SkScalerContext.h revision bfe1572f2484cb928a17b4c45ed2d094e3e57e17 
1/*
2 * Copyright 2006 The Android Open Source Project
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8#ifndef SkScalerContext_DEFINED
9#define SkScalerContext_DEFINED
10
11#include "SkMask.h"
12#include "SkMaskGamma.h"
13#include "SkMatrix.h"
14#include "SkPaint.h"
15
16#ifdef SK_BUILD_FOR_ANDROID
17    //For SkFontID
18    #include "SkTypeface.h"
19#endif
20
21struct SkGlyph;
22class SkDescriptor;
23class SkMaskFilter;
24class SkPathEffect;
25class SkRasterizer;
26
27/*
28 *  To allow this to be forward-declared, it must be its own typename, rather
29 *  than a nested struct inside SkScalerContext (where it started).
30 */
31struct SkScalerContextRec {
32    uint32_t    fOrigFontID;
33    uint32_t    fFontID;
34    SkScalar    fTextSize, fPreScaleX, fPreSkewX;
35    SkScalar    fPost2x2[2][2];
36    SkScalar    fFrameWidth, fMiterLimit;
37
38    //These describe the parameters to create (uniquely identify) the pre-blend.
39    uint32_t    fLumBits;
40    uint8_t     fDeviceGamma; //2.6, (0.0, 4.0) gamma, 0.0 for sRGB
41    uint8_t     fPaintGamma;  //2.6, (0.0, 4.0) gamma, 0.0 for sRGB
42    uint8_t     fContrast;    //0.8+1, [0.0, 1.0] artificial contrast
43    uint8_t     fReservedAlign;
44
45    SkScalar getDeviceGamma() const {
46        return SkIntToScalar(fDeviceGamma) / (1 << 6);
47    }
48    void setDeviceGamma(SkScalar dg) {
49        SkASSERT(0 <= dg && dg < SkIntToScalar(4));
50        fDeviceGamma = SkScalarFloorToInt(dg * (1 << 6));
51    }
52
53    SkScalar getPaintGamma() const {
54        return SkIntToScalar(fPaintGamma) / (1 << 6);
55    }
56    void setPaintGamma(SkScalar pg) {
57        SkASSERT(0 <= pg && pg < SkIntToScalar(4));
58        fPaintGamma = SkScalarFloorToInt(pg * (1 << 6));
59    }
60
61    SkScalar getContrast() const {
62        return SkIntToScalar(fContrast) / ((1 << 8) - 1);
63    }
64    void setContrast(SkScalar c) {
65        SkASSERT(0 <= c && c <= SK_Scalar1);
66        fContrast = SkScalarRoundToInt(c * ((1 << 8) - 1));
67    }
68
69    /**
70     *  Causes the luminance color and contrast to be ignored, and the
71     *  paint and device gamma to be effectively 1.0.
72     */
73    void ignorePreBlend() {
74        setLuminanceColor(0x00000000);
75        setPaintGamma(SK_Scalar1);
76        setDeviceGamma(SK_Scalar1);
77        setContrast(0);
78    }
79
80    uint8_t     fMaskFormat;
81    uint8_t     fStrokeJoin;
82    uint16_t    fFlags;
83    // Warning: when adding members note that the size of this structure
84    // must be a multiple of 4. SkDescriptor requires that its arguments be
85    // multiples of four and this structure is put in an SkDescriptor in
86    // SkPaint::MakeRec.
87
88    void    getMatrixFrom2x2(SkMatrix*) const;
89    void    getLocalMatrix(SkMatrix*) const;
90    void    getSingleMatrix(SkMatrix*) const;
91
92    inline SkPaint::Hinting getHinting() const;
93    inline void setHinting(SkPaint::Hinting);
94
95    SkMask::Format getFormat() const {
96        return static_cast<SkMask::Format>(fMaskFormat);
97    }
98
99    SkColor getLuminanceColor() const {
100        return fLumBits;
101    }
102
103    void setLuminanceColor(SkColor c) {
104        fLumBits = c;
105    }
106};
107
108//The following typedef hides from the rest of the implementation the number of
109//most significant bits to consider when creating mask gamma tables. Two bits
110//per channel was chosen as a balance between fidelity (more bits) and cache
111//sizes (fewer bits). Three bits per channel was chosen when #303942; (used by
112//the Chrome UI) turned out too green.
113typedef SkTMaskGamma<3, 3, 3> SkMaskGamma;
114
115class SkScalerContext {
116public:
117    typedef SkScalerContextRec Rec;
118
119    enum Flags {
120        kFrameAndFill_Flag        = 0x0001,
121        kDevKernText_Flag         = 0x0002,
122        kEmbeddedBitmapText_Flag  = 0x0004,
123        kEmbolden_Flag            = 0x0008,
124        kSubpixelPositioning_Flag = 0x0010,
125        kAutohinting_Flag         = 0x0020,
126        kVertical_Flag            = 0x0040,
127
128        // together, these two flags resulting in a two bit value which matches
129        // up with the SkPaint::Hinting enum.
130        kHinting_Shift            = 7, // to shift into the other flags above
131        kHintingBit1_Flag         = 0x0080,
132        kHintingBit2_Flag         = 0x0100,
133
134        // these should only ever be set if fMaskFormat is LCD16 or LCD32
135        kLCD_Vertical_Flag        = 0x0200,    // else Horizontal
136        kLCD_BGROrder_Flag        = 0x0400,    // else RGB order
137
138        // Generate A8 from LCD source (for GDI), only meaningful if fMaskFormat is kA8
139        // Perhaps we can store this (instead) in fMaskFormat, in hight bit?
140        kGenA8FromLCD_Flag        = 0x0800,
141    };
142
143    // computed values
144    enum {
145        kHinting_Mask   = kHintingBit1_Flag | kHintingBit2_Flag,
146    };
147
148
149    SkScalerContext(const SkDescriptor* desc);
150    virtual ~SkScalerContext();
151
152    SkMask::Format getMaskFormat() const {
153        return (SkMask::Format)fRec.fMaskFormat;
154    }
155
156    bool isSubpixel() const {
157        return SkToBool(fRec.fFlags & kSubpixelPositioning_Flag);
158    }
159
160    // remember our glyph offset/base
161    void setBaseGlyphCount(unsigned baseGlyphCount) {
162        fBaseGlyphCount = baseGlyphCount;
163    }
164
165    /** Return the corresponding glyph for the specified unichar. Since contexts
166        may be chained (under the hood), the glyphID that is returned may in
167        fact correspond to a different font/context. In that case, we use the
168        base-glyph-count to know how to translate back into local glyph space.
169     */
170    uint16_t charToGlyphID(SkUnichar uni);
171
172    /** Map the glyphID to its glyph index, and then to its char code. Unmapped
173        glyphs return zero.
174    */
175    SkUnichar glyphIDToChar(uint16_t glyphID);
176
177    unsigned    getGlyphCount() { return this->generateGlyphCount(); }
178    void        getAdvance(SkGlyph*);
179    void        getMetrics(SkGlyph*);
180    void        getImage(const SkGlyph&);
181    void        getPath(const SkGlyph&, SkPath*);
182    void        getFontMetrics(SkPaint::FontMetrics* mX,
183                               SkPaint::FontMetrics* mY);
184
185#ifdef SK_BUILD_FOR_ANDROID
186    unsigned getBaseGlyphCount(SkUnichar charCode);
187
188    // This function must be public for SkTypeface_android.h, but should not be
189    // called by other callers
190    SkFontID findTypefaceIdForChar(SkUnichar uni) {
191        SkScalerContext* ctx = this;
192        while (NULL != ctx) {
193            if (ctx->generateCharToGlyph(uni)) {
194                return ctx->fRec.fFontID;
195            }
196            ctx = ctx->getNextContext();
197        }
198        return 0;
199    }
200#endif
201
202    static inline void MakeRec(const SkPaint&, const SkMatrix*, Rec* rec);
203    static inline void PostMakeRec(const SkPaint&, Rec*);
204
205    static SkScalerContext* Create(const SkDescriptor*);
206    static SkMaskGamma::PreBlend GetMaskPreBlend(const Rec& rec);
207
208protected:
209    Rec         fRec;
210    unsigned    fBaseGlyphCount;
211
212    virtual unsigned generateGlyphCount() = 0;
213    virtual uint16_t generateCharToGlyph(SkUnichar) = 0;
214    virtual void generateAdvance(SkGlyph*) = 0;
215    virtual void generateMetrics(SkGlyph*) = 0;
216    virtual void generateImage(const SkGlyph&, SkMaskGamma::PreBlend* maskPreBlend) = 0;
217    virtual void generatePath(const SkGlyph&, SkPath*) = 0;
218    virtual void generateFontMetrics(SkPaint::FontMetrics* mX,
219                                     SkPaint::FontMetrics* mY) = 0;
220    // default impl returns 0, indicating failure.
221    virtual SkUnichar generateGlyphToChar(uint16_t);
222
223    void forceGenerateImageFromPath() { fGenerateImageFromPath = true; }
224
225private:
226    SkPathEffect*   fPathEffect;
227    SkMaskFilter*   fMaskFilter;
228    SkRasterizer*   fRasterizer;
229
230    // if this is set, we draw the image from a path, rather than
231    // calling generateImage.
232    bool fGenerateImageFromPath;
233
234    void internalGetPath(const SkGlyph& glyph, SkPath* fillPath,
235                         SkPath* devPath, SkMatrix* fillToDevMatrix);
236
237    // return the next context, treating fNextContext as a cache of the answer
238    SkScalerContext* getNextContext();
239
240    // returns the right context from our link-list for this glyph. If no match
241    // is found, just returns the original context (this)
242    SkScalerContext* getGlyphContext(const SkGlyph& glyph);
243
244    // link-list of context, to handle missing chars. null-terminated.
245    SkScalerContext* fNextContext;
246
247    // converts linear masks to gamma correcting masks.
248    SkMaskGamma::PreBlend fMaskPreBlend;
249};
250
251#define kRec_SkDescriptorTag            SkSetFourByteTag('s', 'r', 'e', 'c')
252#define kPathEffect_SkDescriptorTag     SkSetFourByteTag('p', 't', 'h', 'e')
253#define kMaskFilter_SkDescriptorTag     SkSetFourByteTag('m', 's', 'k', 'f')
254#define kRasterizer_SkDescriptorTag     SkSetFourByteTag('r', 'a', 's', 't')
255
256///////////////////////////////////////////////////////////////////////////////
257
258enum SkAxisAlignment {
259    kNone_SkAxisAlignment,
260    kX_SkAxisAlignment,
261    kY_SkAxisAlignment
262};
263
264/**
265 *  Return the axis (if any) that the baseline for horizontal text will land on
266 *  after running through the specified matrix.
267 *
268 *  As an example, the identity matrix will return kX_SkAxisAlignment
269 */
270SkAxisAlignment SkComputeAxisAlignmentForHText(const SkMatrix& matrix);
271
272///////////////////////////////////////////////////////////////////////////////
273
274SkPaint::Hinting SkScalerContextRec::getHinting() const {
275    unsigned hint = (fFlags & SkScalerContext::kHinting_Mask) >>
276                                            SkScalerContext::kHinting_Shift;
277    return static_cast<SkPaint::Hinting>(hint);
278}
279
280void SkScalerContextRec::setHinting(SkPaint::Hinting hinting) {
281    fFlags = (fFlags & ~SkScalerContext::kHinting_Mask) |
282                                (hinting << SkScalerContext::kHinting_Shift);
283}
284
285
286#endif
287
288