src/third_party/skia/src/core/SkGlyphBuffer.h

/*
 * Copyright 2019 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkGlyphBuffer_DEFINED
#define SkGlyphBuffer_DEFINED

#include "src/core/SkGlyph.h"
#include "src/core/SkZip.h"

class SkStrikeForGPU;
struct SkGlyphPositionRoundingSpec;

// A memory format that allows an SkPackedGlyphID, SkGlyph*, and SkPath* to occupy the same
// memory. This allows SkPackedGlyphIDs as input, and SkGlyph*/SkPath* as output using the same
// memory.
class SkGlyphVariant {
public:
    SkGlyphVariant() : fV{nullptr} { }
    SkGlyphVariant& operator= (SkPackedGlyphID packedID) {
        fV.packedID = packedID;
        SkDEBUGCODE(fTag = kPackedID);
        return *this;
    }
    SkGlyphVariant& operator= (SkGlyph* glyph) {
        fV.glyph = glyph;
        SkDEBUGCODE(fTag = kGlyph);
        return *this;

    }
    SkGlyphVariant& operator= (const SkPath* path) {
        fV.path = path;
        SkDEBUGCODE(fTag = kPath);
        return *this;
    }

    SkGlyph* glyph() const {
        SkASSERT(fTag == kGlyph);
        return fV.glyph;
    }
    const SkPath* path() const {
        SkASSERT(fTag == kPath);
        return fV.path;
    }
    SkPackedGlyphID packedID() const {
        SkASSERT(fTag == kPackedID);
        return fV.packedID;
    }

    operator SkPackedGlyphID() const { return this->packedID(); }
    operator SkGlyph*()        const { return this->glyph();    }
    operator const SkPath*()   const { return this->path();     }

private:
    union {
        SkGlyph* glyph;
        const SkPath* path;
        SkPackedGlyphID packedID;
    } fV;

#ifdef SK_DEBUG
    enum {
        kEmpty,
        kPackedID,
        kGlyph,
        kPath
    } fTag{kEmpty};
#endif
};

// A buffer for converting SkPackedGlyph to SkGlyph* or SkPath*. Initially the buffer contains
// SkPackedGlyphIDs, but those are used to lookup SkGlyph*/SkPath* which are then copied over the
// SkPackedGlyphIDs.
class SkDrawableGlyphBuffer {
public:
    void ensureSize(size_t size);

    // Load the buffer with SkPackedGlyphIDs and positions in source space.
    void startSource(const SkZip<const SkGlyphID, const SkPoint>& source, SkPoint origin);

    // Load the buffer with SkPackedGlyphIDs and positions using the device transform.
    void startDevice(
            const SkZip<const SkGlyphID, const SkPoint>& source,
            SkPoint origin, const SkMatrix& viewMatrix,
            const SkGlyphPositionRoundingSpec& roundingSpec);

    // The input of SkPackedGlyphIDs
    SkZip<SkGlyphVariant, SkPoint> input() {
        SkASSERT(fPhase == kInput);
        SkDEBUGCODE(fPhase = kProcess);
        return SkZip<SkGlyphVariant, SkPoint>{fInputSize, fMultiBuffer, fPositions};
    }

    // Store the glyph in the next drawable slot, using the position information located at index
    // from.
    void push_back(SkGlyph* glyph, size_t from) {
        SkASSERT(fPhase == kProcess);
        SkASSERT(fDrawableSize <= from);
        fPositions[fDrawableSize] = fPositions[from];
        fMultiBuffer[fDrawableSize] = glyph;
        fDrawableSize++;
    }

    // Store the path in the next drawable slot, using the position information located at index
    // from.
    void push_back(const SkPath* path, size_t from) {
        SkASSERT(fPhase == kProcess);
        SkASSERT(fDrawableSize <= from);
        fPositions[fDrawableSize] = fPositions[from];
        fMultiBuffer[fDrawableSize] = path;
        fDrawableSize++;
    }

    // The result after a series of push_backs of drawable SkGlyph* or SkPath*.
    SkZip<SkGlyphVariant, SkPoint> drawable() {
        SkASSERT(fPhase == kProcess);
        SkDEBUGCODE(fPhase = kDraw);
        return SkZip<SkGlyphVariant, SkPoint>{fDrawableSize, fMultiBuffer, fPositions};
    }

    void reset();

private:
    size_t fMaxSize{0};
    size_t fInputSize{0};
    size_t fDrawableSize{0};
    SkAutoTMalloc<SkGlyphVariant> fMultiBuffer;
    SkAutoTMalloc<SkPoint> fPositions;

#ifdef SK_DEBUG
    enum {
        kReset,
        kInput,
        kProcess,
        kDraw
    } fPhase{kReset};
#endif
};
#endif  // SkGlyphBuffer_DEFINED