Real-Time Rendering, Third Edition, 3rd Edition

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18.4. Case Studies 859

zero (facing away from the light). If so, the program sends a KIL command,

which terminates the fragment if the dot product is less than zero. Assume

that the interval result of the dot product is [−1.2, −0.3]. This means that

all possible combinations of the light vectors, l,andthenormals,n,forthe

fragments in the current tile evaluate to a negative dot product. The tile

is then culled because the diffuse shading is guaranteed to be zero.

Assume that the tile size is 8 × 8 pixels, and that the cull shader pro-

gram uses four

7

times [513] as many instructions as the fragment shader

program. This is so because evaluating