Created
April 19, 2023 18:33
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Luminance testing on scroll for a given x/y coordinate
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| <html> | |
| <head> | |
| <style> | |
| body { | |
| margin: 0; | |
| padding: 0; | |
| } | |
| .nav { | |
| position: fixed; | |
| background: #FFF; | |
| top: 10px; | |
| left: 10px; | |
| width: calc(100% - 20px); | |
| } | |
| .nav ul { | |
| list-style: none; | |
| margin: 0; | |
| } | |
| .nav li { | |
| display: inline-block; | |
| margin: 10px 20px; | |
| vertical-align: middle; | |
| } | |
| </style> | |
| </head> | |
| <body> | |
| <div class="test-bg-color" style="background-color: rgba(0,0,0,0.7); height: 600px"></div> | |
| <div class="test-bg-color" style="background-color: #fff; height: 600px"></div> | |
| <div class="test-bg-color" style="background-color: #F4F3FA; height: 600px"></div> | |
| <div class="test-bg-color" style="background-color: rgba(0,0,0,1); height: 600px"></div> | |
| <div class="test-bg-color" style="background-color: #F4F3FA; height: 600px"></div> | |
| <div class="test-bg-color" style="background-color: #fff; height: 600px"></div> | |
| <div id="nav" class="nav"> | |
| <ul> | |
| <li>Link 1</li> | |
| <li>Link 2</li> | |
| <li>Link 3</li> | |
| </ul> | |
| </div> | |
| <script> | |
| function getRgbish(c) { // https://stackoverflow.com/questions/7543818/regex-javascript-to-match-both-rgb-and-rgba | |
| var i = 0, itm, | |
| M = c.replace(/ +/g, '').match(/(rgba?)|(\d+(\.\d+)?%?)|(\.\d+)/g); | |
| if (M && M.length > 3) { | |
| while (i < 3) { | |
| itm = M[++i]; | |
| if (itm.indexOf('%') != -1) { | |
| itm = Math.round(parseFloat(itm) * 2.55); | |
| } | |
| else itm = parseInt(itm); | |
| if (itm < 0 || itm > 255) return NaN; | |
| M[i] = itm; | |
| } | |
| if (c.indexOf('rgba') === 0) { | |
| if (M[4] == undefined || M[4] < 0 || M[4] > 1) return NaN; | |
| } | |
| else if (M[4]) return NaN; | |
| return M.slice(1); | |
| } | |
| return NaN; | |
| } | |
| const nav = document.getElementById('nav') | |
| window.addEventListener('scroll', function () { | |
| const eles = document.elementsFromPoint(nav.offsetLeft, nav.offsetTop).filter(ele => ele.classList.contains('test-bg-color')) | |
| if (eles.length) { | |
| const color = getRgbish(eles[0].style.backgroundColor) | |
| const luminance = Math.sqrt(0.299 * Math.pow(color[0], 2) + 0.587 * Math.pow(color[1], 2) + 0.114 * Math.pow(color[2], 2)) | |
| if (luminance < 127.5) { | |
| console.log('make nav light') | |
| } else { | |
| console.log('make nav dark') | |
| } | |
| } else { | |
| console.log('unable to determine bg color - ensure a .test-bg-color element is present') | |
| } | |
| }) | |
| </script> | |
| </body> | |
| </html> |
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