tree 9ea3fbb589b1df1cc6604c20850c1883c7dba699
parent 161a76e152419ddec89a81503e05cc7c74315de1
author Nicolas Capens <capn@google.com> 1511381218 -0500
committer Nicolas Capens <nicolascapens@google.com> 1512142453 +0000

Compute cube LOD based on Manhattan distance.

We previously computed the LOD of cube maps using the 3D Euclidean
distance between the intersections of the sampling rays of a quad with
the cube. This underestimates the gradient at the edges where these
rays intersect multiple faces. Instead use the Manhattan distance. This
may overestimate the footprint dimensions, but only leads to slight
blurring instead of aliasing.

Change-Id: I5ddbb39765462b1c55c4143b5806154cbdfe7130
Reviewed-on: https://swiftshader-review.googlesource.com/5173
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>