Game Physics Engine Development, 2nd Edition

454 Chapter 17 Putting It All Together

one frame. In practice objects on either side of this peak should also get some force,

but to a lesser extent. The force equation,

f

a

=

⎧

⎪

⎪

⎪

⎨

⎪

⎪

⎪

⎩

f

b

(1 − (st − d)/kw) when st − kw  d < st

f

b

when st  d < st + w

f

b

(d − st − w)/kw when st + w  d < st + (k + 1)w

0otherwise

has proved useful for me. In it st is the position of the back of the wavefront (i.e., the

speed times the time), k is the w idth of the tail-off on either side of the wave, d is

the distance of an object from the center of the blast, f

a

is the applied force, and f

b

is

the peak blast force, which we’ll calculate in a moment. The equation simply provid ...