| 摘要 |
A method of simulating the appearance of smoke in an electronically generated video image that uses one or more intersecting opaque spheres. Each sphere has a nonuniform smoke density that produces feathered edges. The smoke sphere is an object modeled as a center point (the coordinates of the center of the sphere in three dimensions), a radius (in database coordinates), and a set of parameters that include density and color. The center point is transformed into display screen coordinates, and the radius is transformed into a screen coordinate length. The sphere is projected into a circle in screen coordinates, and a bounding square is generated in screen coordinates that is centered at the sphere center point. The bounding square is then converted into a transparency having color and density attributes added to its data structure. Thus the bounding square has the same data structure as transparent or opaque objects and is processed in the same manner. The transparency is clipped to the boundaries of the display screen. Occlusion processing may then be performed wherein objects located within the smoke cloud are occluded, based upon their relative distance into the cloud. After occlusion processing, a stack of distance-sorted objects are generated to produce an output pixel. If a object has not been occluded for a pixel, it is displayed on the display screen, along with the smoke and other objects. A typical smoke cloud includes several spheres, including one or two large ones that intersect terrain surfaces to appear as hemispheres. The present method forms a smoke cloud that is perspectively invariant, and offers much greater flexibility to provide for dynamic changes in the shape of the smoke cloud.
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