skia2/include/core/SkScalerContext.h

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef SkScalerContext_DEFINED
#define SkScalerContext_DEFINED

#include "SkMask.h"
#include "SkMatrix.h"
#include "SkPaint.h"
#include "SkPath.h"
#include "SkPoint.h"

class SkDescriptor;
class SkMaskFilter;
class SkPathEffect;
class SkRasterizer;

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

struct SkGlyph {
    void*       fImage;
    SkPath*     fPath;
    SkFixed     fAdvanceX, fAdvanceY;

    uint32_t    fID;
    uint16_t    fWidth, fHeight;
    int16_t     fTop, fLeft;

    uint8_t     fMaskFormat;
    int8_t      fRsbDelta, fLsbDelta;  // used by auto-kerning
    
    unsigned rowBytes() const {
        unsigned rb = fWidth;
        if (SkMask::kBW_Format == fMaskFormat) {
            rb = (rb + 7) >> 3;
        } else {
            rb = SkAlign4(rb);
        }
        return rb;
    }
    
    bool isJustAdvance() const {
        return MASK_FORMAT_JUST_ADVANCE == fMaskFormat;
    }
    
    bool isFullMetrics() const {
        return MASK_FORMAT_JUST_ADVANCE != fMaskFormat;
    }
    
    uint16_t getGlyphID() const {
        return ID2Code(fID);
    }

    unsigned getGlyphID(unsigned baseGlyphCount) const {
        unsigned code = ID2Code(fID);
        SkASSERT(code >= baseGlyphCount);
        return code - baseGlyphCount;
    }
    
    unsigned getSubX() const {
        return ID2SubX(fID);
    }
    
    SkFixed getSubXFixed() const {
        return SubToFixed(ID2SubX(fID));
    }
    
    SkFixed getSubYFixed() const {
        return SubToFixed(ID2SubY(fID));
    }
    
    size_t computeImageSize() 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();
    
    enum {
        kSubBits = 2,
        kSubMask = ((1 << kSubBits) - 1),
        kSubShift = 24, // must be large enough for glyphs and unichars
        kCodeMask = ((1 << kSubShift) - 1),
        // relative offsets for X and Y subpixel bits
        kSubShiftX = kSubBits,
        kSubShiftY = 0
    };

    static unsigned ID2Code(uint32_t id) {
        return id & kCodeMask;
    }
    
    static unsigned ID2SubX(uint32_t id) {
        return id >> (kSubShift + kSubShiftX);
    }
    
    static unsigned ID2SubY(uint32_t id) {
        return (id >> (kSubShift + kSubShiftY)) & kSubMask;
    }
    
    static unsigned FixedToSub(SkFixed n) {
        return (n >> (16 - kSubBits)) & kSubMask;
    }
    
    static SkFixed SubToFixed(unsigned sub) {
        SkASSERT(sub <= kSubMask);
        return sub << (16 - kSubBits);
    }
    
    static uint32_t MakeID(unsigned code) {
        return code;
    }
    
    static uint32_t MakeID(unsigned code, SkFixed x, SkFixed y) {
        SkASSERT(code <= kCodeMask);
        x = FixedToSub(x);
        y = FixedToSub(y);
        return (x << (kSubShift + kSubShiftX)) |
               (y << (kSubShift + kSubShiftY)) |
               code;
    }
    
    void toMask(SkMask* mask) const;

    /** Given a glyph which is has a mask format of LCD or VerticalLCD, take
        the A8 plane in fImage and produce a valid LCD plane from it.
    */
    void expandA8ToLCD() const;
};

class SkScalerContext {
public:
    enum Flags {
        kFrameAndFill_Flag  = 0x01,
        kDevKernText_Flag   = 0x02,
        kGammaForBlack_Flag = 0x04, // illegal to set both Gamma flags
        kGammaForWhite_Flag = 0x08, // illegal to set both Gamma flags
        // together, these two flags resulting in a two bit value which matches
        // up with the SkPaint::Hinting enum.
        kHintingBit1        = 0x10,
        kHintingBit2        = 0x20,
    };
    struct Rec {
        uint32_t    fFontID;
        SkScalar    fTextSize, fPreScaleX, fPreSkewX;
        SkScalar    fPost2x2[2][2];
        SkScalar    fFrameWidth, fMiterLimit;
        bool        fSubpixelPositioning;
        uint8_t     fMaskFormat;
        uint8_t     fStrokeJoin;
        uint8_t     fFlags;

        void    getMatrixFrom2x2(SkMatrix*) const;
        void    getLocalMatrix(SkMatrix*) const;
        void    getSingleMatrix(SkMatrix*) const;

        SkPaint::Hinting getHinting() const {
            return static_cast<SkPaint::Hinting>((fFlags >> 4) & 3);
        }

        void setHinting(SkPaint::Hinting hinting) {
            fFlags = (fFlags & ~(kHintingBit1 | kHintingBit2)) |
                     (static_cast<int>(hinting) << 4);
        }
    };

    SkScalerContext(const SkDescriptor* desc);
    virtual ~SkScalerContext();

    // remember our glyph offset/base
    void setBaseGlyphCount(unsigned baseGlyphCount) {
        fBaseGlyphCount = baseGlyphCount;
    }

    /** Return the corresponding glyph for the specified unichar. Since contexts
        may be chained (under the hood), the glyphID that is returned may in
        fact correspond to a different font/context. In that case, we use the
        base-glyph-count to know how to translate back into local glyph space.
     */
    uint16_t    charToGlyphID(SkUnichar uni);

    unsigned    getGlyphCount() const { return this->generateGlyphCount(); }
    void        getAdvance(SkGlyph*);
    void        getMetrics(SkGlyph*);
    void        getImage(const SkGlyph&);
    void        getPath(const SkGlyph&, SkPath*);
    void        getFontMetrics(SkPaint::FontMetrics* mX,
                               SkPaint::FontMetrics* mY);

    static inline void MakeRec(const SkPaint&, const SkMatrix*, Rec* rec);
    static SkScalerContext* Create(const SkDescriptor*);

protected:
    Rec         fRec;
    unsigned    fBaseGlyphCount;

    virtual unsigned generateGlyphCount() const = 0;
    virtual uint16_t generateCharToGlyph(SkUnichar) = 0;
    virtual void generateAdvance(SkGlyph*) = 0;
    virtual void generateMetrics(SkGlyph*) = 0;
    virtual void generateImage(const SkGlyph&) = 0;
    virtual void generatePath(const SkGlyph&, SkPath*) = 0;
    virtual void generateFontMetrics(SkPaint::FontMetrics* mX,
                                     SkPaint::FontMetrics* mY) = 0;

private:
    SkPathEffect*   fPathEffect;
    SkMaskFilter*   fMaskFilter;
    SkRasterizer*   fRasterizer;
    SkScalar        fDevFrameWidth;

    void internalGetPath(const SkGlyph& glyph, SkPath* fillPath,
                         SkPath* devPath, SkMatrix* fillToDevMatrix);

    // return the next context, treating fNextContext as a cache of the answer
    SkScalerContext* getNextContext();

    // returns the right context from our link-list for this glyph. If no match
    // is found, just returns the original context (this)
    SkScalerContext* getGlyphContext(const SkGlyph& glyph);

    // link-list of context, to handle missing chars. null-terminated.
    SkScalerContext* fNextContext;
};

#define kRec_SkDescriptorTag            SkSetFourByteTag('s', 'r', 'e', 'c')
#define kPathEffect_SkDescriptorTag     SkSetFourByteTag('p', 't', 'h', 'e')
#define kMaskFilter_SkDescriptorTag     SkSetFourByteTag('m', 's', 'k', 'f')
#define kRasterizer_SkDescriptorTag     SkSetFourByteTag('r', 'a', 's', 't')

#endif