Another commit for raytracing, now with glass refraction & fresnel!

Changelog:

- enable refraction with button "Ray Transp" in Material buttons.
- set "Angular Index" value for amount of refraction.
- use the "Alpha" value to define transparency.
- remember to set a higher "Depth" too... glass can bounce quite some
  more than expected.
- for correct refraction, 3D models MUST have normals pointing in the
  right direction (consistently pointing outside).
- refraction 'sees' the thickness of glass based on what you model. So
  make for realistic glass both sides of a surface.

- I needed to do some rewriting for correct mirroring/refraction,
  especially to prevent specularity being blended away.
  Solved this with localizing shading results in the rendercore.c.
  Now specularity correctly is added, and reduces the 'mirror' value.
- Localizing more parts of the render code is being planned. The old
  render heavily relies on struct Render and struct Osa to store globals.
  For scanline render no problem, but recursive raytracing dislikes that.

- done test with gamma-corrected summation of colors during tracing, is
  commented out still. But this will give more balanced reflections. Now
  dark reflections that are reflected in a bright surface seem incorrect.

- Introduced 'Fresnel' effect for Mirror and Transparency. This
  influences the amount of mirror/transparency based at viewing angle.
  Next to a new Fresnel slider, also a 'falloff' button has been added to
  define the way it spreads.
- Fresnel also works for Ztransp rendering

- created new Panel for Raytrace options
  I have to evaluate still where it all should be logically located.
- material preview shows fake reflection and fake refraction as well.

1 files changed, 95 insertions, 22 deletions

diff --git a/source/blender/src/previewrender.c b/source/blender/src/previewrender.c
index 5b4bff52cb2..0b302a40602 100644
--- a/source/blender/src/previewrender.c
+++ b/source/blender/src/previewrender.c
@@ -86,8 +86,8 @@
 
 #include "RE_renderconverter.h"
 
-#define PR_RECTX	121
-#define PR_RECTY	121
+#define PR_RECTX	141
+#define PR_RECTY	141
 #define PR_XMIN		10
 #define PR_YMIN		5
 #define PR_XMAX		200
@@ -219,6 +219,14 @@ static int ray_previewrender(int x,
 
 static unsigned int previewback(int type, int x, int y)
 {
+	
+	/* checkerboard, for later
+	x+= PR_RECTX/2;
+	y+= PR_RECTX/2;
+	if( ((x/24) + (y/24)) & 1) return 0x40404040;
+	else return 0xa0a0a0a0;
+	*/
+	
 	if(type & MA_DARK) {
 		if(abs(x)>abs(y)) return 0;
 		else return 0x40404040;
@@ -667,8 +675,40 @@ static float pr2_lamp[3]= {-8.8, -5.6, -1.5};
 static float pr1_col[3]= {0.8, 0.8, 0.8};
 static float pr2_col[3]= {0.5, 0.6, 0.7};
 
+static void refraction_prv(int *x, int *y, float *n, float index)
+{
+	float dot, fac, view[3], len;
+
+
+	if(index==0.0) return;
+
+	view[0]= index*(float)*x;
+	view[1]= ((float)*y)/index;
+	view[2]= 20.0;
+	len= Normalise(view);
+	
+	dot= view[0]*n[0] + view[1]*n[1] + view[2]*n[2];
+
+	if(dot>0.0) {
+		fac= 1.0 - (1.0 - dot*dot)*index*index;
+		if(fac<= 0.0) return;
+		fac= -dot*index + sqrt(fac);
+	}
+	else {
+		index = 1.0/index;
+		fac= 1.0 - (1.0 - dot*dot)*index*index;
+		if(fac<= 0.0) return;
+		fac= -dot*index - sqrt(fac);
+	}
+
+	*x= (int)(len*(index*view[0] + fac*n[0]));
+	*y= (int)(len*(index*view[1] + fac*n[1]));
+}
+
+
 static void shade_preview_pixel(float *vec, int x, int y,char *rect, int smooth)
 {
+	extern float fresnel_fac(float *view, float *vn, float fresnel, float falloff);
 	Material *mat;
 	float v1,inp, inprspec=0, isr=0.0, isb=0.0, isg=0.0;
 	float ir=0.0, ib=0.0, ig=0.0;
@@ -678,13 +718,6 @@ static void shade_preview_pixel(float *vec, int x, int y,char *rect, int smooth)
 	char tracol;
 	
 	mat= R.matren;
-	/* pr1_lamp[0]= mat->mtex[0]->ofs[0]; */
-	/* pr1_lamp[1]= mat->mtex[0]->ofs[1]; */
-	/* pr1_lamp[2]= mat->mtex[0]->ofs[2]; */
-
-	/* pr2_lamp[0]= mat->mtex[0]->size[0]; */
-	/* pr2_lamp[1]= mat->mtex[0]->size[1]; */
-	/* pr2_lamp[2]= mat->mtex[0]->size[2]; */
 
 	v1= 1.0/PR_RECTX;
 	view[0]= v1*x;
@@ -738,7 +771,8 @@ static void shade_preview_pixel(float *vec, int x, int y,char *rect, int smooth)
 			
 			inp= -2.0*(R.vn[0]*view[0]+R.vn[1]*view[1]+R.vn[2]*view[2]);
 			R.ref[0]= (view[0]+inp*R.vn[0]);
-			R.ref[1]= -(view[1]+inp*R.vn[1]);
+			R.ref[1]= (view[1]+inp*R.vn[1]);
+			if(smooth) R.ref[1]= -R.ref[1];
 			R.ref[2]= (view[2]+inp*R.vn[2]);
 		}
 
@@ -815,6 +849,38 @@ static void shade_preview_pixel(float *vec, int x, int y,char *rect, int smooth)
 			ig+= inp*la[1];
 			ib+= inp*la[2];
 		}
+		
+		/* drawing checkerboard and sky */
+		if(mat->mode & MA_RAYMIRROR) {
+			float col, div, y, z;
+			int fac;
+			
+			/* rotate a bit in x */
+			y= R.ref[1]; z= R.ref[2];
+			R.ref[1]= 0.98*y - 0.17*z;
+			R.ref[2]= 0.17*y + 0.98*z;
+			
+			/* scale */
+			div= (0.85*R.ref[1]);
+			
+			R.refcol[0]= mat->ray_mirror*fresnel_fac(view, R.vn, mat->fresnel_mir, mat->falloff_mir);;
+
+			if(div<0.0) {
+				/* minus 0.5 prevents too many small tiles in distance */
+				fac= (int)(R.ref[0]/(div-0.1) ) + (int)(R.ref[2]/(div-0.1) );
+				if(fac & 1) col= 0.8;
+				else col= 0.3;
+
+				R.refcol[1]= R.refcol[0]*col;
+				R.refcol[2]= R.refcol[1];
+				R.refcol[3]= R.refcol[2];
+			}
+			else {
+				R.refcol[1]= 0.0;
+				R.refcol[2]= R.refcol[0]*0.3*div;
+				R.refcol[3]= R.refcol[0]*0.8*div;
+			}
+		}
 
 		if(R.refcol[0]==0.0) {
 			a= 255.0*( mat->r*ir +mat->ambr +isr);
@@ -840,18 +906,25 @@ static void shade_preview_pixel(float *vec, int x, int y,char *rect, int smooth)
 		}
 	}
 
-	if(mat->alpha!=1.0) {
-		
-		alpha= mat->alpha;
-		
-			/* ztra shade */
-		if(mat->spectra!=0.0) {
-			inp= mat->spectra*inprspec;
-			if(inp>1.0) inp= 1.0;
-			
-			alpha= (1.0-inp)*alpha+ inp;
+	alpha= mat->alpha;
+	
+	if(mat->mode & (MA_ZTRA|MA_RAYTRANSP)) 
+		if(mat->fresnel_tra!=0.0) 
+			alpha*= fresnel_fac(view, R.vn, mat->fresnel_tra, mat->falloff_tra);
+	
+		/* ztra shade */
+	if(mat->spectra!=0.0) {
+		inp = MAX3(isr, isg, isb);
+		inp *= mat->spectra;
+		if(inp>1.0) inp= 1.0;
+		alpha= (1.0-inp)*alpha+inp;
+	}
+	
+	if(alpha!=1.0) {
+		if(mat->mode & MA_RAYTRANSP) {
+			refraction_prv(&x, &y, R.vn, mat->ang);
 		}
-
+		
 		tracol=  previewback(mat->pr_back, x, y) & 255;
 		
 		tracol= (1.0-alpha)*tracol;
@@ -859,7 +932,6 @@ static void shade_preview_pixel(float *vec, int x, int y,char *rect, int smooth)
 		rect[0]= tracol+ (rect[0]*alpha) ;
 		rect[1]= tracol+ (rect[1]*alpha) ;
 		rect[2]= tracol+ (rect[2]*alpha) ;
-
 	}
 }
 
@@ -924,6 +996,7 @@ void BIF_previewrender(SpaceButs *sbuts)
 	MTC_Mat4One(R.viewinv);
 	
 	R.osatex= 0;
+	
 	if(mat) {
 		/* rendervars */
 		init_render_world();