Fix for bug #8825. find_first_point() finds first points of implicite surface in better way now. It goes

from center of every metalement to 26 directions and try to find every place, where implicite function 
crosses zero value. Size of step is size of polygonization cube. It can be proofed, that smaller size of step 
is useless.

1 files changed, 46 insertions, 18 deletions

diff --git a/source/blender/blenkernel/intern/mball.c b/source/blender/blenkernel/intern/mball.c
index 14e70075e32..16916381c95 100644
--- a/source/blender/blenkernel/intern/mball.c
+++ b/source/blender/blenkernel/intern/mball.c
@@ -1214,8 +1214,8 @@ void converge (MB_POINT *p1, MB_POINT *p2, float v1, float v2,
 		p->y = neg.y;
 		p->z = neg.z;
 		while (1) {
-			p->x = 0.5f*(pos.x + neg.x);
 			if (i++ == RES) return;
+			p->x = 0.5f*(pos.x + neg.x);
 			if ((function(p->x,p->y,p->z)) > 0.0)	pos.x = p->x; else neg.x = p->x; 
 		}
 	}
@@ -1224,8 +1224,8 @@ void converge (MB_POINT *p1, MB_POINT *p2, float v1, float v2,
 		p->x = neg.x;
 		p->z = neg.z;
 		while (1) {
-			p->y = 0.5f*(pos.y + neg.y);
 			if (i++ == RES) return;
+			p->y = 0.5f*(pos.y + neg.y);
 			if ((function(p->x,p->y,p->z)) > 0.0)	pos.y = p->y; else neg.y = p->y;
 		}
   	}
@@ -1234,8 +1234,8 @@ void converge (MB_POINT *p1, MB_POINT *p2, float v1, float v2,
 		p->x = neg.x;
 		p->y = neg.y;
 		while (1) {
-			p->z = 0.5f*(pos.z + neg.z);
 			if (i++ == RES) return;
+			p->z = 0.5f*(pos.z + neg.z);
 			if ((function(p->x,p->y,p->z)) > 0.0)	pos.z = p->z; else neg.z = p->z;
 		}
 	}
@@ -1300,6 +1300,8 @@ void find_first_points(PROCESS *mbproc, MetaBall *mb, int a)
 	int index[3]={1,0,-1};
 	float f =0.0f;
 	float in_v, out_v;
+	MB_POINT workp;
+	float tmp_v, workp_v, max_len, len, dx, dy, dz, nx, ny, nz, MAXN;
 
 	ml = mainb[a];
 
@@ -1360,23 +1362,49 @@ void find_first_points(PROCESS *mbproc, MetaBall *mb, int a)
 
 					out_v = mbproc->function(out.x, out.y, out.z);
 
-					/* find "first point" on Implicit Surface of MetaElemnt ml */
-					converge(&in, &out, in_v, out_v, mbproc->function, &mbproc->start, mb, 0);
-	
-					/* indexes of CUBE, which includes "first point" */
-					c_i= (int)floor(mbproc->start.x/mbproc->size );
-					c_j= (int)floor(mbproc->start.y/mbproc->size );
-					c_k= (int)floor(mbproc->start.z/mbproc->size );
-		
-					mbproc->start.x= mbproc->start.y= mbproc->start.z= 0.0;
+					/* find "first points" on Implicit Surface of MetaElemnt ml */
+					//converge(&in, &out, in_v, out_v, mbproc->function, &mbproc->start, mb, 0);
+					workp = in;
+					workp_v = in_v;
+					max_len = sqrt((out.x-in.x)*(out.x-in.x) + (out.y-in.y)*(out.y-in.y) + (out.z-in.z)*(out.z-in.z));
 
-					/* add CUBE (with indexes c_i, c_j, c_k) to the stack,
-					 * this cube includes found point of Implicit Surface */
-					if (ml->flag & MB_NEGATIVE)
-						add_cube(mbproc, c_i, c_j, c_k, 2);
-					else
-						add_cube(mbproc, c_i, c_j, c_k, 1);
+					nx = abs((out.x - in.x)/mbproc->size);
+					ny = abs((out.y - in.y)/mbproc->size);
+					nz = abs((out.z - in.z)/mbproc->size);
+					
+					MAXN = MAX3(nx,ny,nz);
+
+					dx = (out.x - in.x)/MAXN;
+					dy = (out.y - in.y)/MAXN;
+					dz = (out.z - in.z)/MAXN;
+
+					len = 0.0;
+					while(len<=max_len) {
+						workp.x += dx;
+						workp.y += dy;
+						workp.z += dz;
+						/* compute value of implicite function */
+						tmp_v = mbproc->function(workp.x, workp.y, workp.z);
+						/* add cube to the stack, when value of implicite function crosses zero value */
+						if((tmp_v<0.0 && workp_v>=0.0)||(tmp_v>0.0 && workp_v<=0.0)) {
+
+							/* indexes of CUBE, which includes "first point" */
+							c_i= (int)floor(workp.x/mbproc->size);
+							c_j= (int)floor(workp.y/mbproc->size);
+							c_k= (int)floor(workp.z/mbproc->size);
+
+							/* add CUBE (with indexes c_i, c_j, c_k) to the stack,
+							 * this cube includes found point of Implicit Surface */
+							if (ml->flag & MB_NEGATIVE)
+								add_cube(mbproc, c_i, c_j, c_k, 2);
+							else
+								add_cube(mbproc, c_i, c_j, c_k, 1);
+						}
+						len = sqrt((workp.x-in.x)*(workp.x-in.x) + (workp.y-in.y)*(workp.y-in.y) + (workp.z-in.z)*(workp.z-in.z));
+						workp_v = tmp_v;
+					}
 						
+					mbproc->start.x= mbproc->start.y= mbproc->start.z= 0.0;
 					
 				}
 			}