Bug 126646

Summary:	Subpixel layout: desiredColumnWidth in RenderBlock::calcColumnWidth() needs flooring.
Product:	WebKit	Reporter:	zalan <zalan>
Component:	Layout and Rendering	Assignee:	zalan <zalan>
Status:	RESOLVED INVALID
Severity:	Normal	CC:	jonlee, simon.fraser, webkit-bug-importer
Priority:	P2
Version:	528+ (Nightly build)
Hardware:	Unspecified
OS:	Unspecified
Bug Depends on:
Bug Blocks:	126283

Description zalan 2014-01-08 10:46:06 PST

LayoutUnit desiredColumnWidth = std::max<LayoutUnit>(0, ((availWidth - ((desiredColumnCount - 1) * colGap)) / desiredColumnCount)) produces different CSS pixel results when subpixel is off.

failed case:
  fast/events/document-elementFromPoint.html
  fast/multicol/break-properties.html
  fast/multicol/column-break-with-balancing.html
  fast/multicol/float-paginate-complex.html
  fast/multicol/layers-in-multicol.html
  fast/multicol/overflow-across-columns-percent-height.html
  fast/multicol/overflow-across-columns.html
  fast/multicol/overflow-unsplittable.html
  fast/multicol/scrolling-overflow.html 
  fast/multicol/span/clone-flexbox.html 
  fast/multicol/span/clone-summary.html 
  fast/multicol/table-vertical-align.html
  fast/multicol/vertical-lr/break-properties.html 
  fast/multicol/vertical-lr/column-break-with-balancing.html
  fast/multicol/vertical-lr/float-multicol.html 
  fast/multicol/vertical-rl/break-properties.html
  fast/multicol/vertical-rl/column-break-with-balancing.html 
  fast/multicol/vertical-rl/float-multicol.html 
  fast/multicol/newmulticol/column-rules-fixed-height.html 
  fast/multicol/newmulticol/columns-shorthand-parsing.html
  fast/multicol/newmulticol/layers-in-multicol.html

Comment 1 zalan 2014-01-08 11:17:28 PST

If we start snapping columns widths to CSS pixels, we lose subpixels while layouting the columns content.

Comment 2 Simon Fraser (smfr) 2014-01-08 15:22:04 PST

Need to talk to Dave Hyatt.

Comment 3 zalan 2014-01-14 16:39:33 PST

Matches FF(v26) rendering.