skia2/include/core/SkFont.h

/*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkFont_DEFINED
#define SkFont_DEFINED

#include "SkFontTypes.h"
#include "SkScalar.h"
#include "SkTypeface.h"

class SkMatrix;
class SkPaint;
class SkPath;
struct SkFontMetrics;

/** \class SkFont
    SkFont controls options applied when drawing and measuring text.
*/
class SK_API SkFont {
public:
    /** Whether edge pixels draw opaque or with partial transparency.
    */
    enum class Edging {
        kAlias,              //!< no transparent pixels on glyph edges
        kAntiAlias,          //!< may have transparent pixels on glyph edges
        kSubpixelAntiAlias,  //!< glyph positioned in pixel using transparency
    };

    /** Constructs SkFont with default values.

        @return  default initialized SkFont
    */
    SkFont();

    /** Constructs SkFont with default values with SkTypeface and size in points.

        @param typeface  font and style used to draw and measure text
        @param size      typographic height of text
        @return          initialized SkFont
    */
    SkFont(sk_sp<SkTypeface> typeface, SkScalar size);

    // Experimental
    explicit SkFont(sk_sp<SkTypeface> typeface);


    /** Constructs SkFont with default values with SkTypeface and size in points,
        horizontal scale, and horizontal skew. Horizontal scale emulates condensed
        and expanded fonts. Horizontal skew emulates oblique fonts.

        @param typeface  font and style used to draw and measure text
        @param size      typographic height of text
        @param scaleX    text horizontal scale
        @param skewX     additional shear on x-axis relative to y-axis
        @return          initialized SkFont
    */
    SkFont(sk_sp<SkTypeface> typeface, SkScalar size, SkScalar scaleX, SkScalar skewX);


    /** Compares SkFont and font, and returns true if they are equivalent.
        May return false if SkTypeface has identical contents but different pointers.

        @param font  font to compare
        @return      true if SkFont pair are equivalent
    */
    bool operator==(const SkFont& font) const;
    // Experimental
    bool operator!=(const SkFont& font) const { return !(*this == font); }

    /** If true, instructs the font manager to always hint glyphs.
        Returned value is only meaningful if platform uses FreeType as the font manager.

        @return  true if all glyphs are hinted
    */
    bool isForceAutoHinting() const { return SkToBool(fFlags & kForceAutoHinting_PrivFlag); }

    /** Returns true if font engine may return glyphs from font bitmaps instead of from outlines.

        @return  true if glyphs may be font bitmaps
    */
    bool isEmbeddedBitmaps() const { return SkToBool(fFlags & kEmbeddedBitmaps_PrivFlag); }

    /** Returns true if glyphs at different sub-pixel positions may differ on pixel edge coverage.

        @return  true if glyph positioned in pixel using transparency
    */
    bool isSubpixel() const { return SkToBool(fFlags & kSubpixel_PrivFlag); }

    /** Returns true if text is converted to SkPath before drawing and measuring.

        @return  true glyph hints are never applied
    */
    bool isLinearMetrics() const { return SkToBool(fFlags & kLinearMetrics_PrivFlag); }

    /** Returns true if bold is approximated by increasing the stroke width when creating glyph
        bitmaps from outlines.

        @return  bold is approximated through stroke width
    */
    bool isEmbolden() const { return SkToBool(fFlags & kEmbolden_PrivFlag); }

    /** Sets whether to always hint glyphs.
        If forceAutoHinting is set, instructs the font manager to always hint glyphs.

        Only affects platforms that use FreeType as the font manager.

        @param forceAutoHinting  setting to always hint glyphs
    */
    void setForceAutoHinting(bool forceAutoHinting);

    /** Requests, but does not require, to use bitmaps in fonts instead of outlines.

        @param embeddedBitmaps  setting to use bitmaps in fonts
    */
    void setEmbeddedBitmaps(bool embeddedBitmaps);

    /** Requests, but does not require, that glyphs respect sub-pixel positioning.

        @param subpixel  setting for sub-pixel positioning
    */
    void setSubpixel(bool subpixel);

    /** Requests, but does not require, that glyphs are converted to SkPath
        before drawing and measuring.

        @param linearMetrics  setting for converting glyphs to paths
    */
    void setLinearMetrics(bool linearMetrics);

    /** Increases stroke width when creating glyph bitmaps to approximate a bold typeface.

        @param embolden  setting for bold approximation
    */
    void setEmbolden(bool embolden);

    /** Whether edge pixels draw opaque or with partial transparency.

        @return  one of: Edging::kAlias, Edging::kAntiAlias, Edging::kSubpixelAntiAlias
    */
    Edging getEdging() const { return (Edging)fEdging; }

    /** Requests, but does not require, that edge pixels draw opaque or with
        partial transparency.

        @param edging  one of: Edging::kAlias, Edging::kAntiAlias, Edging::kSubpixelAntiAlias
    */
    void setEdging(Edging edging);

    /** Sets level of glyph outline adjustment.
        Does not check for valid values of hintingLevel.

        @param hintingLevel  one of: SkFontHinting::kNone, SkFontHinting::kSlight,
                                     SkFontHinting::kNormal, SkFontHinting::kFull
    */
    void setHinting(SkFontHinting hintingLevel);

    /** Returns level of glyph outline adjustment.

        @return  one of: SkFontHinting::kNone, SkFontHinting::kSlight, SkFontHinting::kNormal,
                         SkFontHinting::kFull
     */
    SkFontHinting getHinting() const { return (SkFontHinting)fHinting; }

    /** Returns a font with the same attributes of this font, but with the specified size.
        Returns nullptr if size is less than zero, infinite, or NaN.

        @param size  typographic height of text
        @return      initialized SkFont
     */
    SkFont makeWithSize(SkScalar size) const;

    /** Returns SkTypeface if set, or nullptr.
        Does not alter SkTypeface SkRefCnt.

        @return  SkTypeface if previously set, nullptr otherwise
    */
    SkTypeface* getTypeface() const { return fTypeface.get(); }

    /** Returns text size in points.

        @return  typographic height of text
    */
    SkScalar    getSize() const { return fSize; }

    /** Returns text scale on x-axis.
        Default value is 1.

        @return  text horizontal scale
    */
    SkScalar    getScaleX() const { return fScaleX; }

    /** Returns text skew on x-axis.
        Default value is zero.

        @return  additional shear on x-axis relative to y-axis
    */
    SkScalar    getSkewX() const { return fSkewX; }

    /** Increases SkTypeface SkRefCnt by one.

        @return  SkTypeface if previously set, nullptr otherwise
    */
    sk_sp<SkTypeface> refTypeface() const { return fTypeface; }

    /** Sets SkTypeface to typeface, decreasing SkRefCnt of the previous SkTypeface.
        Pass nullptr to clear SkTypeface and use the default typeface. Increments
        tf SkRefCnt by one.

        @param tf  font and style used to draw text
    */
    void setTypeface(sk_sp<SkTypeface> tf) { fTypeface = tf; }

    /** Sets text size in points.
        Has no effect if textSize is not greater than or equal to zero.

        @param textSize  typographic height of text
    */
    void setSize(SkScalar textSize);

    /** Sets text scale on x-axis.
        Default value is 1.

        @param scaleX  text horizontal scale
    */
    void setScaleX(SkScalar scaleX);

    /** Sets text skew on x-axis.
        Default value is zero.

        @param skewX  additional shear on x-axis relative to y-axis
    */
    void setSkewX(SkScalar skewX);

    /** Converts text into glyph indices.
        Returns the number of glyph indices represented by text.
        SkTextEncoding specifies how text represents characters or glyphs.
        glyphs may be nullptr, to compute the glyph count.

        Does not check text for valid character codes or valid glyph indices.

        If byteLength equals zero, returns zero.
        If byteLength includes a partial character, the partial character is ignored.

        If encoding is kUTF8_SkTextEncoding and text contains an invalid UTF-8 sequence,
        zero is returned.

        If maxGlyphCount is not sufficient to store all the glyphs, no glyphs are copied.
        The total glyph count is returned for subsequent buffer reallocation.

        @param text          character storage encoded with SkTextEncoding
        @param byteLength    length of character storage in bytes
        @param encoding      one of: kUTF8_SkTextEncoding, kUTF16_SkTextEncoding,
                             kUTF32_SkTextEncoding, kGlyphID_SkTextEncoding
        @param glyphs        storage for glyph indices; may be nullptr
        @param maxGlyphCount storage capacity
        @return              number of glyphs represented by text of length byteLength
    */
    int textToGlyphs(const void* text, size_t byteLength, SkTextEncoding encoding,
                     SkGlyphID glyphs[], int maxGlyphCount) const;

    /** Returns glyph index for Unicode character.

        @param uni  Unicode character
        @return     glyph index
    */
    uint16_t unicharToGlyph(SkUnichar uni) const {
        return fTypeface->unicharToGlyph(uni);
    }

    /** Returns number of glyphs represented by text.

        @param text          character storage encoded with SkTextEncoding
        @param byteLength    length of character storage in bytes
        @param encoding      one of: kUTF8_SkTextEncoding, kUTF16_SkTextEncoding,
                             kUTF32_SkTextEncoding, kGlyphID_SkTextEncoding
        @return              number of glyphs represented by text of length byteLength
    */
    int countText(const void* text, size_t byteLength, SkTextEncoding encoding) const {
        return this->textToGlyphs(text, byteLength, encoding, nullptr, 0);
    }

    /** Returns true if all text corresponds to a non-zero glyph index.
        Returns false if any characters in text are not supported in
        SkTypeface.

        If SkTextEncoding is kGlyphID_SkTextEncoding,
        returns true if all glyph indices in text are non-zero;
        does not check to see if text contains valid glyph indices for SkTypeface.

        Returns true if byteLength is zero.

        @param text        array of characters or glyphs
        @param byteLength  number of bytes in text array
        @param encoding    text encoding
        @return            true if all text corresponds to a non-zero glyph index
     */
    bool containsText(const void* text, size_t byteLength, SkTextEncoding encoding) const;

    /** Returns the bytes of text that fit within maxWidth.
        The text fragment fits if its advance width is less than or equal to maxWidth.
        Measures only while the advance is less than or equal to maxWidth.
        Returns the advance or the text fragment in measuredWidth if it not nullptr.
        Uses encoding to decode text, SkTypeface to get the font metrics,
        and text size to scale the metrics.
        Does not scale the advance or bounds by fake bold.

        @param text           character codes or glyph indices to be measured
        @param length         number of bytes of text to measure
        @param encoding       text encoding
        @param maxWidth       advance limit; text is measured while advance is less than maxWidth
        @param measuredWidth  returns the width of the text less than or equal to maxWidth
        @return               bytes of text that fit, always less than or equal to length
    */
    size_t breakText(const void* text, size_t length, SkTextEncoding encoding, SkScalar maxWidth,
                     SkScalar* measuredWidth = nullptr) const;

    /** Returns the advance width of text.
        The advance is the normal distance to move before drawing additional text.
        Returns the bounding box of text if bounds is not nullptr.

        @param text        character storage encoded with SkTextEncoding
        @param byteLength  length of character storage in bytes
        @param encoding    one of: kUTF8_SkTextEncoding, kUTF16_SkTextEncoding,
                           kUTF32_SkTextEncoding, kGlyphID_SkTextEncoding
        @param bounds      returns bounding box relative to (0, 0) if not nullptr
        @return            number of glyphs represented by text of length byteLength
    */
    SkScalar measureText(const void* text, size_t byteLength, SkTextEncoding encoding,
                         SkRect* bounds = nullptr) const {
        return this->measureText(text, byteLength, encoding, bounds, nullptr);
    }

    // Experimental
    SkScalar measureText(const void* text, size_t byteLength, SkTextEncoding encoding,
                         SkRect* bounds, const SkPaint*) const;

    /** DEPRECATED
        Retrieves the advance and bounds for each glyph in glyphs.
        Both widths and bounds may be nullptr.
        If widths is not nullptr, widths must be an array of count entries.
        if bounds is not nullptr, bounds must be an array of count entries.

        @param glyphs      array of glyph indices to be measured
        @param count       number of glyphs
        @param widths      returns text advances for each glyph; may be nullptr
        @param bounds      returns bounds for each glyph relative to (0, 0); may be nullptr
    */
    void getWidths(const uint16_t glyphs[], int count, SkScalar widths[], SkRect bounds[]) const {
        this->getWidthsBounds(glyphs, count, widths, bounds, nullptr);
    }

    // DEPRECATED
    void getWidths(const uint16_t glyphs[], int count, SkScalar widths[], std::nullptr_t) const {
        this->getWidths(glyphs, count, widths);
    }

    /** Experimental
        Retrieves the advance and bounds for each glyph in glyphs.
        Both widths and bounds may be nullptr.
        If widths is not nullptr, widths must be an array of count entries.
        if bounds is not nullptr, bounds must be an array of count entries.

        @param glyphs      array of glyph indices to be measured
        @param count       number of glyphs
        @param widths      returns text advances for each glyph
     */
    void getWidths(const uint16_t glyphs[], int count, SkScalar widths[]) const {
        this->getWidthsBounds(glyphs, count, widths, nullptr, nullptr);
    }

    /** Experimental.
        Retrieves the advance and bounds for each glyph in glyphs.
        Both widths and bounds may be nullptr.
        If widths is not nullptr, widths must be an array of count entries.
        if bounds is not nullptr, bounds must be an array of count entries.

        @param glyphs      array of glyph indices to be measured
        @param count       number of glyphs
        @param widths      returns text advances for each glyph; may be nullptr
        @param bounds      returns bounds for each glyph relative to (0, 0); may be nullptr
        @param paint       optional, specifies stroking, SkPathEffect and SkMaskFilter
     */
    void getWidthsBounds(const uint16_t glyphs[], int count, SkScalar widths[], SkRect bounds[],
                         const SkPaint* paint) const;


    /** Experimental.
        Retrieves the bounds for each glyph in glyphs.
        bounds must be an array of count entries.
        If paint is not nullptr, its stroking, SkPathEffect, and SkMaskFilter fields are respected.

        @param glyphs      array of glyph indices to be measured
        @param count       number of glyphs
        @param bounds      returns bounds for each glyph relative to (0, 0); may be nullptr
        @param paint       optional, specifies stroking, SkPathEffect, and SkMaskFilter
     */
    void getBounds(const uint16_t glyphs[], int count, SkRect bounds[],
                   const SkPaint* paint) const {
        this->getWidthsBounds(glyphs, count, nullptr, bounds, paint);
    }

    /** Experimental
        Retrieves the positions for each glyph, beginning at the specified origin. The caller
        must allocated at least count number of elements in the pos[] array.

        @param glyphs   array of glyph indices to be positioned
        @param count    number of glyphs
        @param pos      returns glyphs positions
        @param origin   location of the first glyph. Defaults to {0, 0}.
     */
    void getPos(const uint16_t glyphs[], int count, SkPoint pos[], SkPoint origin = {0, 0}) const;

    /** Experimental
        Retrieves the x-positions for each glyph, beginning at the specified origin. The caller
        must allocated at least count number of elements in the xpos[] array.

        @param glyphs   array of glyph indices to be positioned
        @param count    number of glyphs
        @param xpos     returns glyphs x-positions
        @param origin   x-position of the first glyph. Defaults to 0.
     */
    void getXPos(const uint16_t glyphs[], int count, SkScalar xpos[], SkScalar origin = 0) const;

    /** Returns path corresponding to glyph outline.
        If glyph has an outline, copies outline to path and returns true.
        path returned may be empty.
        If glyph is described by a bitmap, returns false and ignores path parameter.

        @param glyphID  index of glyph
        @param path     pointer to existing SkPath
        @return         true if glyphID is described by path
     */
    bool getPath(uint16_t glyphID, SkPath* path) const;

    /** Returns path corresponding to glyph array.

        @param glyphIDs      array of glyph indices
        @param count         number of glyphs
        @param glyphPathProc function returning one glyph description as path
        @param ctx           function context
   */
    void getPaths(const uint16_t glyphIDs[], int count,
                  void (*glyphPathProc)(const SkPath* pathOrNull, const SkMatrix& mx, void* ctx),
                  void* ctx) const;

    /** Returns SkFontMetrics associated with SkTypeface.
        The return value is the recommended spacing between lines: the sum of metrics
        descent, ascent, and leading.
        If metrics is not nullptr, SkFontMetrics is copied to metrics.
        Results are scaled by text size but does not take into account
        dimensions required by text scale, text skew, fake bold,
        style stroke, and SkPathEffect.

        @param metrics  storage for SkFontMetrics; may be nullptr
        @return         recommended spacing between lines
    */
    SkScalar getMetrics(SkFontMetrics* metrics) const;

    /** Returns the recommended spacing between lines: the sum of metrics
        descent, ascent, and leading.
        Result is scaled by text size but does not take into account
        dimensions required by stroking and SkPathEffect.
        Returns the same result as getMetrics().

        @return  recommended spacing between lines
    */
    SkScalar getSpacing() const { return this->getMetrics(nullptr); }

    /** Deprecated.
    */
    void LEGACY_applyToPaint(SkPaint* paint) const;
    /** Deprecated.
     */
    void LEGACY_applyPaintFlags(uint32_t paintFlags);
    /** Deprecated.
    */
    static SkFont LEGACY_ExtractFromPaint(const SkPaint& paint);

    /** Experimental.
     *  Dumps fields of the font to SkDebugf. May change its output over time, so clients should
     *  not rely on this for anything specific. Used to aid in debugging.
     */
    void dump() const;

private:
    enum PrivFlags {
        kForceAutoHinting_PrivFlag      = 1 << 0,
        kEmbeddedBitmaps_PrivFlag       = 1 << 1,
        kSubpixel_PrivFlag              = 1 << 2,
        kLinearMetrics_PrivFlag         = 1 << 3,
        kEmbolden_PrivFlag              = 1 << 4,
    };

    static constexpr unsigned kAllFlags = 0x07F;

    sk_sp<SkTypeface> fTypeface;
    SkScalar    fSize;
    SkScalar    fScaleX;
    SkScalar    fSkewX;
    uint8_t     fFlags;
    uint8_t     fEdging;
    uint8_t     fHinting;

    SkScalar setupForAsPaths(SkPaint*);
    bool hasSomeAntiAliasing() const;

    void glyphsToUnichars(const SkGlyphID glyphs[], int count, SkUnichar text[]) const;

    friend class GrTextBlob;
    friend class SkCanonicalizeFont;
    friend class SkFontPriv;
    friend class SkGlyphRunListPainter;
    friend class SkPaint;
    friend class SkTextBlobCacheDiffCanvas;
    friend class SVGTextBuilder;
};

#endif