Added basic volume previz in the scene view

ScriptableRenderPipeline/Core/Volume/Volume.cs

 
             return false;
         }
+
+#if UNITY_EDITOR
+        // TODO: Look into a better volume previsualization system
+        List<Collider> m_TempColliders;
+
+        void OnDrawGizmos()
+        {
+            if (m_TempColliders == null)
+                m_TempColliders = new List<Collider>();
+
+            var colliders = m_TempColliders;
+            GetComponents(colliders);
+
+            if (isGlobal || colliders == null)
+                return;
+
+            var scale = transform.localScale;
+            var invScale = new Vector3(1f / scale.x, 1f / scale.y, 1f / scale.z);
+            Gizmos.matrix = Matrix4x4.TRS(transform.position, transform.rotation, scale);
+            Gizmos.color = new Color(0f, 1f, 0.1f, 0.6f);
+
+            // Draw a separate gizmo for each collider
+            foreach (var collider in colliders)
+            {
+                if (!collider.enabled)
+                    continue;
+
+                // We'll just use scaling as an approximation for volume skin. It's far from being
+                // correct (and is completely wrong in some cases). Ultimately we'd use a distance
+                // field or at least a tesselate + push modifier on the collider's mesh to get a
+                // better approximation, but the current Gizmo system is a bit limited and because
+                // everything is dynamic in Unity and can be changed at anytime, it's hard to keep
+                // track of changes in an elegant way (which we'd need to implement a nice cache
+                // system for generated volume meshes).
+                var type = collider.GetType();
+
+                if (type == typeof(BoxCollider))
+                {
+                    var c = (BoxCollider)collider;
+                    Gizmos.DrawCube(c.center, c.size);
+                    Gizmos.DrawWireCube(c.center, c.size + invScale * blendDistance * 2f);
+                }
+                else if (type == typeof(SphereCollider))
+                {
+                    var c = (SphereCollider)collider;
+                    Gizmos.DrawSphere(c.center, c.radius);
+                    Gizmos.DrawWireSphere(c.center, c.radius + invScale.x * blendDistance);
+                }
+                else if (type == typeof(MeshCollider))
+                {
+                    var c = (MeshCollider)collider;
+
+                    // Only convex mesh colliders are allowed
+                    if (!c.convex)
+                        c.convex = true;
+
+                    // Mesh pivot should be centered or this won't work
+                    Gizmos.DrawMesh(c.sharedMesh);
+                    Gizmos.DrawWireMesh(c.sharedMesh, Vector3.zero, Quaternion.identity, Vector3.one + invScale * blendDistance * 2f);
+                }
+
+                // Nothing for capsule (DrawCapsule isn't exposed in Gizmo), terrain, wheel and
+                // other colliders...
+            }
+
+            colliders.Clear();
+        }
+#endif
     }
 }