Pango Interaction

## Pango Interaction Pango Interaction — Using Pango in GDK |

## Synopsis

    #include <gdk/gdk.h>

                GdkPangoRenderer;
                GdkPangoRendererClass;
    PangoRenderer* gdk_pango_renderer_new       (GdkScreen *screen);
    PangoRenderer* gdk_pango_renderer_get_default
                                                (GdkScreen *screen);
    void        gdk_pango_renderer_set_drawable (GdkPangoRenderer *gdk_renderer,
                                                 GdkDrawable *drawable);
    void        gdk_pango_renderer_set_gc       (GdkPangoRenderer *gdk_renderer,
                                                 GdkGC *gc);
    void        gdk_pango_renderer_set_stipple  (GdkPangoRenderer *gdk_renderer,
                                                 PangoRenderPart part,
                                                 GdkBitmap *stipple);
    void        gdk_pango_renderer_set_override_color
                                                (GdkPangoRenderer *gdk_renderer,
                                                 PangoRenderPart part,
                                                 const GdkColor *color);
    PangoContext* gdk_pango_context_get         (void);
    PangoContext* gdk_pango_context_get_for_screen
                                                (GdkScreen *screen);
    void        gdk_pango_context_set_colormap  (PangoContext *context,
                                                 GdkColormap *colormap);
                GdkPangoAttrEmbossed;
                GdkPangoAttrStipple;
    PangoAttribute* gdk_pango_attr_embossed_new (gboolean embossed);
    PangoAttribute* gdk_pango_attr_stipple_new  (GdkBitmap *stipple);
    GdkRegion*  gdk_pango_layout_get_clip_region
                                                (PangoLayout *layout,
                                                 gint x_origin,
                                                 gint y_origin,
                                                 gint *index_ranges,
                                                 gint n_ranges);
    GdkRegion*  gdk_pango_layout_line_get_clip_region
                                                (PangoLayoutLine *line,
                                                 gint x_origin,
                                                 gint y_origin,
                                                 gint *index_ranges,
                                                 gint n_ranges);

## Object Hierarchy

      GObject
       +----PangoRenderer
             +----GdkPangoRenderer

## Properties

      "screen"               GdkScreen             : Read / Write / Construct Only

## 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 7. Using GdkPangoRenderer to draw transformed text

    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);

Figure 1. Output of Example 7, “Using GdkPangoRenderer to draw transformed text”

## Details

### GdkPangoRenderer

    typedef struct _GdkPangoRenderer 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

### GdkPangoRendererClass

    typedef struct {
    } GdkPangoRendererClass;

GdkPangoRenderer is the class structure for GdkPangoRenderer.

Since 2.6

### 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.

`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.

`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.

`gdk_renderer` : | a GdkPangoRenderer
`drawable` : | the new target drawable, or `NULL`

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.

`gdk_renderer` : | a GdkPangoRenderer
`gc` : | the new GC to use for drawing, or `NULL`

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.

`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.

`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.

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.

`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);

### Warning

`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.

`context` : | a PangoContext
`colormap` : | a GdkColormap

### GdkPangoAttrEmbossed

    typedef struct {
      PangoAttribute attr;
      gboolean embossed;
    } GdkPangoAttrEmbossed;

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

PangoAttribute `attr`; | the PangoAttribute.
gboolean `embossed`; | the embossed bitmap.

### GdkPangoAttrStipple

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

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

PangoAttribute `attr`; | the PangoAttribute.
GdkBitmap *`stipple`; | the stipple bitmap.

### gdk_pango_attr_embossed_new ()

    PangoAttribute* gdk_pango_attr_embossed_new (gboolean embossed);

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

`embossed` : | a bitmap to be set as 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.

`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,
                                                 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.

`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,
                                                 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.

`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

## Property Details

### The "`screen`" property

      "screen"               GdkScreen             : Read / Write / Construct Only

the GdkScreen for the renderer.