Instant Extended: Reduce clipping in omnibox

chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.h"
 
 #include <Carbon/Carbon.h>  // kVK_Return
 
 #include "base/mac/foundation_util.h"
 #include "base/string_util.h"
@@ skipping 137 matching lines @@
   [field_ setObserver:this];
 
   // Needed so that editing doesn't lose the styling.
   [field_ setAllowsEditingTextAttributes:YES];
 
   // Get the appropriate line height for the font that we use.
   scoped_nsobject<NSLayoutManager>
       layoutManager([[NSLayoutManager alloc] init]);
   [layoutManager setUsesScreenFonts:YES];
   line_height_ = [layoutManager defaultLineHeightForFont:GetFieldFont()];
+
+  // Extended instant uses a larger font so increase line height to reduce
+  // clipping.
+  if (chrome::IsInstantExtendedAPIEnabled())
+    line_height_ += 1;

[Scott Hess - ex-Googler, 2013/05/22 23:39:39]

I'm still questioning this guy.  I feel like someone is conflating clipping with
drawing, somewhere?  Or am I missing something?

Hmm.  Using this font in TextEdit, the accents rise above the selection box one
pixel.  Also happens with Lucida Grande.

How do -[NSFont ascender], -[NSFont descender], -[NSFont xHeight] and -[NSFont
capHeight] compare on this?  AFAICT the top pixel is a total of 16 pixels above
the baseline, which match the font size, so maybe [NSFont
ascender]+[NSLayoutManager defaultBaselineOffsetForFont:font] would work.  Or
maybe not.

Is line_height_ literally the selection-rect height?  Since we actually want
that to be a specific value, another possibility would be to pull it from some
new method on AutocompleteTextField.  That would mean some potential for the
font and size to get out of sync, but that's why we're even looking at this CL,
so we haven't gained anything.  I'm assuming that that field has already been
placed at its final size at this point?

[sail, 2013/05/23 19:46:32]

Replaced this with -[AutocompleteTextFieldCell lineHeight] and used fixed values
instead.

I took a look at the font metrics and I couldn't find anything helpful there.
Here are the font metrics for Helvetica Neue 16pt:
  line_height_: 18
  ascender: 15
  descender: -3
  xHeight: 8
  capHeight: 11
  defaultBaselineOffsetForFont: 15

for the system font 13pt the metrics are:
  line_height_: 16
  ascender: 12
  descender: -2
  xHeight: 6
  capHeight: 9
  defaultBaselineOffsetForFont: 13

+
   DCHECK_GT(line_height_, 0);
 }
 
 OmniboxViewMac::~OmniboxViewMac() {
   // Destroy popup view before this object in case it tries to call us
   // back in the destructor.
   popup_view_.reset();
 
   // Disconnect from |field_|, it outlives this object.
   [field_ setObserver:NULL];
@@ skipping 809 matching lines @@
 
 NSUInteger OmniboxViewMac::GetTextLength() const {
   return [field_ currentEditor] ?  [[[field_ currentEditor] string] length] :
                                    [[field_ stringValue] length];
 }
 
 bool OmniboxViewMac::IsCaretAtEnd() const {
   const NSRange selection = GetSelectedRange();
   return NSMaxRange(selection) == GetTextLength();
 }