Edit 3D collision shapes

- Passive -> direct voice
- Remove parens in sentences
- Tweak some sentences' wording
- Fix typos
- Add missing Oxford commas

tutorials/physics/collision_shapes_3d.rst

@@ -3,19 +3,24 @@
 Collision shapes (3D)
 =====================
 
+This guide explains:
+
+- The types of collision shapes available in 3D in Godot.
+- Using a convex or a concave mesh as a collision shape.
+- Performance considerations regarding 3D collisions.
+
 Godot provides many kinds of collision shapes, with different performance and
 accuracy tradeoffs.
 
-You can define the body form of a :ref:`class_PhysicsBody` by adding one or more
-:ref:`CollisionShapes <class_CollisionShape>` as child nodes. These nodes act as
-shape holders. In these child nodes, you must add a :ref:`class_Shape`
-*resource* that will define the actual shape of the collision.
+You can define the shape of a :ref:`class_PhysicsBody` by adding one or more
+:ref:`CollisionShapes <class_CollisionShape>` as child nodes. Note that you must
+add a :ref:`class_Shape` *resource* to collision shape nodes in the Inspector
+dock.
 
 .. note::
 
     When you add multiple collision shapes to a single PhysicsBody, you don't
-    have to worry about overlapping shapes since these won't "collide" with each
-    other.
+    have to worry about them overlapping. They won't "collide" with each other.
 
 Primitive collision shapes
 --------------------------
@@ -25,16 +30,16 @@ Godot provides the following primitive collision shape types:
 - :ref:`class_BoxShape`
 - :ref:`class_SphereShape`
 - :ref:`class_CapsuleShape`
-- :ref:`class_CylinderShape` (only when using the Bullet physics engine)
+- :ref:`class_CylinderShape`. It is only available when using the Bullet physics
+  engine.
 
-Using one or several primitive collision shapes, you can represent the collision
-of most smaller objects well. However, for more complex objects such as a large
-ship or a whole level, you may want to use convex shapes or concave shapes
-instead (see below).
+You can represent the collision of most smaller objects using one or more
+primitive shapes. However, for more complex objects, such as a large ship or a
+whole level, you may need convex or concave shapes instead. More on that below.
 
-Primitive shapes are recommended for dynamic objects such as RigidBodies and
-KinematicBodies, as their behavior usually is the most reliable and predictable.
-On top of that, they often provide better performance as well.
+We recommend favoring primitive shapes for dynamic objects such as RigidBodies
+and KinematicBodies as their behavior is the most reliable. They often provide
+better performance as well.
 
 Convex collision shapes
 -----------------------
@@ -43,78 +48,74 @@ Convex collision shapes
 between primitive collision shapes and concave collision shapes. They can
 represent shapes of any complexity, but with an important caveat. As their name
 implies, an individual shape can only represent a *convex* shape. For instance,
-a pyramid is *convex* but a hollow box is *concave*. To represent a concave
-object with a single collision shape, you need to use a concave collision shape
-(see below).
-
-However, depending on the object's complexity, you may get better performance by
-using multiple convex shapes instead of a concave collision shape. This is why
-Godot lets you make use of *convex decomposition* to generate convex shapes that
-roughly match a concave object. That said, this performance advantage no longer
-applies after a certain amount of convex shapes. Due to this, for large and
-complex objects such as a whole level, it's recommended to use concave shapes
-instead.
+a pyramid is *convex*, but a hollow box is *concave*. To define a concave object
+with a single collision shape, you need to use a concave collision shape.
+
+Depending on the object's complexity, you may get better performance by using
+multiple convex shapes instead of a concave collision shape. Godot lets you use
+*convex decomposition* to generate convex shapes that roughly match a hollow
+object. Note this performance advantage no longer applies after a certain amount
+of convex shapes. For large and complex objects such as a whole level, we
+recommend using concave shapes instead.
 
 You can generate one or several convex collision shapes from the editor by
 selecting a MeshInstance and using the **Mesh** menu at the top of the 3D
 viewport. The editor exposes two generation modes:
 
-- **Create Single Convex Collision Sibling** uses the Quickhull algorithm.
-  It creates one CollisionShape node with an automatically generated convex
-  collision shape. Since it only generates a single shape, it provides better
-  performance and is recommended for small objects.
+- **Create Single Convex Collision Sibling** uses the Quickhull algorithm. It
+  creates one CollisionShape node with an automatically generated convex
+  collision shape. Since it only generates a single shape, it provides good
+  performance and is ideal for small objects.
 
-- **Create Multiple Convex Collision Siblings** uses the V-HACD algorithm.
-  It creates several CollisionShape nodes, each with their own convex collision
-  shape. Since it generates multiple shapes, it is more accurate for concave
-  objects at the cost of performance. For objects with medium complexity, it
-  will likely be faster than using a single concave collision shape.
+- **Create Multiple Convex Collision Siblings** uses the V-HACD algorithm. It
+  creates several CollisionShape nodes, each with a convex shape. Since it
+  generates multiple shapes, it is more accurate for concave objects at the cost
+  of performance. For objects with medium complexity, it will likely be faster
+  than using a single concave collision shape.
 
-Concave (trimesh) collision shapes
-----------------------------------
+Concave or trimesh collision shapes
+-----------------------------------
 
-:ref:`Concave collision shapes <class_ConcavePolygonShape>` (also called trimesh
-collision shapes) can take any form, from a few triangles to thousands of
-triangles. Concave shapes are the slowest option, but are also the most accurate
-collision shapes available in Godot. **Concave shapes can only be used within
-StaticBodies.** They will not work with KinematicBodies or RigidBodies unless
-the RigidBody's mode is set to Static.
+:ref:`Concave collision shapes <class_ConcavePolygonShape>`, also called trimesh
+collision shapes, can take any form, from a few triangles to thousands of
+triangles. Concave shapes are the slowest option but are also the most accurate
+in Godot. **You can only use concave shapes within StaticBodies.** They will not
+work with KinematicBodies or RigidBodies unless the RigidBody's mode is Static.
 
 .. note::
 
     Even though concave shapes offer the most accurate *collision*, contact
-    reporting can be less accurate compared to primitive shapes.
+    reporting can be less precise than primitive shapes.
 
-When not using GridMaps for level design, concave collision shapes are usually
-the best approach for level collision. That said, if your level has small
-details, you will probably want to exclude those from collision for better
-performance and reliability. To do so, you can build a simplified collision mesh
-in a 3D modeler and have Godot generate a collision shape for it automatically
-(see below).
+When not using GridMaps for level design, concave shapes are the best approach
+for a level's collision. That said, if your level has small details, you may
+want to exclude those from collision for performance and game feel. To do so,
+you can build a simplified collision mesh in a 3D modeler and have Godot
+generate a collision shape for it automatically. More on that below
 
 Note that unlike primitive and convex shapes, a concave collision shape doesn't
-have an actual "volume". Objects can be placed both *outside* of the shape as
+have an actual "volume". You can place objects both *outside* of the shape as
 well as *inside*.
 
 You can generate a concave collision shape from the editor by selecting a
-MeshInstance and using the **Mesh** menu at the top of the 3D viewport.
-The editor exposes two generation options:
+MeshInstance and using the **Mesh** menu at the top of the 3D viewport. The
+editor exposes two options:
 
-- **Create Trimesh Static Body** is a convenience option. It will create a
-  StaticBody containing a concave shape matching the mesh's geometry.
+- **Create Trimesh Static Body** is a convenient option. It creates a StaticBody
+  containing a concave shape matching the mesh's geometry.
 
-- **Create Trimesh Collision Sibling** will create a CollisionShape node
-  containing the a concave shape matching the mesh's geometry.
+- **Create Trimesh Collision Sibling** creates a CollisionShape node with a
+  concave shape matching the mesh's geometry.
 
 .. note::
 
-    If you need to make a RigidBody *slide* on a concave collision shape, you
-    may notice that sometimes, the RigidBody will bump upwards. To solve this,
-    open **Project > Project Settings** and enable
+    Suppose you need to make a RigidBody *slide* on a concave collision shape.
+    In that case, you may notice that sometimes, the RigidBody will bump
+    upwards. To solve this, open **Project > Project Settings** and enable
     **Physics > 3d > Smooth Trimesh Collision**.
 
     Once you've enabled smooth trimesh collision, make sure the concave shape is
-    the only shape of your StaticBody and that it's at located at its origin
+    the only shape of your StaticBody and that it's located at its origin
     without any rotation. This way, the RigidBody should slide perfectly on the
     StaticBody.
 
@@ -127,19 +128,19 @@ The editor exposes two generation options:
 Performance caveats
 -------------------
 
-While you aren't limited to a single collision shape per PhysicsBody, it's
-recommended to keep the number of shapes as low as possible to improve
-performance. This is especially true for dynamic objects such as RigidBodies and
-KinematicBodies. On top of that, avoid translating, rotating or scaling
+You aren't limited to a single collision shape per PhysicsBody. Still, we
+recommend keeping the number of shapes as low as possible to improve
+performance, especially for dynamic objects like RigidBodies and
+KinematicBodies. On top of that, avoid translating, rotating, or scaling
 CollisionShapes to benefit from the physics engine's internal optimizations.
 
-When a single non-transformed collision shape is used in a StaticBody, the
+When using a single non-transformed collision shape in a StaticBody, the
 engine's *broad phase* algorithm can discard inactive PhysicsBodies. The *narrow
-phase* will then only have to take into account the active bodies's shapes. If a
-StaticBody has many collision shapes, the broad phase would fail and the narrow
-phase (which is slower) must perform a collision check against each shape.
+phase* will then only have to take into account the active bodies' shapes. If a
+StaticBody has many collision shapes, the broad phase will fail. The narrow
+phase, which is slower, must then perform a collision check against each shape.
 
 If you run into performance issues, you may have to make tradeoffs in terms of
-accuracy. Most games out there don't actually have 100% accurate collision. They
-just find creative ways to hide it or otherwise make it unnoticeable during
-normal gameplay :)
+accuracy. Most games out there don't have a 100% accurate collision. They find
+creative ways to hide it or otherwise make it unnoticeable during normal
+gameplay.