Extract glyph find and position code.

src/core/SkDraw.cpp

Index: src/core/SkDraw.cpp
diff --git a/src/core/SkDraw.cpp b/src/core/SkDraw.cpp
index e83bdb74b9ad5cd4f73740fcdee861997ee9fbd0..0b650bea441fdc25fa87a78f190232fb4a9d97bc 100644
--- a/src/core/SkDraw.cpp
+++ b/src/core/SkDraw.cpp
@@ -12,6 +12,7 @@
 #include "SkColorPriv.h"
 #include "SkDevice.h"
 #include "SkDeviceLooper.h"
+#include "SkFindAndPlaceGlyph.h"
 #include "SkFixed.h"
 #include "SkMaskFilter.h"
 #include "SkMatrix.h"
@@ -1729,491 +1730,6 @@ void SkDraw::drawPosText_asPaths(const char text[], size_t byteLength,
     }
 }
 
-////////////////////////////////////////////////////////////////////////////////////////////////////
-// Calculate a type with the same size as the max of all the Ts.
-template <typename... Ts> struct MaxSizeOf;
-
-template <> struct MaxSizeOf<> { static const size_t value = 0; };
-
-template <typename H, typename... Ts> struct MaxSizeOf<H, Ts...> {
-    static const size_t value =
-        sizeof(H) >= MaxSizeOf<Ts...>::value ? sizeof(H) : MaxSizeOf<Ts...>::value;
-};
-
-// UntaggedVariant is a pile of memory that can hold one of the Ts. It provides a way
-// to initialize that memory in a typesafe way.
-template <typename... Ts>
-class UntaggedVariant {
-public:
-    UntaggedVariant() {}
-    ~UntaggedVariant() {}
-    UntaggedVariant(const UntaggedVariant&) = delete;
-    UntaggedVariant& operator=(const UntaggedVariant&) = delete;
-    UntaggedVariant(UntaggedVariant&&) = delete;
-    UntaggedVariant& operator=(UntaggedVariant&&) = delete;
-
-    template <typename Variant, typename... Args>
-    void initialize(Args &&... args) {
-        SkASSERT(sizeof(Variant) <= sizeof(fSpace));
-    #if defined(_MSC_VER) && _MSC_VER < 1900
-        #define alignof __alignof
-    #endif
-        SkASSERT(alignof(Variant) <= alignof(Space));
-        new (&fSpace) Variant(skstd::forward<Args>(args)...);
-    }
-
-private:
-    typedef SkAlignedSStorage<MaxSizeOf<Ts...>::value> Space;
-    Space fSpace;
-};
-
-// PolymorphicVariant holds subclasses of Base without slicing. Ts must be subclasses of Base.
-template <typename Base, typename... Ts>
-class PolymorphicVariant {
-public:
-    typedef UntaggedVariant<Ts...> Variants;
-    template <typename Initializer>
-    PolymorphicVariant(Initializer&& initializer) {
-        initializer(&fVariants);
-    }
-    ~PolymorphicVariant() { get()->~Base(); }
-    Base* get() const { return reinterpret_cast<Base*>(&fVariants); }
-    Base* operator->() const { return get(); }
-    Base& operator*() const { return *get(); }
-
-private:
-    mutable Variants fVariants;
-};
-
-// PositionReaderInterface reads a point from the pos vector.
-// * HorizontalPositions - assumes a common Y for many X values.
-// * ArbitraryPositions - a list of (X,Y) pairs.
-class PositionReaderInterface {
-public:
-    virtual ~PositionReaderInterface() { }
-    virtual SkPoint nextPoint() = 0;
-};
-
-class HorizontalPositions final : public PositionReaderInterface {
-public:
-    explicit HorizontalPositions(const SkScalar* positions)
-        : fPositions(positions) { }
-
-    SkPoint nextPoint() override {
-        SkScalar x = *fPositions++;
-        return {x, 0};
-    }
-private:
-    const SkScalar* fPositions;
-};
-
-class ArbitraryPositions final : public PositionReaderInterface {
-public:
-    explicit ArbitraryPositions(const SkScalar* positions)
-        : fPositions(positions) { }
-    SkPoint nextPoint() override {
-        SkPoint to_return {fPositions[0], fPositions[1]};
-        fPositions += 2;
-        return to_return;
-    }
-
-private:
-    const SkScalar* fPositions;
-};
-
-typedef PolymorphicVariant<PositionReaderInterface, HorizontalPositions, ArbitraryPositions>
-    PositionReader;
-
-// MapperInterface given a point map it through the matrix. There are several shortcut variants.
-// * TranslationMapper - assumes a translation only matrix.
-// * XScaleMapper - assumes an X scaling and a translation.
-// * GeneralMapper - Does all other matricies.
-class MapperInterface {
-public:
-    virtual ~MapperInterface() {}
-    virtual SkPoint map(SkPoint position) const = 0;
-};
-
-class TranslationMapper final : public MapperInterface {
-public:
-    TranslationMapper(const SkMatrix& matrix, const SkPoint origin)
-        : fTranslate(matrix.mapXY(origin.fX, origin.fY)) { }
-    SkPoint map(SkPoint position) const override {
-        return position + fTranslate;
-    }
-
-private:
-    const SkPoint fTranslate;
-};
-
-class XScaleMapper final : public MapperInterface {
-public:
-    XScaleMapper(const SkMatrix& matrix, const SkPoint origin)
-        : fTranslate(matrix.mapXY(origin.fX, origin.fY))
-        , fXScale(matrix.getScaleX()) { }
-    SkPoint map(SkPoint position) const override {
-        return {fXScale * position.fX + fTranslate.fX, fTranslate.fY};
-    }
-
-private:
-    const SkPoint fTranslate;
-    const SkScalar fXScale;
-};
-
-// The caller must keep matrix alive while this class is used.
-class GeneralMapper final : public MapperInterface {
-public:
-    GeneralMapper(const SkMatrix& matrix, const SkPoint origin)
-        : fOrigin(origin)
-        , fMatrix(matrix)
-        , fMapProc(matrix.getMapXYProc()) { }
-    SkPoint map(SkPoint position) const override {
-        SkPoint result;
-        fMapProc(fMatrix, position.fX + fOrigin.fX, position.fY + fOrigin.fY, &result);
-        return result;
-    }
-
-private:
-    const SkPoint fOrigin;
-    const SkMatrix& fMatrix;
-    const SkMatrix::MapXYProc fMapProc;
-};
-
-typedef PolymorphicVariant<MapperInterface, TranslationMapper, XScaleMapper, GeneralMapper> Mapper;
-
-////////////////////////////////////////////////////////////////////////////////////////////////////
-// Text alignment handles shifting the glyph based on its width.
-static SkPoint text_alignment_adjustment(SkPaint::Align textAlignment, const SkGlyph& glyph) {
-    switch (textAlignment) {
-        case SkPaint::kLeft_Align:
-            return {0.0f, 0.0f};
-            break;
-        case SkPaint::kCenter_Align:
-            return {SkFixedToScalar(glyph.fAdvanceX >> 1),
-                    SkFixedToScalar(glyph.fAdvanceY >> 1)};
-            break;
-        case SkPaint::kRight_Align:
-            return {SkFixedToScalar(glyph.fAdvanceX),
-                    SkFixedToScalar(glyph.fAdvanceY)};
-            break;
-    }
-    // Even though the entire enum is covered above, MVSC doesn't think so. Make it happy.
-    SkFAIL("Should never get here.");
-    return {0.0f, 0.0f};
-}
-
-// The "call" to SkFixedToScalar is actually a macro. It's macros all the way down.
-static const SkScalar kSubpixelRounding = SkFixedToScalar(SkGlyph::kSubpixelRound);
-
-////////////////////////////////////////////////////////////////////////////////////////////////////
-// Functions for handling sub-pixel aligned positions.
-// The subpixel_position_rounding function returns a point suitable for rounding a sub-pixel
-// positioned glyph.
-static SkPoint subpixel_position_rounding(SkAxisAlignment axisAlignment) {
-    switch (axisAlignment) {
-        case kX_SkAxisAlignment:
-            return {SkFixedToScalar(SkGlyph::kSubpixelRound), SK_ScalarHalf};
-        case kY_SkAxisAlignment:
-            return {SK_ScalarHalf, kSubpixelRounding};
-        case kNone_SkAxisAlignment:
-            return {kSubpixelRounding, kSubpixelRounding};
-    }
-    SkFAIL("Should not get here.");
-    return {0.0f, 0.0f};
-}
-
-// The subpixel_position_alignment function produces a suitable position for the glyph cache to
-// produce the correct sub-pixel alignment. If a position is aligned with an axis a shortcut of 0
-// is used for the sub-pixel position.
-static SkIPoint subpixel_position_alignment(SkAxisAlignment axisAlignment, SkPoint position) {
-    switch (axisAlignment) {
-        case kX_SkAxisAlignment:
-            return {SkScalarToFixed(position.fX + kSubpixelRounding), 0};
-        case kY_SkAxisAlignment:
-            return {0, SkScalarToFixed(position.fY + kSubpixelRounding)};
-        case kNone_SkAxisAlignment:
-            return {SkScalarToFixed(position.fX + kSubpixelRounding),
-                    SkScalarToFixed(position.fY + kSubpixelRounding)};
-    }
-    SkFAIL("Should not get here.");
-    return {0, 0};
-}
-
-// GlyphFindAndPlaceInterface given the text and position finds the correct glyph and does glyph
-// specific position adjustment. The findAndPositionGlyph method takes text and position and calls
-// processOneGlyph with the correct glyph, final position and rounding terms. The final position
-// is not rounded yet and is the responsibility of processOneGlyph.
-template <typename ProcessOneGlyph>
-class GlyphFindAndPlaceInterface : SkNoncopyable {
-public:
-    struct Result {
-        const SkGlyph* fGlyph;
-        Sk48Dot16 fX;
-        Sk48Dot16 fY;
-    };
-    virtual ~GlyphFindAndPlaceInterface() { };
-    // This should be a pure virtual, but some versions of GCC <= 4.8 have a bug that causes a
-    // compile error.
-    // See GCC bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60277
-    virtual void findAndPositionGlyph(const char** text, SkPoint position,
-                                      ProcessOneGlyph&& processOneGlyph) {};
-};
-
-// GlyphFindAndPlaceForSubpixel handles finding and placing glyphs when sub-pixel positioning is
-// requested. After it has found and placed the glyph it calls the templated function
-// ProcessOneGlyph in order to actually perform an action.
-template <typename ProcessOneGlyph, SkPaint::Align kTextAlignment, SkAxisAlignment kAxisAlignment>
-class GlyphFindAndPlaceForSubpixel final : public GlyphFindAndPlaceInterface<ProcessOneGlyph> {
-public:
-    GlyphFindAndPlaceForSubpixel(SkGlyphCache* cache, SkDrawCacheProc glyphCacheProc)
-        : fCache(cache)
-        , fGlyphCacheProc(glyphCacheProc) {
-    }
-    void findAndPositionGlyph(const char** text, SkPoint position,
-                              ProcessOneGlyph&& processOneGlyph) override {
-        SkPoint finalPosition = position;
-        if (kTextAlignment != SkPaint::kLeft_Align) {
-            // Get the width of an un-sub-pixel positioned glyph for calculating the alignment.
-            // This is not needed for kLeftAlign because its adjustment is always {0, 0}.
-            const char* tempText = *text;
-            const SkGlyph& metricGlyph = fGlyphCacheProc(fCache, &tempText, 0, 0);
-
-            if (metricGlyph.fWidth <= 0) {
-                return;
-            }
-
-            // Adjust the final position by the alignment adjustment.
-            finalPosition -= text_alignment_adjustment(kTextAlignment, metricGlyph);
-        }
-
-        // Find the glyph.
-        SkIPoint lookupPosition = subpixel_position_alignment(kAxisAlignment, finalPosition);
-        const SkGlyph& renderGlyph = fGlyphCacheProc(
-            fCache, text, lookupPosition.fX, lookupPosition.fY);
-
-        // If the glyph has no width (no pixels) then don't bother processing it.
-        if (renderGlyph.fWidth > 0) {
-            processOneGlyph(renderGlyph, finalPosition, subpixel_position_rounding(kAxisAlignment));
-        }
-    }
-
-private:
-    SkGlyphCache* const fCache;
-    SkDrawCacheProc fGlyphCacheProc;
-};
-
-// GlyphFindAndPlaceForFullPixel handles finding and placing glyphs when no sub-pixel positioning
-// is requested.
-template <typename ProcessOneGlyph, SkPaint::Align kTextAlignment>
-class GlyphFindAndPlaceForFullPixel final : public GlyphFindAndPlaceInterface<ProcessOneGlyph> {
-public:
-    GlyphFindAndPlaceForFullPixel(SkGlyphCache* cache, SkDrawCacheProc glyphCacheProc)
-        : fCache(cache)
-        , fGlyphCacheProc(glyphCacheProc) { }
-    void findAndPositionGlyph(const char** text, SkPoint position,
-                              ProcessOneGlyph&& processOneGlyph) override {
-        SkPoint finalPosition = position;
-        const SkGlyph& glyph = fGlyphCacheProc(fCache, text, 0, 0);
-        if (glyph.fWidth <= 0) {
-            return;
-        }
-        finalPosition -= text_alignment_adjustment(kTextAlignment, glyph);
-        processOneGlyph(glyph, finalPosition, {SK_ScalarHalf, SK_ScalarHalf});
-    }
-
-private:
-    SkGlyphCache* const fCache;
-    SkDrawCacheProc fGlyphCacheProc;
-};
-
-// GlyphFindAndPlace is a large variant that encapsulates the multiple types of finding and
-// placing a glyph. There are three factors that go into the different factors.
-// * Is sub-pixel positioned - a boolean that says whether to use sub-pixel positioning.
-// * Text alignment - indicates if the glyph should be placed to the right, centered or left of a
-//   given position.
-// * Axis alignment - indicates if the glyphs final sub-pixel position should be rounded to a
-//   whole pixel if the glyph is aligned with an axis. This is only used for sub-pixel positioning
-//   and allows the baseline to look crisp.
-template <typename ProcessOneGlyph>
-using GlyphFindAndPlace =
-    PolymorphicVariant<
-        GlyphFindAndPlaceInterface<ProcessOneGlyph>,
-        // Subpixel
-        GlyphFindAndPlaceForSubpixel<ProcessOneGlyph, SkPaint::kLeft_Align,   kNone_SkAxisAlignment>,
-        GlyphFindAndPlaceForSubpixel<ProcessOneGlyph, SkPaint::kLeft_Align,   kX_SkAxisAlignment   >,
-        GlyphFindAndPlaceForSubpixel<ProcessOneGlyph, SkPaint::kLeft_Align,   kY_SkAxisAlignment   >,
-        GlyphFindAndPlaceForSubpixel<ProcessOneGlyph, SkPaint::kCenter_Align, kNone_SkAxisAlignment>,
-        GlyphFindAndPlaceForSubpixel<ProcessOneGlyph, SkPaint::kCenter_Align, kX_SkAxisAlignment   >,
-        GlyphFindAndPlaceForSubpixel<ProcessOneGlyph, SkPaint::kCenter_Align, kY_SkAxisAlignment   >,
-        GlyphFindAndPlaceForSubpixel<ProcessOneGlyph, SkPaint::kRight_Align,  kNone_SkAxisAlignment>,
-        GlyphFindAndPlaceForSubpixel<ProcessOneGlyph, SkPaint::kRight_Align,  kX_SkAxisAlignment   >,
-        GlyphFindAndPlaceForSubpixel<ProcessOneGlyph, SkPaint::kRight_Align,  kY_SkAxisAlignment   >,
-        // Full pixel
-        GlyphFindAndPlaceForFullPixel<ProcessOneGlyph, SkPaint::kLeft_Align  >,
-        GlyphFindAndPlaceForFullPixel<ProcessOneGlyph, SkPaint::kCenter_Align>,
-        GlyphFindAndPlaceForFullPixel<ProcessOneGlyph, SkPaint::kRight_Align >
-    >;
-
-// init_subpixel is a helper function for initializing all the variants of
-// GlyphFindAndPlaceForSubpixel.
-template <typename ProcessOneGlyph, SkPaint::Align kTextAlignment>
-static void init_subpixel(
-    typename GlyphFindAndPlace<ProcessOneGlyph>::Variants* to_init,
-    SkAxisAlignment axisAlignment,
-    SkGlyphCache* cache,
-    SkDrawCacheProc glyphCacheProc) {
-    switch (axisAlignment) {
-        case kX_SkAxisAlignment:
-            to_init->template initialize<GlyphFindAndPlaceForSubpixel<
-                ProcessOneGlyph, kTextAlignment, kX_SkAxisAlignment>>(
-                cache, glyphCacheProc);
-            break;
-        case kNone_SkAxisAlignment:
-            to_init->template initialize<GlyphFindAndPlaceForSubpixel<
-                ProcessOneGlyph, kTextAlignment, kNone_SkAxisAlignment>>(
-                cache, glyphCacheProc);
-            break;
-        case kY_SkAxisAlignment:
-            to_init->template initialize<GlyphFindAndPlaceForSubpixel<
-                ProcessOneGlyph, kTextAlignment, kY_SkAxisAlignment>>(
-                cache, glyphCacheProc);
-            break;
-    }
-}
-
-// specialized_process_pos_text is a version of ProcessPosText that de-virtualizes the different
-// components used. It returns true if it can handle the situation, otherwise it returns false.
-// This allows greater inlining freedom to the compiler. Currently, there is only one specialized
-// variant: sub-pixel position, left-aligned, x-axis-aligned, translation, and one scalar per
-// position entry.
-// * This is by far the most common type of text Blink draws.
-template <typename ProcessOneGlyph>
-static bool specialized_process_pos_text(const char* const text, size_t byteLength,
-                                         const SkPoint& offset, const SkMatrix& matrix,
-                                         const SkScalar pos[], int scalarsPerPosition,
-                                         SkPaint::Align textAlignment,
-                                         SkDrawCacheProc& glyphCacheProc,
-                                         SkGlyphCache* cache, ProcessOneGlyph&& processOneGlyph) {
-    SkAxisAlignment axisAlignment = SkComputeAxisAlignmentForHText(matrix);
-    uint32_t mtype = matrix.getType();
-    if (scalarsPerPosition == 1
-        && textAlignment == SkPaint::kLeft_Align
-        && axisAlignment == kX_SkAxisAlignment
-        && cache->isSubpixel()
-        && mtype <= SkMatrix::kTranslate_Mask) {
-        typedef GlyphFindAndPlaceForSubpixel<
-            ProcessOneGlyph, SkPaint::kLeft_Align, kX_SkAxisAlignment> Positioner;
-        HorizontalPositions positions{pos};
-        TranslationMapper mapper{matrix, offset};
-        Positioner positioner(cache, glyphCacheProc);
-        const char *cursor = text;
-        const char *stop = text + byteLength;
-        while (cursor < stop) {
-            SkPoint mappedPoint = mapper.TranslationMapper::map(
-                positions.HorizontalPositions::nextPoint());
-            positioner.Positioner::findAndPositionGlyph(
-                &cursor, mappedPoint, skstd::forward<ProcessOneGlyph>(processOneGlyph));
-        }
-        return true;
-    }
-    return false;
-}
-
-// ProcessPosText handles all cases for finding and positioning glyphs. It has a very large
-// multiplicity. It figures out the glyph, position and rounding and pass those parameters to
-// processOneGlyph.
-//
-// The routine processOneGlyph passed in by the client has the following signature:
-// void f(const SkGlyph& glyph, SkPoint position, SkPoint rounding);
-//
-// * Sub-pixel positioning (2) - use sub-pixel positioning.
-// * Text alignment (3) - text alignment with respect to the glyph's width.
-// * Matrix type (3) - special cases for translation and X-coordinate scaling.
-// * Components per position (2) - the positions vector can have a common Y with different Xs, or
-//   XY-pairs.
-// * Axis Alignment (for sub-pixel positioning) (3) - when using sub-pixel positioning, round to
-// a whole coordinate instead of using sub-pixel positioning.
-// The number of variations is 108 for sub-pixel and 36 for full-pixel.
-// This routine handles all of them using inline polymorphic variable (no heap allocation).
-template <typename ProcessOneGlyph>
-static void process_pos_text(const char text[], size_t byteLength,
-                             const SkPoint& offset, const SkMatrix& matrix,
-                             const SkScalar pos[], int scalarsPerPosition,
-                             SkPaint::Align textAlignment, SkDrawCacheProc& glyphCacheProc,
-                             SkGlyphCache* cache, ProcessOneGlyph&& processOneGlyph) {
-
-    PositionReader positionReader {
-        [&](PositionReader::Variants* to_init) {
-            if (2 == scalarsPerPosition) {
-                to_init->initialize<ArbitraryPositions>(pos);
-            } else {
-                to_init->initialize<HorizontalPositions>(pos);
-            }
-        }
-    };
-
-    Mapper mapper {
-        [&] (Mapper::Variants* to_init) {
-            uint32_t mtype = matrix.getType();
-            if (mtype & (SkMatrix::kAffine_Mask | SkMatrix::kPerspective_Mask)
-                || scalarsPerPosition == 2) {
-                to_init->initialize<GeneralMapper>(matrix, offset);
-            } else if (mtype & SkMatrix::kScale_Mask) {
-                to_init->initialize<XScaleMapper>(matrix, offset);
-            } else {
-                to_init->initialize<TranslationMapper>(matrix, offset);
-            }
-        }
-    };
-
-    GlyphFindAndPlace<ProcessOneGlyph> findAndPosition{
-        [&](typename GlyphFindAndPlace<ProcessOneGlyph>::Variants* to_init) {
-            if (cache->isSubpixel()) {
-                SkAxisAlignment axisAlignment = SkComputeAxisAlignmentForHText(matrix);
-                switch (textAlignment) {
-                    case SkPaint::kLeft_Align:
-                        init_subpixel<ProcessOneGlyph, SkPaint::kLeft_Align>(
-                            to_init, axisAlignment, cache, glyphCacheProc);
-                        break;
-                    case SkPaint::kCenter_Align:
-                        init_subpixel<ProcessOneGlyph, SkPaint::kCenter_Align>(
-                            to_init, axisAlignment, cache, glyphCacheProc);
-                        break;
-                    case SkPaint::kRight_Align:
-                        init_subpixel<ProcessOneGlyph, SkPaint::kRight_Align>(
-                            to_init, axisAlignment, cache, glyphCacheProc);
-                        break;
-                }
-            } else {
-                switch (textAlignment) {
-                    case SkPaint::kLeft_Align:
-                        to_init->template initialize<GlyphFindAndPlaceForFullPixel<ProcessOneGlyph,
-                            SkPaint::kLeft_Align>>(
-                            cache, glyphCacheProc);
-                        break;
-                    case SkPaint::kCenter_Align:
-                        to_init->template initialize<GlyphFindAndPlaceForFullPixel<ProcessOneGlyph,
-                            SkPaint::kCenter_Align>>(
-                            cache, glyphCacheProc);
-                        break;
-                    case SkPaint::kRight_Align:
-                        to_init->template initialize<GlyphFindAndPlaceForFullPixel<ProcessOneGlyph,
-                            SkPaint::kRight_Align>>(
-                            cache, glyphCacheProc);
-                        break;
-                }
-            }
-        }
-    };
-
-    const char* stop = text + byteLength;
-    while (text < stop) {
-        SkPoint mappedPoint = mapper->map(positionReader->nextPoint());
-        findAndPosition->findAndPositionGlyph(
-            &text, mappedPoint, skstd::forward<ProcessOneGlyph>(processOneGlyph));
-    }
-}
-
 void SkDraw::drawPosText(const char text[], size_t byteLength,
                          const SkScalar pos[], int scalarsPerPosition,
                          const SkPoint& offset, const SkPaint& paint) const {
@@ -2258,9 +1774,11 @@ void SkDraw::drawPosText(const char text[], size_t byteLength,
         };
 
     SkPaint::Align textAlignment = paint.getTextAlign();
-    if (!specialized_process_pos_text(text, byteLength, offset, *fMatrix, pos, scalarsPerPosition,
-            textAlignment, glyphCacheProc, cache, processOneGlyph)) {
-        process_pos_text(text, byteLength, offset, *fMatrix, pos, scalarsPerPosition,
+    if (!SkFindAndPlaceGlyph::SpecializedProcessPosText(
+        text, byteLength, offset, *fMatrix, pos, scalarsPerPosition,
+        textAlignment, glyphCacheProc, cache, processOneGlyph)) {
+        SkFindAndPlaceGlyph::ProcessPosText(
+            text, byteLength, offset, *fMatrix, pos, scalarsPerPosition,
             textAlignment, glyphCacheProc, cache, processOneGlyph);
     }
 }