gtk-demo: Add paintable demo

demos/gtk-demo/demo.gresource.xml

@@ -182,6 +182,7 @@
     <file>overlay.c</file>
     <file>overlay2.c</file>
     <file>pagesetup.c</file>
+    <file>paintable.c</file>
     <file>panes.c</file>
     <file>pickers.c</file>
     <file>pixbufs.c</file>

demos/gtk-demo/meson.build

@@ -45,6 +45,7 @@ demos = files([
   'modelbutton.c',
   'overlay.c',
   'overlay2.c',
+  'paintable.c',
   'panes.c',
   'pickers.c',
   'pixbufs.c',

demos/gtk-demo/paintable.c

@@ -0,0 +1,149 @@
+/* Paintable/A simple paintable
+ *
+ * GdkPaintable is an interface used by GTK for drawings of any sort
+ * that do not require layouting or positioning.
+ *
+ * This demo code gives a simple example on how a paintable can
+ * be created.
+ *
+ * Paintables can be used in many places inside GTK widgets, but the
+ * most common usage is inside GtkImage and that's what we're going
+ * to do here.
+ */
+
+#include <gtk/gtk.h>
+
+static GtkWidget *window = NULL;
+
+/* First, add the boilerplate for the object itself.
+ * This part would normally go in the header.
+ */
+#define GTK_TYPE_NUCLEAR_ICON (gtk_nuclear_icon_get_type ())
+G_DECLARE_FINAL_TYPE (GtkNuclearIcon, gtk_nuclear_icon, GTK, NUCLEAR_ICON, GObject)
+
+GdkPaintable *gtk_nuclear_icon_new (void);
+
+/* Declare the struct. We have no custom data, so it's very
+ * bare.
+ */
+struct _GtkNuclearIcon
+{
+  GObject parent_instance;
+};
+
+struct _GtkNuclearIconClass
+{
+  GObjectClass parent_class;
+};
+
+/* Here, we implement the functionality required by the GdkPaintable interface */
+static void
+gtk_nuclear_icon_snapshot (GdkPaintable *paintable,
+                           GdkSnapshot  *snapshot,
+                           double        width,
+                           double        height)
+{
+#define RADIUS 0.3
+  cairo_t *cr;
+  double size;
+
+  /* The snapshot function is the only function we need to implement.
+   * It does the actual drawing of the paintable.
+   */
+
+  gtk_snapshot_append_color (snapshot,
+                             &(GdkRGBA) { 0.9, 0.75, 0.15, 1.0 },
+                             &GRAPHENE_RECT_INIT (0, 0, width, height),
+                             "Yellow background");
+
+  size = MIN (width, height);
+  cr = gtk_snapshot_append_cairo (snapshot,
+                                  &GRAPHENE_RECT_INIT ((width - size) / 2.0,
+                                                       (height - size) / 2.0,
+                                                       size, size),
+                                  "Radioactive Icon");
+  cairo_translate (cr, width / 2.0, height / 2.0);
+  cairo_scale (cr, size, size);
+
+  cairo_arc (cr, 0, 0, 0.1, - G_PI, G_PI);
+  cairo_fill (cr);
+
+  cairo_set_line_width (cr, RADIUS);
+  cairo_set_dash (cr, (double[1]) { RADIUS * G_PI / 3 }, 1, 0.0);
+  cairo_arc (cr, 0, 0, RADIUS, - G_PI, G_PI);
+  cairo_stroke (cr);
+
+  cairo_destroy (cr);
+}
+
+static GdkPaintableFlags
+gtk_nuclear_icon_get_flags (GdkPaintable *paintable)
+{
+  /* The flags are very useful to let GTK know that this image
+   * is never going to change.
+   * This allows many optimizations and should therefore always
+   * be set.
+   */
+  return GDK_PAINTABLE_STATIC_CONTENTS | GDK_PAINTABLE_STATIC_SIZE;
+}
+
+static void
+gtk_nuclear_icon_paintable_init (GdkPaintableInterface *iface)
+{
+  iface->snapshot = gtk_nuclear_icon_snapshot;
+  iface->get_flags = gtk_nuclear_icon_get_flags;
+}
+
+/* When defining the GType, we need to implement the GdkPaintable interface */
+G_DEFINE_TYPE_WITH_CODE (GtkNuclearIcon, gtk_nuclear_icon, G_TYPE_OBJECT,
+                         G_IMPLEMENT_INTERFACE (GDK_TYPE_PAINTABLE,
+                                                gtk_nuclear_icon_paintable_init))
+
+/* Here's the boilerplate for the GObject declaration.
+ * We don't need to do anything special here, because we keep no
+ * data of our own.
+ */
+static void
+gtk_nuclear_icon_class_init (GtkNuclearIconClass *klass)
+{
+}
+
+static void
+gtk_nuclear_icon_init (GtkNuclearIcon *nuclear)
+{
+}
+
+/* And finally, we add the simple constructor we declared in the header. */
+GdkPaintable *
+gtk_nuclear_icon_new (void)
+{
+  return g_object_new (GTK_TYPE_NUCLEAR_ICON, NULL);
+}
+
+GtkWidget *
+do_paintable (GtkWidget *do_widget)
+{
+  GdkPaintable *nuclear;
+  GtkWidget *image;
+
+  if (!window)
+    {
+      window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+      gtk_window_set_display (GTK_WINDOW (window),
+                              gtk_widget_get_display (do_widget));
+      gtk_window_set_title (GTK_WINDOW (window), "Nuclear Icon");
+      gtk_window_set_default_size (GTK_WINDOW (window), 300, 200);
+
+      nuclear = gtk_nuclear_icon_new ();
+      image = gtk_image_new_from_paintable (nuclear);
+      gtk_container_add (GTK_CONTAINER (window), image);
+      g_object_unref (nuclear);
+    }
+
+  if (!gtk_widget_get_visible (window))
+    gtk_widget_show (window);
+  else
+    gtk_widget_destroy (window);
+
+  return window;
+}