Snap GDI matrix when snapping height.

Snap GDI matrix when snapping height.

When using GDI to render, ensure that the GDI matrix does not attempt to
add subpixel height. This ensures that rotated text is always the same
height as axis aligned text and prevents subpixel drift metrics when they
are unwanted.

R=reed@google.com

Committed: https://code.google.com/p/skia/source/detail?r=11592

[bungeman-skia, 2013-10-03 14:06:48]

After the great _blink / _layout bot outage, I've finally been able to verify
this doesn't break too much. This change will require three gm rebaselines and
~30 Blink layout test rebaselines (only on Windows). All of these are a pixel
here and a pixel there on rotated text.

[reed1, 2013-10-03 14:21:07]

https://codereview.chromium.org/25739002/diff/6001/src/ports/SkFontHost_win.cpp
File src/ports/SkFontHost_win.cpp (right):

https://codereview.chromium.org/25739002/diff/6001/src/ports/SkFontHost_win.c...
src/ports/SkFontHost_win.cpp:669: SkScalar textSize =
SkScalarRoundToScalar(realTextSize);
can we rename this something more distinct from realTextSize, like
"integralTextSize" or something?

Alternatively, can we just defer the rounding til the actual calculation for
scale, and place the round() call right there?

scale = (some predicate) ? invert(textSize) : invert(round(textSize));

[bungeman-skia, 2013-10-03 15:48:31]

ptal

https://codereview.chromium.org/25739002/diff/6001/src/ports/SkFontHost_win.cpp
File src/ports/SkFontHost_win.cpp (right):

https://codereview.chromium.org/25739002/diff/6001/src/ports/SkFontHost_win.c...
src/ports/SkFontHost_win.cpp:669: SkScalar textSize =
SkScalarRoundToScalar(realTextSize);
On 2013/10/03 14:21:07, reed1 wrote:
> can we rename this something more distinct from realTextSize, like
> "integralTextSize" or something?
> 
> Alternatively, can we just defer the rounding til the actual calculation for
> scale, and place the round() call right there?
> 
> scale = (some predicate) ? invert(textSize) : invert(round(textSize));

I'd hate to have two separate calls to SkScalarInvert, as that makes these two
look unrelated, though they are very much related. Also, we need to make sure
that 'textSize' doesn't end up 0, if it does bad things tend to happen in GDI.
Also, the abs is still needed. A better name for 'textSize' here would probably
be 'gdiTextSize'.

[reed1, 2013-10-03 15:56:45]

lgtm

[bungeman-skia, 2013-10-03 20:17:53]

Committed patchset #3 manually as r11592 (presubmit successful).