Commits on Feb 22, 2018

1. Use Pathfinder's more accurate area approximation for distance AA. …

   Smoothstep is not a very good approximation because it has zero
   derivatives at 0.0 and 1.0. It makes edges too sharp (i.e. more
   aliased).
   
   From the comments in `prim_shared.glsl`:
   
   This cubic polynomial approximates the area of a 1x1 pixel square under a
   line, given the signed Euclidean distance from the center of the square to
   that line. Calculating the *exact* area would require taking into account
   not only this distance but also the angle of the line. However, in
   practice, this complexity is not required, as the area is roughly the same
   regardless of the angle.
   
   The coefficients of this polynomial were determined through least-squares
   regression and are accurate to within 2.16% of the total area of the pixel
   square 95% of the time, with a maximum error of 3.53%.

   

   pcwalton authored and gw3583 committed Feb 22, 2018
   6e08d20

2. Update Linux-specific reftests

   

   gw3583 committed Feb 22, 2018

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