User Fonts 3 CAIRO Library
User Fonts Font support with font data provided by the user

## Synopsis

    #define             CAIRO_HAS_USER_FONT
    cairo_status_t      (*cairo_user_scaled_font_init_func_t)
                                                            (cairo_scaled_font_t *scaled_font,
                                                             cairo_t *cr,
                                                             cairo_font_extents_t *extents);
    cairo_status_t      (*cairo_user_scaled_font_render_glyph_func_t)
                                                            (cairo_scaled_font_t *scaled_font,
                                                             unsigned long  glyph,
                                                             cairo_t *cr,
                                                             cairo_text_extents_t *extents);
    cairo_status_t      (*cairo_user_scaled_font_text_to_glyphs_func_t)
                                                            (cairo_scaled_font_t *scaled_font,
                                                             const char *utf8,
                                                             int utf8_len,
                                                             cairo_glyph_t **glyphs,
                                                             int *num_glyphs,
                                                             cairo_text_cluster_t **clusters,
                                                             int *num_clusters,
                                                             cairo_text_cluster_flags_t *cluster_flags);
    cairo_status_t      (*cairo_user_scaled_font_unicode_to_glyph_func_t)
                                                            (cairo_scaled_font_t *scaled_font,
                                                             unsigned long  unicode,
                                                             unsigned long *glyph_index);
    cairo_font_face_t * cairo_user_font_face_create         (void);
    void                cairo_user_font_face_set_init_func  (cairo_font_face_t *font_face,
                                                             cairo_user_scaled_font_init_func_t init_func);
    cairo_user_scaled_font_init_func_t cairo_user_font_face_get_init_func
                                                            (cairo_font_face_t *font_face);
    void                cairo_user_font_face_set_render_glyph_func
                                                            (cairo_font_face_t *font_face,
                                                             cairo_user_scaled_font_render_glyph_func_t render_glyph_func);
    cairo_user_scaled_font_render_glyph_func_t cairo_user_font_face_get_render_glyph_func
                                                            (cairo_font_face_t *font_face);
    void                cairo_user_font_face_set_unicode_to_glyph_func
                                                            (cairo_font_face_t *font_face,
                                                             cairo_user_scaled_font_unicode_to_glyph_func_t unicode_to_glyph_func);
    cairo_user_scaled_font_unicode_to_glyph_func_t cairo_user_font_face_get_unicode_to_glyph_func
                                                            (cairo_font_face_t *font_face);
    void                cairo_user_font_face_set_text_to_glyphs_func
                                                            (cairo_font_face_t *font_face,
                                                             cairo_user_scaled_font_text_to_glyphs_func_t text_to_glyphs_func);
    cairo_user_scaled_font_text_to_glyphs_func_t cairo_user_font_face_get_text_to_glyphs_func
                                                            (cairo_font_face_t *font_face);

## Description

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.

## Details

### CAIRO_HAS_USER_FONT

    #define CAIRO_HAS_USER_FONT 1

Defined if the user font backend is available. This macro can be used to conditionally compile backend-specific code. The user font backend is always built in versions of cairo that support this feature (1.8 and later).

Since 1.8

CAIRO_HAS_USER_FONT

### cairo_user_scaled_font_init_func_t ()

    cairo_status_t      (*cairo_user_scaled_font_init_func_t)
                                                            (cairo_scaled_font_t *scaled_font,
                                                             cairo_t *cr,
                                                             cairo_font_extents_t *extents);

cairo_user_scaled_font_init_func_t is the type of function which is called when a scaled-font needs to be created for a user font-face.

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

Returns :

  `CAIRO_STATUS_SUCCESS` upon success, or an error status on error.

Since 1.8

cairo_user_scaled_font_init_func_t

### cairo_user_scaled_font_render_glyph_func_t ()

    cairo_status_t      (*cairo_user_scaled_font_render_glyph_func_t)
                                                            (cairo_scaled_font_t *scaled_font,
                                                             unsigned long  glyph,
                                                             cairo_t *cr,
                                                             cairo_text_extents_t *extents);

cairo_user_scaled_font_render_glyph_func_t is the type of function which is called when a user scaled-font needs to render a glyph.

The callback is mandatory, and expected to draw the glyph with code glyph to the cairo 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 `cairo_mask()` instead of `cairo_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

Returns :

  `CAIRO_STATUS_SUCCESS` upon success, or `CAIRO_STATUS_USER_FONT_ERROR` or any other error status on error.

Since 1.8

cairo_user_scaled_font_render_glyph_func_t

### cairo_user_scaled_font_text_to_glyphs_func_t ()

    cairo_status_t      (*cairo_user_scaled_font_text_to_glyphs_func_t)
                                                            (cairo_scaled_font_t *scaled_font,
                                                             const char *utf8,
                                                             int utf8_len,
                                                             cairo_glyph_t **glyphs,
                                                             int *num_glyphs,
                                                             cairo_text_cluster_t **clusters,
                                                             int *num_clusters,
                                                             cairo_text_cluster_flags_t *cluster_flags);

cairo_user_scaled_font_text_to_glyphs_func_t is the type of function which is called to convert input text to an array of glyphs. This is used by the `cairo_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 shaping required for scripts like Arabic and Indic.

The num_glyphs argument is preset to the number of glyph entries available in the glyphs buffer. If the glyphs buffer is `NULL`, the value of num_glyphs will be zero. If the provided glyph array is too short for the conversion (or for convenience), a new glyph array may be allocated using `cairo_glyph_allocate()` and placed in glyphs. Upon return, num_glyphs should contain the number of generated glyphs. If the value glyphs points at has changed after the call, the caller will free the allocated glyph array using `cairo_glyph_free()`. The caller will also free the original value of glyphs, so the callback shouldn't do so. The callback should populate the glyph indices and positions (in font space) assuming that the text is to be shown at the origin.

If clusters is not `NULL`, num_clusters and cluster_flags are also non-`NULL`, and cluster mapping should be computed. The semantics of how cluster array allocation works is similar to the glyph array. That is, if clusters initially points to a non-`NULL` value, that array may be used as a cluster buffer, and num_clusters points to the number of cluster entries available there. If the provided cluster array is too short for the conversion (or for convenience), a new cluster array may be allocated using `cairo_text_cluster_allocate()` and placed in clusters. In this case, the original value of clusters will still be freed by the caller. Upon return, num_clusters should contain the number of generated clusters. If the value clusters points at has changed after the call, the caller will free the allocated cluster array using `cairo_text_cluster_free()`.

The callback is optional. If num_glyphs is negative upon the callback returning or if the return value is `CAIRO_STATUS_USER_FONT_NOT_IMPLEMENTED`, the unicode_to_glyph callback is tried. See cairo_user_scaled_font_unicode_to_glyph_func_t.

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

utf8 :

  a string of text encoded in UTF-8

utf8_len :

  length of utf8 in bytes

glyphs :

  pointer to array of glyphs to fill, in font space

num_glyphs :

  pointer to number of glyphs

clusters :

  pointer to array of cluster mapping information to fill, or `NULL`

num_clusters :

  pointer to number of clusters

cluster_flags :

  pointer to location to store cluster flags corresponding to the output clusters

Returns :

  `CAIRO_STATUS_SUCCESS` upon success, `CAIRO_STATUS_USER_FONT_NOT_IMPLEMENTED` if fallback options should be tried, or `CAIRO_STATUS_USER_FONT_ERROR` or any other error status on error.

Since 1.8

cairo_user_scaled_font_text_to_glyphs_func_t

### cairo_user_scaled_font_unicode_to_glyph_func_t ()

    cairo_status_t      (*cairo_user_scaled_font_unicode_to_glyph_func_t)
                                                            (cairo_scaled_font_t *scaled_font,
                                                             unsigned long  unicode,
                                                             unsigned long *glyph_index);

cairo_user_scaled_font_unicode_to_glyph_func_t is the type of function which is called to convert an input Unicode character to a single glyph. This is used by the `cairo_show_text()` operation.

This callback is used to provide the same functionality as the text_to_glyphs callback does (see cairo_user_scaled_font_text_to_glyphs_func_t) 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 or if it returns `CAIRO_STATUS_USER_FONT_NOT_IMPLEMENTED`, 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

Returns :

  `CAIRO_STATUS_SUCCESS` upon success, `CAIRO_STATUS_USER_FONT_NOT_IMPLEMENTED` if fallback options should be tried, or `CAIRO_STATUS_USER_FONT_ERROR` or any other error status on error.

Since 1.8

cairo_user_scaled_font_unicode_to_glyph_func_t

### cairo_user_font_face_create ()

    cairo_font_face_t * cairo_user_font_face_create         (void);

Creates a new user font-face.

Use the setter functions to associate callbacks with the returned user font. The only mandatory callback is render_glyph.

After the font-face is created, the user can attach arbitrary data (the actual font data) to it using `cairo_font_face_set_user_data()` and access it from the user-font callbacks by using `cairo_scaled_font_get_font_face()` followed by `cairo_font_face_get_user_data()`.

Returns :

  a newly created cairo_font_face_t. Free with `cairo_font_face_destroy()` when you are done using it.

Since 1.8

cairo_user_font_face_create

### cairo_user_font_face_set_init_func ()

    void                cairo_user_font_face_set_init_func  (cairo_font_face_t *font_face,
                                                             cairo_user_scaled_font_init_func_t init_func);

Sets the scaled-font initialization function of a user-font. See cairo_user_scaled_font_init_func_t 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.

font_face :

  A user font face

init_func :

  The init callback, or `NULL`

Since 1.8

cairo_user_font_face_set_init_func

### cairo_user_font_face_get_init_func ()

    cairo_user_scaled_font_init_func_t cairo_user_font_face_get_init_func
                                                            (cairo_font_face_t *font_face);

Gets the scaled-font initialization function of a user-font.

font_face :

  A user font face

Returns :

  The init callback of font_face or `NULL` if none set or an error has occurred.

Since 1.8

cairo_user_font_face_get_init_func

### cairo_user_font_face_set_render_glyph_func ()

    void                cairo_user_font_face_set_render_glyph_func
                                                            (cairo_font_face_t *font_face,
                                                             cairo_user_scaled_font_render_glyph_func_t render_glyph_func);

Sets the glyph rendering function of a user-font. See cairo_user_scaled_font_render_glyph_func_t 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 font_face, a `CAIRO_STATUS_USER_FONT_ERROR` will occur.

font_face :

  A user font face

render_glyph_func :

  The render_glyph callback, or `NULL`

Since 1.8

cairo_user_font_face_set_render_glyph_func

### cairo_user_font_face_get_render_glyph_func ()

    cairo_user_scaled_font_render_glyph_func_t cairo_user_font_face_get_render_glyph_func
                                                            (cairo_font_face_t *font_face);

Gets the glyph rendering function of a user-font.

font_face :

  A user font face

Returns :

  The render_glyph callback of font_face or `NULL` if none set or an error has occurred.

Since 1.8

cairo_user_font_face_get_render_glyph_func

### cairo_user_font_face_set_unicode_to_glyph_func ()

    void                cairo_user_font_face_set_unicode_to_glyph_func
                                                            (cairo_font_face_t *font_face,
                                                             cairo_user_scaled_font_unicode_to_glyph_func_t unicode_to_glyph_func);

Sets the unicode-to-glyph conversion function of a user-font. See cairo_user_scaled_font_unicode_to_glyph_func_t 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.

font_face :

  A user font face

unicode_to_glyph_func :

  The unicode_to_glyph callback, or `NULL`

Since 1.8

cairo_user_font_face_set_unicode_to_glyph_func

### cairo_user_font_face_get_unicode_to_glyph_func ()

    cairo_user_scaled_font_unicode_to_glyph_func_t cairo_user_font_face_get_unicode_to_glyph_func
                                                            (cairo_font_face_t *font_face);

Gets the unicode-to-glyph conversion function of a user-font.

font_face :

  A user font face

Returns :

  The unicode_to_glyph callback of font_face or `NULL` if none set or an error occurred.

Since 1.8

cairo_user_font_face_get_unicode_to_glyph_func

### cairo_user_font_face_set_text_to_glyphs_func ()

    void                cairo_user_font_face_set_text_to_glyphs_func
                                                            (cairo_font_face_t *font_face,
                                                             cairo_user_scaled_font_text_to_glyphs_func_t text_to_glyphs_func);

Sets th text-to-glyphs conversion function of a user-font. See cairo_user_scaled_font_text_to_glyphs_func_t 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.

font_face :

  A user font face

text_to_glyphs_func :

  The text_to_glyphs callback, or `NULL`

Since 1.8

cairo_user_font_face_set_text_to_glyphs_func

### cairo_user_font_face_get_text_to_glyphs_func ()

    cairo_user_scaled_font_text_to_glyphs_func_t cairo_user_font_face_get_text_to_glyphs_func
                                                            (cairo_font_face_t *font_face);

Gets the text-to-glyphs conversion function of a user-font.

font_face :

  A user font face

Returns :

  The text_to_glyphs callback of font_face or `NULL` if none set or an error occurred.

Since 1.8

cairo_user_font_face_get_text_to_glyphs_func