cairo_scaled_font_t

typedef struct _cairo_scaled_font cairo_scaled_font_t;

A cairo_scaled_font_t is a font scaled to a particular size and device resolution. A cairo_scaled_font_t is most useful for low-level font usage where a library or application wants to cache a reference to a scaled font to speed up the computation of metrics.

There are various types of scaled fonts, depending on the font backend they use. The type of a scaled font can be queried using cairo_scaled_font_get_type().

Memory management of cairo_scaled_font_t is done with cairo_scaled_font_reference() and cairo_scaled_font_destroy().

cairo_scaled_font_create ()

cairo_scaled_font_t * cairo_scaled_font_create          (cairo_font_face_t *font_face,
                                                         const cairo_matrix_t *font_matrix,
                                                         const cairo_matrix_t *ctm,
                                                         const cairo_font_options_t *options);

Creates a cairo_scaled_font_t object from a font face and matrices that describe the size of the font and the environment in which it will be used.

cairo_scaled_font_reference ()

cairo_scaled_font_t * cairo_scaled_font_reference       (cairo_scaled_font_t *scaled_font);

Increases the reference count on scaled_font by one. This prevents scaled_font from being destroyed until a matching call to cairo_scaled_font_destroy() is made.

The number of references to a cairo_scaled_font_t can be get using cairo_scaled_font_get_reference_count().

cairo_scaled_font_destroy ()

void                cairo_scaled_font_destroy           (cairo_scaled_font_t *scaled_font);

Decreases the reference count on font by one. If the result is zero, then font and all associated resources are freed. See cairo_scaled_font_reference().

cairo_scaled_font_status ()

cairo_status_t      cairo_scaled_font_status            (cairo_scaled_font_t *scaled_font);

Checks whether an error has previously occurred for this scaled_font.

cairo_font_extents_t

typedef struct {
    double ascent;
    double descent;
    double height;
    double max_x_advance;
    double max_y_advance;
} cairo_font_extents_t;

The cairo_font_extents_t structure stores metric information for a font. Values are given in the current user-space coordinate system.

Because font metrics are in user-space coordinates, they are mostly, but not entirely, independent of the current transformation matrix. If you call cairo_scale(cr, 2.0, 2.0), text will be drawn twice as big, but the reported text extents will not be doubled. They will change slightly due to hinting (so you can't assume that metrics are independent of the transformation matrix), but otherwise will remain unchanged.

cairo_scaled_font_extents ()

void                cairo_scaled_font_extents           (cairo_scaled_font_t *scaled_font,
                                                         cairo_font_extents_t *extents);

Gets the metrics for a cairo_scaled_font_t.

cairo_text_extents_t

typedef struct {
    double x_bearing;
    double y_bearing;
    double width;
    double height;
    double x_advance;
    double y_advance;
} cairo_text_extents_t;

The cairo_text_extents_t structure stores the extents of a single glyph or a string of glyphs in user-space coordinates. Because text extents are in user-space coordinates, they are mostly, but not entirely, independent of the current transformation matrix. If you call cairo_scale(cr, 2.0, 2.0), text will be drawn twice as big, but the reported text extents will not be doubled. They will change slightly due to hinting (so you can't assume that metrics are independent of the transformation matrix), but otherwise will remain unchanged.

cairo_scaled_font_text_extents ()

void                cairo_scaled_font_text_extents      (cairo_scaled_font_t *scaled_font,
                                                         const char *utf8,
                                                         cairo_text_extents_t *extents);

Gets the extents for a string of text. The extents describe a user-space rectangle that encloses the "inked" portion of the text drawn at the origin (0,0) (as it would be drawn by cairo_show_text() if the cairo graphics state were set to the same font_face, font_matrix, ctm, and font_options as scaled_font). Additionally, the x_advance and y_advance values indicate the amount by which the current point would be advanced by cairo_show_text().

Note that whitespace characters do not directly contribute to the size of the rectangle (extents.width and extents.height). They do contribute indirectly by changing the position of non-whitespace characters. In particular, trailing whitespace characters are likely to not affect the size of the rectangle, though they will affect the x_advance and y_advance values.

Since 1.2

cairo_scaled_font_glyph_extents ()

void                cairo_scaled_font_glyph_extents     (cairo_scaled_font_t *scaled_font,
                                                         const cairo_glyph_t *glyphs,
                                                         int num_glyphs,
                                                         cairo_text_extents_t *extents);

Gets the extents for an array of glyphs. The extents describe a user-space rectangle that encloses the "inked" portion of the glyphs, (as they would be drawn by cairo_show_glyphs() if the cairo graphics state were set to the same font_face, font_matrix, ctm, and font_options as scaled_font). Additionally, the x_advance and y_advance values indicate the amount by which the current point would be advanced by cairo_show_glyphs().

Note that whitespace glyphs do not contribute to the size of the rectangle (extents.width and extents.height).

cairo_scaled_font_text_to_glyphs ()

cairo_status_t      cairo_scaled_font_text_to_glyphs    (cairo_scaled_font_t *scaled_font,
                                                         double x,
                                                         double y,
                                                         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);

Converts UTF-8 text to an array of glyphs, optionally with cluster mapping, that can be used to render later using scaled_font.

If glyphs initially points to a non-NULL value, that array is used as a glyph buffer, and num_glyphs should point to the number of glyph entries available there. If the provided glyph array is too short for the conversion, a new glyph array is allocated using cairo_glyph_allocate() and placed in glyphs. Upon return, num_glyphs always contains the number of generated glyphs. If the value glyphs points to has changed after the call, the user is responsible for freeing the allocated glyph array using cairo_glyph_free(). This may happen even if the provided array was large enough.

If clusters is not NULL, num_clusters and cluster_flags should not be NULL, and cluster mapping will 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 is used as a cluster buffer, and num_clusters should point to the number of cluster entries available there. If the provided cluster array is too short for the conversion, a new cluster array is allocated using cairo_text_cluster_allocate() and placed in clusters. Upon return, num_clusters always contains the number of generated clusters. If the value clusters points at has changed after the call, the user is responsible for freeing the allocated cluster array using cairo_text_cluster_free(). This may happen even if the provided array was large enough.

In the simplest case, glyphs and clusters can point to NULL initially and a suitable array will be allocated. In code:

cairo_status_t status;

cairo_glyph_t *glyphs = NULL;
int num_glyphs;
cairo_text_cluster_t *clusters = NULL;
int num_clusters;
cairo_text_cluster_flags_t cluster_flags;

status = cairo_scaled_font_text_to_glyphs (scaled_font,
                                           x, y,
                                           utf8, utf8_len,
                                           &glyphs, &num_glyphs,
                                           &clusters, &num_clusters, &cluster_flags);

if (status == CAIRO_STATUS_SUCCESS) {
    cairo_show_text_glyphs (cr,
                            utf8, utf8_len,
                            glyphs, num_glyphs,
                            clusters, num_clusters, cluster_flags);

    cairo_glyph_free (glyphs);
    cairo_text_cluster_free (clusters);
}

If no cluster mapping is needed:

cairo_status_t status;

cairo_glyph_t *glyphs = NULL;
int num_glyphs;

status = cairo_scaled_font_text_to_glyphs (scaled_font,
                                           x, y,
                                           utf8, utf8_len,
                                           &glyphs, &num_glyphs,
                                           NULL, NULL,
                                           NULL);

if (status == CAIRO_STATUS_SUCCESS) {
    cairo_show_glyphs (cr, glyphs, num_glyphs);
    cairo_glyph_free (glyphs);
}

If stack-based glyph and cluster arrays are to be used for small arrays:

cairo_status_t status;

cairo_glyph_t stack_glyphs[40];
cairo_glyph_t *glyphs = stack_glyphs;
int num_glyphs = sizeof (stack_glyphs) / sizeof (stack_glyphs[0]);
cairo_text_cluster_t stack_clusters[40];
cairo_text_cluster_t *clusters = stack_clusters;
int num_clusters = sizeof (stack_clusters) / sizeof (stack_clusters[0]);
cairo_text_cluster_flags_t cluster_flags;

status = cairo_scaled_font_text_to_glyphs (scaled_font,
                                           x, y,
                                           utf8, utf8_len,
                                           &glyphs, &num_glyphs,
                                           &clusters, &num_clusters, &cluster_flags);

if (status == CAIRO_STATUS_SUCCESS) {
    cairo_show_text_glyphs (cr,
                            utf8, utf8_len,
                            glyphs, num_glyphs,
                            clusters, num_clusters, cluster_flags);

    if (glyphs != stack_glyphs)
        cairo_glyph_free (glyphs);
    if (clusters != stack_clusters)
        cairo_text_cluster_free (clusters);
}

For details of how clusters, num_clusters, and cluster_flags map input UTF-8 text to the output glyphs see cairo_show_text_glyphs().

The output values can be readily passed to cairo_show_text_glyphs() cairo_show_glyphs(), or related functions, assuming that the exact same scaled_font is used for the operation.

Since 1.8

cairo_scaled_font_get_font_face ()

cairo_font_face_t * cairo_scaled_font_get_font_face     (cairo_scaled_font_t *scaled_font);

Gets the font face that this scaled font uses. This is the font face passed to cairo_scaled_font_create().

Since 1.2

cairo_scaled_font_get_font_options ()

void                cairo_scaled_font_get_font_options  (cairo_scaled_font_t *scaled_font,
                                                         cairo_font_options_t *options);

Stores the font options with which scaled_font was created into options.

Since 1.2

cairo_scaled_font_get_font_matrix ()

void                cairo_scaled_font_get_font_matrix   (cairo_scaled_font_t *scaled_font,
                                                         cairo_matrix_t *font_matrix);

Stores the font matrix with which scaled_font was created into matrix.

Since 1.2

cairo_scaled_font_get_ctm ()

void                cairo_scaled_font_get_ctm           (cairo_scaled_font_t *scaled_font,
                                                         cairo_matrix_t *ctm);

Stores the CTM with which scaled_font was created into ctm. Note that the translation offsets (x0, y0) of the CTM are ignored by cairo_scaled_font_create(). So, the matrix this function returns always has 0,0 as x0,y0.

Since 1.2

cairo_scaled_font_get_scale_matrix ()

void                cairo_scaled_font_get_scale_matrix  (cairo_scaled_font_t *scaled_font,
                                                         cairo_matrix_t *scale_matrix);

Stores the scale matrix of scaled_font into matrix. The scale matrix is product of the font matrix and the ctm associated with the scaled font, and hence is the matrix mapping from font space to device space.

Since 1.8

cairo_scaled_font_get_type ()

cairo_font_type_t   cairo_scaled_font_get_type          (cairo_scaled_font_t *scaled_font);

This function returns the type of the backend used to create a scaled font. See cairo_font_type_t for available types. However, this function never returns CAIRO_FONT_TYPE_TOY.

Since 1.2

cairo_scaled_font_get_reference_count ()

unsigned int        cairo_scaled_font_get_reference_count
                                                        (cairo_scaled_font_t *scaled_font);

Returns the current reference count of scaled_font.

Since 1.4

cairo_scaled_font_set_user_data ()

cairo_status_t      cairo_scaled_font_set_user_data     (cairo_scaled_font_t *scaled_font,
                                                         const cairo_user_data_key_t *key,
                                                         void *user_data,
                                                         cairo_destroy_func_t destroy);

Attach user data to scaled_font. To remove user data from a surface, call this function with the key that was used to set it and NULL for data.

Since 1.4

cairo_scaled_font_get_user_data ()

void *              cairo_scaled_font_get_user_data     (cairo_scaled_font_t *scaled_font,
                                                         const cairo_user_data_key_t *key);

Return user data previously attached to scaled_font using the specified key. If no user data has been attached with the given key this function returns NULL.

Since 1.4