[webkit-dev] Why does Ahem have different vertical metrics in Qt?

[Ryosuke Niwa]

I vaguely remember Qt folks mentioning that there's a font-related bug in Qt
DRT.

- Ryosuke

On Wed, Feb 9, 2011 at 4:42 AM, Dan Bernstein <mitz at apple.com> wrote:

> In an attempt to give layout tests consistent results across platforms, I
> ofter use the Ahem font. However, I’ve noticed that Qt still requires
> platform-specific results when I do that. One recent example is
> fast/dynamic/unicode-bidi.html
>
> $ diff -u LayoutTests/platform/qt/fast/dynamic/unicode-bidi-expected.txt
>  LayoutTests/fast/dynamic/unicode-bidi-expected.txt
> --- LayoutTests/platform/qt/fast/dynamic/unicode-bidi-expected.txt 2011-02-03
> 09:02:59.000000000 -0800
> +++ LayoutTests/fast/dynamic/unicode-bidi-expected.txt 2011-01-28
> 10:46:32.000000000 -0800
> @@ -3,14 +3,14 @@
>  layer at (0,0) size 800x600 layerType: background only
>  layer at (8,8) size 100x50
>    RenderBlock (positioned) zI: -1 {DIV} at (8,8) size 100x50
> [color=#FF0000]
> -    RenderInline {SPAN} at (0,0) size 50x49 [color=#008000]
> -      RenderText {#text} at (0,0) size 50x49
> +    RenderInline {SPAN} at (0,0) size 50x50 [color=#008000]
> +      RenderText {#text} at (0,0) size 50x50
>          text run at (0,0) width 50: "x"
> -    RenderText zI: -1 {#text} at (50,0) size 50x49
> +    RenderText zI: -1 {#text} at (50,0) size 50x50
>        text run at (50,0) width 50: "x"
>  layer at (0,0) size 800x600 layerType: foreground only
>    RenderBlock {HTML} at (0,0) size 800x600
>      RenderBody {BODY} at (8,8) size 784x584
>        RenderBlock {DIV} at (0,0) size 784x50 [color=#008000]
> -        RenderText {#text} at (0,0) size 100x49
> +        RenderText {#text} at (0,0) size 100x50
>            text run at (0,0) width 100 RTL override: "xp"
>
> Here, all the 50px Ahem text has a height of 49 pixels on Qt. The pixel
> results, though, show it having the same height it does in Mac OS X (and
> presumably other platforms).
>
> What is causing this difference? How does it affect other fonts and real
> websites? Is there a way to fix this?
>
> Thanks,
> —Dan
>
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>
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