skia2/site/user/api/SkFont_Reference.md

SkFont Reference

class SkFont {
    // SkFont interface
};

Font_Size adjusts the overall text size in points. Font_Size can be set to any positive value or zero. Font_Size defaults to 12. Font_Size

Font_Scale_X adjusts the text horizontal scale. Text scaling approximates condensed and expanded type faces when the actual face is not available. Font_Scale_X can be set to any value. Font_Scale_X defaults to 1.

Font_Skew_X adjusts the text horizontal slant. Text skewing approximates italic and oblique type faces when the actual face is not available. Font_Skew_X can be set to any value. Font_Skew_X defaults to 0.

Font_Embolden approximates the bold font style accompanying a normal font when a bold font face is not available. Skia does not provide font substitution; it is up to the client to find the bold font face using the platform Font_Manager.

Use Font_Skew_X to approximate an italic font style when the italic font face is not available.

A FreeType based port may define SK_USE_FREETYPE_EMBOLDEN at compile time to direct the font engine to create the bold Glyphs. Otherwise, the extra bold is computed by increasing the stroke width and setting the SkPaint::Style to SkPaint::kStrokeAndFill_Style as needed.

Font_Embolden is disabled by default.

If Hinting is set to SkFontHinting::kFull, Hinting_Spacing adjusts the character spacing by the difference of the hinted and unhinted Left_Side_Bearing and Right_Side_Bearing. Hinting_Spacing only applies to platforms that use FreeType as their Font_Engine.

Hinting_Spacing is not related to text kerning, where the space between a specific pair of characters is adjusted using data in the font kerning tables.

Font_Linear selects whether text is rendered as a Glyph or as a Path. If Font_Linear is set, it has the same effect as setting Hinting to SkFontHinting::kNormal. If Font_Linear is clear, it is the same as setting Hinting to SkFontHinting::kNone.

Font_Subpixel uses the pixel transparency to represent a fractional offset. As the opaqueness of the color increases, the edge of the glyph appears to move towards the outside of the pixel.

When set, Anti_Alias positions glyphs within a pixel, using alpha and possibly RGB striping. It can take advantage of the organization of RGB stripes that create a color, and relies on the small size of the stripe and visual perception to make the color fringing imperceptible.

Anti_Alias can be enabled on devices that orient stripes horizontally or vertically, and that order the color components as RGB or BGR. Internally, the glyph cache may store multiple copies of the same glyph with different sub-pixel positions, requiring more memory.

If Hinting is set to SkFontHinting::kNormal or SkFontHinting::kFull, Force_Hinting instructs the Font_Manager to always hint Glyphs. Force_Hinting has no effect if Hinting is set to SkFontHinting::kNone or SkFontHinting::kSlight.

Force_Hinting only affects platforms that use FreeType as the Font_Manager.

Embedded_Bitmaps allows selecting custom sized bitmap Glyphs. Embedded_Bitmaps when set chooses an embedded bitmap glyph over an outline contained in a font if the platform supports this option.

FreeType selects the bitmap glyph if available when Embedded_Bitmaps is set, and selects the outline glyph if Embedded_Bitmaps is clear. Windows may select the bitmap glyph but is not required to do so. OS_X and iOS do not support this option.

---

SkFont controls options applied when drawing and measuring text.

class SkFont {

    enum class Edging {
        kAlias,
        kAntiAlias,
        kSubpixelAntiAlias,
    };

    SkFont();
    SkFont(sk_sp<SkTypeface> typeface, SkScalar size);
    SkFont(sk_sp<SkTypeface> typeface, SkScalar size, SkScalar scaleX, SkScalar skewX);
    bool operator==(const SkFont& font) const;
    bool isForceAutoHinting() const;
    bool isEmbeddedBitmaps() const;
    bool isSubpixel() const;
    bool isLinearMetrics() const;
    bool isEmbolden() const;
    void setForceAutoHinting(bool forceAutoHinting);
    void setEmbeddedBitmaps(bool embeddedBitmaps);
    void setSubpixel(bool subpixel);
    void setLinearMetrics(bool linearMetrics);
    void setEmbolden(bool embolden);
    Edging getEdging() const;
    void setEdging(Edging edging);
    void setHinting(SkFontHinting hintingLevel);
    SkFontHinting getHinting() const;
    SkFont makeWithSize(SkScalar size) const;
    SkTypeface* getTypeface() const;
    SkScalar getSize() const;
    SkScalar getScaleX() const;
    SkScalar getSkewX() const;
    sk_sp<SkTypeface> refTypeface() const;
    void setTypeface(sk_sp<SkTypeface> tf);
    void setSize(SkScalar textSize);
    void setScaleX(SkScalar scaleX);
    void setSkewX(SkScalar skewX);
    int textToGlyphs(const void* text, size_t byteLength, SkTextEncoding encoding,
                     SkGlyphID glyphs[], int maxGlyphCount) const;
    uint16_t unicharToGlyph(SkUnichar uni) const;
    int countText(const void* text, size_t byteLength, SkTextEncoding encoding) const;
    bool containsText(const void* text, size_t byteLength, SkTextEncoding encoding) const;
    size_t breakText(const void* text, size_t length, SkTextEncoding encoding, SkScalar maxWidth,
                     SkScalar* measuredWidth = nullptr) const;
    SkScalar measureText(const void* text, size_t byteLength, SkTextEncoding encoding,
                         SkRect* bounds = nullptr) const;
    bool getPath(uint16_t glyphID, SkPath* path) const;
    void getPaths(const uint16_t glyphIDs[], int count,
                  void (*glyphPathProc)(const SkPath* pathOrNull, const SkMatrix& mx, void* ctx),
                  void* ctx) const;
    SkScalar getMetrics(SkFontMetrics* metrics) const;
    SkScalar getSpacing() const;
};

---

    enum class Edging {
        kAlias,
        kAntiAlias,
        kSubpixelAntiAlias,
    };

Whether edge pixels draw opaque or with partial transparency.

Constants

Const	Value	Description
SkFont::Edging::kAlias		no transparent pixels on glyph edges
SkFont::Edging::kAntiAlias		may have transparent pixels on glyph edges
SkFont::Edging::kSubpixelAntiAlias		glyph positioned in pixel using transparency

Example

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SkFont()

Constructs SkFont with default values.

Return Value

default initialized SkFont

Example

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SkFont(sk_sp<SkTypeface> typeface, SkScalar size)

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

Parameters

typeface	font and style used to draw and measure text
size	typographic height of text

Return Value

initialized SkFont

Example

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SkFont(sk_sp<SkTypeface> typeface, SkScalar size, SkScalar scaleX, SkScalar skewX)

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.

Parameters

typeface	font and style used to draw and measure text
size	typographic height of text
scaleX	text horizontal scale
skewX	additional shear on x-axis relative to y-axis

Return Value

initialized SkFont

Example

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bool operator==(const SkFont& font)const

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

Parameters

font	font to compare

Return Value

true if SkFont pair are equivalent

Example

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bool isForceAutoHinting()const

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

Return Value

true if all glyphs are hinted

Example

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bool isEmbeddedBitmaps()const

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

Return Value

true if glyphs may be font bitmaps

Example

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bool isSubpixel()const

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

Return Value

true if glyph positioned in pixel using transparency

Example

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bool isLinearMetrics()const

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

Return Value

true glyph hints are never applied

Example

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bool isEmbolden()const

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

Return Value

bold is approximated through stroke width

Example

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void setForceAutoHinting(bool forceAutoHinting)

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.

Parameters

forceAutoHinting

setting to always hint glyphs

Example

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void setEmbeddedBitmaps(bool embeddedBitmaps)

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

Parameters

embeddedBitmaps

setting to use bitmaps in fonts

Example

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void setSubpixel(bool subpixel)

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

Parameters

subpixel

setting for sub-pixel positioning

Example

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void setLinearMetrics(bool linearMetrics)

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

Parameters

linearMetrics

setting for converting glyphs to paths

Example

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void setEmbolden(bool embolden)

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

Parameters

embolden

setting for bold approximation

Example

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Edging getEdging()const

Whether edge pixels draw opaque or with partial transparency.

Return Value

one of: Edging::kAlias, Edging::kAntiAlias, Edging::kSubpixelAntiAlias

Example

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void setEdging(Edging edging)

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

Parameters

edging

one of: Edging::kAlias, Edging::kAntiAlias, Edging::kSubpixelAntiAlias

Example

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void setHinting(SkFontHinting hintingLevel)

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

Parameters

hintingLevel

one of: SkFontHinting::kNone, SkFontHinting::kSlight,

SkFontHinting::kNormal, SkFontHinting::kFull

Example

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SkFontHinting getHinting()const

Returns level of glyph outline adjustment.

Return Value

one of: SkFontHinting::kNone, SkFontHinting::kSlight, SkFontHinting::kNormal,

SkFontHinting::kFull

Example

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SkFont makeWithSize(SkScalar size)const

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.

Parameters

size	typographic height of text

Return Value

initialized SkFont

Example

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SkTypeface* getTypeface()const

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

Return Value

SkTypeface if previously set, nullptr otherwise

Example

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SkScalar    getSize()const

Returns text size in points.

Return Value

typographic height of text

Example

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SkScalar    getScaleX()const

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

Return Value

text horizontal scale

Example

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SkScalar    getSkewX()const

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

Return Value

additional shear on x-axis relative to y-axis

Example

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sk_sp<SkTypeface> refTypeface()const

Increases SkTypeface SkRefCnt by one.

Return Value

SkTypeface if previously set, nullptr otherwise

Example

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void setTypeface(sk_sp<SkTypeface> tf)

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.

Parameters

tf	font and style used to draw text

Example

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void setSize(SkScalar textSize)

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

Parameters

textSize

typographic height of text

Example

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void setScaleX(SkScalar scaleX)

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

Parameters

scaleX

text horizontal scale

Example

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void setSkewX(SkScalar skewX)

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

Parameters

skewX

additional shear on x-axis relative to y-axis

Example

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int textToGlyphs(const void* text, size_t byteLength, SkTextEncoding encoding, SkGlyphID glyphs[],
                 int maxGlyphCount)const

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 SkTextEncoding::kUTF8 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.

Parameters

text	character storage encoded with SkTextEncoding
byteLength	length of character storage in bytes
encoding	one of: SkTextEncoding::kUTF8, SkTextEncoding::kUTF16,

SkTextEncoding::kUTF32, SkTextEncoding::kGlyphID

Parameters

glyphs	storage for glyph indices; may be nullptr
maxGlyphCount	storage capacity

Return Value

number of glyphs represented by text of length byteLength

Example

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uint16_t unicharToGlyph(SkUnichar uni)const

Returns glyph index for Unicode character.

Parameters

uni	Unicode character

Return Value

glyph index

Example

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int countText(const void* text, size_t byteLength, SkTextEncoding encoding)const

Returns number of glyphs represented by text.

Parameters

text	character storage encoded with SkTextEncoding
byteLength	length of character storage in bytes
encoding	one of: SkTextEncoding::kUTF8, SkTextEncoding::kUTF16,

SkTextEncoding::kUTF32, SkTextEncoding::kGlyphID

Return Value

number of glyphs represented by text of length byteLength

Example

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bool containsText(const void* text, size_t byteLength, SkTextEncoding encoding)const

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 SkTextEncoding::kGlyphID, 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.

Parameters

text	array of characters or glyphs
byteLength	number of bytes in text array
encoding	text encoding

Return Value

true if all text corresponds to a non-zero glyph index

Example

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size_t breakText(const void* text, size_t length, SkTextEncoding encoding, SkScalar maxWidth,
                 SkScalar* measuredWidth = nullptr)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.

Parameters

text	character codes or glyph indices to be measured
length	number of bytes of text to measure
encoding	text encoding
maxWidth	advance limit; text is measured while advance is less than maxWidth
measuredWidth	returns the width of the text less than or equal to maxWidth

Return Value

bytes of text that fit, always less than or equal to length

Example

Line under "Breakfast" shows desired width, shorter than available characters. Line under "Bre" shows measured width after breaking text.

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SkScalar measureText(const void* text, size_t byteLength, SkTextEncoding encoding,
                     SkRect* bounds = 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.

Parameters

text	character storage encoded with SkTextEncoding
byteLength	length of character storage in bytes
encoding	one of: SkTextEncoding::kUTF8, SkTextEncoding::kUTF16,

SkTextEncoding::kUTF32, SkTextEncoding::kGlyphID

Parameters

bounds

returns bounding box relative to (0, 0) if not nullptr

Return Value

number of glyphs represented by text of length byteLength

Example

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bool getPath(uint16_t glyphID, SkPath* path)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.

Parameters

glyphID	index of glyph
path	pointer to existing SkPath

Return Value

true if glyphID is described by path

Example

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void getPaths(const uint16_t glyphIDs[], int count, void (*glyphPathProc) (const SkPath* pathOrNull,
              const SkMatrix& mx, void* ctx) , void* ctx)const

Returns path corresponding to glyph array.

Parameters

glyphIDs	array of glyph indices
count	number of glyphs
glyphPathProc	function returning one glyph description as path
ctx	function context

Example

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SkScalar getMetrics(SkFontMetrics* metrics)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.

Parameters

metrics

storage for SkFontMetrics; may be nullptr

Return Value

recommended spacing between lines

Example

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SkScalar getSpacing()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 Value

recommended spacing between lines

Example

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