Cycles: Adding Hilbert Spiral as a tile order for rendering

This patch adds the "Hilbert Spiral", a custom-designed continuous space-filling curve, as a tile order for rendering in Cycles.
It essentially works by dividing the tiles into tile blocks which are processed in a spiral outwards from the center. Inside each
block, the tiles are processed in a regular Hilbert curve pattern. By rotating that pattern according to the spiral direction,
a continuous curve is obtained, which helps with cache coherency and therefore rendering speed.

The curve is a compromise between the faster-rendering Bottom-to-Top etc. orders and the Center order, which is a bit slower,
but starts with the more important areas. The Hilbert Spiral also starts in the center (unless huge tiles are used) and is still
marginally slower than Bottom-to-Top, but noticeably faster than Center.

Reviewers: sergey, #cycles, dingto

Reviewed By: #cycles, dingto

Subscribers: iscream, gregzaal, sergey, mib2berlin

Differential Revision: https://developer.blender.org/D1166

1 files changed, 1 insertions, 0 deletions

diff --git a/intern/cycles/blender/addon/properties.py b/intern/cycles/blender/addon/properties.py
index f48bc93cabf..a64a033591a 100644
--- a/intern/cycles/blender/addon/properties.py
+++ b/intern/cycles/blender/addon/properties.py
@@ -92,6 +92,7 @@ enum_tile_order = (
     ('LEFT_TO_RIGHT', "Left to Right", "Render from left to right"),
     ('TOP_TO_BOTTOM', "Top to Bottom", "Render from top to bottom"),
     ('BOTTOM_TO_TOP', "Bottom to Top", "Render from bottom to top"),
+    ('HILBERT_SPIRAL', "Hilbert Spiral", "Render in a Hilbert Spiral"),
     )
 
 enum_use_layer_samples = (