Bug 1600470 - Reduce the emboldening strength used for synthetic-bold faces with FreeType. r=lsalzman

Differential Revision: https://phabricator.services.mozilla.com/D57246

--HG--
extra : moz-landing-system : lando

gfx/2d/Factory.cpp

@@ -65,6 +65,8 @@
 #ifdef MOZ_ENABLE_FREETYPE
 #  include "ft2build.h"
 #  include FT_FREETYPE_H
+#  include FT_OUTLINE_H
+#  include FT_SYNTHESIS_H
 #endif
 #include "MainThreadUtils.h"
 #include "mozilla/Preferences.h"
@@ -195,6 +197,40 @@ void mozilla_LockFTLibrary(FT_Library aFTLibrary) {
 void mozilla_UnlockFTLibrary(FT_Library aFTLibrary) {
   mozilla::gfx::Factory::UnlockFTLibrary(aFTLibrary);
 }
+
+// Custom version of FT_GlyphSlot_Embolden to be less aggressive with outline
+// fonts than the default implementation in FreeType.
+void mozilla_GlyphSlot_Embolden_Less(FT_GlyphSlot slot) {
+  if (!slot) {
+    return;
+  }
+  if (slot->format != FT_GLYPH_FORMAT_OUTLINE) {
+    // For non-outline glyphs, just fall back to FreeType's function.
+    FT_GlyphSlot_Embolden(slot);
+    return;
+  }
+
+  FT_Face face = slot->face;
+
+  // FT_GlyphSlot_Embolden uses a divisor of 24 here; we'll be only half as
+  // bold.
+  FT_Pos strength =
+      FT_MulFix(face->units_per_EM, face->size->metrics.y_scale) / 48;
+  FT_Outline_Embolden(&slot->outline, strength);
+
+  // Adjust metrics to suit the fattened glyph.
+  if (slot->advance.x) {
+    slot->advance.x += strength;
+  }
+  if (slot->advance.y) {
+    slot->advance.y += strength;
+  }
+  slot->metrics.width += strength;
+  slot->metrics.height += strength;
+  slot->metrics.horiAdvance += strength;
+  slot->metrics.vertAdvance += strength;
+  slot->metrics.horiBearingY += strength;
+}
 }
 #endif
 

gfx/skia/generate_mozbuild.py

@@ -72,6 +72,10 @@ if CONFIG['MOZ_ENABLE_SKIA_PDF_SFNTLY']:
 if CONFIG['MOZ_TREE_FREETYPE']:
     DEFINES['SK_CAN_USE_DLOPEN'] = 0
 
+# Reduce strength of synthetic-emboldening used in the freetype backend
+# (see bug 1600470).
+DEFINES['SK_OUTLINE_EMBOLDEN_DIVISOR'] = 48
+
 # Suppress warnings in third-party code.
 CXXFLAGS += [
     '-Wno-deprecated-declarations',

gfx/skia/skia/src/ports/SkFontHost_cairo.cpp

@@ -58,7 +58,6 @@ typedef enum FT_LcdFilter_
 
 static bool gFontHintingEnabled = true;
 static FT_Error (*gSetLcdFilter)(FT_Library, FT_LcdFilter) = nullptr;
-static void (*gGlyphSlotEmbolden)(FT_GlyphSlot) = nullptr;
 
 extern "C"
 {
@@ -70,6 +69,7 @@ extern "C"
     int mozilla_LockSharedFTFace(void* aContext, void* aOwner);
     void mozilla_UnlockSharedFTFace(void* aContext);
     FT_Error mozilla_LoadFTGlyph(FT_Face aFace, uint32_t aGlyphIndex, int32_t aFlags);
+    void mozilla_GlyphSlot_Embolden_Less(FT_GlyphSlot slot);
 }
 
 void SkInitCairoFT(bool fontHintingEnabled)
@@ -77,10 +77,8 @@ void SkInitCairoFT(bool fontHintingEnabled)
     gFontHintingEnabled = fontHintingEnabled;
 #if SK_CAN_USE_DLOPEN
     gSetLcdFilter = (FT_Error (*)(FT_Library, FT_LcdFilter))dlsym(RTLD_DEFAULT, "FT_Library_SetLcdFilter");
-    gGlyphSlotEmbolden = (void (*)(FT_GlyphSlot))dlsym(RTLD_DEFAULT, "FT_GlyphSlot_Embolden");
 #else
     gSetLcdFilter = &FT_Library_SetLcdFilter;
-    gGlyphSlotEmbolden = &FT_GlyphSlot_Embolden;
 #endif
     // FT_Library_SetLcdFilter may be provided but have no effect if FreeType
     // is built without FT_CONFIG_OPTION_SUBPIXEL_RENDERING.
@@ -486,9 +484,9 @@ bool SkScalerContext_CairoFT::generateAdvance(SkGlyph* glyph)
 
 void SkScalerContext_CairoFT::prepareGlyph(FT_GlyphSlot glyph)
 {
-    if (fRec.fFlags & SkScalerContext::kEmbolden_Flag &&
-        gGlyphSlotEmbolden) {
-        gGlyphSlotEmbolden(glyph);
+    if (fRec.fFlags & SkScalerContext::kEmbolden_Flag) {
+        // Not FT_GlyphSlot_Embolden because we want a less extreme effect.
+        mozilla_GlyphSlot_Embolden_Less(glyph);
     }
 }
 

gfx/thebes/gfxFT2FontBase.cpp

@@ -500,6 +500,16 @@ FT_Vector gfxFT2FontBase::GetEmboldenStrength(FT_Face aFace) {
   if (!mEmbolden) {
     return strength;
   }
+
+  // If it's an outline glyph, we'll be using GlyphSlot_Embolden_Less,
+  // so we need to match its strength here.
+  if (aFace->glyph->format == FT_GLYPH_FORMAT_OUTLINE) {
+    strength.x =
+        FT_MulFix(aFace->units_per_EM, aFace->size->metrics.y_scale) / 48;
+    strength.y = strength.x;
+    return strength;
+  }
+
   // This is the embolden "strength" used by FT_GlyphSlot_Embolden.
   strength.x =
       FT_MulFix(aFace->units_per_EM, aFace->size->metrics.y_scale) / 24;

gfx/wr/webrender/src/platform/unix/font.rs

@@ -106,7 +106,7 @@ ft_dyn_fn!(FT_Done_MM_Var(library: FT_Library, desc: *mut FT_MM_Var) -> FT_Error
 ft_dyn_fn!(FT_Set_Var_Design_Coordinates(face: FT_Face, num_vals: FT_UInt, vals: *mut FT_Fixed) -> FT_Error);
 
 extern "C" {
-    fn FT_GlyphSlot_Embolden(slot: FT_GlyphSlot);
+    fn mozilla_GlyphSlot_Embolden_Less(slot: FT_GlyphSlot);
 }
 
 enum FontFile {
@@ -495,7 +495,7 @@ impl FontContext {
         assert!(slot != ptr::null_mut());
 
         if font.flags.contains(FontInstanceFlags::SYNTHETIC_BOLD) {
-            unsafe { FT_GlyphSlot_Embolden(slot) };
+            unsafe { mozilla_GlyphSlot_Embolden_Less(slot) };
         }
 
         let format = unsafe { (*slot).format };

layout/reftests/css-break/reftest.list

@@ -1,6 +1,6 @@
 == box-decoration-break-1.html box-decoration-break-1-ref.html
 fuzzy(0-1,0-20) fuzzy-if(skiaContent,0-1,0-700) == box-decoration-break-with-inset-box-shadow-1.html box-decoration-break-with-inset-box-shadow-1-ref.html
-skip-if(verify) fuzzy(0-45,0-460) fuzzy-if(skiaContent,0-57,0-439) fuzzy-if(Android,0-57,0-1330) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == box-decoration-break-with-outset-box-shadow-1.html box-decoration-break-with-outset-box-shadow-1-ref.html # Bug 1386543, bug 1392106
+skip-if(verify) fuzzy(0-45,0-460) fuzzy-if(skiaContent,0-57,0-439) fuzzy-if(Android,0-70,0-1330) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == box-decoration-break-with-outset-box-shadow-1.html box-decoration-break-with-outset-box-shadow-1-ref.html # Bug 1386543, bug 1392106
 random-if(!gtkWidget||webrender) == box-decoration-break-border-image.html box-decoration-break-border-image-ref.html
 == box-decoration-break-block-border-padding.html box-decoration-break-block-border-padding-ref.html
 == box-decoration-break-block-margin.html box-decoration-break-block-margin-ref.html

layout/reftests/text/synthetic-bold-metrics-01-notref.html

@@ -8,7 +8,7 @@
 }
 
 p {
-  font-family: dejavu; /* family with only a single weight */
+  font: 32px dejavu; /* family with only a single weight */
 }
 
 .test {

layout/reftests/text/synthetic-bold-metrics-01.html

@@ -8,7 +8,7 @@
 }
 
 p {
-  font-family: dejavu; /* family with only a single weight */
+  font: 32px dejavu; /* family with only a single weight */
 }
 
 .test {