Pango Interaction

Pango Interaction — Using Pango in GDK

Includes

#include <gdk/gdk.h>

Description

Pango is the text layout system used by GDK and GTK+. The functions and types in this section are used to obtain clip regions for PangoLayouts, and to get PangoContexts that can be used with GDK.

Creating a PangoLayout object is the first step in rendering text, and requires getting a handle to a PangoContext. For GTK+ programs, you’ll usually want to use gtk_widget_get_pango_context(), or gtk_widget_create_pango_layout(), rather than using the lowlevel gdk_pango_context_get_for_screen(). Once you have a PangoLayout, you can set the text and attributes of it with Pango functions like pango_layout_set_text() and get its size with pango_layout_get_size(). (Note that Pango uses a fixed point system internally, so converting between Pango units and pixels using PANGO_SCALE or the PANGO_PIXELS() macro.)

Rendering a Pango layout is done most simply with pango_cairo_show_layout(); you can also draw pieces of the layout with pango_cairo_show_layout_line().

Draw transformed text with Pango and cairo

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
#define RADIUS 100
#define N_WORDS 10
#define FONT "Sans Bold 18"

PangoContext *context;
PangoLayout *layout;
PangoFontDescription *desc;

double radius;
int width, height;
int i;

// Set up a transformation matrix so that the user space coordinates for
// where we are drawing are [-RADIUS, RADIUS], [-RADIUS, RADIUS]
// We first center, then change the scale

width = gdk_window_get_width (window);
height = gdk_window_get_height (window);
radius = MIN (width, height) / 2.;

cairo_translate (cr,
                 radius + (width - 2 * radius) / 2,
                 radius + (height - 2 * radius) / 2);
                 cairo_scale (cr, radius / RADIUS, radius / RADIUS);

// Create a PangoLayout, set the font and text
context = gdk_pango_context_get_for_screen (screen);
layout = pango_layout_new (context);
pango_layout_set_text (layout, "Text", -1);
desc = pango_font_description_from_string (FONT);
pango_layout_set_font_description (layout, desc);
pango_font_description_free (desc);

// Draw the layout N_WORDS times in a circle
for (i = 0; i < N_WORDS; i++)
  {
    double red, green, blue;
    double angle = 2 * G_PI * i / n_words;

    cairo_save (cr);

    // Gradient from red at angle == 60 to blue at angle == 300
    red = (1 + cos (angle - 60)) / 2;
    green = 0;
    blue = 1 - red;

    cairo_set_source_rgb (cr, red, green, blue);
    cairo_rotate (cr, angle);

    // Inform Pango to re-layout the text with the new transformation matrix
    pango_cairo_update_layout (cr, layout);

    pango_layout_get_size (layout, &width, &height);

    cairo_move_to (cr, - width / 2 / PANGO_SCALE, - DEFAULT_TEXT_RADIUS);
    pango_cairo_show_layout (cr, layout);

    cairo_restore (cr);
  }

g_object_unref (layout);
g_object_unref (context);

Output of the example above.

Functions

gdk_pango_layout_get_clip_region ()

cairo_region_t *
gdk_pango_layout_get_clip_region (PangoLayout *layout,
                                  gint x_origin,
                                  gint y_origin,
                                  const gint *index_ranges,
                                  gint n_ranges);

Obtains a clip region which contains the areas where the given ranges of text would be drawn. x_origin and y_origin are the top left point to center the layout. index_ranges should contain ranges of bytes in the layout’s text.

Note that the regions returned correspond to logical extents of the text ranges, not ink extents. So the drawn layout may in fact touch areas out of the clip region. The clip region is mainly useful for highlightling parts of text, such as when text is selected.

[skip]

Parameters

layout

a PangoLayout

 

x_origin

X pixel where you intend to draw the layout with this clip

 

y_origin

Y pixel where you intend to draw the layout with this clip

 

index_ranges

array of byte indexes into the layout, where even members of array are start indexes and odd elements are end indexes

 

n_ranges

number of ranges in index_ranges , i.e. half the size of index_ranges

 

Returns

a clip region containing the given ranges


gdk_pango_layout_line_get_clip_region ()

cairo_region_t *
gdk_pango_layout_line_get_clip_region (PangoLayoutLine *line,
                                       gint x_origin,
                                       gint y_origin,
                                       const gint *index_ranges,
                                       gint n_ranges);

Obtains a clip region which contains the areas where the given ranges of text would be drawn. x_origin and y_origin are the top left position of the layout. index_ranges should contain ranges of bytes in the layout’s text. The clip region will include space to the left or right of the line (to the layout bounding box) if you have indexes above or below the indexes contained inside the line. This is to draw the selection all the way to the side of the layout. However, the clip region is in line coordinates, not layout coordinates.

Note that the regions returned correspond to logical extents of the text ranges, not ink extents. So the drawn line may in fact touch areas out of the clip region. The clip region is mainly useful for highlightling parts of text, such as when text is selected.

[skip]

Parameters

line

a PangoLayoutLine

 

x_origin

X pixel where you intend to draw the layout line with this clip

 

y_origin

baseline pixel where you intend to draw the layout line with this clip

 

index_ranges

array of byte indexes into the layout, where even members of array are start indexes and odd elements are end indexes.

[array]

n_ranges

number of ranges in index_ranges , i.e. half the size of index_ranges

 

Returns

a clip region containing the given ranges


gdk_pango_context_get ()

PangoContext *
gdk_pango_context_get (void);

Creates a PangoContext for the default GDK screen.

The context must be freed when you’re finished with it.

When using GTK+, normally you should use gtk_widget_get_pango_context() instead of this function, to get the appropriate context for the widget you intend to render text onto.

The newly created context will have the default font options (see cairo_font_options_t) for the default screen; if these options change it will not be updated. Using gtk_widget_get_pango_context() is more convenient if you want to keep a context around and track changes to the screen’s font rendering settings.

Returns

a new PangoContext for the default display.

[transfer full]


gdk_pango_context_get_for_screen ()

PangoContext *
gdk_pango_context_get_for_screen (GdkScreen *screen);

Creates a PangoContext for screen .

The context must be freed when you’re finished with it.

When using GTK+, normally you should use gtk_widget_get_pango_context() instead of this function, to get the appropriate context for the widget you intend to render text onto.

The newly created context will have the default font options (see cairo_font_options_t) for the screen; if these options change it will not be updated. Using gtk_widget_get_pango_context() is more convenient if you want to keep a context around and track changes to the screen’s font rendering settings.

Parameters

screen

the GdkScreen for which the context is to be created.

 

Returns

a new PangoContext for screen .

[transfer full]

Since: 2.2


gdk_pango_context_get_for_display ()

PangoContext *
gdk_pango_context_get_for_display (GdkDisplay *display);

Creates a PangoContext for display .

The context must be freed when you’re finished with it.

When using GTK+, normally you should use gtk_widget_get_pango_context() instead of this function, to get the appropriate context for the widget you intend to render text onto.

The newly created context will have the default font options (see cairo_font_options_t) for the display; if these options change it will not be updated. Using gtk_widget_get_pango_context() is more convenient if you want to keep a context around and track changes to the font rendering settings.

Parameters

display

the GdkDisplay for which the context is to be created

 

Returns

a new PangoContext for display .

[transfer full]

Since: 3.22

Types and Values