cairo_glyph_t

typedef struct {
    unsigned long        index;
    double               x;
    double               y;
} cairo_glyph_t;

The cairo_glyph_t structure holds information about a single glyph when drawing or measuring text. A font is (in simple terms) a collection of shapes used to draw text. A glyph is one of these shapes. There can be multiple glyphs for a single character (alternates to be used in different contexts, for example), or a glyph can be a ligature of multiple characters. Cairo doesn't expose any way of converting input text into glyphs, so in order to use the Cairo interfaces that take arrays of glyphs, you must directly access the appropriate underlying font system.

Note that the offsets given by x and y are not cumulative. When drawing or measuring text, each glyph is individually positioned with respect to the overall origin

enum cairo_font_slant_t

typedef enum _cairo_font_slant {
    CAIRO_FONT_SLANT_NORMAL,
    CAIRO_FONT_SLANT_ITALIC,
    CAIRO_FONT_SLANT_OBLIQUE
} cairo_font_slant_t;

Specifies variants of a font face based on their slant.

enum cairo_font_weight_t

typedef enum _cairo_font_weight {
    CAIRO_FONT_WEIGHT_NORMAL,
    CAIRO_FONT_WEIGHT_BOLD
} cairo_font_weight_t;

Specifies variants of a font face based on their weight.

cairo_text_cluster_t

typedef struct {
    int        num_bytes;
    int        num_glyphs;
} cairo_text_cluster_t;

The cairo_text_cluster_t structure holds information about a single text cluster. A text cluster is a minimal mapping of some glyphs corresponding to some UTF-8 text.

For a cluster to be valid, both num_bytes and num_glyphs should be non-negative, and at least one should be non-zero. Note that clusters with zero glyphs are not as well supported as normal clusters. For example, PDF rendering applications typically ignore those clusters when PDF text is being selected.

See cairo_show_text_glyphs() for how clusters are used in advanced text operations.

Since 1.8

enum cairo_text_cluster_flags_t

typedef enum _cairo_text_cluster_flags {
    CAIRO_TEXT_CLUSTER_FLAG_BACKWARD = 0x00000001
} cairo_text_cluster_flags_t;

Specifies properties of a text cluster mapping.

Since 1.8

cairo_select_font_face ()

void                cairo_select_font_face              (cairo_t *cr,
                                                         const char *family,
                                                         cairo_font_slant_t slant,
                                                         cairo_font_weight_t weight);

Note: The cairo_select_font_face() function call is part of what the cairo designers call the "toy" text API. It is convenient for short demos and simple programs, but it is not expected to be adequate for serious text-using applications.

Selects a family and style of font from a simplified description as a family name, slant and weight. Cairo provides no operation to list available family names on the system (this is a "toy", remember), but the standard CSS2 generic family names, ("serif", "sans-serif", "cursive", "fantasy", "monospace"), are likely to work as expected.

If family starts with the string "cairo:", or if no native font backends are compiled in, cairo will use an internal font family. The internal font family recognizes many modifiers in the family string, most notably, it recognizes the string "monospace". That is, the family name "cairo:monospace" will use the monospace version of the internal font family.

For "real" font selection, see the font-backend-specific font_face_create functions for the font backend you are using. (For example, if you are using the freetype-based cairo-ft font backend, see cairo_ft_font_face_create_for_ft_face() or cairo_ft_font_face_create_for_pattern().) The resulting font face could then be used with cairo_scaled_font_create() and cairo_set_scaled_font().

Similarly, when using the "real" font support, you can call directly into the underlying font system, (such as fontconfig or freetype), for operations such as listing available fonts, etc.

It is expected that most applications will need to use a more comprehensive font handling and text layout library, (for example, pango), in conjunction with cairo.

If text is drawn without a call to cairo_select_font_face(), (nor cairo_set_font_face() nor cairo_set_scaled_font()), the default family is platform-specific, but is essentially "sans-serif". Default slant is CAIRO_FONT_SLANT_NORMAL, and default weight is CAIRO_FONT_WEIGHT_NORMAL.

This function is equivalent to a call to cairo_toy_font_face_create() followed by cairo_set_font_face().

cairo_set_font_size ()

void                cairo_set_font_size                 (cairo_t *cr,
                                                         double size);

Sets the current font matrix to a scale by a factor of size, replacing any font matrix previously set with cairo_set_font_size() or cairo_set_font_matrix(). This results in a font size of size user space units. (More precisely, this matrix will result in the font's em-square being a size by size square in user space.)

If text is drawn without a call to cairo_set_font_size(), (nor cairo_set_font_matrix() nor cairo_set_scaled_font()), the default font size is 10.0.

cairo_set_font_matrix ()

void                cairo_set_font_matrix               (cairo_t *cr,
                                                         const cairo_matrix_t *matrix);

Sets the current font matrix to matrix. The font matrix gives a transformation from the design space of the font (in this space, the em-square is 1 unit by 1 unit) to user space. Normally, a simple scale is used (see cairo_set_font_size()), but a more complex font matrix can be used to shear the font or stretch it unequally along the two axes

cairo_get_font_matrix ()

void                cairo_get_font_matrix               (cairo_t *cr,
                                                         cairo_matrix_t *matrix);

Stores the current font matrix into matrix. See cairo_set_font_matrix().

cairo_set_font_options ()

void                cairo_set_font_options              (cairo_t *cr,
                                                         const cairo_font_options_t *options);

Sets a set of custom font rendering options for the cairo_t. Rendering options are derived by merging these options with the options derived from underlying surface; if the value in options has a default value (like CAIRO_ANTIALIAS_DEFAULT), then the value from the surface is used.

cairo_get_font_options ()

void                cairo_get_font_options              (cairo_t *cr,
                                                         cairo_font_options_t *options);

Retrieves font rendering options set via cairo_set_font_options. Note that the returned options do not include any options derived from the underlying surface; they are literally the options passed to cairo_set_font_options().

cairo_set_font_face ()

void                cairo_set_font_face                 (cairo_t *cr,
                                                         cairo_font_face_t *font_face);

Replaces the current cairo_font_face_t object in the cairo_t with font_face. The replaced font face in the cairo_t will be destroyed if there are no other references to it.

cairo_get_font_face ()

cairo_font_face_t * cairo_get_font_face                 (cairo_t *cr);

Gets the current font face for a cairo_t.

cairo_set_scaled_font ()

void                cairo_set_scaled_font               (cairo_t *cr,
                                                         const cairo_scaled_font_t *scaled_font);

Replaces the current font face, font matrix, and font options in the cairo_t with those of the cairo_scaled_font_t. Except for some translation, the current CTM of the cairo_t should be the same as that of the cairo_scaled_font_t, which can be accessed using cairo_scaled_font_get_ctm().

Since 1.2

cairo_get_scaled_font ()

cairo_scaled_font_t * cairo_get_scaled_font             (cairo_t *cr);

Gets the current scaled font for a cairo_t.

Since 1.4

cairo_show_text ()

void                cairo_show_text                     (cairo_t *cr,
                                                         const char *utf8);

A drawing operator that generates the shape from a string of UTF-8 characters, rendered according to the current font_face, font_size (font_matrix), and font_options.

This function first computes a set of glyphs for the string of text. The first glyph is placed so that its origin is at the current point. The origin of each subsequent glyph is offset from that of the previous glyph by the advance values of the previous glyph.

After this call the current point is moved to the origin of where the next glyph would be placed in this same progression. That is, the current point will be at the origin of the final glyph offset by its advance values. This allows for easy display of a single logical string with multiple calls to cairo_show_text().

Note: The cairo_show_text() function call is part of what the cairo designers call the "toy" text API. It is convenient for short demos and simple programs, but it is not expected to be adequate for serious text-using applications. See cairo_show_glyphs() for the "real" text display API in cairo.

cairo_show_glyphs ()

void                cairo_show_glyphs                   (cairo_t *cr,
                                                         const cairo_glyph_t *glyphs,
                                                         int num_glyphs);

A drawing operator that generates the shape from an array of glyphs, rendered according to the current font face, font size (font matrix), and font options.

cairo_show_text_glyphs ()

void                cairo_show_text_glyphs              (cairo_t *cr,
                                                         const char *utf8,
                                                         int utf8_len,
                                                         const cairo_glyph_t *glyphs,
                                                         int num_glyphs,
                                                         const cairo_text_cluster_t *clusters,
                                                         int num_clusters,
                                                         cairo_text_cluster_flags_t cluster_flags);

This operation has rendering effects similar to cairo_show_glyphs() but, if the target surface supports it, uses the provided text and cluster mapping to embed the text for the glyphs shown in the output. If the target does not support the extended attributes, this function acts like the basic cairo_show_glyphs() as if it had been passed glyphs and num_glyphs.

The mapping between utf8 and glyphs is provided by an array of clusters. Each cluster covers a number of text bytes and glyphs, and neighboring clusters cover neighboring areas of utf8 and glyphs. The clusters should collectively cover utf8 and glyphs in entirety.

The first cluster always covers bytes from the beginning of utf8. If cluster_flags do not have the CAIRO_TEXT_CLUSTER_FLAG_BACKWARD set, the first cluster also covers the beginning of glyphs, otherwise it covers the end of the glyphs array and following clusters move backward.

See cairo_text_cluster_t for constraints on valid clusters.

Since 1.8

cairo_font_extents ()

void                cairo_font_extents                  (cairo_t *cr,
                                                         cairo_font_extents_t *extents);

Gets the font extents for the currently selected font.

cairo_text_extents ()

void                cairo_text_extents                  (cairo_t *cr,
                                                         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, (as it would be drawn by cairo_show_text()). 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.

cairo_glyph_extents ()

void                cairo_glyph_extents                 (cairo_t *cr,
                                                         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()). 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_toy_font_face_create ()

cairo_font_face_t * cairo_toy_font_face_create          (const char *family,
                                                         cairo_font_slant_t slant,
                                                         cairo_font_weight_t weight);

Creates a font face from a triplet of family, slant, and weight. These font faces are used in implementation of the the cairo_t "toy" font API.

If family is the zero-length string "", the platform-specific default family is assumed. The default family then can be queried using cairo_toy_font_face_get_family().

The cairo_select_font_face() function uses this to create font faces. See that function for limitations and other details of toy font faces.

Since 1.8

cairo_toy_font_face_get_family ()

const char *        cairo_toy_font_face_get_family      (cairo_font_face_t *font_face);

Gets the familly name of a toy font.

Since 1.8

cairo_toy_font_face_get_slant ()

cairo_font_slant_t  cairo_toy_font_face_get_slant       (cairo_font_face_t *font_face);

Gets the slant a toy font.

Since 1.8

cairo_toy_font_face_get_weight ()

cairo_font_weight_t  cairo_toy_font_face_get_weight     (cairo_font_face_t *font_face);

Gets the weight a toy font.

Since 1.8

cairo_glyph_allocate ()

cairo_glyph_t *     cairo_glyph_allocate                (int num_glyphs);

Allocates an array of cairo_glyph_t's. This function is only useful in implementations of cairo_user_scaled_font_text_to_glyphs_func_t where the user needs to allocate an array of glyphs that cairo will free. For all other uses, user can use their own allocation method for glyphs.

This function returns NULL if num_glyphs is not positive, or if out of memory. That means, the NULL return value signals out-of-memory only if num_glyphs was positive.

Since 1.8

cairo_glyph_free ()

void                cairo_glyph_free                    (cairo_glyph_t *glyphs);

Frees an array of cairo_glyph_t's allocated using cairo_glyph_allocate(). This function is only useful to free glyph array returned by cairo_scaled_font_text_to_glyphs() where cairo returns an array of glyphs that the user will free. For all other uses, user can use their own allocation method for glyphs.

Since 1.8

cairo_text_cluster_allocate ()

cairo_text_cluster_t * cairo_text_cluster_allocate      (int num_clusters);

Allocates an array of cairo_text_cluster_t's. This function is only useful in implementations of cairo_user_scaled_font_text_to_glyphs_func_t where the user needs to allocate an array of text clusters that cairo will free. For all other uses, user can use their own allocation method for text clusters.

This function returns NULL if num_clusters is not positive, or if out of memory. That means, the NULL return value signals out-of-memory only if num_clusters was positive.

Since 1.8

cairo_text_cluster_free ()

void                cairo_text_cluster_free             (cairo_text_cluster_t *clusters);

Frees an array of cairo_text_cluster's allocated using cairo_text_cluster_allocate(). This function is only useful to free text cluster array returned by cairo_scaled_font_text_to_glyphs() where cairo returns an array of text clusters that the user will free. For all other uses, user can use their own allocation method for text clusters.

Since 1.8