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Pango Interaction

Pango Interaction — Using Pango in GDK

Properties

GdkScreen * screen Read / Write / Construct Only

Object Hierarchy

    GObject
    ╰── PangoRenderer
        ╰── GdkPangoRenderer

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 render Pango objects to GDK. drawables, and also extend the set of Pango attributes to include stippling and embossing.

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 gdk_draw_layout(); you can also draw pieces of the layout with gdk_draw_layout() or gdk_draw_glyphs(). GdkPangoRenderer is a subclass of PangoRenderer that is used internally to implement these functions. Using it directly or subclassing it can be useful in some cases. See the GdkPangoRenderer documentation for details.

Example 8. Using GdkPangoRenderer to draw transformed text

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#define RADIUS 100
#define N_WORDS 10
#define FONT "Sans Bold 18"
GdkScreen *screen = gdk_drawable_get_screen (drawable);
PangoRenderer *renderer;
GdkGC *gc;
PangoMatrix matrix = PANGO_MATRIX_INIT;
PangoContext *context;
PangoLayout *layout;
PangoFontDescription *desc;
double device_radius;
int width, height;
int i;
/* Get the default renderer for the screen, and set it up for drawing  */
renderer = gdk_pango_renderer_get_default (screen);
gdk_pango_renderer_set_drawable (GDK_PANGO_RENDERER (renderer), drawable);
gc = gdk_gc_new (drawable);
gdk_pango_renderer_set_gc (GDK_PANGO_RENDERER (renderer), gc);
/* 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 */
gdk_drawable_get_size (drawable, &width, &height);
device_radius = MIN (width, height) / 2.;
pango_matrix_translate (&matrix,
                        device_radius + (width - 2 * device_radius) / 2,
                        device_radius + (height - 2 * device_radius) / 2);
pango_matrix_scale (&matrix, device_radius / RADIUS, device_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++)
  {
    GdkColor color;
    PangoMatrix rotated_matrix = matrix;
    int width, height;
    double angle = (360. * i) / N_WORDS;
    /* Gradient from red at angle == 60 to blue at angle == 300 */
    color.red   = 65535 * (1 + cos ((angle - 60) * M_PI / 180.)) / 2;
    color.green = 0;
    color.blue  = 65535  - color.red;
    gdk_pango_renderer_set_override_color (GDK_PANGO_RENDERER (renderer),
                                           PANGO_RENDER_PART_FOREGROUND, &color);
    pango_matrix_rotate (&rotated_matrix, angle);
    pango_context_set_matrix (context, &rotated_matrix);
    /* Inform Pango to re-layout the text with the new transformation matrix */
    pango_layout_context_changed (layout);
    pango_layout_get_size (layout, &width, &height);
    pango_renderer_draw_layout (renderer, layout,
                                - width / 2, - RADIUS * PANGO_SCALE);
  }
/* Clean up default renderer, since it is shared */
gdk_pango_renderer_set_override_color (GDK_PANGO_RENDERER (renderer),
                                       PANGO_RENDER_PART_FOREGROUND, NULL);
gdk_pango_renderer_set_drawable (GDK_PANGO_RENDERER (renderer), NULL);
gdk_pango_renderer_set_gc (GDK_PANGO_RENDERER (renderer), NULL);
/* free the objects we created */
g_object_unref (layout);
g_object_unref (context);
g_object_unref (gc);


Functions

gdk_pango_renderer_new ()

PangoRenderer *
gdk_pango_renderer_new (GdkScreen *screen);

Creates a new PangoRenderer for screen . Normally you can use the results of gdk_pango_renderer_get_default() rather than creating a new renderer.

Parameters

screen

a GdkScreen

 

Returns

a newly created PangoRenderer. Free with g_object_unref().

Since: 2.6


gdk_pango_renderer_get_default ()

PangoRenderer *
gdk_pango_renderer_get_default (GdkScreen *screen);

Gets the default PangoRenderer for a screen. This default renderer is shared by all users of the display, so properties such as the color or transformation matrix set for the renderer may be overwritten by functions such as gdk_draw_layout().

Before using the renderer, you need to call gdk_pango_renderer_set_drawable() and gdk_pango_renderer_set_gc() to set the drawable and graphics context to use for drawing.

Parameters

screen

a GdkScreen

 

Returns

the default PangoRenderer for screen . The renderer is owned by GTK+ and will be kept around until the screen is closed.

Since: 2.6


gdk_pango_renderer_set_drawable ()

void
gdk_pango_renderer_set_drawable (GdkPangoRenderer *gdk_renderer,
                                 GdkDrawable *drawable);

Sets the drawable the renderer draws to.

Parameters

gdk_renderer

a GdkPangoRenderer

 

drawable

the new target drawable, or NULL.

[allow-none]

Since: 2.6


gdk_pango_renderer_set_gc ()

void
gdk_pango_renderer_set_gc (GdkPangoRenderer *gdk_renderer,
                           GdkGC *gc);

Sets the GC the renderer draws with. Note that the GC must not be modified until it is unset by calling the function again with NULL for the gc parameter, since GDK may make internal copies of the GC which won't be updated to follow changes to the original GC.

Parameters

gdk_renderer

a GdkPangoRenderer

 

gc

the new GC to use for drawing, or NULL.

[allow-none]

Since: 2.6


gdk_pango_renderer_set_stipple ()

void
gdk_pango_renderer_set_stipple (GdkPangoRenderer *gdk_renderer,
                                PangoRenderPart part,
                                GdkBitmap *stipple);

Sets the stipple for one render part (foreground, background, underline, etc.) Note that this is overwritten when iterating through the individual styled runs of a PangoLayout or PangoLayoutLine. This function is thus only useful when you call low level functions like pango_renderer_draw_glyphs() directly, or in the 'prepare_run' virtual function of a subclass of GdkPangoRenderer.

Parameters

gdk_renderer

a GdkPangoRenderer

 

part

the part to render with the stipple

 

stipple

the new stipple value.

 

Since: 2.6


gdk_pango_renderer_set_override_color ()

void
gdk_pango_renderer_set_override_color (GdkPangoRenderer *gdk_renderer,
                                       PangoRenderPart part,
                                       const GdkColor *color);

Sets the color for a particular render part (foreground, background, underline, etc.), overriding any attributes on the layouts renderered with this renderer.

Parameters

gdk_renderer

a GdkPangoRenderer

 

part

the part to render to set the color of

 

color

the color to use, or NULL to unset a previously set override color.

[allow-none]

Since: 2.6


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


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

Since: 2.2


gdk_pango_context_set_colormap ()

void
gdk_pango_context_set_colormap (PangoContext *context,
                                GdkColormap *colormap);

gdk_pango_context_set_colormap is deprecated and should not be used in newly-written code.

This function used to set the colormap to be used for drawing with context . The colormap is now always derived from the graphics context used for drawing, so calling this function is no longer necessary.

Parameters

context

a PangoContext

 

colormap

a GdkColormap

 

gdk_pango_attr_emboss_color_new ()

PangoAttribute *
gdk_pango_attr_emboss_color_new (const GdkColor *color);

Creates a new attribute specifying the color to emboss text with.

Parameters

color

a GdkColor representing the color to emboss with

 

Returns

new PangoAttribute

Since: 2.12


gdk_pango_attr_embossed_new ()

PangoAttribute *
gdk_pango_attr_embossed_new (gboolean embossed);

Creates a new attribute flagging a region as embossed or not.

Parameters

embossed

if the region should be embossed

 

Returns

new PangoAttribute


gdk_pango_attr_stipple_new ()

PangoAttribute *
gdk_pango_attr_stipple_new (GdkBitmap *stipple);

Creates a new attribute containing a stipple bitmap to be used when rendering the text.

Parameters

stipple

a bitmap to be set as stipple

 

Returns

new PangoAttribute


gdk_pango_layout_get_clip_region ()

GdkRegion *
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 same position you would pass to gdk_draw_layout_line(). 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.

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 ()

GdkRegion *
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 same position you would pass to gdk_draw_layout_line(). 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.

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

 

n_ranges

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

 

Returns

a clip region containing the given ranges

Types and Values

struct GdkPangoRenderer

struct GdkPangoRenderer;

GdkPangoRenderer is a subclass of PangoRenderer used for rendering Pango objects into GDK drawables. The default renderer for a particular screen is obtained with gdk_pango_renderer_get_default(); Pango functions like pango_renderer_draw_layout() and pango_renderer_draw_layout_line() are then used to draw objects with the renderer.

In most simple cases, applications can just use gdk_draw_layout(), and don't need to directly use GdkPangoRenderer at all. Using the GdkPangoRenderer directly is most useful when working with a transformation such as a rotation, because the Pango drawing functions take user space coordinates (coordinates before the transformation) instead of device coordinates.

In certain cases it can be useful to subclass GdkPangoRenderer. Examples of reasons to do this are to add handling of custom attributes by overriding 'prepare_run' or to do custom drawing of embedded objects by overriding 'draw_shape'.

Since: 2.6


struct GdkPangoRendererClass

struct GdkPangoRendererClass {
};

GdkPangoRenderer is the class structure for GdkPangoRenderer.

Since: 2.6


struct GdkPangoAttrEmbossed

struct GdkPangoAttrEmbossed {
  PangoAttribute attr;
  gboolean embossed;
};

A Pango text attribute containing a embossed bitmap to be used when rendering the text.

Members

PangoAttribute attr;

the PangoAttribute.

 

gboolean embossed;

the embossed bitmap.

 

struct GdkPangoAttrEmbossColor

struct GdkPangoAttrEmbossColor {
  PangoAttribute attr;
  PangoColor color;
};

A Pango text attribute specifying the color to emboss text with.

Members

PangoAttribute attr;

the PangoAttribute

 

PangoColor color;

the color

 

struct GdkPangoAttrStipple

struct GdkPangoAttrStipple {
  PangoAttribute attr;
  GdkBitmap *stipple;
};

A Pango text attribute containing a stipple bitmap to be used when rendering the text.

Members

PangoAttribute attr;

the PangoAttribute.

 

GdkBitmap *stipple;

the stipple bitmap.

 

Property Details

The “screen” property

  “screen”                   GdkScreen *

the GdkScreen for the renderer.

Flags: Read / Write / Construct Only

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