Functions
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, 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.
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.
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_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.
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_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.
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_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.
Returns
The text_to_glyphs callback of font_face
or NULL if none set or an error occurred.
Since: 1.8