javascript - 单击按钮时如何使 Canvas 文本消失

Question

如何让文本“?”消失？当我点击一个按钮时在 Canvas 中？

这是我的代码的链接:https://codepen.io/firassyazwani/pen/NWWKMGK

function draw() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.fillStyle = '#FFFF33';
  ctx.fillRect(rect.x, rect.y, rect.w, rect.h);
  if (currentHandle) {
    var posHandle = point(0, 0);
    switch (currentHandle) {
      case 'topright':
        posHandle.x = rect.x + rect.w;
        posHandle.y = rect.y;
        break;
      case 'bottomright':
        posHandle.x = rect.x + rect.w;
        posHandle.y = rect.y + rect.h;
        break;
    }
    ctx.globalCompositeOperation = 'xor';
    ctx.beginPath();
    ctx.arc(posHandle.x, posHandle.y, handlesSize, 0, 2 * Math.PI);
    ctx.fill();
    ctx.globalCompositeOperation = 'source-over';
  }

Answer 1

您可以在绘制问号之前放置一个条件，if (enableText) 并在 disableText() 方法中重绘 Canvas :

...
  ctx.font = "30px Comic Sans MS";
  if (enableText)
    ctx.strokeText("?",
...
function disableText() {
  enableText = false;
  draw();
}
...

var canvas = document.getElementById('canvas'),
  ctx = canvas.getContext('2d'),
  rect = {
    x: 0,
    y: 0,
    w: 100,
    h: 100
  },
  handlesSize = 8,
  currentHandle = false,
  drag = false,
  prevW = rect.w,
  prevH = rect.h,
  enableDrag = true,
  enableText = true;

function init() {
  canvas.addEventListener('mousedown', mouseDown, false);
  canvas.addEventListener('mouseup', mouseUp, false);
  canvas.addEventListener('mousemove', mouseMove, false);
}

function point(x, y) {
  return {
    x: x,
    y: y
  };
}

function dist(p1, p2) {
  return Math.sqrt((p2.x - p1.x) * (p2.x - p1.x) + (p2.y - p1.y) * (p2.y - p1.y));
}

function getHandle(mouse) {
  if (dist(mouse, point(rect.x + rect.w, rect.y)) <= handlesSize)
    return 'topright';
  if (dist(mouse, point(rect.x + rect.w, rect.y + rect.h)) <= handlesSize)
    return 'bottomright';
}

function mouseDown(e) {
  if (currentHandle)
    drag = true && enableDrag;
  draw();
}

function mouseUp() {
  drag = false;
  currentHandle = false;
  prevW = rect.w;
  prevH = rect.h;
  draw();
}

function mouseMove(e) {
  var previousHandle = currentHandle;
  if (!drag)
    currentHandle = getHandle(point(e.pageX - this.offsetLeft, e.pageY - this.offsetTop));
  if (currentHandle && drag) {
    var mousePos = point(e.pageX - this.offsetLeft, e.pageY - this.offsetTop);
    switch (currentHandle) {
      case 'topright':
        rect.w = rect.h;
        rect.h += rect.y - mousePos.y;
        rect.y = mousePos.y;
        break;
      case 'bottomright':
        rect.w = rect.h;
        rect.h = mousePos.y - rect.y;
        break;
    }
  }
  if (drag || currentHandle != previousHandle)
    draw();
}

function draw() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.fillStyle = '#FFC0CB';
  ctx.strokeStyle = "#000000";
  ctx.font = "30px Comic Sans MS";
  if (enableText)
    ctx.strokeText("?",
      rect.x + rect.w + 10,
      rect.y + rect.h / 2 + 5), (20);
  ctx.lineWidth = 4;
  var fillRect = true;
  ctx.rect(rect.x, rect.y, rect.w, rect.h);
  if (fillRect) {
    ctx.fill();
  }
  ctx.stroke();
  if (currentHandle) {
    var posHandle = point(0, 0);
    switch (currentHandle) {
      case 'topright':
        posHandle.x = rect.x + rect.w;
        posHandle.y = rect.y;
        break;
      case 'bottomright':
        posHandle.x = rect.x + rect.w;
        posHandle.y = rect.y + rect.h;
        break;
    }
    ctx.globalCompositeOperation = 'xor';
    ctx.beginPath();
    ctx.arc(posHandle.x, posHandle.y, handlesSize, 0, 2 * Math.PI);
    ctx.fill();
    ctx.globalCompositeOperation = 'source-over';
  }
  if (drag) {
    if (rect.w != prevW) {
      var width = Math.round(rect.w / 30);
      document.getElementById("width").innerHTML = width;
    }
    if (rect.h != prevH) {
      var height = Math.round(rect.h / 30);
    }

    var perimeter = (width + height) * 2;
    document.getElementById("perimeter").innerHTML = perimeter;
    document.getElementById("perimeter2").innerHTML = perimeter;

    $("#buttonDone").fadeIn(2000).removeClass('hidden');
  }
}

function disableDrag() {
  enableDrag = false;
}


function disableText() {
  enableText = false;
  draw();
  //mouseUp();
}

init();
draw();

body {
  background-color: #a3d5d3;
}

#canvas {
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  margin: auto;
}

#button {
  top: 0;
  left: 0;
  display: block;
}

<button id="button" onclick="disableText();">disable text</button>
<canvas id="canvas" width="500" height="500"></canvas>