Vertical Text

Vertical Text — Laying text out in vertical directions

Synopsis




enum                PangoGravity;
#define             PANGO_TYPE_GRAVITY
enum                PangoGravityHint;
#define             PANGO_TYPE_GRAVITY_HINT
#define             PANGO_GRAVITY_IS_VERTICAL           (gravity)
PangoGravity        pango_gravity_get_for_matrix        (const PangoMatrix *matrix);
PangoGravity        pango_gravity_get_for_script        (PangoScript script,
                                                         PangoGravity base_gravity,
                                                         PangoGravityHint hint);

Description

Since 1.16, Pango is able to correctly lay vertical text out. In fact, it can set layouts of mixed vertical and non-vertical text. This section describes the types used for setting vertical text parameters.

The way this is implemented is through the concept of gravity. Gravity of normal Latin text is south. A gravity value of east means that glyphs will be rotated ninety degrees counterclockwise. So, to render vertical text one needs to set the gravity and rotate the layout using the matrix machinery already in place. This has the huge advantage that most algorithms working on a PangoLayout do not need any change as the assumption that lines run in the X direction and stack in the Y direction holds even for vertical text layouts.

Applications should only need to set base gravity on PangoContext in use, and let Pango decide the gravity assigned to each run of text. This automatically handles text with mixed scripts. A very common use is to set the context base gravity to auto and rotate the layout normally. Pango will make sure that Asian languages take the right form, while other scripts are rotated normally.

Details

enum PangoGravity

typedef enum {
  PANGO_GRAVITY_SOUTH,
  PANGO_GRAVITY_EAST,
  PANGO_GRAVITY_NORTH,
  PANGO_GRAVITY_WEST,
  PANGO_GRAVITY_AUTO
} PangoGravity;

The PangoGravity type represents the orientation of glyphs in a segment of text. This is useful when rendering vertical text layouts. In those situations, the layout is rotated using a non-identity PangoMatrix, and then glyph orientation is controlled using PangoGravity. Not every value in this enumeration makes sense for every usage of PangoGravity; for example, PANGO_GRAVITY_AUTO only can be passed to pango_context_set_base_gravity() and can only be returned by pango_context_get_base_gravity().

See also: PangoGravityHint

PANGO_GRAVITY_SOUTH Glyphs stand upright (default)
PANGO_GRAVITY_EAST Glyphs are rotated 90 degrees clockwise
PANGO_GRAVITY_NORTH Glyphs are upside-down
PANGO_GRAVITY_WEST Glyphs are rotated 90 degrees counter-clockwise
PANGO_GRAVITY_AUTO Gravity is resolved from the context matrix

Since 1.16

PANGO_TYPE_GRAVITY

#define PANGO_TYPE_GRAVITY (pango_gravity_get_type())

The GObject type for PangoGravity.

enum PangoGravityHint

typedef enum {
  PANGO_GRAVITY_HINT_NATURAL,
  PANGO_GRAVITY_HINT_STRONG,
  PANGO_GRAVITY_HINT_LINE
} PangoGravityHint;

The PangoGravityHint defines how horizontal scripts should behave in a vertical context. That is, English excerpt in a vertical paragraph for example.

See PangoGravity.

PANGO_GRAVITY_HINT_NATURAL scripts will take their natural gravity based on the base gravity and the script. This is the default.
PANGO_GRAVITY_HINT_STRONG always use the base gravity set, regardless of the script.
PANGO_GRAVITY_HINT_LINE for scripts not in their natural direction (eg. Latin in East gravity), choose per-script gravity such that every script respects the line progression. This means, Latin and Arabic will take opposite gravities and both flow top-to-bottom for example.

Since 1.16

PANGO_TYPE_GRAVITY_HINT

#define PANGO_TYPE_GRAVITY_HINT (pango_gravity_hint_get_type())

The GObject type for PangoGravity.

PANGO_GRAVITY_IS_VERTICAL()

#define             PANGO_GRAVITY_IS_VERTICAL(gravity)

Whether a PangoGravity represents vertical writing directions.

gravity : the PangoGravity to check

Since 1.16

pango_gravity_get_for_matrix ()

PangoGravity        pango_gravity_get_for_matrix        (const PangoMatrix *matrix);

Finds the gravity that best matches the rotation component in a PangoMatrix.

matrix : a PangoMatrix
Returns : the gravity of matrix, which will never be PANGO_GRAVITY_AUTO, or PANGO_GRAVITY_SOUTH if matrix is NULL

Since 1.16

pango_gravity_get_for_script ()

PangoGravity        pango_gravity_get_for_script        (PangoScript script,
                                                         PangoGravity base_gravity,
                                                         PangoGravityHint hint);

Based on the script, base gravity, and hint, returns actual gravity to use in laying out a single PangoItem.

If base_gravity is PANGO_GRAVITY_AUTO, it is first replaced with the preferred gravity of script. To get the preferred gravity of a script, pass PANGO_GRAVITY_AUTO and PANGO_GRAVITY_HINT_STRONG in.

script : PangoScript to query
base_gravity : base gravity of the paragraph
hint : orientation hint
Returns : resolved gravity suitable to use for a run of text

Since 1.16