Vertical Text
Vertical Text — Laying text out in vertical directions
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Object Hierarchy
GEnum
├── PangoGravity
╰── PangoGravityHint
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 using pango_context_set_base_gravity()
and rotate the layout normally. Pango will make sure that
Asian languages take the right form, while other scripts are rotated normally.
The correct way to set gravity on a layout is to set it on the context
associated with it using pango_context_set_base_gravity(). The context
of a layout can be accessed using pango_layout_get_context(). The currently
set base gravity of the context can be accessed using
pango_context_get_base_gravity() and the resolved
gravity of it using pango_context_get_gravity(). The resolved gravity is
the same as the base gravity for the most part, except that if the base
gravity is set to PANGO_GRAVITY_AUTO, the resolved gravity will depend
on the current matrix set on context, and is derived using
pango_gravity_get_for_matrix().
The next thing an application may want to set on the context is the
gravity hint. A PangoGravityHint instructs how
different scripts should react to the set base gravity.
Font descriptions have a gravity property too, that can be set using
pango_font_description_set_gravity() and accessed using
pango_font_description_get_gravity(). However, those are rarely useful
from application code and are mainly used by PangoLayout internally.
Last but not least, one can create PangoAttributes for gravity
and gravity hint using pango_attr_gravity_new() and
pango_attr_gravity_hint_new().
Functions
PANGO_GRAVITY_IS_IMPROPER()
#define PANGO_GRAVITY_IS_IMPROPER(gravity)
Whether a PangoGravity represents a gravity that results in reversal of text direction.
Since: 1.32
PANGO_GRAVITY_IS_VERTICAL()
#define PANGO_GRAVITY_IS_VERTICAL(gravity)
Whether a PangoGravity represents vertical writing directions.
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.
Since: 1.16
pango_gravity_get_for_script_and_width ()
PangoGravity
pango_gravity_get_for_script_and_width
(PangoScript script,
gboolean wide,
PangoGravity base_gravity,
PangoGravityHint hint);
Based on the script, East Asian width, base gravity, and hint,
returns actual gravity to use in laying out a single character
or PangoItem.
This function is similar to pango_gravity_get_for_script() except
that this function makes a distinction between narrow/half-width and
wide/full-width characters also. Wide/full-width characters always
stand upright, that is, they always take the base gravity,
whereas narrow/full-width characters are always rotated in vertical
context.
If base_gravity
is PANGO_GRAVITY_AUTO, it is first replaced with the
preferred gravity of script
.
Returns
resolved gravity suitable to use for a run of text
with script
and wide
.
Since: 1.26
Types and Values
enum 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.
Since: 1.16