tree f566eec58f6d8a688a406645ce4fa7710338aa82
parent 740c330b7300df15fc61765fb166ebaac0862f5a
author Nicolas Capens <capn@google.com> 1660184892 -0400
committer Nicolas Capens <nicolascapens@google.com> 1661533072 +0000

Compute fragment coordinates for wider SIMD groups

This change removes precomputing a 'quad' of the primitive's
origin coordinates, instead just storing the coordinates of the primary
vertex. For point primitives this corresponds to the PointCoord builtin.

Fragments are laid out within a SIMD group as a Z-order curve, also
known as Morton order. The new compactEvenBits() function assists with
computing the relative x and y coordinates of each fragment and is
based on code by Fabian Giesen: https://fgiesen.wordpress.com/2009/12/13/decoding-morton-codes/

Note this change removes work from the setup routine, but adds the minor
cost of two SIMD additions per subgroup in the pixel routine. If the JIT
compiler doesn't already optimize this through loop-invariant code
motion, we could precompute it ourselves once per rasterized primitive.

Bug: b/237494823
Change-Id: I9f0956e5937a4c8687ba7461291ab8a7a9d67307
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/67448
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Sean Risser <srisser@google.com>