Rendering

Rendering — Functions to run the rendering pipeline

Synopsis




            PangoContext;
            PangoItem;
            PangoAnalysis;
enum        PangoDirection;
#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);
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);

gboolean    pango_get_mirror_char           (gunichar ch,
                                             gunichar *mirrored_ch);
PangoDirection pango_unichar_direction      (gunichar ch);
PangoDirection pango_find_base_dir          (const gchar *text,
                                             gint length);


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,
                                             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.


PangoItem

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

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.

PangoAnalysis

typedef struct {
  PangoEngineShape *shape_engine;
  PangoEngineLang  *lang_engine;
  PangoFont *font;
  guint8 level;
  PangoLanguage *language;
  GSList *extra_attrs;
} PangoAnalysis;

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;
guint8 level;the bidrectional level for this segment.
PangoLanguage *language;
GSList *extra_attrs;

enum PangoDirection

typedef enum {
  PANGO_DIRECTION_LTR,
  PANGO_DIRECTION_RTL,
  PANGO_DIRECTION_TTB_LTR,
  PANGO_DIRECTION_TTB_RTL,
  PANGO_DIRECTION_WEAK_LTR,
  PANGO_DIRECTION_WEAK_RTL,
  PANGO_DIRECTION_NEUTRAL
} PangoDirection;

The PangoDirection type represents a direction in the Unicode bidirectional algorithm; not every value in this enumeration makes sense for every usage of PangoDirection; for example, the return value of pango_unichar_direction() and pango_find_base_direction() cannot be PANGO_DIRECTION_WEAK_LTR or PANGO_DIRECTION_WEAK_RTL, since every character is either neutral or has a strong direction; on the other hand PANGO_DIRECTION_NEUTRAL doesn't make sense to pass to pango_log2vis_get_embedding_levels().

The PANGO_DIRECTION_TTB_LTR, PANGO_DIRECTION_TTB_RTL values come from an earlier interpretation of this enumeration as the writing direction of a block of text and are no longer used; See the Text module of the CSS3 spec for how vertical text is planned to be handled in a future version of Pango. The explanation of why PANGO_DIRECTION_TTB_LTR is treated as PANGO_DIRECTION_RTL can be found there as well.

PANGO_DIRECTION_LTR A strong left-to-right direction
PANGO_DIRECTION_RTL A strong right-to-left direction
PANGO_DIRECTION_TTB_LTR Deprecated value; treated the same as PANGO_DIRECTION_RTL.
PANGO_DIRECTION_TTB_RTL Deprecated value; treated the same as PANGO_DIRECTION_LTR
PANGO_DIRECTION_WEAK_LTR A weak left-to-right direction
PANGO_DIRECTION_WEAK_RTL A weak right-to-left direction
PANGO_DIRECTION_NEUTRAL No direction specified

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 explicitely 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.

pango_item_free ()

void        pango_item_free                 (PangoItem *item);

Free a PangoItem and all associated memory.

item : a PangoItem

pango_item_copy ()

PangoItem*  pango_item_copy                 (PangoItem *item);

Copy an existing PangoItem structure.

item : a PangoItem
Returns : the new PangoItem

pango_item_new ()

PangoItem*  pango_item_new                  (void);

Creates a new PangoItem structure initialized to default values.

Returns : the new PangoItem

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

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 mail otaylorredhat.com 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 value.

This function is only useful when implementing a new backend for Pango, something applications won't do. You should use the context creation function for the backend you are using, for example, pango_xft_get_context(), pango_win32_get_context() or, pango_ft2_font_map_create_context().

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

Returns : the new PangoContext

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.

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_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 coordiantes 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 font 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
language : language tag used to determine which script to get the metrics for, or NULL to indicate to get the metrics for the entire font.
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_get_mirror_char ()

gboolean    pango_get_mirror_char           (gunichar ch,
                                             gunichar *mirrored_ch);

Warning

pango_get_mirror_char is deprecated and should not be used in newly-written code.

If ch has the Unicode mirrored property and there is another unicode character that typically has a glyph that is the mirror image of ch's glyph, puts that character in the address pointed to by mirrored_ch.

Use g_unichar_get_mirror_char() instead; the docs for that function provide full details.

ch : a unicode character
mirrored_ch : location to store the mirrored character
Returns : TRUE if ch has a mirrored character and mirrored_ch is filled in, FALSE otherwise

pango_unichar_direction ()

PangoDirection pango_unichar_direction      (gunichar ch);

Determines the direction of a character; either PANGO_DIRECTION_LTR, PANGO_DIRECTION_LTR, or PANGO_DIRECTION_NEUTRAL.

ch :character to examine
Returns : the direction of a character, as used in the Unicode bidirectional algorithm.

pango_find_base_dir ()

PangoDirection pango_find_base_dir          (const gchar *text,
                                             gint length);

Searches a string the first character that has a strong direction, according to the Unicode bidirectional algorithm.

text : the text to process
length : length of text in bytes (may be -1 if text is nul-terminated)
Returns : The direction corresponding to the first strong character. If no such character is found, then PANGO_DIRECTION_NEUTRAL is returned.

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.

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; this function is mostly useful for chaining up from a language engine override. 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() or 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; 
} PangoLogAttr;

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

guint is_line_break : 1;
guint is_mandatory_break : 1;
guint is_char_break : 1;
guint is_white : 1;
guint is_cursor_position : 1;
guint is_word_start : 1;
guint is_word_end : 1;
guint is_sentence_boundary : 1;
guint is_sentence_start : 1;
guint is_sentence_end : 1;
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.

pango_shape ()

void        pango_shape                     (const gchar *text,
                                             gint length,
                                             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 PangoItemize
glyphs : glyph string in which to store results