Cycles: Pole merging for spherical stereo

The idea of pole merge is to fade interocular distance after a certain
altitude to zero when altitude goes closer to a pole. This should prevent
annoyances looking up in the sky or down to the bottom.

Works for both panorama and perspective cameras when Spherical Stereo
is enabled.

Reviewers: dfelinto, brecht

Reviewed By: brecht

Subscribers: sebastian_k

Differential Revision: https://developer.blender.org/D1998

release/scripts/startup/bl_ui/properties_data_camera.py

@@ -165,7 +165,15 @@ class DATA_PT_camera_stereoscopy(CameraButtonsPanel, Panel):
 
         if is_spherical_stereo:
             col.separator()
-            col.prop(st, "use_spherical_stereo")
+            row = col.row()
+            row.prop(st, "use_spherical_stereo")
+            sub = row.row()
+            sub.active = st.use_spherical_stereo
+            sub.prop(st, "use_pole_merge")
+            row = col.row(align=True)
+            row.active = st.use_pole_merge
+            row.prop(st, "pole_merge_angle_from")
+            row.prop(st, "pole_merge_angle_to")
 
         col.label(text="Pivot:")
         row = col.row()