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!

6 files changed, 45 insertions, 14 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;
 }
diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 8bb3ab9d5ff..9631bcc958a 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -3929,6 +3929,7 @@ static void do_versions(Main *main)
 		Material *ma= main->mat.first;
 		Scene *sce;
 		Lamp *la;
+		World *wrld;
 		
 		while(ma) {
 			if(ma->fresnel_tra_i==0.0) ma->fresnel_tra_i= 1.25;
@@ -3963,6 +3964,14 @@ static void do_versions(Main *main)
 			if(la->area_sizez==0.0) la->area_sizez= 1.0;
 			la= la->id.next;
 		}
+		wrld= main->world.first;
+		while(wrld) {
+			if(wrld->range==0.0) {
+				wrld->range= 1.0/wrld->exposure;
+				wrld->exposure= 0.0;
+			}
+			wrld= wrld->id.next;
+		}
 	}
 	/* don't forget to set version number in blender.c! */
 }
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];
 
diff --git a/source/blender/render/intern/source/rendercore.c b/source/blender/render/intern/source/rendercore.c
index ba86ca6319f..99648750781 100644
--- a/source/blender/render/intern/source/rendercore.c
+++ b/source/blender/render/intern/source/rendercore.c
@@ -1457,7 +1457,9 @@ float Toon_Diff( float *n, float *l, float *v, float size, float smooth )
 }
 
 /* Oren Nayar diffuse */
-/* nl is either dot product, or return value of area light */
+
+/* 'nl' is either dot product, or return value of area light */
+/* in latter case, only last multiplication uses 'nl' */
 float OrenNayar_Diff_i(float nl, float *n, float *l, float *v, float rough )
 {
 	float i, nh, nv, vh, realnl, h[3];
@@ -1477,7 +1479,7 @@ float OrenNayar_Diff_i(float nl, float *n, float *l, float *v, float rough )
 	
 	realnl= n[0]*l[0]+n[1]*l[1]+n[2]*l[2]; /* Dot product between surface normal and light vector */
 	if(realnl<=0.0) return 0.0;
-	if(nl<0.0) nl= 0.0;		/* value from area light */
+	if(nl<0.0) return 0.0;		/* value from area light */
 	
 	vh= v[0]*h[0]+v[1]*h[1]+v[2]*h[2]; /* Dot product between view vector and halfway vector */
 	if(vh<=0.0) vh= 0.0;
@@ -1510,7 +1512,7 @@ float OrenNayar_Diff_i(float nl, float *n, float *l, float *v, float rough )
 	A = 1 - (0.5 * ((rough * rough) / ((rough * rough) + 0.33)));
 	B = 0.45 * ((rough * rough) / ((rough * rough) + 0.09));
 	
-	b*= 0.95;	/* prevent tangens from shooting to inf, nl here can be not a dot product here. */
+	b*= 0.95;	/* prevent tangens from shooting to inf, 'nl' can be not a dot product here. */
 				/* overflow only happens with extreme size area light, and higher roughness */
 	i = nl * ( A + ( B * t * sin(a) * tan(b) ) );
 	
@@ -2441,6 +2443,13 @@ temp_y= floor(y);
 		
 		VecAddf(col, shr.diff, shr.spec);
 		
+		/* exposure correction */
+		if(R.wrld.exposure!=0.0 || R.wrld.range!=1.0) {
+			col[0]= R.wrld.linfac*(1.0-exp( col[0]*R.wrld.logfac) );
+			col[1]= R.wrld.linfac*(1.0-exp( col[1]*R.wrld.logfac) );
+			col[2]= R.wrld.linfac*(1.0-exp( col[2]*R.wrld.logfac) );
+		}
+		
 		/* MIST */
 		if( (R.wrld.mode & WO_MIST) && (shi.matren->mode & MA_NOMIST)==0 ){
 			alpha= mistfactor(shi.co);
diff --git a/source/blender/renderconverter/intern/convertBlenderScene.c b/source/blender/renderconverter/intern/convertBlenderScene.c
index 185e8ca9c05..b8738968db4 100644
--- a/source/blender/renderconverter/intern/convertBlenderScene.c
+++ b/source/blender/renderconverter/intern/convertBlenderScene.c
@@ -1827,7 +1827,7 @@ void RE_add_render_lamp(Object *ob, int doshadbuf)
 	lar->mode= la->mode;
 
 	lar->energy= la->energy;
-	lar->energy= la->energy*R.wrld.exposure;
+	lar->energy= la->energy;
 	if(la->mode & LA_NEG) lar->energy= -lar->energy;
 
 	lar->vec[0]= -mat[2][0];
diff --git a/source/blender/src/buttons_shading.c b/source/blender/src/buttons_shading.c
index 65d5dcadf2a..fa3428e0f5f 100644
--- a/source/blender/src/buttons_shading.c
+++ b/source/blender/src/buttons_shading.c
@@ -1531,8 +1531,9 @@ static void world_panel_mistaph(World *wrld)
 
 	uiSetButLock(wrld->id.lib!=0, "Can't edit library data");
 
-	uiDefBut(block, MENU|SHO, 1, "Physics %t|None %x1|Sumo %x2|ODE %x3 |Dynamo %x4|",	
-			10,180,140,19, &wrld->pad1, 0, 0, 0, 0, "Physics Engine");
+	/* disabled, pad1 should not be used even! */
+	// uiDefBut(block, MENU|SHO, 1, "Physics %t|None %x1|Sumo %x2|ODE %x3 |Dynamo %x4|",	
+	//		10,180,140,19, &wrld->pad1, 0, 0, 0, 0, "Physics Engine");
 	
 	/* Gravitation for the game worlds */
 	uiDefButF(block, NUMSLI,0, "Grav ", 150,180,150,19,	&(wrld->gravity), 0.0, 25.0, 0, 0,  "Sets the gravitation constant of the game world");
@@ -1602,9 +1603,11 @@ static void world_panel_world(World *wrld)
 	uiDefButF(block, NUMSLI,B_MATPRV,"AmbR ",	10,50,145,19,	&(wrld->ambr), 0.0, 1.0 ,0,0, "Sets the amount of red ambient colour");
 	uiDefButF(block, NUMSLI,B_MATPRV,"AmbG ",	10,30,145,19,	&(wrld->ambg), 0.0, 1.0 ,0,0, "Sets the amount of green ambient colour");
 	uiDefButF(block, NUMSLI,B_MATPRV,"AmbB ",	10,10,145,19,	&(wrld->ambb), 0.0, 1.0 ,0,0, "Sets the amount of blue ambient colour");
-	uiBlockEndAlign(block);
 
-	uiDefButF(block, NUMSLI,0, "Expos ",		160,10,145,19,	&(wrld->exposure), 0.2, 5.0, 0, 0, "Sets the lighting time and exposure");
+	uiBlockBeginAlign(block);
+	uiBlockSetCol(block, TH_BUT_SETTING1);
+	uiDefButF(block, NUMSLI,0, "Exp ",			160,30,145,19,	&(wrld->exposure), 0.0, 1.0, 0, 2, "Sets amount of exponential color correction for light");
+	uiDefButF(block, NUMSLI,0, "Range ",		160,10,145,19,	&(wrld->range), 0.2, 5.0, 0, 2, "Sets the color amount that will be mapped on color 1.0");
 
 
 }