Add runtime control for DirectWrite system font rendering params on Windows

Author: vladimirsamsonov

patches/ext_SkTypeface_win_dw.patch

@@ -0,0 +1,59 @@
+diff --git a/src/ports/SkTypeface_win_dw.cpp b/src/ports/SkTypeface_win_dw.cpp
+index b9d69ab303204b68f97a1cae3bafbb1f77f0ac67..e434abba3b0c75dff4a48600e34c91ac6e9d766a 100644
+--- a/src/ports/SkTypeface_win_dw.cpp
++++ b/src/ports/SkTypeface_win_dw.cpp
+@@ -543,6 +543,12 @@ std::unique_ptr<SkScalerContext> DWriteFontTypeface::onCreateScalerContext(
+             sk_ref_sp(const_cast<DWriteFontTypeface*>(this)), effects, desc);
+ }
+ 
++static std::atomic<int> gUseSystemRenderingParams{-1};
++
++extern "C" void DWriteTypeface_UseSystemRenderingParams(int value) {
++    gUseSystemRenderingParams.store(value);
++}
++
+ void DWriteFontTypeface::onFilterRec(SkScalerContextRec* rec) const {
+     if (rec->fFlags & SkScalerContext::kLCD_Vertical_Flag) {
+         rec->fMaskFormat = SkMask::kA8_Format;
+@@ -561,19 +567,31 @@ void DWriteFontTypeface::onFilterRec(SkScalerContextRec* rec) const {
+     }
+     rec->setHinting(h);
+ 
++    int setting = gUseSystemRenderingParams.load();
++    bool useSystem;
++    if (setting == -1) {
+ #if defined(SK_FONT_HOST_USE_SYSTEM_SETTINGS)
+-    IDWriteFactory* factory = sk_get_dwrite_factory();
+-    if (factory != nullptr) {
+-        SkTScopedComPtr<IDWriteRenderingParams> defaultRenderingParams;
+-        if (SUCCEEDED(factory->CreateRenderingParams(&defaultRenderingParams))) {
+-            float gamma = defaultRenderingParams->GetGamma();
+-            rec->setDeviceGamma(gamma);
+-            rec->setPaintGamma(gamma);
+-
+-            rec->setContrast(defaultRenderingParams->GetEnhancedContrast());
++        useSystem = true;
++#else
++        useSystem = false;
++#endif
++    } else {
++        useSystem = (setting == 1);
++    }
++
++    if (useSystem) {
++        IDWriteFactory* factory = sk_get_dwrite_factory();
++        if (factory != nullptr) {
++            SkTScopedComPtr<IDWriteRenderingParams> defaultRenderingParams;
++            if (SUCCEEDED(factory->CreateRenderingParams(&defaultRenderingParams))) {
++                float gamma = defaultRenderingParams->GetGamma();
++                rec->setDeviceGamma(gamma);
++                rec->setPaintGamma(gamma);
++
++                rec->setContrast(defaultRenderingParams->GetEnhancedContrast());
++            }
+         }
+     }
+-#endif
+ }
+ 
+ ///////////////////////////////////////////////////////////////////////////////

script/build.py

@@ -70,7 +70,7 @@ def main():
       'skia_use_system_freetype2=false',
       # 'skia_use_angle=true',
       'skia_use_direct3d=true',
-      #'extra_cflags=["-DSK_FONT_HOST_USE_SYSTEM_SETTINGS"]',
+      'extra_cflags=["-DSK_FONT_HOST_USE_SYSTEM_SETTINGS"]',
     ]
   elif 'android' == system:
     args += [