by blabbler » Sat Jul 11, 2009 6:26 am
right, you've got a few things you can play with. you can change the strength of the force, which will determine how fast the fragments fly apart.
you've also got viscocity, which is like air resistance, so with a low force and a high viscocity, the fragments will only move a very short distance before they come to a halt.
you can also animate the radius of the force.
the depth of the force you'll probably want to leave alone (this is the centre of the force sphere in z-space)
you've got to imagine each force as a sphere with falloff, so the force is strongest at the centre of the sphere, weakest at the periphery, and nonexistent outside the sphere.
i would try start with force 1 at zero radius, low strength, turn the viscocity (under physics) up a bit.
position both forces in the centre of your layer
animate the radius of force 1 from zero up to something sufficient to cover the whole layer.
if you animate the radius slowly, it will crack from the centre to the edges.
the fragments velocity will be overpowered by the viscocity, so they just stop and hang in midair after a short while (tweak the strength of force 1 and the viscocity to get this looking like small cracks)
now simultaneously animate in force 2 and bring down the viscocity to get the desired shatter.
you'll need to play with the gravity too to get the fragments moving where you want. for the initial cracking, it would probably be best to have zero gravity so the fragments just drift apart a few pixels.
