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cairo_scaled_font_t

cairo_scaled_font_t — Font face at particular size and options

Description

cairo_scaled_font_t represents a realization of a font face at a particular size and transformation and a certain set of font options.

Functions

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.

Parameters

font_face

a cairo_font_face_t

 

font_matrix

font space to user space transformation matrix for the font. In the simplest case of a N point font, this matrix is just a scale by N, but it can also be used to shear the font or stretch it unequally along the two axes. See cairo_set_font_matrix().

 

ctm

user to device transformation matrix with which the font will be used.

 

options

options to use when getting metrics for the font and rendering with it.

 

Returns

a newly created cairo_scaled_font_t. Destroy with cairo_scaled_font_destroy()

Since: 1.0


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().

Parameters

scaled_font

a cairo_scaled_font_t, (may be NULL in which case this function does nothing)

 

Returns

the referenced cairo_scaled_font_t

Since: 1.0


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().

Parameters

scaled_font

a cairo_scaled_font_t

 

Since: 1.0


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.

Parameters

scaled_font

a cairo_scaled_font_t

 

Returns

CAIRO_STATUS_SUCCESS or another error such as CAIRO_STATUS_NO_MEMORY.

Since: 1.0


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.

Parameters

scaled_font

a cairo_scaled_font_t

 

extents

a cairo_font_extents_t which to store the retrieved extents.

 

Since: 1.0


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.

Parameters

scaled_font

a cairo_scaled_font_t

 

utf8

a NUL-terminated string of text, encoded in UTF-8

 

extents

a cairo_text_extents_t which to store the retrieved extents.

 

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).

Parameters

scaled_font

a cairo_scaled_font_t

 

glyphs

an array of glyph IDs with X and Y offsets.

 

num_glyphs

the number of glyphs in the glyphs array

 

extents

a cairo_text_extents_t which to store the retrieved extents.

 

Since: 1.0


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.

Parameters

scaled_font

a cairo_scaled_font_t

 

x

X position to place first glyph

 

y

Y position to place first glyph

 

utf8

a string of text encoded in UTF-8

 

utf8_len

length of utf8 in bytes, or -1 if it is NUL-terminated

 

glyphs

pointer to array of glyphs to fill

 

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, or NULL

 

cluster_flags

pointer to location to store cluster flags corresponding to the output clusters , or NULL

 

Returns

CAIRO_STATUS_SUCCESS upon success, or an error status if the input values are wrong or if conversion failed. If the input values are correct but the conversion failed, the error status is also set on scaled_font .

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 might be the font face passed to cairo_scaled_font_create(), but this does not hold true for all possible cases.

Parameters

scaled_font

a cairo_scaled_font_t

 

Returns

The cairo_font_face_t with which scaled_font was created. This object is owned by cairo. To keep a reference to it, you must call cairo_scaled_font_reference().

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 .

Parameters

scaled_font

a cairo_scaled_font_t

 

options

return value for the font 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 .

Parameters

scaled_font

a cairo_scaled_font_t

 

font_matrix

return value for the 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.

Parameters

scaled_font

a cairo_scaled_font_t

 

ctm

return value for the CTM

 

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.

Parameters

scaled_font

a cairo_scaled_font_t

 

scale_matrix

return value for the matrix

 

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.

Parameters

scaled_font

a cairo_scaled_font_t

 

Returns

The type of scaled_font .

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 .

Parameters

scaled_font

a cairo_scaled_font_t

 

Returns

the current reference count of scaled_font . If the object is a nil object, 0 will be returned.

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 .

Parameters

scaled_font

a cairo_scaled_font_t

 

key

the address of a cairo_user_data_key_t to attach the user data to

 

user_data

the user data to attach to the cairo_scaled_font_t

 

destroy

a cairo_destroy_func_t which will be called when the cairo_t is destroyed or when new user data is attached using the same key.

 

Returns

CAIRO_STATUS_SUCCESS or CAIRO_STATUS_NO_MEMORY if a slot could not be allocated for the user 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.

Parameters

scaled_font

a cairo_scaled_font_t

 

key

the address of the cairo_user_data_key_t the user data was attached to

 

Returns

the user data previously attached or NULL.

Since: 1.4

Types and Values

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().

Since: 1.0


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.

Members

double ascent;

the distance that the font extends above the baseline. Note that this is not always exactly equal to the maximum of the extents of all the glyphs in the font, but rather is picked to express the font designer's intent as to how the font should align with elements above it.

 

double descent;

the distance that the font extends below the baseline. This value is positive for typical fonts that include portions below the baseline. Note that this is not always exactly equal to the maximum of the extents of all the glyphs in the font, but rather is picked to express the font designer's intent as to how the font should align with elements below it.

 

double height;

the recommended vertical distance between baselines when setting consecutive lines of text with the font. This is greater than ascent +descent by a quantity known as the line spacing or external leading. When space is at a premium, most fonts can be set with only a distance of ascent +descent between lines.

 

double max_x_advance;

the maximum distance in the X direction that the origin is advanced for any glyph in the font.

 

double max_y_advance;

the maximum distance in the Y direction that the origin is advanced for any glyph in the font. This will be zero for normal fonts used for horizontal writing. (The scripts of East Asia are sometimes written vertically.)

 

Since: 1.0


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.

Members

double x_bearing;

the horizontal distance from the origin to the leftmost part of the glyphs as drawn. Positive if the glyphs lie entirely to the right of the origin.

 

double y_bearing;

the vertical distance from the origin to the topmost part of the glyphs as drawn. Positive only if the glyphs lie completely below the origin; will usually be negative.

 

double width;

width of the glyphs as drawn

 

double height;

height of the glyphs as drawn

 

double x_advance;

distance to advance in the X direction after drawing these glyphs

 

double y_advance;

distance to advance in the Y direction after drawing these glyphs. Will typically be zero except for vertical text layout as found in East-Asian languages.

 

Since: 1.0

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