Update PDF backend to support fallback fonts on Android.

src/pdf/SkPDFDevice.cpp

Index: src/pdf/SkPDFDevice.cpp
diff --git a/src/pdf/SkPDFDevice.cpp b/src/pdf/SkPDFDevice.cpp
index d13d30cbfb46efbbbe29f6bc3f22522190af75de..e4b07f04fa794bcd27373564411445a039cd4afe 100644
--- a/src/pdf/SkPDFDevice.cpp
+++ b/src/pdf/SkPDFDevice.cpp
@@ -33,6 +33,22 @@
 #include "SkTypefacePriv.h"
 #include "SkTSet.h"
 
+#ifdef SK_BUILD_FOR_ANDROID
+#include "SkTypeface_android.h"
+
+struct TypefaceFallbackData {
+    SkTypeface* typeface;
+    int lowerBounds;
+    int upperBounds;
+
+    bool operator==(const TypefaceFallbackData& b) const {
+        return typeface == b.typeface &&
+               lowerBounds == b.lowerBounds &&
+               upperBounds == b.upperBounds;
+    }
+};
+#endif
+
 // Utility functions
 
 static void emit_pdf_color(SkColor color, SkWStream* result) {
@@ -1115,6 +1131,112 @@ void SkPDFDevice::drawPosText(const SkDraw& d, const void* text, size_t len,
         return;
     }
 
+#ifdef SK_BUILD_FOR_ANDROID
+    /*
+     * In the case that we have enabled fallback fonts on Android we need to
+     * take the following steps to ensure that the PDF draws all characters,
+     * regardless of their underlying font file, correctly.
+     *
+     * 1. Convert input into GlyphID encoding if it currently is not
+     * 2. Iterate over the glyphIDs and identify the actual typeface that each
+     *    glyph resolves to
+     * 3. Iterate over those typefaces and recursively call this function with
+     *    only the glyphs (and their positions) that the typeface is capable of
+     *    resolving.
+     */
+    if (paint.getPaintOptionsAndroid().isUsingFontFallbacks()) {
+        uint16_t* glyphIDs = NULL;
+        SkGlyphStorage tmpStorage(0);
+        size_t numGlyphs = 0;
+
+        // convert to glyphIDs
+        if (paint.getTextEncoding() == SkPaint::kGlyphID_TextEncoding) {
+            numGlyphs = len / 2;
+            glyphIDs = reinterpret_cast<uint16_t*>(const_cast<void*>(text));
+        } else {
+            numGlyphs = paint.textToGlyphs(text, len, NULL);
+            tmpStorage.reset(numGlyphs);
+            paint.textToGlyphs(text, len, tmpStorage.get());
+            glyphIDs = tmpStorage.get();
+        }
+
+        // if no typeface is provided in the paint get the default
+        SkAutoTUnref<SkTypeface> origFace(SkSafeRef(paint.getTypeface()));
+        if (NULL == origFace.get()) {
+            origFace.reset(SkTypeface::RefDefault());
+        }
+        const uint16_t origGlyphCount = origFace->countGlyphs();
+
+        // keep a list of the already visited typefaces and some data about them
+        SkTDArray<TypefaceFallbackData> visitedTypefaces;
+
+        // find all the typefaces needed to resolve this run of text
+        bool usesOriginalTypeface = false;
+        for (uint16_t x = 0; x < numGlyphs; ++x) {
+            // optimization that checks to see if original typeface can resolve the glyph
+            if (glyphIDs[x] < origGlyphCount) {
+                usesOriginalTypeface = true;
+                continue;
+            }
+
+            // find the fallback typeface that supports this glyph
+            TypefaceFallbackData data;
+            data.typeface = SkGetTypefaceForGlyphID(glyphIDs[x], origFace.get(),
+                                                    paint.getPaintOptionsAndroid(),
+                                                    &data.lowerBounds, &data.upperBounds);
+            // add the typeface and its data if we don't have it
+            if (data.typeface && !visitedTypefaces.contains(data)) {
+                visitedTypefaces.push(data);
+            }
+        }
+
+        // if the original font was used then add it to the list as well
+        if (usesOriginalTypeface) {
+            TypefaceFallbackData* data = visitedTypefaces.push();
+            data->typeface = origFace.get();
+            data->lowerBounds = 0;
+            data->upperBounds = origGlyphCount;
+        }
+
+        // keep a scratch glyph and pos storage
+        SkAutoTMalloc<SkScalar> posStorage(len * scalarsPerPos);
+        SkScalar* tmpPos = posStorage.get();
+        SkGlyphStorage glyphStorage(numGlyphs);
+        uint16_t* tmpGlyphIDs = glyphStorage.get();
+
+        // loop through all the valid typefaces, trim the glyphs to only those
+        // resolved by the typeface, and then draw that run of glyphs
+        for (int x = 0; x < visitedTypefaces.count(); ++x) {
+            const TypefaceFallbackData& data = visitedTypefaces[x];
+
+            int tmpGlyphCount = 0;
+            for (uint16_t y = 0; y < numGlyphs; ++y) {
+                if (glyphIDs[y] >= data.lowerBounds && glyphIDs[y] < data.upperBounds) {
+                    tmpGlyphIDs[tmpGlyphCount] = glyphIDs[y] - data.lowerBounds;
+                    memcpy(&(tmpPos[tmpGlyphCount * scalarsPerPos]),
+                           &(pos[y * scalarsPerPos]),
+                           scalarsPerPos * sizeof(SkScalar));
+                    tmpGlyphCount++;
+                }
+            }
+
+            // recursively call this function with the right typeface
+            SkPaint tmpPaint = paint;
+            tmpPaint.setTypeface(data.typeface);
+            tmpPaint.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
+
+            // turn off fallback chaining
+            SkPaintOptionsAndroid paintOpts = tmpPaint.getPaintOptionsAndroid();
+            paintOpts.setUseFontFallbacks(false);
+            tmpPaint.setPaintOptionsAndroid(paintOpts);
+
+            this->drawPosText(d, tmpGlyphIDs, tmpGlyphCount * 2, tmpPos, constY,
+                              scalarsPerPos, tmpPaint);
+        }
+        return;
+    }
+#endif
+
     SkGlyphStorage storage(0);
     uint16_t* glyphIDs = NULL;
     size_t numGlyphs = force_glyph_encoding(paint, text, len, &storage,