Bug 125757

Summary:

Subpixel layout: Rounding padding vales pushes the content 1px off.

Product:

WebKit

Reporter:

alan <zalan>

Component:

Layout and Rendering

Assignee:

alan <zalan>

Status:

RESOLVED INVALID

Severity:

Normal

CC:

hyatt, jonlee, koivisto, simon.fraser, webkit-bug-importer

Priority:

Keywords:

InRadar

Version:

528+ (Nightly build)

Hardware:

Unspecified

OS:

Unspecified

Bug Depends on:

Bug Blocks:

126283

Attachments:

Description	Flags
test case	none
screenshot(wikipedia)	none
regressed test case (wikipedia)	none
Testing FF's rendering.	none

alan

Reported 2013-12-15 12:22:46 PST

<html> <head> <style> body { font-size: 99%; padding-left: 0.5em; } </style> </head> <body>This line is pushed to left by 1px. (body's padding-left is 0.5em with font-size: 99%.)</body> </html>

Attachments
test case (205 bytes, text/html) 2013-12-15 12:23 PST, alan	no flags	Details
screenshot(wikipedia) (304.78 KB, image/gif) 2013-12-19 17:00 PST, alan	no flags	Details
regressed test case (wikipedia) (139 bytes, text/html) 2013-12-19 17:01 PST, alan	no flags	Details
Testing FF's rendering. (118.77 KB, image/jpeg) 2014-01-14 15:06 PST, alan	no flags	Details
View All Add attachment proposed patch, testcase, etc.

alan

Comment 1 2013-12-15 12:23:50 PST

Created attachment 219279 [details] test case

alan

Comment 2 2013-12-15 12:26:19 PST

<rdar://problem/15665134>

alan

Comment 3 2013-12-16 14:31:54 PST

This is the result of clamping float values at LayoutUnit(float) to int when minimumValueForLength() is called. computed minimum value: 6.8; subpixel on: LayoutUnit value -> 435 (which eventually gets pixelsnapped to 7px) subpixel off: LayoutUnit value -> 6 as the result of the clamping. It mainly (most visibly) effects paddings and margins, but it can push pixels off by 1 at other places too (like with text-indent, width properties) div { font-size: 99%; text-indent: 1em; } div { font-size: 99%; width: 1em; display: inline-block; }

Simon Fraser (smfr)

Comment 4 2013-12-18 11:26:11 PST

I think it's OK to have a behavior change with subpixel when authors are using percentages. We should check Firefox behavior.

alan

Comment 5 2013-12-19 17:00:45 PST

Created attachment 219704 [details] screenshot(wikipedia) Rounding these values would also regress some content including wikipedia. <html> <head> <style> div { margin-top: -1.4em; margin-bottom: 1.4em } </style> </head> <body> <div></div> foo </body> </html>

alan

Comment 6 2013-12-19 17:01:22 PST

Created attachment 219705 [details] regressed test case (wikipedia)

alan

Comment 7 2014-01-14 15:06:30 PST

Created attachment 221209 [details] Testing FF's rendering. The new off-by-one rendering matches FF's (v26.0) rendering. (top to bottom: subpixel on, FF, subpixel off)

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