GPU Pro 5

444 VI Compute

In order to guarantee that the transformed vertices produce rasterizer-friendly

polygons, a distance-based criterion can be used. Indeed, under perspective pro-

jection, the image plane size s at distance z from the camera can be determined

analytically with the relation

s(z)=2z tan



α

2



,

where α ∈ (0,π] is the horizontal field of view. Thus if polygons scale propor-

tionally to s, they are guaranteed to be of approximately constant size in screen

space. Based on this observation, we derived the following routines to determine

whether a node should be split or merged:

float z1 = distance( eye , node_center );

float z2 = distance( eye , parent_center ...