Scaled Fonts

Scaled Fonts — Caching metrics for a particular font size

Synopsis

typedef             cairo_scaled_font_t;
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);
cairo_scaled_font_t* cairo_scaled_font_reference        (cairo_scaled_font_t *scaled_font);
void                cairo_scaled_font_destroy           (cairo_scaled_font_t *scaled_font);
cairo_status_t      cairo_scaled_font_status            (cairo_scaled_font_t *scaled_font);
                    cairo_font_extents_t;
void                cairo_scaled_font_extents           (cairo_scaled_font_t *scaled_font,
                                                         cairo_font_extents_t *extents);
                    cairo_text_extents_t;
void                cairo_scaled_font_text_extents      (cairo_scaled_font_t *scaled_font,
                                                         const char *utf8,
                                                         cairo_text_extents_t *extents);
void                cairo_scaled_font_glyph_extents     (cairo_scaled_font_t *scaled_font,
                                                         cairo_glyph_t *glyphs,
                                                         int num_glyphs,
                                                         cairo_text_extents_t *extents);
cairo_font_face_t*  cairo_scaled_font_get_font_face     (cairo_scaled_font_t *scaled_font);
void                cairo_scaled_font_get_font_options  (cairo_scaled_font_t *scaled_font,
                                                         cairo_font_options_t *options);
void                cairo_scaled_font_get_font_matrix   (cairo_scaled_font_t *scaled_font,
                                                         cairo_matrix_t *font_matrix);
void                cairo_scaled_font_get_ctm           (cairo_scaled_font_t *scaled_font,
                                                         cairo_matrix_t *ctm);
cairo_font_type_t   cairo_scaled_font_get_type          (cairo_scaled_font_t *scaled_font);

Description

Details

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.

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.

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()

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.

scaled_font :

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

Returns :

 the referenced cairo_scaled_font_t

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().

scaled_font :

 a cairo_scaled_font_t

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.

scaled_font :

 a cairo_scaled_font_t

Returns :

 CAIRO_STATUS_SUCCESS or another error such as CAIRO_STATUS_NO_MEMORY.

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_text_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.

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 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 the origin is advanced for any glyph in the font.

double max_y_advance;

 the maximum distance in the Y direction that the 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.)

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.

scaled_font :

 a cairo_scaled_font_t

extents :

 a cairo_font_extents_t which to store the retrieved extents.

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.

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.

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.

scaled_font :

 a cairo_scaled_font_t

utf8 :

 a 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,
                                                         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).

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.

cairo_scaled_font_get_font_face ()

cairo_font_face_t*  cairo_scaled_font_get_font_face     (cairo_scaled_font_t *scaled_font);

scaled_font :

 a cairo_scaled_font_t

Returns :

 The cairo_font_face_t with which scaled_font was created.

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 ctm.

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.

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.

scaled_font :

 a cairo_scaled_font_t

ctm :

 return value for the CTM

Since 1.2

cairo_scaled_font_get_type ()

cairo_font_type_t   cairo_scaled_font_get_type          (cairo_scaled_font_t *scaled_font);

scaled_font :

 a cairo_scaled_font_t

Returns :

 The type of scaled_font. See cairo_font_type_t.

Since 1.2

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