Bug 93263 – [Qt] Monospace font does not render in proper sizes

• Component: Text
• Status: RESOLVED FIXED

[mdesign]

Created attachment 156674 [details]
Test html file

Dear Devs!

Monospace font does not render in proper sizes:

Overview:
 I can't set a monospace font (eg: Courier) to 10CPI size. Theoretically Courier 12pt = 10CPI. 

Steps to Reproduce: 
 Open the attachment in webkit

Actual Results:
 Notice that the text does not fill the grey box

Expected Results:
 Open the text html in Firefox 14, the block with 12pt Courier font exactly fills the box.
 Open a microsoft word or libreoffice writer, create a text with 12pt Courier font, it prints exactly the same size, like firefox.

Build Date & Platform:
 Linux 2.6.32-21-generic-pae #32-Ubuntu SMP Fri Apr 16 09:39:35 UTC 2010 i686 GNU/Linux

Additional Builds and Platforms:
 Linux 3.2.0-27-generic-pae #43-Ubuntu SMP Fri Jul 6 15:06:05 UTC 2012 i686 i686 i386 GNU/Linux
 Windows 7 (WebKit.exe#WebKit-r124698)

[mdesign]

Created attachment 156675 [details]
Firefox 14 - renders right

[mdesign]

Created attachment 156676 [details]
qtwebkit fails

[mdesign]

Created attachment 156678 [details]
WebKit-r124698 fails

[mdesign]

If anyone can help, where can i start hacking the code, don't hesitate, please share with me!:)

[mdesign]

Does anyone know what libs responsible for the font rendering in webkit on different operating systems?

The proper rendering in Firefox 14 and Internet Explorer 9 is done via new DirectWrite API. Before using DirectWrite the monospace rendering failed same way like webkit.

There is a list about different browsers and rendering engines in this article:
http://www.smashingmagazine.com/2012/04/24/a-closer-look-at-font-rendering/

I tested every browser on windows. Just the browsers with DirectWrite engine renders properly.

[Allan Sandfeld Jensen]

Interesting. Have you tried compiling WebKit yourself? If you do, you can try to activate SUBPIXEL_LAYOUT and see if that helps. It looks like sizes are rounded poorly.

[mdesign]

Im using webkit in Qt. I found a workaround:

Commenting out this row in this file makes the monospace fonts render correctly:
/src/3rdparty/webkit/WebCore/platform/graphics/qt/FontPlatformDataQt.cpp
font.setStyleStrategy(QFont::ForceIntegerMetrics);

[Trevor North]

In my testing the workaround suggested in comment #7 also results in a general improvement in font kerning which was previously often very poor.

[Stefan Neufeind]

Any news on this?
Found it mentioned here: https://groups.google.com/forum/?fromgroups=#!topic/wkhtmltopdf-dev/SWLkI5eHi_4

[mdesign]

Dear Allan Sandfeld Jensen!

I using Qt, so i suggested a workaround for it.
But the issue exists in webkit too (as you can see it in the screenshots)

Best regards,
Károly Marton

[Allan Sandfeld Jensen]

I think there a two ways about this. 

One, we need to establish if the bug #36532 still applies on Mac. Can we remove ForceIntegerMetrics.

Second, maybe ForceIntegerMetrics is being too aggressive, and should only force basic metrics to integers but not advances. I can confirm that removing the forced rounding on advances also solves this bug.

[Allan Sandfeld Jensen]

Created attachment 193767 [details]
Patch

[Jocelyn Turcotte]

Comment on attachment 193767 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=193767&action=review

Pierre, any opinion?

> Source/WebCore/platform/graphics/qt/FontPlatformDataQt.cpp:74
> +#if QT_VERSION < QT_VERSION_CHECK(5, 1, 0)

Please add a comment in the code explaining why the version guard is used.

[Allan Sandfeld Jensen]

Created attachment 193814 [details]
Patch

[Pierre Rossi]

Comment on attachment 193814 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=193814&action=review

LGTM. That seems like the sensible approach (not affecting < 5.1 behaviour I mean)

> Source/WebCore/platform/graphics/qt/FontPlatformDataQt.cpp:75
> +    // Kept enabled for Qt<5.1 to maintain stable baselines for 5.0.

coding style: Qt < 5.1. Ah wait no, I'm told it doesn't matter for comments ;)

> Source/WebCore/platform/graphics/qt/FontPlatformDataQt.cpp:76
> +    // FIXME: Remove when we depend on Qt 5.1.

not sure if that was strictly necessary... But it'll go away with the whole ifdef chunk soon enough :)

[Allan Sandfeld Jensen]

Committed r146203: <http://trac.webkit.org/changeset/146203>

[Allan Sandfeld Jensen]

Committed r147544: <http://trac.webkit.org/changeset/147544>