Glyph Storage

Glyph Storage — Structures for storing information about glyphs

Synopsis



#define     PANGO_SCALE
#define     PANGO_PIXELS                    (d)
            PangoRectangle;
#define     PANGO_ASCENT                    (rect)
#define     PANGO_DESCENT                   (rect)
#define     PANGO_LBEARING                  (rect)
#define     PANGO_RBEARING                  (rect)
            PangoMatrix;
#define     PANGO_TYPE_MATRIX
#define     PANGO_MATRIX_INIT
PangoMatrix* pango_matrix_copy              (const PangoMatrix *matrix);
void        pango_matrix_free               (PangoMatrix *matrix);
void        pango_matrix_translate          (PangoMatrix *matrix,
                                             double tx,
                                             double ty);
void        pango_matrix_scale              (PangoMatrix *matrix,
                                             double scale_x,
                                             double scale_y);
void        pango_matrix_rotate             (PangoMatrix *matrix,
                                             double degrees);
void        pango_matrix_concat             (PangoMatrix *matrix,
                                             const PangoMatrix *new_matrix);
typedef     PangoGlyph;
            PangoGlyphInfo;
            PangoGlyphGeometry;
typedef     PangoGlyphUnit;
            PangoGlyphVisAttr;
            PangoGlyphString;
            PangoGlyphItem;
#define     PANGO_TYPE_GLYPH_STRING
PangoGlyphString* pango_glyph_string_new    (void);
PangoGlyphString* pango_glyph_string_copy   (PangoGlyphString *string);
void        pango_glyph_string_set_size     (PangoGlyphString *string,
                                             gint new_len);
void        pango_glyph_string_free         (PangoGlyphString *string);
void        pango_glyph_string_extents      (PangoGlyphString *glyphs,
                                             PangoFont *font,
                                             PangoRectangle *ink_rect,
                                             PangoRectangle *logical_rect);
void        pango_glyph_string_extents_range
                                            (PangoGlyphString *glyphs,
                                             int start,
                                             int end,
                                             PangoFont *font,
                                             PangoRectangle *ink_rect,
                                             PangoRectangle *logical_rect);
void        pango_glyph_string_index_to_x   (PangoGlyphString *glyphs,
                                             char *text,
                                             int length,
                                             PangoAnalysis *analysis,
                                             int index_,
                                             gboolean trailing,
                                             int *x_pos);
void        pango_glyph_string_x_to_index   (PangoGlyphString *glyphs,
                                             char *text,
                                             int length,
                                             PangoAnalysis *analysis,
                                             int x_pos,
                                             int *index_,
                                             int *trailing);
void        pango_glyph_string_get_logical_widths
                                            (PangoGlyphString *glyphs,
                                             const char *text,
                                             int length,
                                             int embedding_level,
                                             int *logical_widths);
PangoGlyphItem* pango_glyph_item_split      (PangoGlyphItem *orig,
                                             const char *text,
                                             int split_index);
GSList*     pango_glyph_item_apply_attrs    (PangoGlyphItem *glyph_item,
                                             const char *text,
                                             PangoAttrList *list);
void        pango_glyph_item_letter_space   (PangoGlyphItem *glyph_item,
                                             const char *text,
                                             PangoLogAttr *log_attrs,
                                             int letter_spacing);
void        pango_glyph_item_free           (PangoGlyphItem *glyph_item);

Description

pango_shape() produces a string of glyphs which can be measured or drawn to the screen. The following structures are used to store information about glyphs.

Details

PANGO_SCALE

#define PANGO_SCALE 1024

The PANGO_SCALE macro represents the scale between dimensions used for Pango distances and device units. (The definition of device units is dependent on the output device; it will typically be pixels for a screen, and points for a printer.) PANGO_SCALE is currently 1024, but this may be changed in the future.

When setting font sizes, device units are always considered to be points (as in "12 point font"), rather than pixels.


PANGO_PIXELS()

#define PANGO_PIXELS(d) (((int)(d) + 512) >> 10)

Converts a dimension to device units.

d :a dimension in Pango units.

PangoRectangle

typedef struct {
  int x;
  int y;
  int width;
  int height;
} PangoRectangle;

The PangoRectangle structure represents a rectangle. It is frequently used to represent the logical or ink extents of a single glyph or section of text. (See, for instance, pango_font_get_glyph_extents())

int x;X coordinate of the left side of the rectangle.
int y;Y coordinate of the the top side of the rectangle.
int width;width of the rectangle.
int height;height of the rectangle.

PANGO_ASCENT()

#define PANGO_ASCENT(rect) (-(rect).y)

Extracts the ascent from a PangoRectangle representing glyph extents. The ascent is the distance from the baseline to the highest point of the character. This is positive if the glyph ascends above the baseline.

rect :a PangoRectangle

PANGO_DESCENT()

#define PANGO_DESCENT(rect) ((rect).y + (rect).height)

Extracts the descent from a PangoRectangle representing glyph extents. The descent is the distance from the baseline to the lowest point of the character. This is positive if the glyph descends below the baseline.

rect :a PangoRectangle

PANGO_LBEARING()

#define PANGO_LBEARING(rect) ((rect).x)

Extracts the left bearing from a PangoRectangle representing glyph extents. The left bearing is the distance from the horizontal origin to the farthest left point of the character. This is positive for characters drawn completely to the right of the glyph origin.

rect :a PangoRectangle

PANGO_RBEARING()

#define PANGO_RBEARING(rect) ((rect).x + (rect).width)

Extracts the right bearing from a PangoRectangle representing glyph extents. The right bearing is the distance from the horizontal origin to the farthest right point of the character. This is positive except for characters drawn completely to the left of the horizontal origin.

rect :a PangoRectangle

PangoMatrix

typedef struct {
  double xx;
  double xy;
  double yx;
  double yy;
  double x0;
  double y0;
} PangoMatrix;

A structure specifying a transformation between user-space coordinates and device coordinates. The transformation is given by

x_device = x_user * matrix->xx + y_user * matrix->xy + matrix->x0;
y_device = x_user * matrix->yx + y_user * matrix->yy + matrix->y0;

double xx; 1st component of the transformation matrix
double xy; 2nd component of the transformation matrix
double yx; 3rd component of the transformation matrix
double yy; 4th component of the transformation matrix
double x0; x translation
double y0; y translation

Since 1.6


PANGO_TYPE_MATRIX

#define PANGO_TYPE_MATRIX (pango_matrix_get_type ())

The GObject type for PangoMatrix


PANGO_MATRIX_INIT

#define PANGO_MATRIX_INIT { 1., 0., 0., 1., 0., 0. }

Constant that can be used to initialize a PangoMatrix to the identity transform.

PangoMatrix matrix = PANGO_MATRIX_INIT;
pango_matrix_rotate (&matrix, 45.);

Since 1.6


pango_matrix_copy ()

PangoMatrix* pango_matrix_copy              (const PangoMatrix *matrix);

Copies a PangoMatrix.

matrix : a PangoMatrix
Returns : a copy of matrix. The result must be freed with pango_matrix_free().

Since 1.6


pango_matrix_free ()

void        pango_matrix_free               (PangoMatrix *matrix);

Free a PangoMatrix created with pango_matrix_copy().

matrix : a PangoMatrix

Since 1.6


pango_matrix_translate ()

void        pango_matrix_translate          (PangoMatrix *matrix,
                                             double tx,
                                             double ty);

Changes the transformation represented by matrix to be the transformation given by first translating by (tx, ty) then applying the original transformation.

matrix : a PangoMatrix
tx : amount to translate in the X direction
ty : amount to translate in the Y direction

Since 1.6


pango_matrix_scale ()

void        pango_matrix_scale              (PangoMatrix *matrix,
                                             double scale_x,
                                             double scale_y);

Changes the transformation represented by matrix to be the transformation given by first scaling by sx in the X direction and sy in the Y direction then applying the original transformation.

matrix : a PangoMatrix
scale_x : amount to scale by in X direction
scale_y : amount to scale by in Y direction

Since 1.6


pango_matrix_rotate ()

void        pango_matrix_rotate             (PangoMatrix *matrix,
                                             double degrees);

Changes the transformation represented by matrix to be the transformation given by first rotating by degrees degrees counter-clokwise then applying the original transformation.

matrix : a PangoMatrix
degrees : degrees to rotate counter-clockwise

Since 1.6


pango_matrix_concat ()

void        pango_matrix_concat             (PangoMatrix *matrix,
                                             const PangoMatrix *new_matrix);

Changes the transformation represented by matrix to be the transformation given by first applying transformation given by new_matrix then applying the original transformation.

matrix : a PangoMatrix
new_matrix : a PangoMatrix

Since 1.6


PangoGlyph

typedef guint32 PangoGlyph;

A PangoGlyph represents a single glyph in the output form of a string.


PangoGlyphInfo

typedef struct {
  PangoGlyph    glyph;
  PangoGlyphGeometry geometry;
  PangoGlyphVisAttr  attr;
} PangoGlyphInfo;

The PangoGlyphInfo structure represents a single glyph together with positioning information and visual attributes. It contains the following fields.

PangoGlyph glyph;the glyph itself.
PangoGlyphGeometry geometry;the positional information about the glyph.
PangoGlyphVisAttr attr;the visual attributes of the glyph.

PangoGlyphGeometry

typedef struct {
  PangoGlyphUnit width;
  PangoGlyphUnit x_offset;  
  PangoGlyphUnit y_offset;
} PangoGlyphGeometry;

The PangoGlyphGeometry structure contains width and positioning information for a single glyph.

PangoGlyphUnit width;the logical width to use for the the character.
PangoGlyphUnit x_offset;horizontal offset from nominal character position.
PangoGlyphUnit y_offset;vertical offset from nominal character position.

PangoGlyphUnit

typedef gint32 PangoGlyphUnit;

The PangoGlyphUnit type is used to store dimensions within Pango. Dimensions are stored in 1/PANGO_SCALE of a device unit. (A device unit might be a pixel for screen display, or a point on a printer.) PANGO_SCALE is currently 1024, and is unlikely to change, but you should not depend on its exact value. The PANGO_PIXELS() macro can be used to convert from glyph units into device units with correct rounding.


PangoGlyphVisAttr

typedef struct {
  guint is_cluster_start : 1;
} PangoGlyphVisAttr;

The PangoGlyphVisAttr is used to communicate information between the shaping phase and the rendering phase. It's contents are still evolving.

guint is_cluster_start : 1;set for the first logical glyph in each cluster. (Clusters are stored in visual order, within the cluster, glyphs are always ordered in logical order, since visual order is meaningless; that is, in Arabic text, accent glyphs follow the glyphs for the base character.)


PangoGlyphString

typedef struct {
  gint num_glyphs;

  PangoGlyphInfo *glyphs;

  /* This is a memory inefficient way of representing the information
   * here - each value gives the byte index within the text
   * corresponding to the glyph string of the start of the cluster to
   * which the glyph belongs.
   */
  gint *log_clusters;
} PangoGlyphString;

The PangoGlyphString structure is used to store strings of glyphs with geometry and visual attribute information. The storage for the glyph information is owned by the structure which simplifies memory management.

gint num_glyphs;the number of glyphs in the string.
PangoGlyphInfo *glyphs;an array of PangoGlyphInfo structures of length num_glyphs.
gint *log_clusters;for each glyph, byte index of the starting character for the cluster. The indices are relative to the start of the text corresponding to the PangoGlyphString.

PangoGlyphItem

typedef struct {
  PangoItem        *item;
  PangoGlyphString *glyphs;
} PangoGlyphItem;

A PangoGlyphItem is a pair of a PangoItem and the glyphs resulting from shaping the text corresponding to an item. As an example of the usage of PangoGlyphItem, the results of shaping text with PangoLayout is a list of PangoLayoutLine, each of which contains a list of PangoGlyphItem.

PangoItem *item;a PangoItem structure that provides information about a segment of text.
PangoGlyphString *glyphs;the glyphs obtained by shaping the text corresponding to item.

PANGO_TYPE_GLYPH_STRING

#define PANGO_TYPE_GLYPH_STRING (pango_glyph_string_get_type ())

The GObject type for PangoGlyphString.


pango_glyph_string_new ()

PangoGlyphString* pango_glyph_string_new    (void);

Create a new PangoGlyphString.

Returns :the new PangoGlyphString

pango_glyph_string_copy ()

PangoGlyphString* pango_glyph_string_copy   (PangoGlyphString *string);

Copy a glyph string and associated storage.

string : a PangoGlyphString.
Returns :the copied PangoGlyphString

pango_glyph_string_set_size ()

void        pango_glyph_string_set_size     (PangoGlyphString *string,
                                             gint new_len);

Resize a glyph string to the given length.

string : a PangoGlyphString.
new_len : the new length of the string.

pango_glyph_string_free ()

void        pango_glyph_string_free         (PangoGlyphString *string);

Free a glyph string and associated storage.

string : a PangoGlyphString.

pango_glyph_string_extents ()

void        pango_glyph_string_extents      (PangoGlyphString *glyphs,
                                             PangoFont *font,
                                             PangoRectangle *ink_rect,
                                             PangoRectangle *logical_rect);

Compute the logical and ink extents of a glyph string. See the documentation for pango_font_get_glyph_extents() for details about the interpretation of the rectangles.

glyphs : a PangoGlyphString
font : a PangoFont
ink_rect : rectangle used to store the extents of the glyph string as drawn or NULL to indicate that the result is not needed.
logical_rect : rectangle used to store the logical extents of the glyph string or NULL to indicate that the result is not needed.

pango_glyph_string_extents_range ()

void        pango_glyph_string_extents_range
                                            (PangoGlyphString *glyphs,
                                             int start,
                                             int end,
                                             PangoFont *font,
                                             PangoRectangle *ink_rect,
                                             PangoRectangle *logical_rect);

Computes the extents of a sub-portion of a glyph string. The extents are relative to the start of the glyph string range (the origin of their coordinate system is at the start of the range, not at the start of the entire glyph string).

glyphs : a PangoGlyphString
start : start index
end : end index (the range is the set of bytes with indices such that start <= index < end)
font : a PangoFont
ink_rect : rectangle used to store the extents of the glyph string range as drawn or NULL to indicate that the result is not needed.
logical_rect : rectangle used to store the logical extents of the glyph string range or NULL to indicate that the result is not needed.

pango_glyph_string_index_to_x ()

void        pango_glyph_string_index_to_x   (PangoGlyphString *glyphs,
                                             char *text,
                                             int length,
                                             PangoAnalysis *analysis,
                                             int index_,
                                             gboolean trailing,
                                             int *x_pos);

Converts from character position to x position. (X position is measured from the left edge of the run). Character positions are computed by dividing up each cluster into equal portions.

glyphs : the glyphs return from pango_shape()
text : the text for the run
length : the number of bytes (not characters) in text.
analysis : the analysis information return from pango_itemize()
index_ : the byte index within text
trailing : whether we should compute the result for the beginning or end of the character.
x_pos : location to store result

pango_glyph_string_x_to_index ()

void        pango_glyph_string_x_to_index   (PangoGlyphString *glyphs,
                                             char *text,
                                             int length,
                                             PangoAnalysis *analysis,
                                             int x_pos,
                                             int *index_,
                                             int *trailing);

Convert from x offset to character position. Character positions are computed by dividing up each cluster into equal portions. In scripts where positioning within a cluster is not allowed (such as Thai), the returned value may not be a valid cursor position; the caller must combine the result with the logical attributes for the text to compute the valid cursor position.

glyphs : the glyphs return from pango_shape()
text : the text for the run
length : the number of bytes (not characters) in text.
analysis : the analysis information return from pango_itemize()
x_pos : the x offset (in PangoGlyphUnit)
index_ : location to store calculated byte index within text
trailing : location to store a integer indicating where whether the user clicked on the leading or trailing edge of the character.

pango_glyph_string_get_logical_widths ()

void        pango_glyph_string_get_logical_widths
                                            (PangoGlyphString *glyphs,
                                             const char *text,
                                             int length,
                                             int embedding_level,
                                             int *logical_widths);

Given a PangoGlyphString resulting from pango_shape() and the corresponding text, determine the screen width corresponding to each character. When multiple characters compose a single cluster, the width of the entire cluster is divided equally among the characters.

glyphs : a PangoGlyphString
text : the text corresponding to the glyphs
length : the length of text, in bytes
embedding_level : the embedding level of the string
logical_widths : an array whose length is g_utf8_strlen (text, length) to be filled in with the resulting character widths.

pango_glyph_item_split ()

PangoGlyphItem* pango_glyph_item_split      (PangoGlyphItem *orig,
                                             const char *text,
                                             int split_index);

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).

This function is similar in function to pango_item_split() (and uses it internally)

orig : a PangoItem
text : text to which positions in orig apply.
split_index : byte index of position to split item, relative to the start of the item
Returns : new item representing text before split_index

Since 1.2


pango_glyph_item_apply_attrs ()

GSList*     pango_glyph_item_apply_attrs    (PangoGlyphItem *glyph_item,
                                             const char *text,
                                             PangoAttrList *list);

Splits a shaped item (PangoGlyphItem) into multiple items based on an attribute list. The idea is that if you have attributes that don't affect shaping, such as color or underline, to avoid affecting shaping, you filter them out (pango_attr_list_filter()), apply the shaping process and then reapply them to the result using this function.

All attributes that start or end inside a cluster are applied to that cluster; for instance, if half of a cluster is underlined and the other-half strikethough, then the cluster will end up with both underline and strikethrough attributes. In these cases, it may happen that item->extra_attrs for some of the result items can have multiple attributes of the same type.

This function takes ownership of glyph_item; it will be reused as one of the elements in the list.

glyph_item : a shaped item
text : text that list applies to
list : a PangoAttrList
Returns : a list of glyph items resulting from splitting glyph_item. Free the elements using pango_glyph_item_free(), the list using g_slist_free().

Since 1.2


pango_glyph_item_letter_space ()

void        pango_glyph_item_letter_space   (PangoGlyphItem *glyph_item,
                                             const char *text,
                                             PangoLogAttr *log_attrs,
                                             int letter_spacing);

Adds spacing between the graphemes of glyph_item to give the effect of typographic letter spacing.b

glyph_item : a PangoGlyphItem
text : text that glyph_item corresponds to (glyph_item->item->offset is an offset from the start of text)
log_attrs : logical attributes for the item (the first logical attribute refers to the position before the first character in the item)
letter_spacing : amount of letter spacing to add in Pango units. May be negative, though too large negative values will give ugly results.

Since 1.6


pango_glyph_item_free ()

void        pango_glyph_item_free           (PangoGlyphItem *glyph_item);

Frees a PangoGlyphItem and memory to which it points.

glyph_item : a PangoGlyphItem