yes!that is it!
I totally forgot the ''bake" is a option in the HyperShade/convert a texture into a File texture......

now I get it.thanks.

http://www.thegnomonworkshop.com/tutorials/gravity_vs_uniform/gravity_vs_uniform.html

this is Ragecgi has pasted before.

I wanna know how to make this effect,

"This can be accomplished by...