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95 lines
2.8 KiB
Markdown
95 lines
2.8 KiB
Markdown
Title: Pango Interaction
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Pango is the text layout system used by GDK and GTK. The functions
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and types in this section are used to obtain clip regions for
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`PangoLayout`s, and to get `PangoContext`s that can be used with
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GDK.
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## Using Pango in GDK
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Creating a `PangoLayout` object is the first step in rendering text,
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and requires getting a handle to a `PangoContext`. For GTK programs,
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you’ll usually want to use [method@Gtk.Widget.get_pango_context], or
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[method@Gtk.Widget.create_pango_layout]. Once you have a `PangoLayout`,
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you can set the text and attributes of it with Pango functions like
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[method@Pango.Layout.set_text] and get its size with
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[method@Pango.Layout.get_size].
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*Note*: Pango uses a fixed point system internally, so converting
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between Pango units and pixels using `PANGO_SCALE` or the `PANGO_PIXELS()`
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macro.
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Rendering a Pango layout is done most simply with [func@PangoCairo.show_layout];
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you can also draw pieces of the layout with [func@PangoCairo.show_layout_line].
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### Draw transformed text with Pango and cairo
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```c
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#define RADIUS 100
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#define N_WORDS 10
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#define FONT "Sans Bold 18"
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PangoContext *context;
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PangoLayout *layout;
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PangoFontDescription *desc;
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double radius;
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int width, height;
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int i;
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// Set up a transformation matrix so that the user space coordinates for
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// where we are drawing are [-RADIUS, RADIUS], [-RADIUS, RADIUS]
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// We first center, then change the scale
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width = gdk_surface_get_width (surface);
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height = gdk_surface_get_height (surface);
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radius = MIN (width, height) / 2.;
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cairo_translate (cr,
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radius + (width - 2 * radius) / 2,
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radius + (height - 2 * radius) / 2);
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cairo_scale (cr, radius / RADIUS, radius / RADIUS);
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// Create a PangoLayout, set the font and text
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context = gdk_pango_context_get_for_display (display);
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layout = pango_layout_new (context);
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pango_layout_set_text (layout, "Text", -1);
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desc = pango_font_description_from_string (FONT);
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pango_layout_set_font_description (layout, desc);
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pango_font_description_free (desc);
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// Draw the layout N_WORDS times in a circle
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for (i = 0; i < N_WORDS; i++)
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{
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double red, green, blue;
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double angle = 2 * G_PI * i / n_words;
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cairo_save (cr);
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// Gradient from red at angle == 60 to blue at angle == 300
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red = (1 + cos (angle - 60)) / 2;
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green = 0;
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blue = 1 - red;
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cairo_set_source_rgb (cr, red, green, blue);
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cairo_rotate (cr, angle);
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// Inform Pango to re-layout the text with the new transformation matrix
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pango_cairo_update_layout (cr, layout);
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pango_layout_get_size (layout, &width, &height);
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cairo_move_to (cr, - width / 2 / PANGO_SCALE, - DEFAULT_TEXT_RADIUS);
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pango_cairo_show_layout (cr, layout);
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cairo_restore (cr);
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}
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g_object_unref (layout);
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g_object_unref (context);
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```
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The example code above will yield the following result:
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