Implement DWriteFontTypeface::onGetVariationDesignPosition on win10.

Copy into 'coordinates' (allocated by the caller) the design variation
coordinates. Return the number of axes, or -1 if there is an error.

Change-Id: Ie2fe88aaae358ec471aafd655b4ed0be80d43ae6
Reviewed-on: https://skia-review.googlesource.com/134329
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Bruce Wang <brucewang@google.com>

2 files changed, 50 insertions, 4 deletions

diff --git a/src/ports/SkTypeface_win_dw.cpp b/src/ports/SkTypeface_win_dw.cpp
index aa88c4c911..a7bad0d24e 100644
--- a/src/ports/SkTypeface_win_dw.cpp
+++ b/src/ports/SkTypeface_win_dw.cpp
@@ -185,6 +185,55 @@ SkTypeface::LocalizedStrings* DWriteFontTypeface::onCreateFamilyNameIterator() c
     return nameIter;
 }
 
+int DWriteFontTypeface::onGetVariationDesignPosition(SkFontArguments::VariationPosition::Coordinate coordinates[],
+    int coordinateCount) const {
+
+#if defined(NTDDI_WIN10_RS3) && NTDDI_VERSION >= NTDDI_WIN10_RS3
+
+    SkTScopedComPtr<IDWriteFontFace5> fontFace5;
+    if (FAILED(fDWriteFontFace->QueryInterface(&fontFace5))) {
+        return -1;
+    }
+
+    // Return 0 if the font is not variable font.
+    if (!fontFace5->HasVariations()) {
+        return 0;
+    }
+
+    UINT32 fontAxisCount = fontFace5->GetFontAxisValueCount();
+    SkTScopedComPtr<IDWriteFontResource> fontResource;
+    HR_GENERAL(fontFace5->GetFontResource(&fontResource), nullptr, -1);
+    int variableAxisCount = 0;
+    for (UINT32 i = 0; i < fontAxisCount; ++i) {
+        if (fontResource->GetFontAxisAttributes(i) & DWRITE_FONT_AXIS_ATTRIBUTES_VARIABLE) {
+            variableAxisCount++;
+        }
+    }
+
+    if (!coordinates || !coordinateCount || !variableAxisCount) {
+        return variableAxisCount;
+    }
+
+    SkAutoSTMalloc<8, DWRITE_FONT_AXIS_VALUE> fontAxisValue(fontAxisCount);
+    HR_GENERAL(fontFace5->GetFontAxisValues(fontAxisValue.get(), fontAxisCount), nullptr, -1);
+    UINT32 minCount = SkMin32(variableAxisCount, SkTo<UINT32>(coordinateCount));
+    UINT32 coordinatesIndex = 0;
+
+    for (UINT32 axisIndex = 0; axisIndex < fontAxisCount; ++axisIndex) {
+        if (fontResource->GetFontAxisAttributes(axisIndex) & DWRITE_FONT_AXIS_ATTRIBUTES_VARIABLE) {
+            coordinates[coordinatesIndex].axis = SkEndian_SwapBE32(fontAxisValue[axisIndex].axisTag);
+            coordinates[coordinatesIndex].value = fontAxisValue[axisIndex].value;
+            if (++coordinatesIndex == minCount) break;
+        }
+    }
+
+    return variableAxisCount;
+
+#endif
+
+    return -1;
+}
+
 int DWriteFontTypeface::onGetTableTags(SkFontTableTag tags[]) const {
     DWRITE_FONT_FACE_TYPE type = fDWriteFontFace->GetType();
     if (type != DWRITE_FONT_FACE_TYPE_CFF &&
diff --git a/src/ports/SkTypeface_win_dw.h b/src/ports/SkTypeface_win_dw.h
index b443c28efe..2d76b39adb 100644
--- a/src/ports/SkTypeface_win_dw.h
+++ b/src/ports/SkTypeface_win_dw.h
@@ -116,10 +116,7 @@ protected:
     void onGetFamilyName(SkString* familyName) const override;
     SkTypeface::LocalizedStrings* onCreateFamilyNameIterator() const override;
     int onGetVariationDesignPosition(SkFontArguments::VariationPosition::Coordinate coordinates[],
-                                     int coordinateCount) const override
-    {
-        return -1;
-    }
+                                     int coordinateCount) const override;
     int onGetTableTags(SkFontTableTag tags[]) const override;
     size_t onGetTableData(SkFontTableTag, size_t offset, size_t length, void* data) const override;