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[css-transforms-2] Interpolation of rotate3D should convert to quaternions instead of a matrix. #9278

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mattwoodrow opened this issue Aug 30, 2023 · 2 comments
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[css-transforms-2] Interpolation of rotate3D should convert to quaternions instead of a matrix. #9278

mattwoodrow opened this issue Aug 30, 2023 · 2 comments
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css-transforms-2

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@mattwoodrow
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The current spec requires that rotate3D should be converted to a matrix (if the rotations are not along the same vector), and then interpolated (by decomposing into quaternions).

Most implementations are just converting rotate3D into quaternions directly and interpolating, and we should probably specify that.
mattwoodrow added a commit to mattwoodrow/WebKit that referenced this issue Aug 31, 2023
@mattwoodrow
Interpolate rotate3D using Quaternions.
a1ce34e 
https://bugs.webkit.org/show_bug.cgi?id=260932
<rdar://114732141>

Reviewed by NOBODY (OOPS!).

Looks like the other engines are doing this (despite it not being what the spec says), and it's needed to pass tests.

Filed w3c/csswg-drafts#9278 to get the spec to reflect reality here.

* LayoutTests/imported/w3c/web-platform-tests/css/css-transforms/animation/rotate-composition-expected.txt:
* LayoutTests/imported/w3c/web-platform-tests/css/css-transforms/animation/rotate-interpolation-expected.txt:
* Source/WebCore/platform/graphics/transforms/Quaternion.cpp:
(WebCore::Quaternion::fromRotate3d):
* Source/WebCore/platform/graphics/transforms/Quaternion.h:
* Source/WebCore/platform/graphics/transforms/RotateTransformOperation.cpp:
(WebCore::RotateTransformOperation::blend):
@mattwoodrow mattwoodrow mentioned this issue Aug 31, 2023
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@tabatkins
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Is there an observable difference in the two behaviors?

@BorisChiou
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BorisChiou commented Aug 31, 2023 •
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I am also working on the Gecko bug for this: https://bugzilla.mozilla.org/show_bug.cgi?id=1737209. Gecko also converts the axis, angle into the quaternion vector directly and then apply slerp. We use this way because we would like to avoid the redundant operations, e.g. convert rotate3d() into 3d matrix, and decompose it. Converting the axis, angle pair into quaternion vector looks simpler.

However, quaternion vector works well only when the rotation angle is in (-360deg, 360deg). Gecko has this bug and I'm fixing it.

@BorisChiou BorisChiou mentioned this issue Aug 31, 2023
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@tabatkins @mattwoodrow @BorisChiou