#[repr(transparent)]
pub struct Layout { /* private fields */ }
Expand description

A Layout structure represents an entire paragraph of text.

While complete access to the layout capabilities of Pango is provided using the detailed interfaces for itemization and shaping, using that functionality directly involves writing a fairly large amount of code. Layout provides a high-level driver for formatting entire paragraphs of text at once. This includes paragraph-level functionality such as line breaking, justification, alignment and ellipsization.

A Layout is initialized with a Context, UTF-8 string and set of attributes for that string. Once that is done, the set of formatted lines can be extracted from the object, the layout can be rendered, and conversion between logical character positions within the layout’s text, and the physical position of the resulting glyphs can be made.

There are a number of parameters to adjust the formatting of a Layout. The following image shows adjustable parameters (on the left) and font metrics (on the right):

Pango Layout Parameters

The following images demonstrate the effect of alignment and justification on the layout of text:

align=leftalign=left, justify
align=centeralign=center, justify
align=rightalign=right, justify

It is possible, as well, to ignore the 2-D setup, and simply treat the results of a Layout as a list of lines.

Implementations

Create a new Layout object with attributes initialized to default values for a particular Context.

context

a Context

Returns

the newly allocated Layout

Forces recomputation of any state in the Layout that might depend on the layout’s context.

This function should be called if you make changes to the context subsequent to creating the layout.

Gets the alignment for the layout: how partial lines are positioned within the horizontal space available.

Returns

the alignment

Gets the attribute list for the layout, if any.

Returns

a AttrList

Gets whether to calculate the base direction for the layout according to its contents.

See set_auto_dir().

Returns

true if the bidirectional base direction is computed from the layout’s contents, false otherwise

Gets the Y position of baseline of the first line in @self.

Returns

baseline of first line, from top of @self

This is supported on crate feature v1_50 only.

Given an index within a layout, determines the positions that of the strong and weak cursors if the insertion point is at that index.

This is a variant of cursor_pos() that applies font metric information about caret slope and offset to the positions it returns.

Caret metrics ## `index_` the byte index of the cursor
Returns
strong_pos

location to store the strong cursor position

weak_pos

location to store the weak cursor position

Returns the number of Unicode characters in the the text of @self.

Returns

the number of Unicode characters in the text of @self

Retrieves the Context used for this layout.

Returns

the Context for the layout

Given an index within a layout, determines the positions that of the strong and weak cursors if the insertion point is at that index.

The position of each cursor is stored as a zero-width rectangle with the height of the run extents.

Cursor positions

The strong cursor location is the location where characters of the directionality equal to the base direction of the layout are inserted. The weak cursor location is the location where characters of the directionality opposite to the base direction of the layout are inserted.

The following example shows text with both a strong and a weak cursor.

Strong and weak cursors

The strong cursor has a little arrow pointing to the right, the weak cursor to the left. Typing a ‘c’ in this situation will insert the character after the ‘b’, and typing another Hebrew character, like ‘ג’, will insert it at the end.

index_

the byte index of the cursor

Returns
strong_pos

location to store the strong cursor position

weak_pos

location to store the weak cursor position

This is supported on crate feature v1_46 only.

Gets the text direction at the given character position in @self.

index

the byte index of the char

Returns

the text direction at @index

Gets the type of ellipsization being performed for @self.

See set_ellipsize().

Use is_ellipsized() to query whether any paragraphs were actually ellipsized.

Returns

the current ellipsization mode for @self

Computes the logical and ink extents of @self.

Logical extents are usually what you want for positioning things. Note that both extents may have non-zero x and y. You may want to use those to offset where you render the layout. Not doing that is a very typical bug that shows up as right-to-left layouts not being correctly positioned in a layout with a set width.

The extents are given in layout coordinates and in Pango units; layout coordinates begin at the top left corner of the layout.

Returns
ink_rect

rectangle used to store the extents of the layout as drawn

logical_rect

rectangle used to store the logical extents of the layout

Gets the font description for the layout, if any.

Returns

a pointer to the layout’s font description, or None if the font description from the layout’s context is inherited.

Gets the height of layout used for ellipsization.

See set_height() for details.

Returns

the height, in Pango units if positive, or number of lines if negative.

Gets the paragraph indent width in Pango units.

A negative value indicates a hanging indentation.

Returns

the indent in Pango units

Returns an iterator to iterate over the visual extents of the layout.

Returns

the new LayoutIter

Gets whether each complete line should be stretched to fill the entire width of the layout.

Returns

the justify value

This is supported on crate feature v1_50 only.

Gets whether the last line should be stretched to fill the entire width of the layout.

Returns

the justify value

Retrieves a particular line from a Layout.

Use the faster line_readonly() if you do not plan to modify the contents of the line (glyphs, glyph widths, etc.).

line

the index of a line, which must be between 0 and pango_layout_get_line_count(layout) - 1, inclusive.

Returns

the requested LayoutLine, or None if the index is out of range. This layout line can be ref’ed and retained, but will become invalid if changes are made to the Layout.

Retrieves the count of lines for the @self.

Returns

the line count

Retrieves a particular line from a Layout.

This is a faster alternative to line(), but the user is not expected to modify the contents of the line (glyphs, glyph widths, etc.).

line

the index of a line, which must be between 0 and pango_layout_get_line_count(layout) - 1, inclusive.

Returns

the requested LayoutLine, or None if the index is out of range. This layout line can be ref’ed and retained, but will become invalid if changes are made to the Layout. No changes should be made to the line.

This is supported on crate feature v1_44 only.

Gets the line spacing factor of @self.

See set_line_spacing().

Returns the lines of the @self as a list.

Use the faster lines_readonly() if you do not plan to modify the contents of the lines (glyphs, glyph widths, etc.).

Returns

a GSList containing the lines in the layout. This points to internal data of the Layout and must be used with care. It will become invalid on any change to the layout’s text or properties.

Returns the lines of the @self as a list.

This is a faster alternative to lines(), but the user is not expected to modify the contents of the lines (glyphs, glyph widths, etc.).

Returns

a GSList containing the lines in the layout. This points to internal data of the Layout and must be used with care. It will become invalid on any change to the layout’s text or properties. No changes should be made to the lines.

Computes the logical and ink extents of @self in device units.

This function just calls extents() followed by two extents_to_pixels() calls, rounding @ink_rect and @logical_rect such that the rounded rectangles fully contain the unrounded one (that is, passes them as first argument to extents_to_pixels()).

Returns
ink_rect

rectangle used to store the extents of the layout as drawn

logical_rect

rectangle used to store the logical extents of the layout

Determines the logical width and height of a Layout in device units.

size() returns the width and height scaled by PANGO_SCALE. This is simply a convenience function around pixel_extents().

Returns
width

location to store the logical width

height

location to store the logical height

Returns the current serial number of @self.

The serial number is initialized to an small number larger than zero when a new layout is created and is increased whenever the layout is changed using any of the setter functions, or the Context it uses has changed. The serial may wrap, but will never have the value 0. Since it can wrap, never compare it with “less than”, always use “not equals”.

This can be used to automatically detect changes to a Layout, and is useful for example to decide whether a layout needs redrawing. To force the serial to be increased, use context_changed().

Returns

The current serial number of @self.

Obtains whether @self is in single paragraph mode.

See set_single_paragraph_mode().

Returns

true if the layout does not break paragraphs at paragraph separator characters, false otherwise

Determines the logical width and height of a Layout in Pango units.

This is simply a convenience function around extents().

Returns
width

location to store the logical width

height

location to store the logical height

Gets the amount of spacing between the lines of the layout.

Returns

the spacing in Pango units

Gets the current TabArray used by this layout.

If no TabArray has been set, then the default tabs are in use and None is returned. Default tabs are every 8 spaces.

The return value should be freed with Pango::TabArray::free().

Returns

a copy of the tabs for this layout

Gets the text in the layout.

The returned text should not be freed or modified.

Returns

the text in the @self

Counts the number of unknown glyphs in @self.

This function can be used to determine if there are any fonts available to render all characters in a certain string, or when used in combination with AttrType::Fallback, to check if a certain font supports all the characters in the string.

Returns

The number of unknown glyphs in @self

Gets the width to which the lines of the Layout should wrap.

Returns

the width in Pango units, or -1 if no width set.

Gets the wrap mode for the layout.

Use is_wrapped() to query whether any paragraphs were actually wrapped.

Returns

active wrap mode.

Converts from byte @index_ within the @self to line and X position.

The X position is measured from the left edge of the line.

index_

the byte index of a grapheme within the layout

trailing

an integer indicating the edge of the grapheme to retrieve the position of. If > 0, the trailing edge of the grapheme, if 0, the leading of the grapheme

Returns
line

location to store resulting line index. (which will between 0 and pango_layout_get_line_count(layout) - 1)

x_pos

location to store resulting position within line (PANGO_SCALE units per device unit)

Converts from an index within a Layout to the onscreen position corresponding to the grapheme at that index.

The return value is represented as rectangle. Note that pos->x is always the leading edge of the grapheme and pos->x + pos->width the trailing edge of the grapheme. If the directionality of the grapheme is right-to-left, then pos->width will be negative.

index_

byte index within @self

Returns
pos

rectangle in which to store the position of the grapheme

Queries whether the layout had to ellipsize any paragraphs.

This returns true if the ellipsization mode for @self is not EllipsizeMode::None, a positive width is set on @self, and there are paragraphs exceeding that width that have to be ellipsized.

Returns

true if any paragraphs had to be ellipsized, false otherwise

Queries whether the layout had to wrap any paragraphs.

This returns true if a positive width is set on @self, ellipsization mode of @self is set to EllipsizeMode::None, and there are paragraphs exceeding the layout width that have to be wrapped.

Returns

true if any paragraphs had to be wrapped, false otherwise

Computes a new cursor position from an old position and a direction.

If @direction is positive, then the new position will cause the strong or weak cursor to be displayed one position to right of where it was with the old cursor position. If @direction is negative, it will be moved to the left.

In the presence of bidirectional text, the correspondence between logical and visual order will depend on the direction of the current run, and there may be jumps when the cursor is moved off of the end of a run.

Motion here is in cursor positions, not in characters, so a single call to this function may move the cursor over multiple characters when multiple characters combine to form a single grapheme.

strong

whether the moving cursor is the strong cursor or the weak cursor. The strong cursor is the cursor corresponding to text insertion in the base direction for the layout.

old_index

the byte index of the current cursor position

old_trailing

if 0, the cursor was at the leading edge of the grapheme indicated by @old_index, if > 0, the cursor was at the trailing edge.

direction

direction to move cursor. A negative value indicates motion to the left

Returns
new_index

location to store the new cursor byte index. A value of -1 indicates that the cursor has been moved off the beginning of the layout. A value of G_MAXINT indicates that the cursor has been moved off the end of the layout.

new_trailing

number of characters to move forward from the location returned for @new_index to get the position where the cursor should be displayed. This allows distinguishing the position at the beginning of one line from the position at the end of the preceding line. @new_index is always on the line where the cursor should be displayed.

This is supported on crate feature v1_50 only.

Serializes the @self for later deserialization via Pango::Layout::deserialize().

There are no guarantees about the format of the output across different versions of Pango and Pango::Layout::deserialize() will reject data that it cannot parse.

The intended use of this function is testing, benchmarking and debugging. The format is not meant as a permanent storage format.

flags

LayoutSerializeFlags

Returns

a GBytes containing the serialized form of @self

Sets the alignment for the layout: how partial lines are positioned within the horizontal space available.

The default alignment is Alignment::Left.

alignment

the alignment

Sets the text attributes for a layout object.

References @attrs, so the caller can unref its reference.

attrs

a AttrList

Sets whether to calculate the base direction for the layout according to its contents.

When this flag is on (the default), then paragraphs in @self that begin with strong right-to-left characters (Arabic and Hebrew principally), will have right-to-left layout, paragraphs with letters from other scripts will have left-to-right layout. Paragraphs with only neutral characters get their direction from the surrounding paragraphs.

When false, the choice between left-to-right and right-to-left layout is done according to the base direction of the layout’s Context. (See Context::set_base_dir()).

When the auto-computed direction of a paragraph differs from the base direction of the context, the interpretation of Alignment::Left and Alignment::Right are swapped.

auto_dir

if true, compute the bidirectional base direction from the layout’s contents

Sets the type of ellipsization being performed for @self.

Depending on the ellipsization mode @ellipsize text is removed from the start, middle, or end of text so they fit within the width and height of layout set with set_width() and set_height().

If the layout contains characters such as newlines that force it to be layed out in multiple paragraphs, then whether each paragraph is ellipsized separately or the entire layout is ellipsized as a whole depends on the set height of the layout.

The default value is EllipsizeMode::None.

See set_height() for details.

ellipsize

the new ellipsization mode for @self

Sets the default font description for the layout.

If no font description is set on the layout, the font description from the layout’s context is used.

desc

the new FontDescription to unset the current font description

Sets the height to which the Layout should be ellipsized at.

There are two different behaviors, based on whether @height is positive or negative.

If @height is positive, it will be the maximum height of the layout. Only lines would be shown that would fit, and if there is any text omitted, an ellipsis added. At least one line is included in each paragraph regardless of how small the height value is. A value of zero will render exactly one line for the entire layout.

If @height is negative, it will be the (negative of) maximum number of lines per paragraph. That is, the total number of lines shown may well be more than this value if the layout contains multiple paragraphs of text. The default value of -1 means that the first line of each paragraph is ellipsized. This behavior may be changed in the future to act per layout instead of per paragraph. File a bug against pango at https://gitlab.gnome.org/gnome/pango if your code relies on this behavior.

Height setting only has effect if a positive width is set on @self and ellipsization mode of @self is not EllipsizeMode::None. The behavior is undefined if a height other than -1 is set and ellipsization mode is set to EllipsizeMode::None, and may change in the future.

height

the desired height of the layout in Pango units if positive, or desired number of lines if negative.

Sets the width in Pango units to indent each paragraph.

A negative value of @indent will produce a hanging indentation. That is, the first line will have the full width, and subsequent lines will be indented by the absolute value of @indent.

The indent setting is ignored if layout alignment is set to Alignment::Center.

The default value is 0.

indent

the amount by which to indent

Sets whether each complete line should be stretched to fill the entire width of the layout.

Stretching is typically done by adding whitespace, but for some scripts (such as Arabic), the justification may be done in more complex ways, like extending the characters.

Note that this setting is not implemented and so is ignored in Pango older than 1.18.

Note that tabs and justification conflict with each other: Justification will move content away from its tab-aligned positions.

The default value is false.

Also see set_justify_last_line().

justify

whether the lines in the layout should be justified

This is supported on crate feature v1_50 only.

Sets whether the last line should be stretched to fill the entire width of the layout.

This only has an effect if set_justify() has been called as well.

The default value is false.

justify

whether the last line in the layout should be justified

This is supported on crate feature v1_44 only.

Sets a factor for line spacing.

Typical values are: 0, 1, 1.5, 2. The default values is 0.

If @factor is non-zero, lines are placed so that

baseline2 = baseline1 + factor * height2

where height2 is the line height of the second line (as determined by the font(s)). In this case, the spacing set with set_spacing() is ignored.

If @factor is zero (the default), spacing is applied as before.

Note: for semantics that are closer to the CSS line-height property, see attr_line_height_new().

factor

the new line spacing factor

Sets the layout text and attribute list from marked-up text.

See Pango Markup).

Replaces the current text and attribute list.

This is the same as set_markup_with_accel(), but the markup text isn’t scanned for accelerators.

markup

marked-up text

length

length of marked-up text in bytes, or -1 if @markup is NUL-terminated

Sets the layout text and attribute list from marked-up text.

See Pango Markup).

Replaces the current text and attribute list.

If @accel_marker is nonzero, the given character will mark the character following it as an accelerator. For example, @accel_marker might be an ampersand or underscore. All characters marked as an accelerator will receive a Underline::Low attribute, and the first character so marked will be returned in @accel_char. Two @accel_marker characters following each other produce a single literal @accel_marker character.

markup

marked-up text (see Pango Markup)

length

length of marked-up text in bytes, or -1 if @markup is NUL-terminated

accel_marker

marker for accelerators in the text

Returns
accel_char

return location for first located accelerator

Sets the single paragraph mode of @self.

If @setting is true, do not treat newlines and similar characters as paragraph separators; instead, keep all text in a single paragraph, and display a glyph for paragraph separator characters. Used when you want to allow editing of newlines on a single text line.

The default value is false.

setting

new setting

Sets the amount of spacing in Pango units between the lines of the layout.

When placing lines with spacing, Pango arranges things so that

line2.top = line1.bottom + spacing

The default value is 0.

Note: Since 1.44, Pango is using the line height (as determined by the font) for placing lines when the line spacing factor is set to a non-zero value with set_line_spacing(). In that case, the @spacing set with this function is ignored.

Note: for semantics that are closer to the CSS line-height property, see attr_line_height_new().

spacing

the amount of spacing

Sets the tabs to use for @self, overriding the default tabs.

Layout will place content at the next tab position whenever it meets a Tab character (U+0009).

By default, tabs are every 8 spaces. If @tabs is None, the default tabs are reinstated. @tabs is copied into the layout; you must free your copy of @tabs yourself.

Note that tabs and justification conflict with each other: Justification will move content away from its tab-aligned positions. The same is true for alignments other than Alignment::Left.

tabs

a TabArray

Sets the text of the layout.

This function validates @text and renders invalid UTF-8 with a placeholder glyph.

Note that if you have used set_markup() or set_markup_with_accel() on @self before, you may want to call set_attributes() to clear the attributes set on the layout from the markup as this function does not clear attributes.

text

the text

length

maximum length of @text, in bytes. -1 indicates that the string is nul-terminated and the length should be calculated. The text will also be truncated on encountering a nul-termination even when @length is positive.

Sets the width to which the lines of the Layout should wrap or ellipsized.

The default value is -1: no width set.

width

the desired width in Pango units, or -1 to indicate that no wrapping or ellipsization should be performed.

Sets the wrap mode.

The wrap mode only has effect if a width is set on the layout with set_width(). To turn off wrapping, set the width to -1.

The default value is WrapMode::Word.

wrap

the wrap mode

This is supported on crate feature v1_50 only.

A convenience method to serialize a layout to a file.

It is equivalent to calling serialize() followed by file_set_contents().

See those two functions for details on the arguments.

It is mostly intended for use inside a debugger to quickly dump a layout to a file for later inspection.

flags

LayoutSerializeFlags

filename

the file to save it to

Returns

true if saving was successful

Converts from X and Y position within a layout to the byte index to the character at that logical position.

If the Y position is not inside the layout, the closest position is chosen (the position will be clamped inside the layout). If the X position is not within the layout, then the start or the end of the line is chosen as described for LayoutLine::x_to_index(). If either the X or Y positions were not inside the layout, then the function returns false; on an exact hit, it returns true.

x

the X offset (in Pango units) from the left edge of the layout

y

the Y offset (in Pango units) from the top edge of the layout

Returns

true if the coordinates were inside text, false otherwise

index_

location to store calculated byte index

trailing

location to store a integer indicating where in the grapheme the user clicked. It will either be zero, or the number of characters in the grapheme. 0 represents the leading edge of the grapheme.

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