A new type of "Sensor" physics object is available in the GE for advanced
collision management. It's called Sensor for its similarities with the
physics objects that underlie the Near and Radar sensors.
Like the Near and Radar object it is:
- static and ghost
- invisible by default
- always active to ensure correct collision detection
- capable of detecting both static and dynamic objects
- ignoring collision with their parent
- capable of broadphase filtering based on:
* Actor option: the collisioning object must have the Actor flag set to be detected
* property/material: as specified in the collision sensors attached to it
Broadphase filtering is important for performance reason: the collision points
will be computed only for the objects that pass the broahphase filter.
- automatically removed from the simulation when no collision sensor is active on it
Unlike the Near and Radar object it can:
- take any shape, including triangle mesh
- be made visible for debugging (just use the Visible actuator)
- have multiple collision sensors using it
Other than that, the sensor objects are ordinary objects. You can move them
freely or parent them. When parented to a dynamic object, they can provide
advanced collision control to this object.
The type of collision capability depends on the shape:
- box, sphere, cylinder, cone, convex hull provide volume detection.
- triangle mesh provides surface detection but you can give some volume
to the suface by increasing the margin in the Advanced Settings panel.
The margin applies on both sides of the surface.
Performance tip:
- Sensor objects perform better than Near and Radar: they do less synchronizations
because of the Scenegraph optimizations and they can have multiple collision sensors
on them (with different property filtering for example).
- Always prefer simple shape (box, sphere) to complex shape whenever possible.
- Always use broadphase filtering (avoid collision sensor with empty propery/material)
- Use collision sensor only when you need them. When no collision sensor is active
on the sensor object, it is removed from the simulation and consume no CPU.
Known limitations:
- When running Blender in debug mode, you will see one warning line of the console:
"warning btCollisionDispatcher::needsCollision: static-static collision!"
In release mode this message is not printed.
- Collision margin has no effect on sphere, cone and cylinder shape.
Other performance improvements:
- Remove unnecessary interpolation for Near and Radar objects and by extension
sensor objects.
- Use direct matrix copy instead of quaternion to synchronize orientation.
Other bug fix:
- Fix Near/Radar position error on newly activated objects. This was causing
several detection problems in YoFrankie
- Fix margin not passed correctly to gImpact shape.
- Disable force/velocity actions on static objects
Use dynamic linked list to handle scenegraph rather than dumb scan
of the whole tree. The performance improvement depends on the fraction
of moving objects. If most objects are static, the speed up is
considerable. The following table compares the time spent on
scenegraph before and after this commit on a scene with 10000 objects
in various configuratons:
Scenegraph time (ms) Before After
(includes culling)
All objects static, 8.8 1.7
all visible but small fraction
in the view frustrum
All objects static, 7,5 0.01
all invisible.
All objects moving, 14.1 8.4
all visible but small fraction
in the view frustrum
This tables shows that static and invisible objects take no CPU at all
for scenegraph and culling. In the general case, this commit will
speed up the scenegraph between 2x and 5x. Compared to 2.48a, it should
be between 4x and 10x faster. Further speed up is possible by making
the scenegraph cache-friendly.
Next round of performance improvement will be on the rasterizer: use
the same dynamic linked list technique for the mesh slots.
This commit contains a number of performance improvements for the
BGE in the Scenegraph (parent relation between objects in the
scene) and view frustrum culling.
The scenegraph improvement consists in avoiding position update
if the object has not moved since last update and the removal
of redundant updates and synchronization with the physics engine.
The view frustrum culling improvement consists in using the DBVT
broadphase facility of Bullet to build a tree of graphical objects
in the scene. The elements of the tree are Aabb boxes (Aligned
Axis Bounding Boxes) enclosing the objects. This provides good
precision in closed and opened scenes. This new culling system
is enabled by default but just in case, it can be disabled with
a button in the World settings. There is no do_version in this
commit but it will be added before the 2.49 release. For now you
must manually enable the DBVT culling option in World settings
when you open an old file.
The above improvements speed up scenegraph and culling up to 5x.
However, this performance improvement is only visible when
you have hundreds or thousands of objects.
The main interest of the DBVT tree is to allow easy occlusion
culling and automatic LOD system. This will be the object of further
improvements.
This situation corresponds to a group containing only a portion
of a parent hierarchy (the Apricot team needed that to avoid
logic duplication). The BGE will instantiate only the
children that are in the group so that it follows the 3D view
more closely.
As a result, the logic links to the objects in the portion of the
hierarchy that was not replicated will point to inactive objects
(if the groups are stored in inactive layers as they should be).
To keep the logic system consistent, these links are automatically
removed.
This last part of the patch is a general fix that could go in
2.47 but as this situation does not normally occurs in pre-2.47
games, it is not needed.
Profiling revealed that the SceneGraph updated every physics object, whether it moved or not, even though the physics object was at the right place. This would cause SOLID to go and update its bounding boxes, overlap tests etc.
This callback handles the special case (parented objects) where the physics scene needs to be informed of changes to the scenegraph.
Added Python attributes (mass, parent, visible, position, orientation, scaling) to the KX_GameObject module.
Make KX_GameObject use the KX_PyMath Python <-> Moto conversion.
(adding)
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
also the Makefile.in's were from previous patch adding
the system depend stuff to configure.ac
Kent
--
mein@cs.umn.edu
