javascript - Div 不在正确的位置

Question

我正在使用这个 color wheel picker ，我正在尝试添加一个 div 作为拖动器，而不是将其嵌入到 Canvas 中。

我创建了一个外部 div(一个 wrapper)，并插入了一个 div(拖动器)，然后是 Canvas 。我将拖动器 div's position 设置为 absolute。然后在 redraw(e) 函数中，我将 left 和 top 设置为如下:

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

这是有效的，即拖动器在它应该移动的时候移动，但它在错误的位置。

如何让拖动器与光标处于同一位置？

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

我通过操纵 currentX 和 currentY 坐标非常接近它。上面的评论者接近解决方案； ~50% 的高度和宽度必须添加到相对位置。我还建议在拖动器上使用 z-index 属性，如果您希望心脏位于顶部并且拖动器位于它和色轮之间。

具有适当偏移量的最终和正确版本:Fiddle

如果拖动器的大小从 15px 减小到 5px，则分别增加 7 和 4px: https://jsfiddle.net/6n9zwahL/ (固定金额)或 https://jsfiddle.net/mak3Lace/ (非固定的、程序化的解决方案)。

        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，但我会创建一个变量并通过查询浏览器的宽度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';

添加了改进用户体验的指针:https://jsfiddle.net/4cLpvu2m/

要进一步详细说明，请使用您拥有的心脏位置代码:

currentX + radiusPlusOffset - 4, currentY + radiusPlusOffset + 4

并在浏览器中查询拖动器 div 的位置。然后简单地从 x-dragger 中减去 x 并从 y-dragger 中减去 y 以获得差异。将差异添加到您的 dragger.style.left 等等(碰巧这些数字是〜204和199)。

Another fork with alerts indicating x/y position values

Jessica 更新的分支，移除 +/-4 以对齐元素: https://jsfiddle.net/hf5k2ecg/