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Rendering

Rendering — Functions to run the rendering pipeline

Synopsis

                    PangoContext;
struct              PangoItem;
struct              PangoAnalysis;
#define             PANGO_ANALYSIS_FLAG_CENTERED_BASELINE
#define             PANGO_TYPE_DIRECTION

GList *             pango_itemize                       (PangoContext *context,
                                                         const char *text,
                                                         int start_index,
                                                         int length,
                                                         PangoAttrList *attrs,
                                                         PangoAttrIterator *cached_iter);
GList *             pango_itemize_with_base_dir         (PangoContext *context,
                                                         PangoDirection base_dir,
                                                         const char *text,
                                                         int start_index,
                                                         int length,
                                                         PangoAttrList *attrs,
                                                         PangoAttrIterator *cached_iter);
void                pango_item_free                     (PangoItem *item);
PangoItem *         pango_item_copy                     (PangoItem *item);
PangoItem *         pango_item_new                      (void);
PangoItem *         pango_item_split                    (PangoItem *orig,
                                                         int split_index,
                                                         int split_offset);
GList *             pango_reorder_items                 (GList *logical_items);

PangoContext *      pango_context_new                   (void);
void                pango_context_set_font_map          (PangoContext *context,
                                                         PangoFontMap *font_map);
PangoFontMap *      pango_context_get_font_map          (PangoContext *context);
PangoFontDescription *     pango_context_get_font_description
                                                        (PangoContext *context);
void                pango_context_set_font_description  (PangoContext *context,
                                                         const PangoFontDescription *desc);
PangoLanguage *     pango_context_get_language          (PangoContext *context);
void                pango_context_set_language          (PangoContext *context,
                                                         PangoLanguage *language);
PangoDirection      pango_context_get_base_dir          (PangoContext *context);
void                pango_context_set_base_dir          (PangoContext *context,
                                                         PangoDirection direction);
PangoGravity        pango_context_get_base_gravity      (PangoContext *context);
void                pango_context_set_base_gravity      (PangoContext *context,
                                                         PangoGravity gravity);
PangoGravity        pango_context_get_gravity           (PangoContext *context);
PangoGravityHint    pango_context_get_gravity_hint      (PangoContext *context);
void                pango_context_set_gravity_hint      (PangoContext *context,
                                                         PangoGravityHint hint);
const PangoMatrix * pango_context_get_matrix            (PangoContext *context);
void                pango_context_set_matrix            (PangoContext *context,
                                                         const PangoMatrix *matrix);
PangoFont *         pango_context_load_font             (PangoContext *context,
                                                         const PangoFontDescription *desc);
PangoFontset *      pango_context_load_fontset          (PangoContext *context,
                                                         const PangoFontDescription *desc,
                                                         PangoLanguage *language);
PangoFontMetrics *  pango_context_get_metrics           (PangoContext *context,
                                                         const PangoFontDescription *desc,
                                                         PangoLanguage *language);
void                pango_context_list_families         (PangoContext *context,
                                                         PangoFontFamily ***families,
                                                         int *n_families);


void                pango_break                         (const gchar *text,
                                                         int length,
                                                         PangoAnalysis *analysis,
                                                         PangoLogAttr *attrs,
                                                         int attrs_len);
void                pango_get_log_attrs                 (const char *text,
                                                         int length,
                                                         int level,
                                                         PangoLanguage *language,
                                                         PangoLogAttr *log_attrs,
                                                         int attrs_len);
void                pango_find_paragraph_boundary       (const gchar *text,
                                                         gint length,
                                                         gint *paragraph_delimiter_index,
                                                         gint *next_paragraph_start);
void                pango_default_break                 (const gchar *text,
                                                         int length,
                                                         PangoAnalysis *analysis,
                                                         PangoLogAttr *attrs,
                                                         int attrs_len);
                    PangoLogAttr;

void                pango_shape                         (const gchar *text,
                                                         gint length,
                                                         const PangoAnalysis *analysis,
                                                         PangoGlyphString *glyphs);

Object Hierarchy

  GObject
   +----PangoContext

Description

The Pango rendering pipeline takes a string of Unicode characters and converts it into glyphs. The functions described in this section accomplish various steps of this process.

Details

PangoContext

typedef struct _PangoContext PangoContext;

The PangoContext structure stores global information used to control the itemization process.


struct PangoItem

struct PangoItem {
  gint offset;
  gint length;
  gint num_chars;
  PangoAnalysis analysis;
};

The PangoItem structure stores information about a segment of text. It contains the following fields:

gint offset;

the offset of the segment from the beginning of the string in bytes.

gint length;

the length of the segment in bytes.

gint num_chars;

the length of the segment in characters.

PangoAnalysis analysis;

the properties of the segment.

struct PangoAnalysis

struct PangoAnalysis {
  PangoEngineShape *shape_engine;
  PangoEngineLang  *lang_engine;
  PangoFont *font;

  guint8 level;
  guint8 gravity; /* PangoGravity */
  guint8 flags;

  guint8 script; /* PangoScript */
  PangoLanguage *language;

  GSList *extra_attrs;
};

The PangoAnalysis structure stores information about the properties of a segment of text. It has the following fields:

PangoEngineShape *shape_engine;

the engine for doing rendering-system-dependent processing.

PangoEngineLang *lang_engine;

the engine for doing rendering-system-independent processing.

PangoFont *font;

the font for this segment.

guint8 level;

the bidirectional level for this segment.

guint8 gravity;

the glyph orientation for this segment (A PangoGravity).

guint8 flags;

boolean flags for this segment (currently only one) (Since: 1.16).

guint8 script;

the detected script for this segment (A PangoScript) (Since: 1.18).

PangoLanguage *language;

the detected language for this segment.

GSList *extra_attrs;

extra attributes for this segment.

PANGO_ANALYSIS_FLAG_CENTERED_BASELINE

#define PANGO_ANALYSIS_FLAG_CENTERED_BASELINE (1 << 0)

Whether the segment should be shifted to center around the baseline. Used in vertical writing directions mostly. Since: 1.16


PANGO_TYPE_DIRECTION

#define PANGO_TYPE_DIRECTION (pango_direction_get_type())

The GObject type for PangoDirection.


pango_itemize ()

GList *             pango_itemize                       (PangoContext *context,
                                                         const char *text,
                                                         int start_index,
                                                         int length,
                                                         PangoAttrList *attrs,
                                                         PangoAttrIterator *cached_iter);

Breaks a piece of text into segments with consistent directional level and shaping engine. Each byte of text will be contained in exactly one of the items in the returned list; the generated list of items will be in logical order (the start offsets of the items are ascending).

cached_iter should be an iterator over attrs currently positioned at a range before or containing start_index; cached_iter will be advanced to the range covering the position just after start_index + length. (i.e. if itemizing in a loop, just keep passing in the same cached_iter).

context :

a structure holding information that affects the itemization process.

text :

the text to itemize.

start_index :

first byte in text to process

length :

the number of bytes (not characters) to process after start_index. This must be >= 0.

attrs :

the set of attributes that apply to text.

cached_iter :

Cached attribute iterator, or NULL

Returns :

a GList of PangoItem structures.

pango_itemize_with_base_dir ()

GList *             pango_itemize_with_base_dir         (PangoContext *context,
                                                         PangoDirection base_dir,
                                                         const char *text,
                                                         int start_index,
                                                         int length,
                                                         PangoAttrList *attrs,
                                                         PangoAttrIterator *cached_iter);

Like pango_itemize(), but the base direction to use when computing bidirectional levels (see pango_context_set_base_dir()), is specified explicitly rather than gotten from the PangoContext.

context :

a structure holding information that affects the itemization process.

base_dir :

base direction to use for bidirectional processing

text :

the text to itemize.

start_index :

first byte in text to process

length :

the number of bytes (not characters) to process after start_index. This must be >= 0.

attrs :

the set of attributes that apply to text.

cached_iter :

Cached attribute iterator, or NULL

Returns :

a GList of PangoItem structures. The items should be freed using pango_item_free() probably in combination with g_list_foreach(), and the list itself using g_list_free().

Since 1.4


pango_item_free ()

void                pango_item_free                     (PangoItem *item);

Free a PangoItem and all associated memory.

item :

a PangoItem, may be NULL

pango_item_copy ()

PangoItem *         pango_item_copy                     (PangoItem *item);

Copy an existing PangoItem structure.

item :

a PangoItem, may be NULL

Returns :

the newly allocated PangoItem, which should be freed with pango_item_free(), or NULL if item was NULL.

pango_item_new ()

PangoItem *         pango_item_new                      (void);

Creates a new PangoItem structure initialized to default values.

Returns :

the newly allocated PangoItem, which should be freed with pango_item_free().

pango_item_split ()

PangoItem *         pango_item_split                    (PangoItem *orig,
                                                         int split_index,
                                                         int split_offset);

Modifies orig to cover only the text after split_index, and returns a new item that covers the text before split_index that used to be in orig. You can think of split_index as the length of the returned item. split_index may not be 0, and it may not be greater than or equal to the length of orig (that is, there must be at least one byte assigned to each item, you can't create a zero-length item). split_offset is the length of the first item in chars, and must be provided because the text used to generate the item isn't available, so pango_item_split() can't count the char length of the split items itself.

orig :

a PangoItem

split_index :

byte index of position to split item, relative to the start of the item

split_offset :

number of chars between start of orig and split_index

Returns :

new item representing text before split_index, which should be freed with pango_item_free().

pango_reorder_items ()

GList *             pango_reorder_items                 (GList *logical_items);

From a list of items in logical order and the associated directional levels, produce a list in visual order. The original list is unmodified.

logical_items :

a GList of PangoItem in logical order.

Returns :

a GList of PangoItem structures in visual order. (Please open a bug if you use this function. It is not a particularly convenient interface, and the code is duplicated elsewhere in Pango for that reason.)

pango_context_new ()

PangoContext *      pango_context_new                   (void);

Creates a new PangoContext initialized to default values.

This function is not particularly useful as it should always be followed by a pango_context_set_font_map() call, and the function pango_font_map_create_context() does these two steps together and hence users are recommended to use that.

If you are using Pango as part of a higher-level system, that system may have it's own way of create a PangoContext. For instance, the GTK+ toolkit has, among others, gdk_pango_context_get_for_screen(), and gtk_widget_get_pango_context(). Use those instead.

Returns :

the newly allocated PangoContext, which should be freed with g_object_unref().

pango_context_set_font_map ()

void                pango_context_set_font_map          (PangoContext *context,
                                                         PangoFontMap *font_map);

Sets the font map to be searched when fonts are looked-up in this context. This is only for internal use by Pango backends, a PangoContext obtained via one of the recommended methods should already have a suitable font map.

context :

a PangoContext

font_map :

the PangoFontMap to set.

pango_context_get_font_map ()

PangoFontMap *      pango_context_get_font_map          (PangoContext *context);

Gets the PangoFontmap used to look up fonts for this context.

context :

a PangoContext

Returns :

the font map for the PangoContext. This value is owned by Pango and should not be unreferenced.

Since 1.6


pango_context_get_font_description ()

PangoFontDescription *     pango_context_get_font_description
                                                        (PangoContext *context);

Retrieve the default font description for the context.

context :

a PangoContext

Returns :

a pointer to the context's default font description. This value must not be modified or freed.

pango_context_set_font_description ()

void                pango_context_set_font_description  (PangoContext *context,
                                                         const PangoFontDescription *desc);

Set the default font description for the context

context :

a PangoContext

desc :

the new pango font description

pango_context_get_language ()

PangoLanguage *     pango_context_get_language          (PangoContext *context);

Retrieves the global language tag for the context.

context :

a PangoContext

Returns :

the global language tag.

pango_context_set_language ()

void                pango_context_set_language          (PangoContext *context,
                                                         PangoLanguage *language);

Sets the global language tag for the context. The default language for the locale of the running process can be found using pango_language_get_default().

context :

a PangoContext

language :

the new language tag.

pango_context_get_base_dir ()

PangoDirection      pango_context_get_base_dir          (PangoContext *context);

Retrieves the base direction for the context. See pango_context_set_base_dir().

context :

a PangoContext

Returns :

the base direction for the context.

pango_context_set_base_dir ()

void                pango_context_set_base_dir          (PangoContext *context,
                                                         PangoDirection direction);

Sets the base direction for the context.

The base direction is used in applying the Unicode bidirectional algorithm; if the direction is PANGO_DIRECTION_LTR or PANGO_DIRECTION_RTL, then the value will be used as the paragraph direction in the Unicode bidirectional algorithm. A value of PANGO_DIRECTION_WEAK_LTR or PANGO_DIRECTION_WEAK_RTL is used only for paragraphs that do not contain any strong characters themselves.

context :

a PangoContext

direction :

the new base direction

pango_context_get_base_gravity ()

PangoGravity        pango_context_get_base_gravity      (PangoContext *context);

Retrieves the base gravity for the context. See pango_context_set_base_gravity().

context :

a PangoContext

Returns :

the base gravity for the context.

Since 1.16


pango_context_set_base_gravity ()

void                pango_context_set_base_gravity      (PangoContext *context,
                                                         PangoGravity gravity);

Sets the base gravity for the context.

The base gravity is used in laying vertical text out.

context :

a PangoContext

gravity :

the new base gravity

Since 1.16


pango_context_get_gravity ()

PangoGravity        pango_context_get_gravity           (PangoContext *context);

Retrieves the gravity for the context. This is similar to pango_context_get_base_gravity(), except for when the base gravity is PANGO_GRAVITY_AUTO for which pango_gravity_get_for_matrix() is used to return the gravity from the current context matrix.

context :

a PangoContext

Returns :

the resolved gravity for the context.

Since 1.16


pango_context_get_gravity_hint ()

PangoGravityHint    pango_context_get_gravity_hint      (PangoContext *context);

Retrieves the gravity hint for the context. See pango_context_set_gravity_hint() for details.

context :

a PangoContext

Returns :

the gravity hint for the context.

Since 1.16


pango_context_set_gravity_hint ()

void                pango_context_set_gravity_hint      (PangoContext *context,
                                                         PangoGravityHint hint);

Sets the gravity hint for the context.

The gravity hint is used in laying vertical text out, and is only relevant if gravity of the context as returned by pango_context_get_gravity() is set PANGO_GRAVITY_EAST or PANGO_GRAVITY_WEST.

context :

a PangoContext

hint :

the new gravity hint

Since 1.16


pango_context_get_matrix ()

const PangoMatrix * pango_context_get_matrix            (PangoContext *context);

Gets the transformation matrix that will be applied when rendering with this context. See pango_context_set_matrix().

context :

a PangoContext

Returns :

the matrix, or NULL if no matrix has been set (which is the same as the identity matrix). The returned matrix is owned by Pango and must not be modified or freed.

Since 1.6


pango_context_set_matrix ()

void                pango_context_set_matrix            (PangoContext *context,
                                                         const PangoMatrix *matrix);

Sets the transformation matrix that will be applied when rendering with this context. Note that reported metrics are in the user space coordinates before the application of the matrix, not device-space coordinates after the application of the matrix. So, they don't scale with the matrix, though they may change slightly for different matrices, depending on how the text is fit to the pixel grid.

context :

a PangoContext

matrix :

a PangoMatrix, or NULL to unset any existing matrix. (No matrix set is the same as setting the identity matrix.)

Since 1.6


pango_context_load_font ()

PangoFont *         pango_context_load_font             (PangoContext *context,
                                                         const PangoFontDescription *desc);

Loads the font in one of the fontmaps in the context that is the closest match for desc.

context :

a PangoContext

desc :

a PangoFontDescription describing the font to load

Returns :

the font loaded, or NULL if no font matched.

pango_context_load_fontset ()

PangoFontset *      pango_context_load_fontset          (PangoContext *context,
                                                         const PangoFontDescription *desc,
                                                         PangoLanguage *language);

Load a set of fonts in the context that can be used to render a font matching desc.

context :

a PangoContext

desc :

a PangoFontDescription describing the fonts to load

language :

a PangoLanguage the fonts will be used for

Returns :

the fontset, or NULL if no font matched.

pango_context_get_metrics ()

PangoFontMetrics *  pango_context_get_metrics           (PangoContext *context,
                                                         const PangoFontDescription *desc,
                                                         PangoLanguage *language);

Get overall metric information for a particular font description. Since the metrics may be substantially different for different scripts, a language tag can be provided to indicate that the metrics should be retrieved that correspond to the script(s) used by that language.

The PangoFontDescription is interpreted in the same way as by pango_itemize(), and the family name may be a comma separated list of figures. If characters from multiple of these families would be used to render the string, then the returned fonts would be a composite of the metrics for the fonts loaded for the individual families.

context :

a PangoContext

desc :

a PangoFontDescription structure. NULL means that the font description from the context will be used.

language :

language tag used to determine which script to get the metrics for. NULL means that the language tag from the context will be used. If no language tag is set on the context, metrics for the default language (as determined by pango_language_get_default()) will be returned.

Returns :

a PangoFontMetrics object. The caller must call pango_font_metrics_unref() when finished using the object.

pango_context_list_families ()

void                pango_context_list_families         (PangoContext *context,
                                                         PangoFontFamily ***families,
                                                         int *n_families);

List all families for a context.

context :

a PangoContext

families :

location to store a pointer to an array of PangoFontFamily *. This array should be freed with g_free().

n_families :

location to store the number of elements in descs

pango_break ()

void                pango_break                         (const gchar *text,
                                                         int length,
                                                         PangoAnalysis *analysis,
                                                         PangoLogAttr *attrs,
                                                         int attrs_len);

Determines possible line, word, and character breaks for a string of Unicode text with a single analysis. For most purposes you may want to use pango_get_log_attrs().

text :

the text to process

length :

length of text in bytes (may be -1 if text is nul-terminated)

analysis :

PangoAnalysis structure from pango_itemize()

attrs :

an array to store character information in

attrs_len :

size of the array passed as attrs

pango_get_log_attrs ()

void                pango_get_log_attrs                 (const char *text,
                                                         int length,
                                                         int level,
                                                         PangoLanguage *language,
                                                         PangoLogAttr *log_attrs,
                                                         int attrs_len);

Computes a PangoLogAttr for each character in text. The log_attrs array must have one PangoLogAttr for each position in text; if text contains N characters, it has N+1 positions, including the last position at the end of the text. text should be an entire paragraph; logical attributes can't be computed without context (for example you need to see spaces on either side of a word to know the word is a word).

text :

text to process

length :

length in bytes of text

level :

embedding level, or -1 if unknown

language :

language tag

log_attrs :

array with one PangoLogAttr per character in text, plus one extra, to be filled in

attrs_len :

length of log_attrs array

pango_find_paragraph_boundary ()

void                pango_find_paragraph_boundary       (const gchar *text,
                                                         gint length,
                                                         gint *paragraph_delimiter_index,
                                                         gint *next_paragraph_start);

Locates a paragraph boundary in text. A boundary is caused by delimiter characters, such as a newline, carriage return, carriage return-newline pair, or Unicode paragraph separator character. The index of the run of delimiters is returned in paragraph_delimiter_index. The index of the start of the paragraph (index after all delimiters) is stored in next_paragraph_start.

If no delimiters are found, both paragraph_delimiter_index and next_paragraph_start are filled with the length of text (an index one off the end).

text :

UTF-8 text

length :

length of text in bytes, or -1 if nul-terminated

paragraph_delimiter_index :

return location for index of delimiter

next_paragraph_start :

return location for start of next paragraph

pango_default_break ()

void                pango_default_break                 (const gchar *text,
                                                         int length,
                                                         PangoAnalysis *analysis,
                                                         PangoLogAttr *attrs,
                                                         int attrs_len);

This is the default break algorithm, used if no language engine overrides it. Normally you should use pango_break() instead. Unlike pango_break(), analysis can be NULL, but only do that if you know what you're doing. If you need an analysis to pass to pango_break(), you need to pango_itemize(). In most cases however you should simply use pango_get_log_attrs().

text :

text to break

length :

length of text in bytes (may be -1 if text is nul-terminated)

analysis :

a PangoAnalysis for the text

attrs :

logical attributes to fill in

attrs_len :

size of the array passed as attrs

PangoLogAttr

typedef struct {
  guint is_line_break : 1;      /* Can break line in front of character */

  guint is_mandatory_break : 1; /* Must break line in front of character */

  guint is_char_break : 1;      /* Can break here when doing char wrap */

  guint is_white : 1;           /* Whitespace character */

  /* Cursor can appear in front of character (i.e. this is a grapheme
   * boundary, or the first character in the text).
   */
  guint is_cursor_position : 1;

  /* Note that in degenerate cases, you could have both start/end set on
   * some text, most likely for sentences (e.g. no space after a period, so
   * the next sentence starts right away).
   */

  guint is_word_start : 1;      /* first character in a word */
  guint is_word_end   : 1;      /* is first non-word char after a word */

  /* There are two ways to divide sentences. The first assigns all
   * intersentence whitespace/control/format chars to some sentence,
   * so all chars are in some sentence; is_sentence_boundary denotes
   * the boundaries there. The second way doesn't assign
   * between-sentence spaces, etc. to any sentence, so
   * is_sentence_start/is_sentence_end mark the boundaries of those
   * sentences.
   */
  guint is_sentence_boundary : 1;
  guint is_sentence_start : 1;  /* first character in a sentence */
  guint is_sentence_end : 1;    /* first non-sentence char after a sentence */

  /* If set, backspace deletes one character rather than
   * the entire grapheme cluster.
   */
  guint backspace_deletes_character : 1;

  /* Only few space variants (U+0020 and U+00A0) have variable
   * width during justification.
   */
  guint is_expandable_space : 1;

  /* Word boundary as defined by UAX#29 */
  guint is_word_boundary : 1; /* is NOT in the middle of a word */
} PangoLogAttr;

The PangoLogAttr structure stores information about the attributes of a single character.

guint is_line_break : 1;

if set, can break line in front of character

guint is_mandatory_break : 1;

if set, must break line in front of character

guint is_char_break : 1;

if set, can break here when doing character wrapping

guint is_white : 1;

is whitespace character

guint is_cursor_position : 1;

if set, cursor can appear in front of character. i.e. this is a grapheme boundary, or the first character in the text. This flag implements Unicode's Grapheme Cluster Boundaries semantics.

guint is_word_start : 1;

is first character in a word

guint is_word_end : 1;

is first non-word char after a word Note that in degenerate cases, you could have both is_word_start and is_word_end set for some character.

guint is_sentence_boundary : 1;

is a sentence boundary. There are two ways to divide sentences. The first assigns all inter-sentence whitespace/control/format chars to some sentence, so all chars are in some sentence; is_sentence_boundary denotes the boundaries there. The second way doesn't assign between-sentence spaces, etc. to any sentence, so is_sentence_start/is_sentence_end mark the boundaries of those sentences.

guint is_sentence_start : 1;

is first character in a sentence

guint is_sentence_end : 1;

is first char after a sentence. Note that in degenerate cases, you could have both is_sentence_start and is_sentence_end set for some character. (e.g. no space after a period, so the next sentence starts right away)

guint backspace_deletes_character : 1;

if set, backspace deletes one character rather than the entire grapheme cluster. This field is only meaningful on grapheme boundaries (where is_cursor_position is set). In some languages, the full grapheme (e.g. letter + diacritics) is considered a unit, while in others, each decomposed character in the grapheme is a unit. In the default implementation of pango_break(), this bit is set on all grapheme boundaries except those following Latin, Cyrillic or Greek base characters.

guint is_expandable_space : 1;

is a whitespace character that can possibly be expanded for justification purposes. (Since: 1.18)

guint is_word_boundary : 1;

is a word boundary. More specifically, means that this is not a position in the middle of a word. For example, both sides of a punctuation mark are considered word boundaries. This flag is particularly useful when selecting text word-by-word. This flag implements Unicode's Word Boundaries semantics. (Since: 1.22)

pango_shape ()

void                pango_shape                         (const gchar *text,
                                                         gint length,
                                                         const PangoAnalysis *analysis,
                                                         PangoGlyphString *glyphs);

Given a segment of text and the corresponding PangoAnalysis structure returned from pango_itemize(), convert the characters into glyphs. You may also pass in only a substring of the item from pango_itemize().

text :

the text to process

length :

the length (in bytes) of text

analysis :

PangoAnalysis structure from pango_itemize()

glyphs :

glyph string in which to store results
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