Added improved exposure calculation

- based at 1.0-exp(-color) trick in Yafray. But to guarantee backwards
  compatibility, and some more control, Stefano Selleri hacked a useful
  formula for it.
- We now have 2 values to set:
  - "exp": the exponential correction value (0-1)
  - "range": the light range that maps on color 1.0 (0-5)
- Using exp(x) (is e^x) we can much better prevent overflows from render,
  which are currently hard-clipped in Blender. Setting a small 'exp' value
  wil efficiently smooth out high energy and map that back to a color for
  display.
- total formula:
  newcol= linfac*(1.0-exp(col*logfac))
    col, newcol are colors
  linfac= 1.0 + 1.0/((2.0*wrld.exp +0.5)^10)
  logfac= log( (linfac-1.0)/linfac )/wrld.range
    wrld.exp and wrld.range are the button values
- default setting: exp=0.0 and range=1.0 give results extremely close to
  previous rendering.
- graph: http://www.selleri.org/Blender/buffer/Image1.png  for 'exp' setting
  ranging from 0-1, and with 'range'=2

Thanks Stefano for the help!

1 files changed, 7 insertions, 3 deletions

diff --git a/source/blender/makesdna/DNA_world_types.h b/source/blender/makesdna/DNA_world_types.h
index 91e205e4038..fd367369bd5 100644
--- a/source/blender/makesdna/DNA_world_types.h
+++ b/source/blender/makesdna/DNA_world_types.h
@@ -56,8 +56,13 @@ typedef struct World {
 	float ambr, ambg, ambb, ambk;
 
 	unsigned int fastcol;	
-
-	float exposure;
+	
+	/**
+	 * New exposure/range control. linfac & logfac are constants... don't belong in
+	 * file, but allocating 8 bytes for temp mem isnt useful either.
+	 */
+	float exposure, range;	
+	float linfac, logfac;
 
 	/**
 	 * Gravitation constant for the game world
@@ -87,7 +92,6 @@ typedef struct World {
 	
 	short dofsta, dofend, dofmin, dofmax;
 
-	int pad1;
 	struct Ipo *ipo;
 	struct MTex *mtex[8];