
    const action = actions[i];
    const key = `${action.x}:${action.y}`;
    const circle = {
      x: action.x,
      y: action.y,
      d: action.d,
      s: false
    };
    if (action.s) selected = key;
    circlesMap.set(key, circle);
  }
  if (selected) {
    circlesMap.get(selected).s = true;
  }
  return [...circlesMap.values()];
}

function getSelected() {
  return getCircles().find(c => c.s);
}

function getHit(coor) {
  let minDistance = Infinity;
  let selected = null;
  for (const circle of getCircles()) {
    const distance = coorDistance(circle, coor);
    if (distance < 0.5 * circle.d && distance < minDistance) {
      minDistance = distance;
      selected = circle;
    }
  }
  return selected;
}

function draw() {
  ctx.fillStyle = '#fff';
  ctx.fillRect(0, 0, 480, 320);
  ctx.fillStyle = '#aaa';
  ctx.strokeStyle = '#000';
  for (const circle of getCircles()) {
    ctx.beginPath();
    ctx.arc(circle.x, circle.y, 0.5 * circle.d, 0, 2*Math.PI);
    ctx.stroke();
    if (circle.s) ctx.fill();
  }
}

function addAction(action) {
  actions[++actionIndex] = action;
  actions.splice(actionIndex + 1);
  draw();
}

function updateAction(action, props) {
  for (const [key, value] of Object.entries(props)) {
    action[key] = value;
  }
  draw();
}

function updateDiameter() {
  const selected = getSelected();
  const action = actions[actionIndex];
  const d = Number(diameterInput.value);
  if (selected.x === action.x &&
      selected.y === action.y) {
    updateAction(action, {d});
  } else {
    addAction({x: selected.x, y: selected.y, d});
  }
}

function selectCreate(event) {
  diameterDialog.close();
  const selected = getHit({x: event.offsetX, y: event.offsetY});
  if (selected) {
    addAction({x: selected.x, y: selected.y, d: selected.d, s: true});
  }
  if (event.button === 0 && !selected) {
    addAction({x: event.offsetX, y: event.offsetY, d: 20, s: true});
  } else if (event.button === 2 && selected) {
    diameterCoor.innerText = `${selected.x}, ${selected.y}`;
    diameterInput.value = selected.d;
    diameterDialog.show();
  }
}

function undo() {
  diameterDialog.close();
  actionIndex = Math.max(-1, actionIndex - 1);
  draw();
}

function redo() {
  diameterDialog.close();
  actionIndex = Math.min(actionIndex + 1, actions.length - 1);
  draw();
}
</script>