c# - 如何将元素的背景颜色与 2 个半透明元素背景颜色相匹配

Question

我做了一个jsfiddle

在 fiddle 中有 3 个 div。

1. 左边的是紫色。
2. 右边的是蓝色。
3. 蓝色 div 上面的那个有一种未知颜色

第三个 div(位于右侧蓝色 div 之上的那个)所需的颜色是左侧 div(紫色那个)的颜色。

问题是所有 div 的不透明度为 0.7，并且必须保持不变(以便看到它们后面的内容)。

那么我的问题是，如何计算左侧紫色和右侧蓝色之间的差异，以便我可以给第三个 div 一种颜色，使其与紫色 div 的颜色相匹配当它覆盖右侧的蓝色 div 时在左侧。

我不是要你用眼睛去猜，因为我有很多其他颜色可以用来做这个，我只是想知道是否有一个计算允许我使用 JQuery 或 Javascript 来做这个？

到目前为止，我还没有任何 JS 代码，因为我什至不知道从哪里开始。


HTML

<div id="target" class="opacity purple"></div>
<div id="actualBackground" class="opacity blue"></div>
<div id="sameColourAsTarget" class="opacity purple2"></div>

CSS

div{
    position:absolute;
}
#target{
    left:0px;
    top:0px;
    height:150px;
    width:150px;
}
#actualBackground{
    left:150px;
    top:0px;
    height:150px;
    width:150px;
}
#sameColourAsTarget{
    left:150px;
    top:50px;
    height:50px;
    width:50px;
}
.opacity{
    opacity:0.7;
}
.purple{
    background-color:rgb(152, 3, 214);
}
.blue{
    background-color:rgb(10, 127, 188);
}
.purple2{
    background-color:rgb(175, 3, 150);
}

非常感谢任何帮助，

谢谢

Answer 1

检查 fiddle here用于纯 Javascript 解决方案。

/**
 * Gets the mixed color obtained by overlaying a front color
 * with the specified opacity over a solid back color.
 */
function mix(back, front, opacity) {
    var mixed = {
        r: (1 - opacity) * back.r + opacity * front.r,
        g: (1 - opacity) * back.g + opacity * front.g,
        b: (1 - opacity) * back.b + opacity * front.b
    }

    return mixed;
}

/**
 * Gets the front color that can be overlaid with the specified
 * opacity over a solid back color to get the same color as the
 * mixed color.
 */
function unmix(mixed, back, opacity) {
    var front = {
        r: (mixed.r - back.r) / opacity + back.r,
        g: (mixed.g - back.g) / opacity + back.g,
        b: (mixed.b - back.b) / opacity + back.b
    }

    return front;
}

/**
 * Converts an rgb string to a color object in the following form
 * {r: 255, g: 255, b: 255}
 */
function rgbToColor(rgb) {
    var matches = rgb.match(/^rgb\((\d+),\s*(\d+),\s*(\d+)\)$/);

    return {
        r: parseInt(matches[1]),
        g: parseInt(matches[2]),
        b: parseInt(matches[3])
    }
}

/**
 * Converts a color object of from {r: 255, g: 255, b: 255} to
 * an rgb string
 */
function colorToRgb(color) {
    var r = Math.round(color.r);
    var g = Math.round(color.g);
    var b = Math.round(color.b);

    return "rgb(" + r + "," + g + "," + b + ")";
}

// get properties of the back element
var backEl = document.getElementById("actualBackground");
var backStyle = window.getComputedStyle(backEl);
var backColor = backStyle.backgroundColor;
var backOpacity = backStyle.opacity;

// get properties of the target element
var mixedEl = document.getElementById("target");
var mixedStyle = window.getComputedStyle(mixedEl);
var mixedColor = mixedStyle.backgroundColor;
var mixedOpacity = mixedStyle.opacity;

// calculate the actual back color by mixing the back element's
// properties with solid white
var back = mix({
    r: 255,
    g: 255,
    b: 255
}, rgbToColor(backColor), backOpacity);

// calculate the actual target color by mixing the target element's
// properties with solid white
var mixed = mix({
    r: 255,
    g: 255,
    b: 255
}, rgbToColor(mixedColor), mixedOpacity);

// calculate the overlay's color by unmixing the back and the target
// colors with an opacity of 0.7 (could also be retrieved from the overlay element
var front = unmix(mixed, back, 0.7);

// get the overlay's element and apply the calculated color
var frontEl = document.getElementById("sameColourAsTarget");
frontEl.style.backgroundColor = colorToRgb(front);
frontEl.style.opacity = 0.7;