[Bf-blender-cvs] CVS commit: blender/source/blender/makesdna DNA_node_types.h blender/source/blender/render/intern/source zbuf.c blender/source/blender/src drawnode.c

[Ton Roosendaal]

ton (Ton Roosendaal) 2006/02/11 14:23:08 CET

  Modified files:
    blender/source/blender/makesdna DNA_node_types.h 
    blender/source/blender/render/intern/source zbuf.c 
    blender/source/blender/src drawnode.c 
  
  Log:
  Two significant improvements in vectorblur:
  
  1) Accumulation buffer alpha handling
  Accumulating colors in an accumulation is simple; a weighting factor can
  make sure colors don't over- or undersaturate.
  For alpha this is a bit more complex... especially because the masks for
  vectorblur are anti-aliased themselves with alpha values. Up to now I just
  premultiplied the mask-alpha with the actual color alpha, which worked OK
  for solid masks, but not for transparent ones. I thought that would be an
  acceptable situation, since 'ztra' faces only get blurred with alpha==1.
  
  However, it gives bad results when using 'mist' in Blender, which just
  gives pixels an alpha value based on camera distance. In these cases the
  alpha became oversaturated, accumulating into too high values.
  
  The solution is to store the mask-alpha separately, only premultiply this
  alpha with the weighting factor to define the accumulation amount.
  This is the math:
  
  blendfactor: the accumulation factor for a vectorblur pass
  passRGBA: color and alpha value of the current to be accumulated pass
  accRGBA: color and alpha value of accumulation buffer (initialized
           with original picture values)
  maskA: the mask's alpha itself
  
  accRGBA = (1 - maskA*blendfactor)*accRGBA + (maskA*blendfactor)*passRGBA
  
  This formula accumulates alpha values equally to colors, only using the
  mask-alpha as 'alpha-over' operation.
  It all sounds very logical, I just write this extensive log because I
  couldn't find any technical doc about this case. :)
  
  2) Creating efficient masks with camera-shake
  
  Vector blur can only work well when there's a clear distinction between
  what moves, and what doesn't move. This you can solve for example by
  rendering complex scenes in multiple layers. This isn't always easy, or
  just a lot of work. Especially when the camera itself moves, the mask
  created by the vectorblur code becomes the entire image.
  A very simple solution is to introduce a small threshold for
  moving pixels, which can efficiently separate the hardly-moving pixels
  from the moving ones, and thus create nice looking masks.
  
  You can find this new option in the VectorBlur node, as 'min speed'.
  This mimimum speed is in pixel units. A value of just 3 will already
  clearly separate the background from foreground.
  Note; to make this work OK, all vectors in an image are scaled 3 pixels
  smaller, to ensure everything keeps looking coherent.
  
  Test renders; 'Elephants Dream' scene with lotsof moving parts; rendered
  without OSA, image textures, shadow or color correction.
  
  No vectorblur:
  http://www.blender.org/bf/vblur.jpg
  
  With vectorblur, showing the alpha-saturation for mist:
  http://www.blender.org/bf/vblur1.jpg
  
  New accumulation formula:
  http://www.blender.org/bf/vblur2.jpg
  
  Same image, but now with a 3 pixel minimum speed threshold:
  http://www.blender.org/bf/vblur3.jpg
  
  Next frame, without minimum speed
  http://www.blender.org/bf/vblur4.jpg
  
  Same frame with speed threshold:
  http://www.blender.org/bf/vblur5.jpg
  
  (Only 20 steps of vectorblur were applied for clarity).
  
  Revision  Changes    Path
  1.6       +3 -2      blender/source/blender/makesdna/DNA_node_types.h
    <http://projects.blender.org/viewcvs/viewcvs.cgi/blender/source/blender/makesdna/DNA_node_types.h.diff?r1=1.5&r2=1.6&cvsroot=bf-blender>
  1.50      +112 -81   blender/source/blender/render/intern/source/zbuf.c
    <http://projects.blender.org/viewcvs/viewcvs.cgi/blender/source/blender/render/intern/source/zbuf.c.diff?r1=1.49&r2=1.50&cvsroot=bf-blender>
  1.13      +5 -2      blender/source/blender/src/drawnode.c
    <http://projects.blender.org/viewcvs/viewcvs.cgi/blender/source/blender/src/drawnode.c.diff?r1=1.12&r2=1.13&cvsroot=bf-blender>