Chapter 6: The World in Action: Handling Collisions

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Answer

1

A collision solid is a shape used to define a mass for collision purposes.

2

CollisionNodes store many variables that determine collision behavior, including collision solids.

3

A CollisionTraverser is an object that does the actual work of checking to see if collisions happen.

4

The traverse method is passed as NodePath, and the NodePath matters because only that NodePath and its children will be checked for collisions; the rest of the scene graph won't.

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Answer

1

They generate events based on collisions, according to the patterns that we define for them.

2

A collision entry object.

3

%fn and %in, which are replaced by the names of the From and Into CollisionNodes, respectively.

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Answer

1

A BitMask is a series of 32 bits that can either be 0 or 1.

2

To limit the amount of possible collisions to the bare minimum to increase the overall performance of the game.

3

Using the setFromCollideMask and setIntoCollideMask methods.

4

A From mask limits what an object can cause a collision with; an Into mask limits what can collide with the masked object.

5

Yes, because bit 5 on both masks is set to 1.

Question number

Answer

1

Using the setPythonTag() method.

2

Any Python object we want.

3

Using the getPythonTag() method.

4

A PythonTag will retain a reference to whatever is put in it, so we have to be careful to remove these references if we want that object to be removed from memory later.

Question number

Answer

1

With the sortEntries() method.

2

To get the CollisionNodes we use the getFromNodePath(), and getIntoNodePath() methods. To get the solids themselves, we use the getFrom() and getInto() methods.

3

Since we had two CollisionRays pointing down from the cycle, we checked to make sure that both of them collided with the track. if either of them didn't, then the cycle went off the track.

4

We used the getSurfacePoint() method of the collision entry object to which we passed render in order to make sure we got the point in the coordinate of the render system. We could pass in a different NodePath to get the point in a different coordinate system.

5

We checked the height of the points where our CollisionRays collided with the track and compared them to determine the slope our cycle was on, and changed our pitch to match it. We did this by placing a reference NodePath at one collision point and telling it to look at the other, which forced the reference NodePath to have the pitch our cycle should have.