Mac: Fix PlatformFontMac::DeriveFont.

ui/gfx/platform_font_mac.mm

Index: ui/gfx/platform_font_mac.mm
diff --git a/ui/gfx/platform_font_mac.mm b/ui/gfx/platform_font_mac.mm
index 1df9e6922196b6df791b3a67db9e676490783a2e..3c87f2ad85c1a84a97bfc7562ed01951a7b9db1e 100644
--- a/ui/gfx/platform_font_mac.mm
+++ b/ui/gfx/platform_font_mac.mm
@@ -19,6 +19,22 @@
 
 namespace {
 
+// Returns the font style for |font|. Disregards FONT::UNDERLINE, since NSFont
+// does not support it as a trait.
+int GetFontStyleFromNSFont(NSFont* font) {
+  int font_style = Font::NORMAL;
+  NSFontSymbolicTraits traits = [[font fontDescriptor] symbolicTraits];
+  if (traits & NSFontItalicTrait)
+    font_style |= Font::ITALIC;
+  return font_style;
+}
+
+// Returns the Font weight for |font|.
+Font::Weight GetFontWeightFromNSFont(NSFont* font) {
+  NSFontSymbolicTraits traits = [[font fontDescriptor] symbolicTraits];
+  return (traits & NSFontBoldTrait) ? Font::Weight::BOLD : Font::Weight::NORMAL;
+}
+
 // Returns an autoreleased NSFont created with the passed-in specifications.
 NSFont* NSFontWithSpec(const std::string& font_name,
                        int font_size,
@@ -64,31 +80,17 @@
 }
 
 PlatformFontMac::PlatformFontMac(NativeFont native_font)
-    : native_font_([native_font retain]),
-      font_name_(base::SysNSStringToUTF8([native_font_ familyName])),
-      font_size_([native_font_ pointSize]),
-      font_style_(Font::NORMAL),
-      font_weight_(Font::Weight::NORMAL) {
-  NSFontSymbolicTraits traits = [[native_font fontDescriptor] symbolicTraits];
-  if (traits & NSFontItalicTrait)
-    font_style_ |= Font::ITALIC;
-  if (traits & NSFontBoldTrait)
-    font_weight_ = Font::Weight::BOLD;
-
-  CalculateMetricsAndInitRenderParams();
-}
+    : PlatformFontMac(native_font,
+                      base::SysNSStringToUTF8([native_font familyName]),
+                      [native_font pointSize],
+                      GetFontStyleFromNSFont(native_font),
+                      GetFontWeightFromNSFont(native_font)) {}
 
 PlatformFontMac::PlatformFontMac(const std::string& font_name, int font_size)
-    : native_font_([NSFontWithSpec(font_name,
-                                   font_size,
-                                   Font::NORMAL,
-                                   Font::Weight::NORMAL) retain]),
-      font_name_(font_name),
-      font_size_(font_size),
-      font_style_(Font::NORMAL),
-      font_weight_(Font::Weight::NORMAL) {
-  CalculateMetricsAndInitRenderParams();
-}
+    : PlatformFontMac(font_name,
+                      font_size,
+                      Font::NORMAL,
+                      Font::Weight::NORMAL) {}
 
 ////////////////////////////////////////////////////////////////////////////////
 // PlatformFontMac, PlatformFont implementation:
@@ -96,16 +98,26 @@
 Font PlatformFontMac::DeriveFont(int size_delta,
                                  int style,
                                  Font::Weight weight) const {
-  if (native_font_ && style == font_style_ && weight == font_weight_) {
-    // System fonts have special attributes starting with 10.11. They should be
-    // requested using the same descriptor to preserve these attributes.
-    return Font(new PlatformFontMac([NSFont
-        fontWithDescriptor:[native_font_ fontDescriptor]
-                      size:font_size_ + size_delta]));
-  }
+  // For some reason, creating fonts using the NSFontDescriptor API's seem to be
+  // unreliable. Hence use the NSFontManager.

[karandeepb, 2016/08/08 12:07:24]

The NSFontDescriptor API's like fontDescriptorWithSymbolicTraits: do not always
seem to work correctly. Hence using the NSFontManager API below.

+  NSFont* derived_font = native_font_;
+  NSFontManager* font_manager = [NSFontManager sharedFontManager];
+
+  NSFontTraitMask bold_trait_mask =
+      weight >= Font::Weight::BOLD ? NSBoldFontMask : NSUnboldFontMask;
+  derived_font =
+      [font_manager convertFont:derived_font toHaveTrait:bold_trait_mask];
 
-  return Font(
-      new PlatformFontMac(font_name_, font_size_ + size_delta, style, weight));
+  NSFontTraitMask italic_trait_mask =
+      (style & Font::ITALIC) ? NSItalicFontMask : NSUnitalicFontMask;
+  derived_font =
+      [font_manager convertFont:derived_font toHaveTrait:italic_trait_mask];
+
+  derived_font =
+      [font_manager convertFont:derived_font toSize:font_size_ + size_delta];
+
+  return Font(new PlatformFontMac(derived_font, font_name_,

[karandeepb, 2016/08/08 12:07:24]

It may happen that the native NSFont instance is not bold, even when the bold
trait was requested. My understanding of the Font/PlatformFont API is that the
font weight should still be returned as bold for the Font instance even though
the underlying native font is not bold. Can you confirm that this is correct?

[Avi (use Gerrit), 2016/08/08 15:50:58]

I don't know; I don't think I've ever really played with fonts. You probably
know more than I do in this area by now :)

+                                  font_size_ + size_delta, style, weight));
 }
 
 int PlatformFontMac::GetHeight() {
@@ -159,9 +171,19 @@
                                  int font_size,
                                  int font_style,
                                  Font::Weight font_weight)
-    : native_font_(
-          [NSFontWithSpec(font_name, font_size, font_style, font_weight)
-              retain]),
+    : PlatformFontMac(
+          NSFontWithSpec(font_name, font_size, font_style, font_weight),
+          font_name,
+          font_size,
+          font_style,
+          font_weight) {}
+
+PlatformFontMac::PlatformFontMac(NativeFont font,
+                                 const std::string& font_name,
+                                 int font_size,
+                                 int font_style,
+                                 Font::Weight font_weight)
+    : native_font_([font retain]),
       font_name_(font_name),
       font_size_(font_size),
       font_style_(font_style),