The user-font feature allows the cairo user to provide drawings for glyphs in a font. This is most useful in implementing fonts in non-standard formats, like SVG fonts and Flash fonts, but can also be used by games and other application to draw "funky" fonts.
Public Types | |
typedef sigc::slot < ErrorStatus, const RefPtr < ScaledFont > &, const RefPtr < Context > &, FontExtents & > | SlotInit |
A SlotInit slot is called when a ScaledFont needs to be created for a UserFontFace. | |
typedef sigc::slot < ErrorStatus, const RefPtr < ScaledFont > &, unsigned long, const RefPtr< Context > &, TextExtents & > | SlotRenderGlyph |
A SlotRenderGlyph slot is called when a user ScaledFont needs to render a glyph. | |
typedef sigc::slot < ErrorStatus, const RefPtr < ScaledFont > &, const std::string &, std::vector < Glyph > &, std::vector < TextCluster > &, TextClusterFlags & > | SlotTextToGlyphs |
A SlotTextToGlyphs slot is called to convert input text to an array of glyphs. | |
typedef sigc::slot < ErrorStatus, const RefPtr < ScaledFont > &, unsigned long, unsigned long & > | SlotUnicodeToGlyph |
A SlotUnicodeToGlyph slot is called to convert an input Unicode character to a single glyph. | |
Public Member Functions | |
void | set_init_func (const SlotInit &init_func) |
Sets the scaled-font initialization function of a user-font. | |
void | set_render_glyph_func (const SlotRenderGlyph &render_glyph_func) |
Sets the glyph rendering function of a user-font. | |
void | set_text_to_glyphs_func (const SlotTextToGlyphs &text_to_glyphs_func) |
Sets the text-to-glyphs conversion function of a user-font. | |
void | set_unicode_to_glyph_func (const SlotUnicodeToGlyph &unicode_to_glyph_func) |
Sets the unicode-to-glyph conversion function of a user-font. | |
virtual | ~UserFontFace () |
Static Public Member Functions | |
static RefPtr< UserFontFace > | create () |
Protected Member Functions | |
UserFontFace () |
typedef sigc::slot<ErrorStatus, const RefPtr<ScaledFont>&, const RefPtr<Context>&, FontExtents&> Cairo::UserFontFace::SlotInit |
A SlotInit slot is called when a ScaledFont needs to be created for a UserFontFace.
For example: ErrorStatus my_init_func(const RefPtr<ScaledFont>& scaled_font, const RefPtr<Context>& cr, FontExtents& extents);
The Cairo::Context cr is not used by the caller, but is prepared in font space, similar to what the cairo contexts passed to the render_glyph method will look like. The callback can use this context for extents computation, for example. After the callback is called, cr is checked for any error status.
The extents argument is where the user font sets the font extents for scaled_font. It is in font space, which means that for most cases its ascent and descent members should add to 1.0. extents is preset to hold a value of 1.0 for ascent, height, and max_x_advance, and 0.0 for descent and max_y_advance members.
The callback is optional. If not set, default font extents as described in the previous paragraph will be used.
Note that scaled_font is not fully initialized at this point and trying to use it for text operations in the callback will result in deadlock.
scaled_font | the scaled-font being created. | |
cr | a cairo context, in font space. | |
extents | font extents to fill in, in font space. |
typedef sigc::slot<ErrorStatus, const RefPtr<ScaledFont>&, unsigned long , const RefPtr<Context>&, TextExtents& > Cairo::UserFontFace::SlotRenderGlyph |
A SlotRenderGlyph slot is called when a user ScaledFont needs to render a glyph.
For example: ErrorStatus my_render_glyph_func(const RefPtr<ScaledFont>& scaled_font, unsigned long glyph, const RefPtr<Context>& cr, TextExtents& metrics);
The callback is mandatory, and expected to draw the glyph with code glyph to the Context cr. cr is prepared such that the glyph drawing is done in font space. That is, the matrix set on cr is the scale matrix of scaled_font, The extents argument is where the user font sets the font extents for scaled_font. However, if user prefers to draw in user space, they can achieve that by changing the matrix on cr. All cairo rendering operations to cr are permitted, however, the result is undefined if any source other than the default source on cr is used. That means, glyph bitmaps should be rendered using Context::mask() instead of Context::paint().
Other non-default settings on cr include a font size of 1.0 (given that it is set up to be in font space), and font options corresponding to scaled_font.
The extents argument is preset to have x_bearing, width, and y_advance of zero, y_bearing set to -font_extents.ascent, height to font_extents.ascent+font_extents.descent, and x_advance to font_extents.max_x_advance. The only field user needs to set in majority of cases is x_advance. If the width field is zero upon the callback returning (which is its preset value), the glyph extents are automatically computed based on the drawings done to cr. This is in most cases exactly what the desired behavior is. However, if for any reason the callback sets the extents, it must be ink extents, and include the extents of all drawing done to cr in the callback.
scaled_font | user scaled-font. | |
glyph | glyph code to render. | |
cr | cairo context to draw to, in font space. | |
extents | glyph extents to fill in, in font space. |
typedef sigc::slot<ErrorStatus, const RefPtr<ScaledFont>&, const std::string& , std::vector<Glyph>& , std::vector<TextCluster>& , TextClusterFlags& > Cairo::UserFontFace::SlotTextToGlyphs |
A SlotTextToGlyphs slot is called to convert input text to an array of glyphs.
This is used by the Cairo::Context::show_text() operation.
Using this callback the user-font has full control on glyphs and their positions. That means, it allows for features like ligatures and kerning, as well as complex <firstterm>shaping</firstterm> required for scripts like Arabic and Indic.
The callback should populate the glyph indices and positions (in font space) assuming that the text is to be shown at the origin.
The callback is optional. If not set, the unicode_to_glyph callback is tried. See SlotUnicodeToGlyph.
Note: While cairo does not impose any limitation on glyph indices, some applications may assume that a glyph index fits in a 16-bit unsigned integer. As such, it is advised that user-fonts keep their glyphs in the 0 to 65535 range. Furthermore, some applications may assume that glyph 0 is a special glyph-not-found glyph. User-fonts are advised to use glyph 0 for such purposes and do not use that glyph value for other purposes.
Returns: CAIRO_STATUS_SUCCESS upon success, or CAIRO_STATUS_USER_FONT_ERROR or any other error status on error.
utf8 | a string of text encoded in UTF-8. | |
glyphs | An array of glyphs to fill, in font space. | |
clusters | An array of cluster mapping information to fill. | |
cluster_flags | This will be set, to specify the text to glyphs mapping flags |
typedef sigc::slot<ErrorStatus, const RefPtr<ScaledFont>&, unsigned long , unsigned long& > Cairo::UserFontFace::SlotUnicodeToGlyph |
A SlotUnicodeToGlyph slot is called to convert an input Unicode character to a single glyph.
This is used by the Context::show_text() operation.
For example: ErrorStatus my_unicode_to_glyph_func(const RefPtr<ScaledFont>& scaled_font, unsigned long unicode, unsigned long& glyph);
This callback is used to provide the same functionality as the text_to_glyphs callback does (see SlotTextToGlyphs) but has much less control on the output, in exchange for increased ease of use. The inherent assumption to using this callback is that each character maps to one glyph, and that the mapping is context independent. It also assumes that glyphs are positioned according to their advance width. These mean no ligatures, kerning, or complex scripts can be implemented using this callback.
The callback is optional, and only used if text_to_glyphs callback is not set or fails to return glyphs. If this callback is not set, an identity mapping from Unicode code-points to glyph indices is assumed.
Note: While cairo does not impose any limitation on glyph indices, some applications may assume that a glyph index fits in a 16-bit unsigned integer. As such, it is advised that user-fonts keep their glyphs in the 0 to 65535 range. Furthermore, some applications may assume that glyph 0 is a special glyph-not-found glyph. User-fonts are advised to use glyph 0 for such purposes and do not use that glyph value for other purposes.
scaled_font | the scaled-font being created. | |
unicode | input unicode character code-point. | |
glyph_index | output glyph index. |
virtual Cairo::UserFontFace::~UserFontFace | ( | ) | [virtual] |
Cairo::UserFontFace::UserFontFace | ( | ) | [protected] |
static RefPtr<UserFontFace> Cairo::UserFontFace::create | ( | ) | [static] |
void Cairo::UserFontFace::set_init_func | ( | const SlotInit & | init_func | ) |
Sets the scaled-font initialization function of a user-font.
See SlotInit for details of how the callback works.
The font-face should not be immutable or a CAIRO_STATUS_USER_FONT_IMMUTABLE error will occur. A user font-face is immutable as soon as a scaled-font is created from it.
init_func | The init callback. |
void Cairo::UserFontFace::set_render_glyph_func | ( | const SlotRenderGlyph & | render_glyph_func | ) |
Sets the glyph rendering function of a user-font.
See SlotRenderGlyph for details of how the callback works.
The font-face should not be immutable or a CAIRO_STATUS_USER_FONT_IMMUTABLE error will occur. A user font-face is immutable as soon as a scaled-font is created from it.
The render_glyph callback is the only mandatory callback of a user-font. If the callback is NULL and a glyph is tried to be rendered using , a CAIRO_STATUS_USER_FONT_ERROR will occur.
render_glyph_func | The render_glyph callback. |
void Cairo::UserFontFace::set_text_to_glyphs_func | ( | const SlotTextToGlyphs & | text_to_glyphs_func | ) |
Sets the text-to-glyphs conversion function of a user-font.
See SlotTextToGlyphs for details of how the callback works.
The font-face should not be immutable or a CAIRO_STATUS_USER_FONT_IMMUTABLE error will occur. A user font-face is immutable as soon as a scaled-font is created from it.
text_to_glyphs_func | The text_to_glyphs callback. |
void Cairo::UserFontFace::set_unicode_to_glyph_func | ( | const SlotUnicodeToGlyph & | unicode_to_glyph_func | ) |
Sets the unicode-to-glyph conversion function of a user-font.
See SlotUnicodeToGlyph for details of how the callback works.
The font-face should not be immutable or a CAIRO_STATUS_USER_FONT_IMMUTABLE error will occur. A user font-face is immutable as soon as a scaled-font is created from it.
unicode_to_glyph_func | The unicode_to_glyph callback. |