On 11/15/22 11:21 AM, 'Christopher Cameron' via blink-dev wrote:
*Contact email:*
ccame...@chromium.org
*Explainer:* None
*Specification:* None
*Summary:*
These fields were accidentally exposed to the web in crrev.com/562990
<http://crrev.com/562990> by way of crrev.com/427153
<http://crrev.com/427153>. They are not part of any specification.
These CLs landed in 2018 and 2016... do we have any UseCounter or usage
data?
These fields allow OffscreenCanvas::convertToBlob to specify a target
color space (srgb, display-p3, and rec2020) and pixel format (uint8
and uint16). This sets a default behavior of setting the color space
sRGB and pixel format of 8 bits per pixel.
When these parameters are removed, the target space for convertToBlob
will default to the color space of the canvas (srgb or display-p3),
and the pixel format will default to the pixel format of the canvas
(uint8 is the only supported pixel format).
*Motivation:*
The behavior caused by these fields at odds with the HTML
specification, section "Serializing bitmaps to a file", which says that
For image types that support color profiles, the serialized image
must include a color profile indicating the color space of the
underlying bitmap.
For example, for a Display P3 canvas, calling convertToBlob with no
arguments should result in a blob that specifies a Display P3 color
profile.
These fields can only degrade the quality of the resulting image,
compared with the behavior from the HTML specification.
*TAG review:* N/A
*Risks:*
When this feature is removed, the images resulting from convertToBlob
are guaranteed to be an equal or higher fidelity representation as
compared with behavior before this feature was removed, because all
OffscreenCanvas elements are 8-bit sRGB or Display P3.
*Interoperability and Compatibility*
Gecko: Never implemented
WebKit: Never implemented
Web developers: No signals
*Debuggability:* N/A
*Is this feature fully tested by web-platform-tests?*
No, there exists one Blink layout test for this feature.
*Tracking bug:* crbug.com/1384538 <http://crbug.com/1384538>
*Link to related intents: *
This was discovered when writing tests for Canvas Floating Point Color
Types <https://chromestatus.com/feature/5086141338877952>, which is a
prerequisite for High Dynamic Range Support for HTMLCanvasElement
<https://chromestatus.com/feature/5703719636172800>.
Link to entry on the Chrome Platform Status
<https://chromestatus.com/feature/5129184450445312>
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