1 files changed, 10 insertions, 0 deletions
diff --git a/components/compositing/constellation.rs b/components/compositing/constellation.rs
index a9271bc0cfd..9b98eb47af9 100644
--- a/components/compositing/constellation.rs
+++ b/components/compositing/constellation.rs
@@ -33,6 +33,7 @@ use std::io::{self, Write};
 use std::marker::PhantomData;
 use std::mem::replace;
 use std::sync::mpsc::{Sender, Receiver, channel};
+use style::viewport::ViewportConstraints;
 use url::Url;
 use util::cursor::Cursor;
 use util::geometry::PagePx;
@@ -417,6 +418,10 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 self.handle_webdriver_command_msg(pipeline_id,
                                                   command);
             }
+            ConstellationMsg::ViewportConstrained(pipeline_id, constraints) => {
+                debug!("constellation got viewport-constrained event message");
+                self.handle_viewport_constrained_msg(pipeline_id, constraints);
+            }
         }
         true
     }
@@ -912,6 +917,11 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
         self.window_size = new_size;
     }
 
+    /// Handle updating actual viewport / zoom due to @viewport rules
+    fn handle_viewport_constrained_msg(&mut self, pipeline_id: PipelineId, constraints: ViewportConstraints) {
+        self.compositor_proxy.send(CompositorMsg::ViewportConstrained(pipeline_id, constraints));
+    }
+
     // Close a frame (and all children)
     fn close_frame(&mut self, frame_id: FrameId, exit_mode: ExitPipelineMode) {
         let frame = self.frames.remove(&frame_id).unwrap();