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drawingarea: Update docs around background handling

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The behavior changed this cycle. Update the docs to recommend
an explicit gtk_render_background call.
This commit is contained in:
Matthias Clasen 2016-02-21 00:46:54 -05:00
parent 52e0ab53dc
commit 5a80a35757
1 changed files with 12 additions and 5 deletions
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17
gtk/gtkdrawingarea.c
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@ -56,9 +56,10 @@
* area to display a circle in the normal widget foreground
* color.
*
* Note that GDK automatically clears the exposed area to the
* background color before sending the expose event, and that
* drawing is implicitly clipped to the exposed area.
* Note that GDK automatically clears the exposed area before sending
* the expose event, and that drawing is implicitly clipped to the exposed
* area. If you want to have a theme-provided background, you need
* to call gtk_render_background() in your ::draw method.
*
* ## Simple GtkDrawingArea usage
*
@ -68,16 +69,22 @@
* {
* guint width, height;
* GdkRGBA color;
* GtkStyleContext *context;
*
* context = gtk_widget_get_style_context (widget);
*
* width = gtk_widget_get_allocated_width (widget);
* height = gtk_widget_get_allocated_height (widget);
*
* gtk_render_background (context, cr, 0, 0, width, height);
*
* cairo_arc (cr,
* width / 2.0, height / 2.0,
* MIN (width, height) / 2.0,
* 0, 2 * G_PI);
*
* gtk_style_context_get_color (gtk_widget_get_style_context (widget),
* 0,
* gtk_style_context_get_color (context,
* gtk_style_context_get_state (context),
* &color);
* gdk_cairo_set_source_rgba (cr, &color);
*