Bug 104944 – [CSS Fragmentation] Implement correct margin truncation at breaks

• Component: WebCore Misc.
• Status: NEW

[Andrei Bucur]

The paragraph at http://www.w3.org/TR/css3-break/#break-margins states the bottom margins before a forced break get truncated. When an unforced break occurs, both the top/bottom margins are truncated. Use this bug to track the progress for the implementation of this mechanism in regions, columns and pages.

[Andrei Bucur]

Created attachment 184806 [details]
A test case with bottom margin not getting truncated after a forced break.

[Andrei Bucur]

Created attachment 184999 [details]
WIP Patch

[WebKit Review Bot]

Attachment 184999 [details] did not pass style-queue:

Failed to run "['Tools/Scripts/check-webkit-style', '--diff-files', u'LayoutTests/fast/block/margin-collapse/webkit-margin-collapse-siblings.html', u'Source/WebCore/rendering/RenderBlock.cpp']" exit_code: 1
Source/WebCore/rendering/RenderBlock.cpp:2030:  When wrapping a line, only indent 4 spaces.  [whitespace/indent] [3]
Total errors found: 1 in 2 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Andrei Bucur]

(In reply to comment #2)
> Created an attachment (id=184999) [details]
> Patch

Very early version of the patch showing the approach to fix the -webkit-margins-collapse properties. Unfortunately there's little to nothing specified about this property http://developer.apple.com/library/safari/#documentation/AppleApplications/Reference/SafariCSSRef/Articles/StandardCSSProperties.html#//apple_ref/css/property/-webkit-margin-collapse

The test is supposed to cover all the possible combinations of that property between siblings. A reference page will pair it in the final patch.

I have a feeling all this logic can be somehow simplified. I'll give this idea a spin in the next version.

[Build Bot]

Comment on attachment 184999 [details]
WIP Patch

Attachment 184999 [details] did not pass mac-ews (mac):
Output: http://queues.webkit.org/results/16152714

New failing tests:
compositing/checkerboard.html
compositing/geometry/abs-position-inside-opacity.html
compositing/geometry/bounds-clipped-composited-child.html
compositing/iframes/become-overlapped-iframe.html
animations/3d/matrix-transform-type-animation.html
compositing/iframes/connect-compositing-iframe-delayed.html
compositing/direct-image-compositing.html
compositing/iframes/connect-compositing-iframe2.html
animations/additive-transform-animations.html
compositing/columns/composited-in-paginated.html
compositing/layers-inside-overflow-scroll.html
compositing/generated-content.html
compositing/geometry/composited-in-columns.html
compositing/iframes/connect-compositing-iframe3.html
accessibility/lists.html
compositing/images/direct-image-background-color.html
compositing/geometry/ancestor-overflow-change.html
compositing/geometry/bounds-ignores-hidden-dynamic-negzindex.html
compositing/iframes/connect-compositing-iframe.html
compositing/iframes/become-composited-nested-iframes.html
compositing/geometry/clipping-foreground.html
compositing/clip-child-by-non-stacking-ancestor.html
compositing/iframes/composited-parent-iframe.html
compositing/compositing-visible-descendant.html
compositing/overflow-trumps-transform-style.html
compositing/iframes/composited-iframe-alignment.html
compositing/backing/no-backing-for-clip.html
compositing/backing/no-backing-for-clip-overlap.html
compositing/backing/no-backing-for-perspective.html
compositing/layer-creation/animation-overlap-with-children.html

[WebKit Review Bot]

Comment on attachment 184999 [details]
WIP Patch

Attachment 184999 [details] did not pass chromium-ews (chromium-xvfb):
Output: http://queues.webkit.org/results/16163696

New failing tests:
compositing/geometry/abs-position-inside-opacity.html
compositing/geometry/bounds-clipped-composited-child.html
animations/3d/matrix-transform-type-animation.html
compositing/direct-image-compositing.html
compositing/backing/no-backing-for-clip-overlap.html
animations/additive-transform-animations.html
accessibility/svg-remote-element.html
compositing/layers-inside-overflow-scroll.html
compositing/sibling-positioning.html
compositing/backing/no-backing-for-perspective.html
compositing/generated-content.html
compositing/self-painting-layers.html
animations/cross-fade-webkit-mask-box-image.html
compositing/flat-with-transformed-child.html
compositing/geometry/ancestor-overflow-change.html
animations/cross-fade-list-style-image.html
compositing/geometry/bounds-ignores-hidden-dynamic-negzindex.html
animations/cross-fade-background-image.html
compositing/columns/composited-in-paginated.html
compositing/geometry/clipping-foreground.html
animations/cross-fade-border-image-source.html
compositing/clip-child-by-non-stacking-ancestor.html
compositing/backface-visibility/backface-visibility-image.html
compositing/compositing-visible-descendant.html
animations/cross-fade-webkit-mask-image.html
compositing/overflow-trumps-transform-style.html
compositing/backing/no-backing-for-clip.html
compositing/backface-visibility/backface-visibility-simple.html
accessibility/svg-bounds.html
compositing/backface-visibility/backface-visibility-webgl.html

[Build Bot]

Comment on attachment 184999 [details]
WIP Patch

Attachment 184999 [details] did not pass mac-wk2-ews (mac-wk2):
Output: http://queues.webkit.org/results/16183410

New failing tests:
compositing/checkerboard.html
compositing/geometry/abs-position-inside-opacity.html
compositing/geometry/bounds-clipped-composited-child.html
compositing/iframes/become-overlapped-iframe.html
animations/3d/matrix-transform-type-animation.html
compositing/iframes/connect-compositing-iframe-delayed.html
compositing/direct-image-compositing.html
compositing/iframes/connect-compositing-iframe2.html
animations/additive-transform-animations.html
accessibility/svg-remote-element.html
compositing/layers-inside-overflow-scroll.html
compositing/generated-content.html
compositing/self-painting-layers.html
compositing/iframes/connect-compositing-iframe3.html
compositing/backing/no-backing-for-clip-overlap.html
accessibility/lists.html
compositing/tiled-layers-hidpi.html
compositing/geometry/ancestor-overflow-change.html
compositing/geometry/bounds-ignores-hidden-dynamic-negzindex.html
compositing/columns/composited-in-paginated.html
compositing/iframes/become-composited-nested-iframes.html
compositing/geometry/clipping-foreground.html
compositing/clip-child-by-non-stacking-ancestor.html
compositing/iframes/composited-parent-iframe.html
compositing/compositing-visible-descendant.html
compositing/overflow-trumps-transform-style.html
compositing/iframes/composited-iframe-alignment.html
compositing/backing/no-backing-for-clip.html
accessibility/svg-bounds.html
compositing/backing/no-backing-for-perspective.html

[Tim Nguyen (:ntim)]

I've removed -webkit-margin-collapse in:

https://github.com/WebKit/WebKit/commit/42888f9d55e6863c9e1a8110cc164f81a63c1158

Hopefully this should be easier.

Created attachment 475160 [details]
minimum html / css reproduction

Bottom margin is incorrectly rendered on 2nd column.

Tested on Version 18.4 (20621.1.15.11.10)