framebuffer: expose viewport getters/setters

This exposes experimental cogl_framebuffer APIs for getting and setting
a viewport without having to refer to the implicit CoglContext. It adds
the following experimental API:

  cogl_framebuffer_set_viewport
  cogl_framebuffer_get_viewport4fv
  cogl_framebuffer_get_viewport_x
  cogl_framebuffer_get_viewport_y
  cogl_framebuffer_get_viewport_width
  cogl_framebuffer_get_viewport_height

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

cogl/cogl-framebuffer.c

@@ -507,11 +507,11 @@ _cogl_framebuffer_set_clip_stack (CoglFramebuffer *framebuffer,
 }
 
 void
-_cogl_framebuffer_set_viewport (CoglFramebuffer *framebuffer,
-                                float x,
-                                float y,
-                                float width,
-                                float height)
+cogl_framebuffer_set_viewport (CoglFramebuffer *framebuffer,
+                               float x,
+                               float y,
+                               float width,
+                               float height)
 {
   g_return_if_fail (width > 0 && height > 0);
 
@@ -533,32 +533,32 @@ _cogl_framebuffer_set_viewport (CoglFramebuffer *framebuffer,
 }
 
 float
-_cogl_framebuffer_get_viewport_x (CoglFramebuffer *framebuffer)
+cogl_framebuffer_get_viewport_x (CoglFramebuffer *framebuffer)
 {
   return framebuffer->viewport_x;
 }
 
 float
-_cogl_framebuffer_get_viewport_y (CoglFramebuffer *framebuffer)
+cogl_framebuffer_get_viewport_y (CoglFramebuffer *framebuffer)
 {
   return framebuffer->viewport_y;
 }
 
 float
-_cogl_framebuffer_get_viewport_width (CoglFramebuffer *framebuffer)
+cogl_framebuffer_get_viewport_width (CoglFramebuffer *framebuffer)
 {
   return framebuffer->viewport_width;
 }
 
 float
-_cogl_framebuffer_get_viewport_height (CoglFramebuffer *framebuffer)
+cogl_framebuffer_get_viewport_height (CoglFramebuffer *framebuffer)
 {
   return framebuffer->viewport_height;
 }
 
 void
-_cogl_framebuffer_get_viewport4fv (CoglFramebuffer *framebuffer,
-                                   float *viewport)
+cogl_framebuffer_get_viewport4fv (CoglFramebuffer *framebuffer,
+                                  float *viewport)
 {
   viewport[0] = framebuffer->viewport_x;
   viewport[1] = framebuffer->viewport_y;