tor-browser

The Tor Browser
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devicepixel2.html (4399B)

      1 <!doctype html>
      2 <link rel="match" href="devicepixel2-ref.html">
      3 <meta name="assert" content="Resize Observer's reported device pixel content box size should be consistent with the actual pixel-snapped painted box size">
      4 <style>
      5  html, body {
      6    margin: 0;
      7  }
      8  .line {
      9    width: 100px;
     10    display: flex;
     11  }
     12  .line>* {
     13    flex: 1;
     14    height: 20px;
     15  }
     16 </style>
     17 <body>
     18  <div></div>
     19  <script type="module">
     20 import createPatternDataURL from './create-pattern-data-url.js';
     21 
     22 const {patternSize, dataURL} = createPatternDataURL();
     23 
     24 /**
     25 * Set the pattern's size on this element so that it draws where
     26 * 1 pixel in the pattern maps to 1 devicePixel and then set
     27 * its position so it's aligned to the pattern of the body element.
     28 */
     29 function setPattern(elem, x, y) {
     30  const oneDevicePixel = 1 / devicePixelRatio;
     31  const patternPixels = oneDevicePixel * patternSize;
     32  elem.style.backgroundImage = `url("${dataURL}")`;
     33  elem.style.backgroundSize = `${patternPixels}px ${patternPixels}px`;
     34  elem.style.backgroundPosition = `${-x * oneDevicePixel}px ${-y * oneDevicePixel}px`;
     35 }
     36 
     37 /*
     38 This test creates elements like this
     39 
     40  <body>
     41    <div>
     42      <div class="line"><div></div><div></div></div>
     43      <div class="line"><div></div><div></div><div></div></div>
     44      <div class="line"><div></div><div></div><div></div><div></div></div>
     45      ...
     46    </div>
     47  </body>
     48 
     49 It has the first `<div>` starting at the top left corner of the page, the
     50 same as the body so they should both have a devicePixel position of 0,0
     51 
     52 The devicePixelContentBoxSize of all the elements is queried with
     53 a ResizeObserver.
     54 
     55 It then sets a repeating background-image, background-size and
     56 background-position on the all of the innermost children elements so
     57 they have a 4x4 checkerboard image at a size that should draw each pixel
     58 of the 4x4 checkerboard pattern in single devicePixels and so they should
     59 all align with the same pattern applied in a similar manner to the body.
     60 
     61 In other words
     62 
     63  <div class="line">
     64    <div></div><div></div><div></div>
     65  </div>
     66 
     67 The first child will be displayed at left = 0 so its background-position is
     68 set to 0px 0px. The second child should be displayed at
     69 
     70 secondChildLeft = entry(firstChild).devicePixelContentBoxSize[0].inlineSize.
     71 
     72 The 3rd child should be displayed at
     73 
     74 thirdChildLeft = entry(firstChild).devicePixelContentBoxSize[0].inlineSize +
     75                 entry(secondChild).devicePixelContentBoxSize[0].inlineSize
     76 
     77 Using the children's device-pixel positions (determined as described above),
     78 we then set each child's background-position to the negated version of the
     79 position that we computed for that child. This effectively makes its pattern's
     80 origin match the document origin.
     81 
     82 If what devicePixelContentBox reports is correct the children's patterns
     83 will align with the pattern in the body and the children will be invisible.
     84 If what devicePixelContentBox reports is incorrect the patterns will not
     85 align and it should be clearly visible.
     86 */
     87 
     88 const wrapperElem = document.querySelector('div');
     89 
     90 const elemToDevicePixelSize = new Map();
     91 
     92 function setPatternsUsingSizeInfo(entries) {
     93  setPattern(document.body, 0, 0);
     94 
     95  for (const entry of entries) {
     96    elemToDevicePixelSize.set(entry.target, {
     97      inlineSize: entry.devicePixelContentBoxSize[0].inlineSize,
     98      blockSize: entry.devicePixelContentBoxSize[0].blockSize,
     99    });
    100  }
    101 
    102  let devicePixelY = 0;
    103  for (const lineElem of wrapperElem.children) {
    104    let devicePixelX = 0;
    105    for (const childElem of lineElem.children) {
    106      setPattern(childElem, devicePixelX, devicePixelY);
    107      const devicePixelSize = elemToDevicePixelSize.get(childElem);
    108      devicePixelX += devicePixelSize.inlineSize;
    109    }
    110 
    111    const lineEntry = elemToDevicePixelSize.get(lineElem);
    112    const lineHeight = lineEntry.blockSize;
    113    devicePixelY += lineHeight;
    114  }
    115 }
    116 
    117 const observer = new ResizeObserver(setPatternsUsingSizeInfo);
    118 observer.observe(document.body);
    119 for (let numFlexItems = 2; numFlexItems < 15; ++numFlexItems) {
    120  const lineElem = document.createElement('div');
    121  lineElem.className = 'line';
    122  observer.observe(lineElem, {box:"device-pixel-content-box"});
    123  for (let j = 0; j < numFlexItems; ++j) {
    124    const inner = document.createElement('div');
    125    lineElem.appendChild(inner);
    126    observer.observe(inner, {box:"device-pixel-content-box"});
    127  }
    128  wrapperElem.appendChild(lineElem);
    129 }
    130  </script>
    131 </body>