Description
The Cairo library is a
vector graphics library with a powerful rendering model. It has such
features as anti-aliased primitives, alpha-compositing, and
gradients. Multiple backends for Cairo are available, to allow
rendering to images, to PDF files, and to the screen on X and on other
windowing systems. The functions in this section allow using Pango
to render to Cairo surfaces.
Using Pango with Cairo is straightforward. A PangoContext created
with pango_cairo_font_map_create_context() can be used on any
Cairo context (cairo_t), but needs to be updated to match the
current transformation matrix and target surface of the Cairo context
using pango_cairo_update_context(). The convenience functions
pango_cairo_create_layout() and pango_cairo_update_layout() handle
the common case where the program doesn't need to manipulate the
properties of the PangoContext.
When you get the metrics of a layout or of a piece of a layout using
functions such as pango_layout_get_extents(), the reported metrics
are in user-space coordinates. If a piece of text is 10 units long,
and you call cairo_scale (cr, 2.0), it still is more-or-less 10
units long. However, the results will be affected by hinting
(that is, the process of adjusting the text to look good on the
pixel grid), so you shouldn't assume they are completely independent
of the current transformation matrix. Note that the basic metrics
functions in Pango report results in integer Pango units. To get
to the floating point units used in Cairo divide by PANGO_SCALE.
Using Pango with Cairo
Once you build and run the example code above, you should see the
following result:

Functions
pango_cairo_font_map_get_default ()
PangoFontMap *
pango_cairo_font_map_get_default (void);
Gets a default PangoCairoFontMap to use with Cairo.
Note that the type of the returned object will depend
on the particular font backend Cairo was compiled to use;
You generally should only use the PangoFontMap and
PangoCairoFontMap interfaces on the returned object.
The default Cairo fontmap can be changed by using
pango_cairo_font_map_set_default(). This can be used to
change the Cairo font backend that the default fontmap
uses for example.
Note that since Pango 1.32.6, the default fontmap is per-thread.
Each thread gets its own default fontmap. In this way,
PangoCairo can be used safely from multiple threads.
Returns
the default PangoCairo fontmap
for the current thread. This object is owned by Pango and must not be freed.
[transfer none]
Since: 1.10
pango_cairo_font_map_set_default ()
void
pango_cairo_font_map_set_default (PangoCairoFontMap *fontmap);
Sets a default PangoCairoFontMap to use with Cairo.
This can be used to change the Cairo font backend that the
default fontmap uses for example. The old default font map
is unreffed and the new font map referenced.
Note that since Pango 1.32.6, the default fontmap is per-thread.
This function only changes the default fontmap for
the current thread. Default fontmaps of exisiting threads
are not changed. Default fontmaps of any new threads will
still be created using pango_cairo_font_map_new().
A value of NULL for fontmap
will cause the current default
font map to be released and a new default font
map to be created on demand, using pango_cairo_font_map_new().
Since: 1.22
pango_cairo_font_map_new ()
PangoFontMap *
pango_cairo_font_map_new (void);
Creates a new PangoCairoFontMap object; a fontmap is used
to cache information about available fonts, and holds
certain global parameters such as the resolution.
In most cases, you can use pango_cairo_font_map_get_default()
instead.
Note that the type of the returned object will depend
on the particular font backend Cairo was compiled to use;
You generally should only use the PangoFontMap and
PangoCairoFontMap interfaces on the returned object.
You can override the type of backend returned by using an
environment variable PANGOCAIRO_BACKEND. Supported types,
based on your build, are fc (fontconfig), win32, and coretext.
If requested type is not available, NULL is returned. Ie.
this is only useful for testing, when at least two backends
are compiled in.
Since: 1.10
pango_cairo_font_map_set_resolution ()
void
pango_cairo_font_map_set_resolution (PangoCairoFontMap *fontmap,
double dpi);
Sets the resolution for the fontmap. This is a scale factor between
points specified in a PangoFontDescription and Cairo units. The
default value is 96, meaning that a 10 point font will be 13
units high. (10 * 96. / 72. = 13.3).
Since: 1.10
pango_cairo_context_set_resolution ()
void
pango_cairo_context_set_resolution (PangoContext *context,
double dpi);
Sets the resolution for the context. This is a scale factor between
points specified in a PangoFontDescription and Cairo units. The
default value is 96, meaning that a 10 point font will be 13
units high. (10 * 96. / 72. = 13.3).
Since: 1.10
pango_cairo_context_get_resolution ()
double
pango_cairo_context_get_resolution (PangoContext *context);
Gets the resolution for the context. See pango_cairo_context_set_resolution()
Returns
the resolution in "dots per inch". A negative value will
be returned if no resolution has previously been set.
Since: 1.10
pango_cairo_context_set_font_options ()
void
pango_cairo_context_set_font_options (PangoContext *context,
const cairo_font_options_t *options);
Sets the font options used when rendering text with this context.
These options override any options that pango_cairo_update_context()
derives from the target surface.
Since: 1.10
pango_cairo_create_context ()
PangoContext *
pango_cairo_create_context (cairo_t *cr);
Creates a context object set up to match the current transformation
and target surface of the Cairo context. This context can then be
used to create a layout using pango_layout_new().
This function is a convenience function that creates a context using
the default font map, then updates it to cr
. If you just need to
create a layout for use with cr
and do not need to access PangoContext
directly, you can use pango_cairo_create_layout() instead.
Since: 1.22
pango_cairo_update_context ()
void
pango_cairo_update_context (cairo_t *cr,
PangoContext *context);
Updates a PangoContext previously created for use with Cairo to
match the current transformation and target surface of a Cairo
context. If any layouts have been created for the context,
it's necessary to call pango_layout_context_changed() on those
layouts.
Since: 1.10
pango_cairo_create_layout ()
PangoLayout *
pango_cairo_create_layout (cairo_t *cr);
Creates a layout object set up to match the current transformation
and target surface of the Cairo context. This layout can then be
used for text measurement with functions like
pango_layout_get_size() or drawing with functions like
pango_cairo_show_layout(). If you change the transformation
or target surface for cr
, you need to call pango_cairo_update_layout()
This function is the most convenient way to use Cairo with Pango,
however it is slightly inefficient since it creates a separate
PangoContext object for each layout. This might matter in an
application that was laying out large amounts of text.
Since: 1.10
pango_cairo_show_glyph_string ()
void
pango_cairo_show_glyph_string (cairo_t *cr,
PangoFont *font,
PangoGlyphString *glyphs);
Draws the glyphs in glyphs
in the specified cairo context.
The origin of the glyphs (the left edge of the baseline) will
be drawn at the current point of the cairo context.
Since: 1.10
pango_cairo_show_glyph_item ()
void
pango_cairo_show_glyph_item (cairo_t *cr,
const char *text,
PangoGlyphItem *glyph_item);
Draws the glyphs in glyph_item
in the specified cairo context,
embedding the text associated with the glyphs in the output if the
output format supports it (PDF for example), otherwise it acts
similar to pango_cairo_show_glyph_string().
The origin of the glyphs (the left edge of the baseline) will
be drawn at the current point of the cairo context.
Note that text
is the start of the text for layout, which is then
indexed by glyph_item->item->offset
.
Since: 1.22
pango_cairo_show_layout_line ()
void
pango_cairo_show_layout_line (cairo_t *cr,
PangoLayoutLine *line);
Draws a PangoLayoutLine in the specified cairo context.
The origin of the glyphs (the left edge of the line) will
be drawn at the current point of the cairo context.
Since: 1.10
pango_cairo_show_layout ()
void
pango_cairo_show_layout (cairo_t *cr,
PangoLayout *layout);
Draws a PangoLayout in the specified cairo context.
The top-left corner of the PangoLayout will be drawn
at the current point of the cairo context.
Since: 1.10
pango_cairo_show_error_underline ()
void
pango_cairo_show_error_underline (cairo_t *cr,
double x,
double y,
double width,
double height);
Draw a squiggly line in the specified cairo context that approximately
covers the given rectangle in the style of an underline used to indicate a
spelling error. (The width of the underline is rounded to an integer
number of up/down segments and the resulting rectangle is centered in the
original rectangle)
Since: 1.14
pango_cairo_glyph_string_path ()
void
pango_cairo_glyph_string_path (cairo_t *cr,
PangoFont *font,
PangoGlyphString *glyphs);
Adds the glyphs in glyphs
to the current path in the specified
cairo context. The origin of the glyphs (the left edge of the baseline)
will be at the current point of the cairo context.
Since: 1.10
pango_cairo_layout_line_path ()
void
pango_cairo_layout_line_path (cairo_t *cr,
PangoLayoutLine *line);
Adds the text in PangoLayoutLine to the current path in the
specified cairo context. The origin of the glyphs (the left edge
of the line) will be at the current point of the cairo context.
Since: 1.10
pango_cairo_layout_path ()
void
pango_cairo_layout_path (cairo_t *cr,
PangoLayout *layout);
Adds the text in a PangoLayout to the current path in the
specified cairo context. The top-left corner of the PangoLayout
will be at the current point of the cairo context.
Since: 1.10
pango_cairo_error_underline_path ()
void
pango_cairo_error_underline_path (cairo_t *cr,
double x,
double y,
double width,
double height);
Add a squiggly line to the current path in the specified cairo context that
approximately covers the given rectangle in the style of an underline used
to indicate a spelling error. (The width of the underline is rounded to an
integer number of up/down segments and the resulting rectangle is centered
in the original rectangle)
Since: 1.14