Game Development Reference
In-Depth Information
How it works...
The
createSegment
method creates a new bridge segment that is sphere shaped, both
in
physicsSpace
and the visible world. This is the part that has a mass and can be se-
lected by clicking on it, since
Ray
only collides with spatials.
The
createJoint
method creates the visible connection between the newly created seg-
ment, and the currently selected one. It does this using
Point2PointJoin
t. This is dif-
ferent from, for example,
HingeJoint
, since it's not fixed in space, when several
Point2Pointjoints
are connected and you have something that resembles a bridge.
The mouse selection is covered more in depth in other chapters, but it works by shooting
Ray
from the mouse's position on the screen, inwards into the game world. Once
Ray
hits
Geometry
(which has
BoundingSphere
that is slightly larger than the visible mesh for
increased selectability), the corresponding
RigidBodyControl
will be selected.
There's no challenge in a bridge-building game if the segments don't have a maximum
force they can handle before they break. This is what we take care of in the
update
meth-
od where we check
appliedImpulse
on each segment. If it goes above a certain
threshold, it can be considered to be overloaded and removed, often with disastrous results.
We also set
linearVelocity
along the
z
axis on each segment to
0
since it's a 2D game
and we don't want anything to move to the depth layer.
We start the game with the physics simulation off by setting the speed of
bulletAp-
pState
to
0
. Without doing so, building the game will get tricky pretty fast as everything
will fall down. Pressing the Space bar will start the physics, and let the player know wheth-
er their engineering skills are up to par.
