I get good guy help in this fourm! Thanks!
now , I meet a problem again!
the following quote from J. Kr¨uger and R. Westermann “Acceleration Techniques for GPU-based Volume Rendering”
The essential mechanism that allows us to effectively integrate early ray termination and empty-space skipping into the ray-casting process is the early z-test. It is applied before the shader program is executed for a particular fragment, and it can be used to avoid the execution thus enabling a fragment processor to process the next incoming fragment. The early z-test, however, is only enabled if all other per-fragment tests are disabled and the fragments depth value is not modified in the shader. The effect of the early z-test can be demonstrated quite easily, by simply drawing an opaque quadrilateral occluding parts of a volume prior to rendering the volume. If the depth test is enabled and depth values have been written in the first pass, a considerable speed up can be perceived that is directly proportional to the area of the occluded parts of the volume.
I can not understand why early z-test can avoid execution of current fragment and make a fragment processor to process the next incoming fragment? who can explain it ? And I want to find some detail information about it and empty space , who can give me some informatin or example code which use the empty space skip technique?
thanks advanced!
