[MathML] Use unstretched size for minsize/maxsize default and percentages by Ahmad-S792 · Pull Request #59200 · WebKit/WebKit

Ahmad-S792 · 2026-02-22T07:27:51Z

`e142f1f`

[MathML] Use unstretched size for minsize/maxsize default and percentages
https://bugs.webkit.org/show_bug.cgi?id=308423
rdar://170908253

Reviewed by Frédéric Wang.

Per MathML Core section 3.2.4.3 "Layout of operators"
(https://w3c.github.io/mathml-core/#layout-of-operators), under the
block (vertical) stretch axis path, the spec says:

"Let minsize and maxsize be the minsize and maxsize properties on the
operator. Percentage values are interpreted relative to the height of g."

This says percentage values for minsize/maxsize are relative to the
height of the base glyph (the unstretched size). Store the unstretched
size in MathOperator during reset() and use it as the reference value
for minsize/maxsize calculations.

Per step 5 of the layout algorithm, the spec also says:

"If minsize < 0 then set minsize to 0. If maxsize < minsize then set
maxsize to minsize."

This clamping is performed in stretchTo() to match the spec's algorithm
structure, where minSize()/maxSize() return unclamped values.

Note that minsize/maxsize only appear in the block (vertical) stretch
axis section of the spec. The inline (horizontal) stretch path has no
minsize/maxsize step, so we only compute the unstretched size for
vertical operators.

* LayoutTests/imported/w3c/web-platform-tests/mathml/presentation-markup/operators/mo-minsize-maxsize-001-expected.txt: Progressions
* LayoutTests/imported/w3c/web-platform-tests/mathml/presentation-markup/operators/size-and-position-of-stretchy-fences-with-default-font-001-expected.txt: Rebaseline
* LayoutTests/platform/glib/mathml/opentype/vertical-expected.txt: Ditto
* LayoutTests/platform/ios/imported/w3c/web-platform-tests/mathml/presentation-markup/operators/size-and-position-of-stretchy-fences-with-default-font-001-expected.txt: Platform Specific Expectation
* Source/WebCore/rendering/mathml/MathOperator.cpp:
(WebCore::MathOperator::reset):
* Source/WebCore/rendering/mathml/MathOperator.h:
(WebCore::MathOperator::unstretchedSize const):
* Source/WebCore/rendering/mathml/RenderMathMLOperator.cpp:
(WebCore::RenderMathMLOperator::minSize const):
(WebCore::RenderMathMLOperator::maxSize const):
(WebCore::RenderMathMLOperator::stretchTo):

Canonical link: https://commits.webkit.org/309764@main

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webkit-early-warning-system · 2026-02-22T07:27:58Z

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webkit-early-warning-system · 2026-02-22T08:09:14Z

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fred-wang · 2026-02-22T08:47:10Z

@Ahmad-S792

Does WebKit support minsize/maxsize for horizontal operators? MathML Core only mentions it for vertical operators?
Can you please indicate which part of the spec you are using? I see https://w3c.github.io/mathml-core/#layout-of-operators ; but I don't understand your 1em fallback or the clamping of maxsize above 0 (should be minsize?).

webkit-early-warning-system · 2026-03-09T17:09:06Z

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Ahmad-S792 · 2026-03-09T17:10:55Z

@Ahmad-S792

Does WebKit support minsize/maxsize for horizontal operators? MathML Core only mentions it for vertical operators?

Can you please indicate which part of the spec you are using? I see https://w3c.github.io/mathml-core/#layout-of-operators ; but I don't understand your 1em fallback or the clamping of maxsize above 0 (should be minsize?).

You are right about both issues:

The 1em fallback was mistake — the unstretched size should always be set when minSize()/maxSize() are called, since reset() returns early if no base glyph is found, and stretching only proceeds with a valid operator. I've replaced it now.
The maxsize clamping to 0 was wrong. The spec says: "If minsize < 0 then set minsize to 0. If maxsize < minsize then set maxsize to minsize." So now fixed it as well.
In last, updated commit message.

webkit-early-warning-system · 2026-03-09T20:13:24Z

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fred-wang

LGTM, but please see comments.

Source/WebCore/rendering/mathml/RenderMathMLOperator.cpp

webkit-early-warning-system · 2026-03-21T10:46:27Z

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webkit-early-warning-system · 2026-03-21T23:01:17Z

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fred-wang

Thanks.

…ages https://bugs.webkit.org/show_bug.cgi?id=308423 rdar://170908253 Reviewed by Frédéric Wang. Per MathML Core section 3.2.4.3 "Layout of operators" (https://w3c.github.io/mathml-core/#layout-of-operators), under the block (vertical) stretch axis path, the spec says: "Let minsize and maxsize be the minsize and maxsize properties on the operator. Percentage values are interpreted relative to the height of g." This says percentage values for minsize/maxsize are relative to the height of the base glyph (the unstretched size). Store the unstretched size in MathOperator during reset() and use it as the reference value for minsize/maxsize calculations. Per step 5 of the layout algorithm, the spec also says: "If minsize < 0 then set minsize to 0. If maxsize < minsize then set maxsize to minsize." This clamping is performed in stretchTo() to match the spec's algorithm structure, where minSize()/maxSize() return unclamped values. Note that minsize/maxsize only appear in the block (vertical) stretch axis section of the spec. The inline (horizontal) stretch path has no minsize/maxsize step, so we only compute the unstretched size for vertical operators. * LayoutTests/imported/w3c/web-platform-tests/mathml/presentation-markup/operators/mo-minsize-maxsize-001-expected.txt: Progressions * LayoutTests/imported/w3c/web-platform-tests/mathml/presentation-markup/operators/size-and-position-of-stretchy-fences-with-default-font-001-expected.txt: Rebaseline * LayoutTests/platform/glib/mathml/opentype/vertical-expected.txt: Ditto * LayoutTests/platform/ios/imported/w3c/web-platform-tests/mathml/presentation-markup/operators/size-and-position-of-stretchy-fences-with-default-font-001-expected.txt: Platform Specific Expectation * Source/WebCore/rendering/mathml/MathOperator.cpp: (WebCore::MathOperator::reset): * Source/WebCore/rendering/mathml/MathOperator.h: (WebCore::MathOperator::unstretchedSize const): * Source/WebCore/rendering/mathml/RenderMathMLOperator.cpp: (WebCore::RenderMathMLOperator::minSize const): (WebCore::RenderMathMLOperator::maxSize const): (WebCore::RenderMathMLOperator::stretchTo): Canonical link: https://commits.webkit.org/309764@main

webkit-commit-queue · 2026-03-23T16:40:27Z

Committed 309764@main (e142f1f): https://commits.webkit.org/309764@main

Reviewed commits have been landed. Closing PR #59200 and removing active labels.

Ahmad-S792 self-assigned this Feb 22, 2026

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[MathML] Use unstretched size for minsize/maxsize default and percentages#59200

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