commit c7520549812464deb45b1ad5d40274a70f05e1c2
author Ben Wagner <bungeman@google.com> Mon Apr 29 15:31:09 2019 -0400
committer Skia Commit-Bot <skia-commit-bot@chromium.org> Tue Apr 30 14:20:48 2019 +0000
tree 4082ec1bc645d2ecc59bfb55707140071a6cdf6a
parent 494aa3db9e7883337c969257eef4e572366cb45f

Use linear metrics with new FreeType light autohint.

Starting in FreeType 2.8 the light hinting setting only hints in the y
direction and can be used with linear metrics and subpixel positioning.

Change-Id: I6e478a904001216ade7f319fe98aa863ac6bd672
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/211105
Auto-Submit: Ben Wagner <bungeman@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>

src/ports/SkFontHost_FreeType.cpp

diff --git a/src/ports/SkFontHost_FreeType.cpp b/src/ports/SkFontHost_FreeType.cpp
index 4f09d54..5627db6 100644
--- a/src/ports/SkFontHost_FreeType.cpp
+++ b/src/ports/SkFontHost_FreeType.cpp
@@ -129,6 +129,7 @@
         , fGetVarAxisFlags(nullptr)
         , fLibrary(nullptr)
         , fIsLCDSupported(false)
+        , fLightHintingIsYOnly(false)
         , fLCDExtra(0)
     {
         if (FT_New_Library(&gFTMemory, &fLibrary)) {
@@ -176,6 +177,16 @@
         }
 #endif
 
+// The 'light' hinting is vertical only starting in 2.8.0.
+#if SK_FREETYPE_MINIMUM_RUNTIME_VERSION >= 0x02080000
+        fLightHintingIsYOnly = true;
+#else
+        if (major > 2 || ((major == 2 && minor > 8) || (major == 2 && minor == 8 && patch >= 0))) {
+            fLightHintingIsYOnly = true;
+        }
+#endif
+
+
 #if SK_FREETYPE_MINIMUM_RUNTIME_VERSION >= 0x02080100
         fGetVarAxisFlags = FT_Get_Var_Axis_Flags;
 #elif SK_FREETYPE_MINIMUM_RUNTIME_VERSION & SK_FREETYPE_DLOPEN
@@ -205,6 +216,7 @@
     FT_Library library() { return fLibrary; }
     bool isLCDSupported() { return fIsLCDSupported; }
     int lcdExtra() { return fLCDExtra; }
+    bool lightHintingIsYOnly() { return fLightHintingIsYOnly; }
 
     // FT_Get_{MM,Var}_{Blend,Design}_Coordinates were added in FreeType 2.7.1.
     // Prior to this there was no way to get the coordinates out of the FT_Face.
@@ -222,6 +234,7 @@
 private:
     FT_Library fLibrary;
     bool fIsLCDSupported;
+    bool fLightHintingIsYOnly;
     int fLCDExtra;
 
     // FT_Library_SetLcdFilterWeights was introduced in FreeType 2.4.0.
@@ -864,6 +877,9 @@
                 break;
             case kSlight_SkFontHinting:
                 loadFlags = FT_LOAD_TARGET_LIGHT;  // This implies FORCE_AUTOHINT
+                if (gFTLibrary->lightHintingIsYOnly()) {
+                    linearMetrics = true;
+                }
                 break;
             case kNormal_SkFontHinting:
                 loadFlags = FT_LOAD_TARGET_NORMAL;