onscreen: Adds support for resizable windows

This adds api to be able to request that the window system allows a
given onscreen framebuffer to be resizable, and api to add and remove
resize handlers to be called whenever the framebuffer does actually
change size.

The new functions are:
  cogl_onscreen_{get,set}_resizable()
  cogl_onscreen_{add,remove}_resize_handler()

The examples cogl-hello and cogl-x11-foreign have been updated to use
the new api. To smoke test how Cogl updates the viewport automatically
in response to window resizes the cogl-hello test doesn't explicitly
respond to resize events by setting the viewport and cogl-x11-foreign
responds by setting a viewport that is offset by a quarter of the
window's width/height and half the width and height of the window.

Reviewed-by: Neil Roberts <neil@linux.intel.com>

(cherry picked from commit a1a8cc00bfa2cecaf1007aec5f3dd95dc07b1786)

2 files changed, 23 insertions, 3 deletions

diff --git a/examples/cogl-hello.c b/examples/cogl-hello.c
index a0b002d1..cf0e8f6d 100644
--- a/examples/cogl-hello.c
+++ b/examples/cogl-hello.c
@@ -59,6 +59,8 @@ main (int argc, char **argv)
     cogl_onscreen_show (onscreen);
     data.fb = COGL_FRAMEBUFFER (onscreen);
 
+    cogl_onscreen_set_resizable (onscreen, TRUE);
+
     data.triangle = cogl_primitive_new_p2c4 (data.ctx,
                                              COGL_VERTICES_MODE_TRIANGLES,
                                              3, triangle_vertices);
diff --git a/examples/cogl-x11-foreign.c b/examples/cogl-x11-foreign.c
index 70049f2f..9397f4d4 100644
--- a/examples/cogl-x11-foreign.c
+++ b/examples/cogl-x11-foreign.c
@@ -31,6 +31,16 @@ update_cogl_x11_event_mask (CoglOnscreen *onscreen,
                            &attrs);
 }
 
+static void
+resize_handler (CoglOnscreen *onscreen,
+                int width,
+                int height,
+                void *user_data)
+{
+  CoglFramebuffer *fb = user_data;
+  cogl_framebuffer_set_viewport (fb, width / 4, height / 4, width / 2, height / 2);
+}
+
 int
 main (int argc, char **argv)
 {
@@ -149,6 +159,9 @@ main (int argc, char **argv)
 
   fb = COGL_FRAMEBUFFER (onscreen);
 
+  cogl_onscreen_set_resizable (onscreen, TRUE);
+  cogl_onscreen_add_resize_handler (onscreen, resize_handler, onscreen);
+
   triangle = cogl_primitive_new_p2c4 (ctx, COGL_VERTICES_MODE_TRIANGLES,
                                       3, triangle_vertices);
   pipeline = cogl_pipeline_new (ctx);
@@ -170,13 +183,18 @@ main (int argc, char **argv)
             }
           cogl_xlib_renderer_handle_event (renderer, &event);
         }
-      cogl_framebuffer_clear4f (fb, COGL_BUFFER_BIT_COLOR, 0, 0, 0, 1);
-      cogl_framebuffer_draw_primitive (fb, pipeline, triangle);
-      cogl_onscreen_swap_buffers (onscreen);
 
+      /* After forwarding native events directly to Cogl you should
+       * then allow Cogl to dispatch any corresponding event
+       * callbacks, such as resize notification callbacks...
+       */
       cogl_poll_get_info (ctx, &poll_fds, &n_poll_fds, &timeout);
       g_poll ((GPollFD *) poll_fds, n_poll_fds, 0);
       cogl_poll_dispatch (ctx, poll_fds, n_poll_fds);
+
+      cogl_framebuffer_clear4f (fb, COGL_BUFFER_BIT_COLOR, 0, 0, 0, 1);
+      cogl_framebuffer_draw_primitive (fb, pipeline, triangle);
+      cogl_onscreen_swap_buffers (onscreen);
     }
 
   return 0;