Bug 36525 – MathML Fraction and Subsup incorrect layout

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

[Stephen Loo]

Created attachment 51489 [details]
An example of MathML of <mfrac> and <msubsup>

In my attachment example, I combine <mfrac> and <msubsup> to use, but the layout is incorrect. Please see attached xhtml for references. And the correct layout should be same as attached png.

[Stephen Loo]

Created attachment 51490 [details]
Correct layout of the xhtml.

[François Sausset]

The problem does not come from the mfrac element, but from the mrow in which the msubsup is embedded. See the attachment.

[François Sausset]

Created attachment 52497 [details]
Test showing the bug when msubsup is embedded in an mrow element.

[Alex Milowski]

Actually, math and mrow are almost the exact same rendering object (RenderMathMLRow).  The cause of this is a row containing another row and stretching.  The row operator stretching algorithm is doing something strange to the layout of msubsup in this context.

The new layout patch in https://bugs.webkit.org/show_bug.cgi?id=40986 doesn't fix this yet.

[François Sausset]

Created attachment 60058 [details]
Patch fixing the bug

[Darin Adler]

Comment on attachment 60058 [details]
Patch fixing the bug

> +    if (base->firstChild()->isRenderMathMLBlock()) {

What guarantees that base->firstChild() is non-null?

Otherwise, this patch looks good to me.

[François Sausset]

Created attachment 60064 [details]
Updated patch

I added a test to be sure that base->firstChild() exists.

However, lines 100 and 101 of RenderMathMLSubSup.cpp should guarantee it.

[Darin Adler]

(In reply to comment #7)
> I added a test to be sure that base->firstChild() exists.
> 
> However, lines 100 and 101 of RenderMathMLSubSup.cpp should guarantee it.

We don't need both a test and a guarantee! Only one or the other.

[François Sausset]

Comment on attachment 60064 [details]
Updated patch

Revert to previous patch to avoid unnecessary test.

[WebKit Commit Bot]

Comment on attachment 60058 [details]
Patch fixing the bug

Clearing flags on attachment: 60058

Committed r62152: <http://trac.webkit.org/changeset/62152>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.