Text

## Text Text — Rendering text and sets of glyphs |

## Synopsis

                cairo_glyph_t;
    enum        cairo_font_slant_t;
    enum        cairo_font_weight_t;
    void        cairo_select_font_face          (cairo_t *cr,
                                                 const char *family,
                                                 cairo_font_slant_t slant,
                                                 cairo_font_weight_t weight);
    void        cairo_set_font_size             (cairo_t *cr,
                                                 double size);
    void        cairo_set_font_matrix           (cairo_t *cr,
                                                 const cairo_matrix_t *matrix);
    void        cairo_get_font_matrix           (cairo_t *cr,
                                                 cairo_matrix_t *matrix);
    void        cairo_set_font_options          (cairo_t *cr,
                                                 const cairo_font_options_t *options);
    void        cairo_get_font_options          (cairo_t *cr,
                                                 cairo_font_options_t *options);
    void        cairo_show_text                 (cairo_t *cr,
                                                 const char *utf8);
    void        cairo_show_glyphs               (cairo_t *cr,
                                                 cairo_glyph_t *glyphs,
                                                 int num_glyphs);
    cairo_font_face_t* cairo_get_font_face      (cairo_t *cr);
    void        cairo_font_extents              (cairo_t *cr,
                                                 cairo_font_extents_t *extents);
    void        cairo_set_font_face             (cairo_t *cr,
                                                 cairo_font_face_t *font_face);
    void        cairo_text_extents              (cairo_t *cr,
                                                 const char *utf8,
                                                 cairo_text_extents_t *extents);
    void        cairo_glyph_extents             (cairo_t *cr,
                                                 cairo_glyph_t *glyphs,
                                                 int num_glyphs,
                                                 cairo_text_extents_t *extents);

## Description

## Details

### 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

unsigned long `index`; | glyph index in the font. The exact interpretation of the glyph index depends on the font technology being used.
double `x`; | the offset in the X direction between the origin used for drawing or measuring the string and the origin of this glyph.
double `y`; | the offset in the Y direction between the origin used for drawing or measuring the string and the origin of this glyph.

### 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;

### enum cairo_font_weight_t

    typedef enum _cairo_font_weight {
      CAIRO_FONT_WEIGHT_NORMAL,
      CAIRO_FONT_WEIGHT_BOLD
    } cairo_font_weight_t;

### 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);

Selects a family and style of font from a simplified description as a family name, slant and weight. This function is meant to be used only for applications with simple font needs: Cairo doesn't provide for operations such as listing all available fonts on the system, and it is expected that most applications will need to use a more comprehensive font handling and text layout library in addition to cairo.

`cr` : | a cairo_t
`family` : | a font family name, encoded in UTF-8
`slant` : | the slant for the font
`weight` : | the weight for the font

### 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.)

`cr` : | a cairo_t
`size` : | the new font size, in user space units

### 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

`cr` : | a cairo_t
`matrix` : | a cairo_matrix_t describing a transform to be applied to the current font.

### 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()`.

`cr` : | a cairo_t
`matrix` : | return value for the 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.

`cr` : | a cairo_t
`options` : | font options to use

### 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()`.

`cr` : | a cairo_t
`options` : | a cairo_font_options_t object into which to store the retrieved options. All existing values are overwritten

### 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 the most serious of text-using applications. See `cairo_show_glyphs()` for the "real" text display API in cairo.

`cr` : | a cairo context
`utf8` : | a string of text encoded in UTF-8

### cairo_show_glyphs ()

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

`cr` : |
`glyphs` : |
`num_glyphs` : |

### cairo_get_font_face ()

    cairo_font_face_t* cairo_get_font_face      (cairo_t *cr);

Gets the current font face for a cairo_t.

`cr` : | a cairo_t
Returns : | the current font object. Can return `NULL` on out-of-memory or if the context is already in an error state. This object is owned by cairo. To keep a reference to it, you must call `cairo_font_face_reference()`.

### cairo_font_extents ()

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

Gets the font extents for the currently selected font.

`cr` : | a cairo_t
`extents` : | a cairo_font_extents_t object into which the results will be stored.

### 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.

`cr` : | a cairo_t
`font_face` : | a cairo_font_face_t, or `NULL` to restore to the default 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.

`cr` : | a cairo_t
`utf8` : | a string of text, encoded in UTF-8
`extents` : | a cairo_text_extents_t object into which the results will be stored

### cairo_glyph_extents ()

    void        cairo_glyph_extents             (cairo_t *cr,
                                                 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).

`cr` : | a cairo_t
`glyphs` : | an array of cairo_glyph_t objects
`num_glyphs` : | the number of elements in `glyphs`
`extents` : | a cairo_text_extents_t object into which the results will be stored