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.

Since: 1.8

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, when this callback is set with cairo_user_font_face_set_render_glyph_func(), 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().

When this callback is set with cairo_user_font_face_set_render_color_glyph_func(), the default source is black. Setting the source is a valid operation. cairo_user_scaled_font_get_foreground_marker() or cairo_user_scaled_font_get_foreground_source() may be called to obtain the current source at the time the glyph is rendered.

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.

Where both color and non-color callbacks has been set using cairo_user_font_face_set_render_color_glyph_func(), and cairo_user_font_face_set_render_glyph_func(), the color glyph callback will be called first. If the color glyph callback returns CAIRO_STATUS_USER_FONT_NOT_IMPLEMENTED, any drawing operations are discarded and the non-color callback will be called. This is the only case in which the CAIRO_STATUS_USER_FONT_NOT_IMPLEMENTED may be returned from a render callback. This fallback sequence allows a user font face to contain a combination of both color and non-color glyphs.

Since: 1.8

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.

Since: 1.8

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.

Since: 1.8

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.

Since: 1.8

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.

Since: 1.8

cairo_user_font_face_get_render_color_glyph_func ()

cairo_user_scaled_font_render_glyph_func_t
cairo_user_font_face_get_render_color_glyph_func
                               (cairo_font_face_t *font_face);

Gets the color glyph rendering function of a user-font.

Since: 1.18

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.

Since: 1.8

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.

Since: 1.8

cairo_user_scaled_font_get_foreground_marker ()

cairo_pattern_t *
cairo_user_scaled_font_get_foreground_marker
                               (cairo_scaled_font_t *scaled_font);

Gets the foreground pattern of the glyph currently being rendered. A cairo_user_scaled_font_render_glyph_func_t function that has been set with cairo_user_font_face_set_render_color_glyph_func() may call this function to retrieve the current foreground pattern for the glyph being rendered. The function should not be called outside of a cairo_user_font_face_set_render_color_glyph_func() callback.

The foreground marker pattern contains an internal marker to indicate that it is to be substituted with the current source when rendered to a surface. Querying the foreground marker will reveal a solid black color, however this is not representative of the color that will actually be used. Similarly, setting a solid black color will render black, not the foreground pattern when the glyph is painted to a surface. Using the foreground marker as the source instead of cairo_user_scaled_font_get_foreground_source() in a color render callback has the following benefits:

The one drawback of the using foreground marker is the render callback can not access the color components of the pattern as the actual foreground pattern is not available at the time the render callback is invoked. If the render callback needs to query the foreground pattern, use cairo_user_scaled_font_get_foreground_source().

If the render callback simply wants to call cairo_set_source() with the foreground pattern, cairo_user_scaled_font_get_foreground_marker() is the preferred function to use as it results in better performance than cairo_user_scaled_font_get_foreground_source().

Since: 1.18

cairo_user_scaled_font_get_foreground_source ()

cairo_pattern_t *
cairo_user_scaled_font_get_foreground_source
                               (cairo_scaled_font_t *scaled_font);

Gets the foreground pattern of the glyph currently being rendered. A cairo_user_scaled_font_render_glyph_func_t function that has been set with cairo_user_font_face_set_render_color_glyph_func() may call this function to retrieve the current foreground pattern for the glyph being rendered. The function should not be called outside of a cairo_user_font_face_set_render_color_glyph_func() callback.

This function returns the current source at the time the glyph is rendered. Compared with cairo_user_scaled_font_get_foreground_marker(), this function returns the actual source pattern that will be used to render the glyph. The render callback is free to query the pattern and extract color components or other pattern data. For example if the render callback wants to create a gradient stop based on colors in the foreground source pattern, it will need to use this function in order to be able to query the colors in the foreground pattern.

While this function does not have the restrictions on using the pattern that cairo_user_scaled_font_get_foreground_marker() has, it does incur a performance penalty. If a render callback calls this function:

Since: 1.18

CAIRO_HAS_USER_FONT

#define CAIRO_HAS_USER_FONT

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