[Webkit-unassigned] [Bug 104573] New: [EFL][WK2] Layers are shifted vertically by 1-2 pixels in compositing/geometry tests.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=104573

           Summary: [EFL][WK2] Layers are shifted vertically by 1-2 pixels
                    in compositing/geometry tests.
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: ostap73 at gmail.com


This bug is to keep track and summarize my findings about compositing/geometry tests on EFL port.
Currently it doesn't apply to EFL/wk1 because accelerated compositing is disabled.
Probably GTK port has the same problem, but they do not support AC now.

The easiest way problem reproduced on compositing/geometry/composited-in-columns.html tests. Other geometry tests also may fail or flaky.

Problem appears when RenderBoxes are positioned during layout. Layout is based on line height + line gap. For SimpleFontDataFreeType line hight is calculated like ascender + descender (FontMetrics.h) . Line gap is calculated like font_extents.height - font_extents.ascent - font_extents.descent (SimpleFontData::platformInit()).
When I run this test font_extents.height is less than font_extents.ascent + font_extents.descent and line gap becomes negative (-1) and this affects page layout.
font_extents are received from cairo_scaled_font_extents call and internally cairo gets it from freetype font library.
Freetype loads LiberationSerif-Regular.ttf font and it seems if this font is loaded 1st it gets wrong metric in face->size->metrics . 
I tried loading this test into Minibrowser. In this case font is loaded with correct metrics and page layouts correctly.
The problem looks very similar to this bug in freetype library: http://savannah.nongnu.org/bugs/?34156
EFL currently uses 2.4.2. I tried upgrading to 2.4.10 and it didn't help.

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