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[cssom-view] Return real values for colorDepth and pixelDepth (closes #993) #994

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Mar 13, 2017
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[cssom-view] Return real values for colorDepth and pixelDepth (closes #993) #994

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38 changes: 32 additions & 6 deletions cssom-view/Overview.bs
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Expand Up @@ -81,6 +81,7 @@ urlPrefix: http://heycam.github.io/webidl/
text: long
type: dfn; text: converted to an IDL value; url: dfn-convert-ecmascript-to-idl-value
url: https://www.w3.org/TR/DOM-Level-3-Events/#interface-MouseEvent; type: interface; text: MouseEvent
url: https://drafts.csswg.org/mediaqueries-4/#mf-colors; type: dfn; text: color media query
</pre>

<pre class='link-defaults'>
Expand Down Expand Up @@ -896,13 +897,38 @@ screen area</a>. <!--fingerprint-->
The <dfn attribute for=Screen>height</dfn> attribute must return the height of the <a>Web-exposed
screen area</a>. <!--fingerprint-->

The <dfn attribute for=Screen>colorDepth</dfn> attribute must return 24.

The <dfn attribute for=Screen>pixelDepth</dfn> attribute must return 24.

Note: The {{colorDepth}} and {{pixelDepth}} attributes are useless but are
included for compatibility.
The <dfn attribute for=Screen>colorDepth</dfn> and <dfn attribute
for=Screen>pixelDepth</dfn> attributes should return the number of bits
allocated to colors for a pixel in the output device, excluding the alpha
channel. If the user agent is not able to return the number of bits used by the
output device, it should return the closest estimation such as, for example, the
number of bits used by the frame buffer sent to the display or any internal
representation that would be the closest to the value the output device would
use. The user agent must return a value for these attributes at least equal to
the value of <a>color media query</a> multiplied by three. If the different
color components are not represented with the same number of bits, the returned
value may be greater than three times <a>color media query</a>. If the user
agent does not know the color depth or does not want to return it for privacy
considerations, it should return 24.

Note: The {{colorDepth}} and {{pixelDepth}} attributes return the same value for
compatibility reasons.

Note: Some non-conforming implementations are known to return 32 instead of 24.

<div class='example'>
<code>colorDepth</code> can be used in the context of selecting SDR/HDR in
addition with other information. For example, combined with color gamut.

<pre class='lang-javascript'>
if (screen.colorDepth >= 48 && window.matchMedia('(color-gamut: p3)').matches &&
/* other checks */) {
// Use HDR content.
} else {
// Use SDR content.
}
</pre>
</div>

Extensions to the {{Document}} Interface {#extensions-to-the-document-interface}
================================================================================
Expand Down