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Subpixel positioning fails since ac5525a #8166

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paulrouget opened this issue Oct 23, 2015 · 5 comments
Closed

Subpixel positioning fails since ac5525a #8166

paulrouget opened this issue Oct 23, 2015 · 5 comments
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A-gfx/rendering

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@paulrouget
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When an iframe is present in the document, top:0.5px is drawn at 1px.

It's started with ac5525a.

<style>

  div {
    position: absolute;
    left: 0;
    top: 10.5px;
    width: 200px;
    height: 200px;
    background: red;
  }

  iframe {
    border: none;
  }

  .foo { display: none; }

</style>

<script>
  setInterval(() => {
    document.querySelector('iframe').classList.toggle('foo');
  }, 1000);
</script>

<body>
  <div></div>
  <iframe></iframe>
</body>
@paulrouget paulrouget mentioned this issue Oct 23, 2015
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@paulrouget
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/cc @mrobinson

@paulrouget
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Using to_nearest_pixel instead of to_nearest_px in components/gfx/paint_task.rs appears to solve the issue. I'll submit a PR.

@paulrouget
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I don't know how to get the pixel density in build_layer_properties. Usually, we use page_rect and screen_screen, but here, I don't know how to get this info.

@mrobinson
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I think one issue here is that the layer boundaries are rounded instead of expanded to pixel boundaries. I have a fix for this which depends on servo/app_units#3 (though I don't have a readily accessible hidpi screen to test it on).

@glennw
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glennw commented Oct 27, 2015

@mrobinson Depending on what you're testing, you may be able to use --device-pixel-ratio=2 even on a non-hidpi monitor to test with.

@mrobinson mrobinson mentioned this issue Oct 27, 2015
Closed
mrobinson added a commit to mrobinson/servo that referenced this issue Oct 29, 2015
@mrobinson
Expand DisplayList layer bounds to whole pixel
3f9084e 
Before passing these layers to the paint task, expand them to pixel
boundaries. This ensures that subpixel edges of the layer will not be
clipped away and helps prevent rounding issues with layer contents.

Fixes servo#8166.
mrobinson added a commit to mrobinson/servo that referenced this issue Oct 29, 2015
@mrobinson
Expand DisplayList layer bounds to whole pixels
a7a58e4 
Before passing these layers to the paint task, expand them to pixel
boundaries. This ensures that subpixel edges of the layer will not be
clipped away and helps prevent rounding issues with layer contents.

Fixes servo#8166.
@mrobinson mrobinson mentioned this issue Oct 29, 2015
Merged
bors-servo pushed a commit that referenced this issue Oct 29, 2015
Auto merge of #8244 - mrobinson:layer-size, r=pcwalton
94ca87e 
Expand DisplayList layer bounds to whole pixels

Before passing these layers to the paint task, expand them to pixel
boundaries. This ensures that subpixel edges of the layer will not be
clipped away and helps prevent rounding issues with layer contents.

Fixes #8166.

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@mrobinson @jdm @paulrouget @glennw