Question

我正在使用此color wheel picker，我正在尝试添加div作为拖动器，而不是将其嵌入画布中。

我创建了一个外部div（一个wrapper），并插入了一个div（dragger），然后是画布。我将拖网div's position设为absolute。然后在redraw(e) function中，我将left和top设置为以下内容：

dragger.style.left = currentX + 'px';
dragger.style.top = currentY + 'px';

这样可行，即拖拉机应该移动，但它位于错误的位置。

如何让拖动器与光标位于同一位置？

JSFiddle

var b = document.body;
var c = document.getElementsByTagName('canvas')[0];
var a = c.getContext('2d');


var wrapper = document.getElementById('wrapper');
var dragger = document.createElement('div');
dragger.id = 'dragger';
wrapper.appendChild(dragger);
wrapper.insertBefore(dragger, c);


document.body.clientWidth; // fix bug in webkit: http://qfox.nl/weblog/218

(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];

    dragger.style.left = currentX + 'px';
    dragger.style.top = currentY + 'px';
    // Reset to color wheel and draw a spot on the current location. 
    a.putImageData(imageData, 0, 0);

    // Draw the current spot.
    // I have tried a rectangle, circle, and heart shape.
    /*
    // Rectangle:
    a.fillStyle = '#000';
    a.fillRect(currentX+radiusPlusOffset,currentY+radiusPlusOffset, 6, 6);
    */
    /*
    // Circle:
    a.beginPath();  
    a.strokeStyle = '#000';
    a.arc(~~currentX+radiusPlusOffset,~~currentY+radiusPlusOffset, 4, 0, PI2);
    a.stroke();
    */

    // 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;
}
#dragger {
  background-color: orange;
  width: 15px;
  height: 15px;
  border-radius: 50%;
  position: relative;
}

<div id='wrapper'>
  <canvas id="c"></canvas>
</div>

Answer 1

通过操纵currentX和currentY坐标我非常接近。上述评论者接近解决方案;必须将~50％的高度和宽度添加到相对位置。我还建议在拖动器上使用 z-index 属性，如果您希望心脏在顶部以及它与色轮之间的拖动器。

具有适当偏移量的最终版本：Fiddle

如果拖动器的尺寸从15px减小到5px，则分别添加7和4px： https://jsfiddle.net/6n9zwahL/（固定金额）或https://jsfiddle.net/mak3Lace/（非固定，程序化解决方案）。

        dragger.style.left = (currentX + radiusPlusOffset + (radiusPlusOffset/30)) + 'px';
        dragger.style.top = (currentY + radiusPlusOffset+(radiusPlusOffset/40)) + 'px';

在我有时间编辑之前保留历史回复：

Forked Fiddle

代码 - 这里是以像素为单位手动完成的，但是我通过查询浏览器的宽度来创建变量并将其设置为更准确的值：

        dragger.style.left = currentX + 210 + 'px';
        dragger.style.top = currentY +195 + 'px';

New Fiddle, with dragger exactly aligned to heart

新职位：

dragger.style.left = currentX + 204 + 'px';
dragger.style.top = currentY +199 + 'px';

添加了改进ux的指针：https://jsfiddle.net/4cLpvu2m/

进一步详细说明，使用心脏位置代码：

currentX + radiusPlusOffset - 4, currentY + radiusPlusOffset + 4

并查询浏览器以获取您的展示位置div的位置。然后简单地从x-dragger中减去x，从y-dragger中减去y以获得差异。将差异添加到dragger.style.left等等（碰巧这些数字是~204和199）。

Another fork with alerts indicating x/y position values

杰西卡的更新，删除+/- 4以对齐元素： https://jsfiddle.net/hf5k2ecg/

Answer 2

在这里添加radiusPlusOffset：

dragger.style.left = currentX + radiusPlusOffset + 'px';
dragger.style.top = currentY + radiusPlusOffset + 'px';

https://jsfiddle.net/qsvmyh3z/1/

同时调整/减去高度＆amp;拖动器的宽度指向正确的位置。

Div不在正确的位置

JSFiddle

2 个答案: