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, 9 insertions, 3 deletions

diff --git a/source/blender/blenkernel/intern/world.c b/source/blender/blenkernel/intern/world.c
index b482140e373..ea4f9bd790b 100644
--- a/source/blender/blenkernel/intern/world.c
+++ b/source/blender/blenkernel/intern/world.c
@@ -86,11 +86,13 @@ World *add_world(char *name)
 	
 	wrld->horb= 0.6f;
 	wrld->skytype= WO_SKYBLEND;
-	wrld->exposure= 1.0f;
 	wrld->stardist= 15.0f;
 	wrld->starsize= 2.0f;
 	wrld->gravity= 9.8f;
-		
+	
+	wrld->exposure= 0.0f;
+	wrld->range= 1.0f;
+
 	return wrld;
 }
 
@@ -199,6 +201,10 @@ void init_render_world()
 	}
 	else {
 		memset(&R.wrld, 0, sizeof(World));
-		R.wrld.exposure= 1.0;
+		R.wrld.exposure= 0.0;
+		R.wrld.range= 1.0;
 	}
+
+	R.wrld.linfac= 1.0 + pow((2.0*R.wrld.exposure + 0.5), -10);
+	R.wrld.logfac= log( (R.wrld.linfac-1.0)/R.wrld.linfac )/R.wrld.range;
 }