获取鼠标点击位置

我正在使用这个色轮，我想在色轮上添加一个黑色封面覆盖，这样，当使用色轮下的滑块更改hsv的值（v）时，色轮会变暗。

我在canvas中添加了一个包装div，在wrapper中添加了另一个div（overlay），并将背景颜色设置为黑色。然后，我将wrapper的位置设置为relative，对于overlay，我将位置设置为absolute。

（我将wrapper设置为relative，使得overlay（具有absolute）将包含在wrapper中。）

由于wrapper设置为relative，因此色轮选择不准确。拾取器没有完全跟随鼠标。

我认为这个问题可以通过编辑以下代码来解决：（在redraw()函数中，第69行。）

currentX = e.pageX - c.offsetLeft - radiusPlusOffset || currentX;
currentY = e.pageY - c.offsetTop - radiusPlusOffset  || currentY;

但我不知道该改变什么。即使wrapper设置为relative，如何使pickers指针跟随鼠标？

JSFiddle

(function() {
  // Declare constants and variables to help with minification
  // Some of these are inlined (with comments to the side with the actual equation)
  var doc = document;
  doc.c = doc.createElement;
  b.a = b.appendChild;
  var width = c.width = c.height = 400,
    label = b.a(doc.c("p")),
    input = b.a(doc.c("input")),
    imageData = a.createImageData(width, width),
    pixels = imageData.data,
    oneHundred = input.value = input.max = 100,
    circleOffset = 10,
    diameter = 380, //width-circleOffset*2,
    radius = 190, //diameter / 2,
    radiusPlusOffset = 200, //radius + circleOffset
    radiusSquared = radius * radius,
    two55 = 255,
    currentY = oneHundred,
    currentX = -currentY,
    wheelPixel = 16040; // circleOffset*4*width+circleOffset*4;
  // Math helpers
  var math = Math,
    PI = math.PI,
    PI2 = PI * 2,
    sqrt = math.sqrt,
    atan2 = math.atan2;
  // Setup DOM properties
  b.style.textAlign = "center";
  label.style.font = "2em courier";
  input.type = "range";
  // Load color wheel data into memory.
  for (y = input.min = 0; y < width; y++) {
    for (x = 0; x < width; x++) {
      var rx = x - radius,
        ry = y - radius,
        d = rx * rx + ry * ry,
        rgb = hsvToRgb(
          (atan2(ry, rx) + PI) / PI2, // Hue
          sqrt(d) / radius, // Saturation
          1 // Value
        );
      // Print current color, but hide if outside the area of the circle
      pixels[wheelPixel++] = rgb[0];
      pixels[wheelPixel++] = rgb[1];
      pixels[wheelPixel++] = rgb[2];
      pixels[wheelPixel++] = d > radiusSquared ? 0 : two55;
    }
  }
  // Bind Event Handlers
  input.onchange = redraw;
  c.onmousedown = doc.onmouseup = function(e) {
    // Unbind mousemove if this is a mouseup event, or bind mousemove if this a mousedown event
    doc.onmousemove = /p/.test(e.type) ? 0 : (redraw(e), redraw);
  }
  // Handle manual calls + mousemove event handler + input change event handler all in one place.
  function redraw(e) {
    // Only process an actual change if it is triggered by the mousemove or mousedown event.
    // Otherwise e.pageX will be undefined, which will cause the result to be NaN, so it will fallback to the current value
    currentX = e.pageX - c.offsetLeft - radiusPlusOffset || currentX;
    currentY = e.pageY - c.offsetTop - radiusPlusOffset || currentY;
    // Scope these locally so the compiler will minify the names.  Will manually remove the 'var' keyword in the minified version.
    var theta = atan2(currentY, currentX),
      d = currentX * currentX + currentY * currentY;
    // If the x/y is not in the circle, find angle between center and mouse point:
    //   Draw a line at that angle from center with the distance of radius
    //   Use that point on the circumference as the draggable location
    if (d > radiusSquared) {
      currentX = radius * math.cos(theta);
      currentY = radius * math.sin(theta);
      theta = atan2(currentY, currentX);
      d = currentX * currentX + currentY * currentY;
    }
    label.textContent = b.style.background = hsvToRgb(
      (theta + PI) / PI2, // Current hue (how many degrees along the circle)
      sqrt(d) / radius, // Current saturation (how close to the middle)
      input.value / oneHundred // Current value (input type="range" slider value)
    )[3];
    // Reset to color wheel and draw a spot on the current location. 
    a.putImageData(imageData, 0, 0);
    // Heart:
    a.font = "1em arial";
    a.fillText("♥", currentX + radiusPlusOffset - 4, currentY + radiusPlusOffset + 4);
  }
  // Created a shorter version of the HSV to RGB conversion function in TinyColor
  // https://github.com/bgrins/TinyColor/blob/master/tinycolor.js
  function hsvToRgb(h, s, v) {
    h *= 6;
    var i = ~~h,
      f = h - i,
      p = v * (1 - s),
      q = v * (1 - f * s),
      t = v * (1 - (1 - f) * s),
      mod = i % 6,
      r = [v, q, p, p, t, v][mod] * two55,
      g = [t, v, v, q, p, p][mod] * two55,
      b = [p, p, t, v, v, q][mod] * two55;
    return [r, g, b, "rgb(" + ~~r + "," + ~~g + "," + ~~b + ")"];
  }
  // Kick everything off
  redraw(0);
  /*
  // Just an idea I had to kick everything off with some changing colors…
  // Probably no way to squeeze this into 1k, but it could probably be a lot smaller than this:
  currentX = currentY = 1;
  var interval = setInterval(function() {
      currentX--;
      currentY*=1.05;
      redraw(0)
  }, 7);
    
  setTimeout(function() {
      clearInterval(interval)
  }, 700)
  */
})();

#wrapper {
  width: 400px;
  height: 400px;
  position: relative;
}
#blackBackground {
  background-color: black;
  width: 100%;
  height: 100%;
  position: absolute;
  border-radius: 50%;
  opacity: .5;
  pointer-events: none;
}

<div>
  Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aenean commodo ligula eget dolor. Aenean massa. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Donec quam felis, ultricies nec, pellentesque eu, pretium quis,
  sem. Nulla consequat massa quis enim. Donec pede justo, fringilla vel, aliquet nec, vulputate eget, arcu. In enim justo, rhoncus ut, imperdiet a, venenatis vitae, justo. Nullam dictum felis eu pede mollis pretium. Integer tincidunt. Cras dapibus. Vivamus
  elementum semper nisi. Aenean vulputate eleifend tellus. Aenean leo ligula, porttitor eu, consequat vitae, eleifend ac, enim. Aliquam lorem ante, dapibus in, viverra quis, feugiat a, tellus. Phasellus viverra nulla ut metus varius laoreet. Quisque rutrum.
  Aenean imperdiet. Etiam ultricies nisi vel augue. Curabitur ullamcorper ultricies nisi. Nam eget dui. Etiam rhoncus. Maecenas tempus, tellus eget condimentum rhoncus, sem quam semper libero, sit amet adipiscing sem neque sed ipsum. Nam quam nunc, blandit
  vel, luctus pulvinar, hendrerit id, lorem. Maecenas nec odio et ante tincidunt tempus. Donec vitae sapien ut libero venenatis faucibus. Nullam quis ante. Etiam sit amet orci eget eros faucibus tincidunt. Duis leo. Sed fringilla mauris sit amet nibh.
  Donec sodales sagittis magna. Sed consequat, leo eget bibendum sodales, augue velit cursus nunc,
</div>
<div id="wrapper">
  <div id="blackBackground"></div>
  <canvas id="c"></canvas>
</div>
<script>
  var b = document.body;
  var c = document.getElementsByTagName('canvas')[0];
  var a = c.getContext('2d');
  document.body.clientWidth; // fix bug in webkit: http://qfox.nl/weblog/218
</script>