The compostor used a fixed size of 4 floats to hold pixel data. this
patch will select size of a pixel based on its type.
It uses 1 float for Value, 3 float for vector and 4 floats for color
data types.
When benchmarking on shots (opening shot of caminandes) we get a
reduction of memory of 30% and a tiny speedup as less data
transformations needs to take place (but these are negligable.
More information of the patch can be found on
https://developer.blender.org/D627 and
http://wiki.blender.org/index.php/Dev:Ref/Proposals/Compositor2014_p1.1_TD
Developers: jbakker & mdewanchand
Thanks for Sergey for his indept review.
Buffers should actually be cleared before running operations on them,
but this doesn't work for some reason.
Note also that the sunbeams node can show some creases and hard aliasing
when the source point is close to a bright area with strong gradient.
To fix this a better filtering algorithm, dithering or ray sampling
would need to be implemented. In the meantime simply blurring the
sunbeams result a bit should help (or simply avoid putting the source on
a bright spot).
This ensures that the beams color does not darken along borders,
by using the last valid color of the ray as the border color (extending
colors in the direction of the source point).
The sunbeams node was clamping the range of influence to start at 1
pixel distance from the source. This was a poor fix for artifacts caused
by an off set in buffer coordinates. Since the u coordinate starts at
ceil(umax) the v coordinate also has to use ceil. This also fixes some
discontinuities that became visible when the source point is close to
a sharp line in the input image.
This allows adding a "fake" sun beam effect, simulating crepuscular rays
from light being scattered in a medium like the atmosphere or deep water.
Such effects can be created also by renderers using volumetric lighting,
but the compositor feature is a lot cheaper and is independent from 3D
rendering. This makes it ideally suited for motion graphics.
The implementation uses am optimized accumulation method for gathering
color values along a line segment. The inner buffer loop uses fixed
offset increments to avoid unnecessary multiplications and avoids
variables by using compile-time specialization (see inline comments
for further details).
