src/core/SkGlyph.h

/*
 * Copyright 2006 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkGlyph_DEFINED
#define SkGlyph_DEFINED

#include "include/core/SkPath.h"
#include "include/core/SkTypes.h"
#include "include/private/SkChecksum.h"
#include "include/private/SkFixed.h"
#include "include/private/SkTo.h"
#include "include/private/SkVx.h"
#include "src/core/SkMask.h"

class SkArenaAlloc;
class SkScalerContext;

// needs to be != to any valid SkMask::Format
#define MASK_FORMAT_UNKNOWN         (0xFF)
#define MASK_FORMAT_JUST_ADVANCE    MASK_FORMAT_UNKNOWN

// A combination of SkGlyphID and sub-pixel position information.
struct SkPackedGlyphID {
    static constexpr uint32_t kImpossibleID = ~0u;
    enum {
        // Lengths
        kGlyphIDLen     = 16u,
        kSubPixelPosLen = 2u,

        // Bit positions
        kSubPixelX = 0u,
        kGlyphID   = kSubPixelPosLen,
        kSubPixelY = kGlyphIDLen + kSubPixelPosLen,
        kEndData   = kGlyphIDLen + 2 * kSubPixelPosLen,

        // Masks
        kGlyphIDMask     = (1u << kGlyphIDLen) - 1,
        kSubPixelPosMask = (1u << kSubPixelPosLen) - 1,
        kMaskAll         = (1u << kEndData) - 1,

        // Location of sub pixel info in a fixed pointer number.
        kFixedPointBinaryPointPos = 16u,
        kFixedPointSubPixelPosBits = kFixedPointBinaryPointPos - kSubPixelPosLen,
    };

    static constexpr SkScalar kSubpixelRound = 1.f / (1u << (SkPackedGlyphID::kSubPixelPosLen + 1));

    static constexpr SkIPoint kXYFieldMask{kSubPixelPosMask << kSubPixelX,
                                           kSubPixelPosMask << kSubPixelY};

    constexpr explicit SkPackedGlyphID(SkGlyphID glyphID)
            : fID{(uint32_t)glyphID << kGlyphID} { }

    constexpr SkPackedGlyphID(SkGlyphID glyphID, SkFixed x, SkFixed y)
            : fID {PackIDXY(glyphID, x, y)} { }

    constexpr SkPackedGlyphID(SkGlyphID glyphID, uint32_t x, uint32_t y)
            : fID {PackIDSubXSubY(glyphID, x, y)} { }

    SkPackedGlyphID(SkGlyphID glyphID, SkPoint pt, SkIPoint mask)
        : fID{PackIDSkPoint(glyphID, pt, mask)} { }

    constexpr explicit SkPackedGlyphID(uint32_t v) : fID{v & kMaskAll} { }

    constexpr SkPackedGlyphID() : fID{kImpossibleID} {}

    bool operator==(const SkPackedGlyphID& that) const {
        return fID == that.fID;
    }
    bool operator!=(const SkPackedGlyphID& that) const {
        return !(*this == that);
    }
    bool operator<(SkPackedGlyphID that) const {
        return this->fID < that.fID;
    }

    SkGlyphID glyphID() const {
        return (fID >> kGlyphID) & kGlyphIDMask;
    }

    uint32_t value() const {
        return fID;
    }

    SkFixed getSubXFixed() const {
        return this->subToFixed(kSubPixelX);
    }

    SkFixed getSubYFixed() const {
        return this->subToFixed(kSubPixelY);
    }

    uint32_t hash() const {
        return SkChecksum::CheapMix(fID);
    }

    SkString dump() const {
        SkString str;
        str.appendf("glyphID: %d, x: %d, y:%d", glyphID(), getSubXFixed(), getSubYFixed());
        return str;
    }

private:
    static constexpr uint32_t PackIDSubXSubY(SkGlyphID glyphID, uint32_t x, uint32_t y) {
        SkASSERT(x < (1u << kSubPixelPosLen));
        SkASSERT(y < (1u << kSubPixelPosLen));

        return (x << kSubPixelX) | (y << kSubPixelY) | (glyphID << kGlyphID);
    }

    // Assumptions: pt is properly rounded. mask is set for the x or y fields.
    //
    // A sub-pixel field is a number on the interval [2^kSubPixel, 2^(kSubPixel + kSubPixelPosLen)).
    // Where kSubPixel is either kSubPixelX or kSubPixelY. Given a number x on [0, 1) we can
    // generate a sub-pixel field using:
    //    sub-pixel-field = x * 2^(kSubPixel + kSubPixelPosLen)
    //
    // We can generate the integer sub-pixel field by &-ing the integer part of sub-filed with the
    // sub-pixel field mask.
    //    int-sub-pixel-field = int(sub-pixel-field) & (kSubPixelPosMask << kSubPixel)
    //
    // The last trick is to extend the range from [0, 1) to [0, 2). The extend range is
    // necessary because the modulo 1 calculation (pt - floor(pt)) generates numbers on [-1, 1).
    // This does not round (floor) properly when converting to integer. Adding one to the range
    // causes truncation and floor to be the same. Coincidentally, masking to produce the field also
    // removes the +1.
    static uint32_t PackIDSkPoint(SkGlyphID glyphID, SkPoint pt, SkIPoint mask) {
    #if 0
        // TODO: why does this code not work on GCC 8.3 x86 Debug builds?
        using namespace skvx;
        using XY = Vec<2, float>;
        using SubXY = Vec<2, int>;

        const XY magic = {1.f * (1u << (kSubPixelPosLen + kSubPixelX)),
                          1.f * (1u << (kSubPixelPosLen + kSubPixelY))};
        XY pos{pt.x(), pt.y()};
        XY subPos = (pos - floor(pos)) + 1.0f;
        SubXY sub = cast<int>(subPos * magic) & SubXY{mask.x(), mask.y()};
    #else
        const float magicX = 1.f * (1u << (kSubPixelPosLen + kSubPixelX)),
                    magicY = 1.f * (1u << (kSubPixelPosLen + kSubPixelY));

        float x = pt.x(),
              y = pt.y();
        x = (x - floorf(x)) + 1.0f;
        y = (y - floorf(y)) + 1.0f;
        int sub[] = {
            (int)(x * magicX) & mask.x(),
            (int)(y * magicY) & mask.y(),
        };
    #endif

        SkASSERT(sub[0] / (1u << kSubPixelX) < (1u << kSubPixelPosLen));
        SkASSERT(sub[1] / (1u << kSubPixelY) < (1u << kSubPixelPosLen));
        return (glyphID << kGlyphID) | sub[0] | sub[1];
    }

    static constexpr uint32_t PackIDXY(SkGlyphID glyphID, SkFixed x, SkFixed y) {
        return PackIDSubXSubY(glyphID, FixedToSub(x), FixedToSub(y));
    }

    static constexpr uint32_t FixedToSub(SkFixed n) {
        return ((uint32_t)n >> kFixedPointSubPixelPosBits) & kSubPixelPosMask;
    }

    constexpr SkFixed subToFixed(uint32_t subPixelPosBit) const {
        uint32_t subPixelPosition = (fID >> subPixelPosBit) & kSubPixelPosMask;
        return subPixelPosition << kFixedPointSubPixelPosBits;
    }

    uint32_t fID;
};

class SkGlyphRect;
namespace skglyph {
SkGlyphRect rect_union(SkGlyphRect, SkGlyphRect);
SkGlyphRect rect_intersection(SkGlyphRect, SkGlyphRect);
}  // namespace skglyph

// SkGlyphRect encodes rectangles with coordinates on [-32767, 32767]. It is specialized for
// rectangle union and intersection operations.
class SkGlyphRect {
public:
    SkGlyphRect(int16_t left, int16_t top, int16_t right, int16_t bottom)
            : fRect{left, top, (int16_t)-right, (int16_t)-bottom} {
        SkDEBUGCODE(const int32_t min = std::numeric_limits<int16_t>::min());
        SkASSERT(left != min && top != min && right != min && bottom != min);
    }
    bool empty() const {
        return fRect[0] >= -fRect[2] || fRect[1] >= -fRect[3];
    }
    SkRect rect() const {
        return SkRect::MakeLTRB(fRect[0], fRect[1], -fRect[2], -fRect[3]);
    }
    SkIRect iRect() const {
        return SkIRect::MakeLTRB(fRect[0], fRect[1], -fRect[2], -fRect[3]);
    }
    friend SkGlyphRect skglyph::rect_union(SkGlyphRect, SkGlyphRect);
    friend SkGlyphRect skglyph::rect_intersection(SkGlyphRect, SkGlyphRect);

private:
    using Storage = skvx::Vec<4, int16_t>;
    SkGlyphRect(Storage rect) : fRect{rect} { }
    Storage fRect;
};

namespace skglyph {
inline SkGlyphRect empty_rect() {
    constexpr int16_t max = std::numeric_limits<int16_t>::max();
    return {max,  max, -max, -max};
}
inline SkGlyphRect full_rect() {
    constexpr int16_t max = std::numeric_limits<int16_t>::max();
    return {-max,  -max, max, max};
}
inline SkGlyphRect rect_union(SkGlyphRect a, SkGlyphRect b) {
    return skvx::min(a.fRect, b.fRect);
}
inline SkGlyphRect rect_intersection(SkGlyphRect a, SkGlyphRect b) {
    return skvx::max(a.fRect, b.fRect);
}
}  // namespace skglyph

struct SkGlyphPrototype;

class SkGlyph {
public:
    // SkGlyph() is used for testing.
    constexpr SkGlyph() : fID{SkPackedGlyphID()} { }
    constexpr explicit SkGlyph(SkPackedGlyphID id) : fID{id} { }

    SkVector advanceVector() const { return SkVector{fAdvanceX, fAdvanceY}; }
    SkScalar advanceX() const { return fAdvanceX; }
    SkScalar advanceY() const { return fAdvanceY; }

    SkGlyphID getGlyphID() const { return fID.glyphID(); }
    SkPackedGlyphID getPackedID() const { return fID; }
    SkFixed getSubXFixed() const { return fID.getSubXFixed(); }
    SkFixed getSubYFixed() const { return fID.getSubYFixed(); }

    size_t rowBytes() const;
    size_t rowBytesUsingFormat(SkMask::Format format) const;

    // Call this to set all of the metrics fields to 0 (e.g. if the scaler
    // encounters an error measuring a glyph). Note: this does not alter the
    // fImage, fPath, fID, fMaskFormat fields.
    void zeroMetrics();

    SkMask mask() const;

    SkMask mask(SkPoint position) const;

    // Image
    // If we haven't already tried to associate an image with this glyph
    // (i.e. setImageHasBeenCalled() returns false), then use the
    // SkScalerContext or const void* argument to set the image.
    bool setImage(SkArenaAlloc* alloc, SkScalerContext* scalerContext);
    bool setImage(SkArenaAlloc* alloc, const void* image);

    // Merge the from glyph into this glyph using alloc to allocate image data. Return the number
    // of bytes allocated. Copy the width, height, top, left, format, and image into this glyph
    // making a copy of the image using the alloc.
    size_t setMetricsAndImage(SkArenaAlloc* alloc, const SkGlyph& from);

    // Returns true if the image has been set.
    bool setImageHasBeenCalled() const {
        return fImage != nullptr || this->isEmpty() || this->imageTooLarge();
    }

    // Return a pointer to the path if the image exists, otherwise return nullptr.
    const void* image() const { SkASSERT(this->setImageHasBeenCalled()); return fImage; }

    // Return the size of the image.
    size_t imageSize() const;

    // Path
    // If we haven't already tried to associate a path to this glyph
    // (i.e. setPathHasBeenCalled() returns false), then use the
    // SkScalerContext or SkPath argument to try to do so.  N.B. this
    // may still result in no path being associated with this glyph,
    // e.g. if you pass a null SkPath or the typeface is bitmap-only.
    //
    // This setPath() call is sticky... once you call it, the glyph
    // stays in its state permanently, ignoring any future calls.
    //
    // Returns true if this is the first time you called setPath()
    // and there actually is a path; call path() to get it.
    bool setPath(SkArenaAlloc* alloc, SkScalerContext* scalerContext);
    bool setPath(SkArenaAlloc* alloc, const SkPath* path);

    // Returns true if that path has been set.
    bool setPathHasBeenCalled() const { return fPathData != nullptr; }

    // Return a pointer to the path if it exists, otherwise return nullptr. Only works if the
    // path was previously set.
    const SkPath* path() const;

    // Format
    bool isColor() const { return fMaskFormat == SkMask::kARGB32_Format; }
    SkMask::Format maskFormat() const { return static_cast<SkMask::Format>(fMaskFormat); }
    size_t formatAlignment() const;

    // Bounds
    int maxDimension() const { return std::max(fWidth, fHeight); }
    SkIRect iRect() const { return SkIRect::MakeXYWH(fLeft, fTop, fWidth, fHeight); }
    SkRect rect()   const { return SkRect::MakeXYWH(fLeft, fTop, fWidth, fHeight);  }
    int left()   const { return fLeft;   }
    int top()    const { return fTop;    }
    int width()  const { return fWidth;  }
    int height() const { return fHeight; }
    bool isEmpty() const {
        // fHeight == 0 -> fWidth == 0;
        SkASSERT(fHeight != 0 || fWidth == 0);
        return fWidth == 0;
    }
    bool imageTooLarge() const { return fWidth >= kMaxGlyphWidth; }

    // Make sure that the intercept information is on the glyph and return it, or return it if it
    // already exists.
    // * bounds - either end of the gap for the character.
    // * scale, xPos - information about how wide the gap is.
    // * array - accumulated gaps for many characters if not null.
    // * count - the number of gaps.
    void ensureIntercepts(const SkScalar bounds[2], SkScalar scale, SkScalar xPos,
                          SkScalar* array, int* count, SkArenaAlloc* alloc);

private:
    // There are two sides to an SkGlyph, the scaler side (things that create glyph data) have
    // access to all the fields. Scalers are assumed to maintain all the SkGlyph invariants. The
    // consumer side has a tighter interface.
    friend class RandomScalerContext;
    friend class RemoteStrike;
    friend class SkScalerContext;
    friend class SkScalerContextProxy;
    friend class SkScalerContext_Empty;
    friend class SkScalerContext_FreeType;
    friend class SkScalerContext_FreeType_Base;
    friend class SkScalerContext_DW;
    friend class SkScalerContext_GDI;
    friend class SkScalerContext_Mac;
    friend class SkStrikeClientImpl;
    friend class SkTestScalerContext;
    friend class SkTestSVGScalerContext;
    friend class SkUserScalerContext;
    friend class TestSVGTypeface;
    friend class TestTypeface;

    static constexpr uint16_t kMaxGlyphWidth = 1u << 13u;

    // Support horizontal and vertical skipping strike-through / underlines.
    // The caller walks the linked list looking for a match. For a horizontal underline,
    // the fBounds contains the top and bottom of the underline. The fInterval pair contains the
    // beginning and end of of the intersection of the bounds and the glyph's path.
    // If interval[0] >= interval[1], no intersection was found.
    struct Intercept {
        Intercept* fNext;
        SkScalar   fBounds[2];    // for horz underlines, the boundaries in Y
        SkScalar   fInterval[2];  // the outside intersections of the axis and the glyph
    };

    struct PathData {
        Intercept* fIntercept{nullptr};
        SkPath     fPath;
        bool       fHasPath{false};
    };

    size_t allocImage(SkArenaAlloc* alloc);

    // path == nullptr indicates that there is no path.
    void installPath(SkArenaAlloc* alloc, const SkPath* path);

    // The width and height of the glyph mask.
    uint16_t  fWidth  = 0,
              fHeight = 0;

    // The offset from the glyphs origin on the baseline to the top left of the glyph mask.
    int16_t   fTop  = 0,
              fLeft = 0;

    // fImage must remain null if the glyph is empty or if width > kMaxGlyphWidth.
    void*     fImage    = nullptr;

    // Path data has tricky state. If the glyph isEmpty, then fPathData should always be nullptr,
    // else if fPathData is not null, then a path has been requested. The fPath field of fPathData
    // may still be null after the request meaning that there is no path for this glyph.
    PathData* fPathData = nullptr;

    // The advance for this glyph.
    float     fAdvanceX = 0,
              fAdvanceY = 0;

    // This is a combination of SkMask::Format and SkGlyph state. The SkGlyph can be in one of two
    // states, just the advances have been calculated, and all the metrics are available. The
    // illegal mask format is used to signal that only the advances are available.
    uint8_t   fMaskFormat = MASK_FORMAT_UNKNOWN;

    // Used by the DirectWrite scaler to track state.
    int8_t    fForceBW = 0;

    const SkPackedGlyphID fID;
};

#endif