A method for generating realistic image data of particle system objects locations
of which change as time passes, in a light operation load and a little storage
capacity. The method for generating image data of a virtual space viewed from a
predetermined view point, comprises: providing a particle system object group comprising
at least one particle system object in the virtual space, according to a predetermined
rule, continuously or intermittently; determining a displacement point in the virtual
space; moving the displacement point in a predetermined direction as time passes;
and moving the particle system object group on the basis of the displacement point.
