Merge branch 'master' of ssh://vo20.nl/git/uva

graphics/ass9/source/main.c

@@ -5,13 +5,10 @@
  * Date ............ 29.10.2007
  * Created by ...... Paul Melis
  *
- * Student name ....
- * Student email ...
- * Collegekaart ....
- * Date ............
- * Comments ........
- *
- * (always fill in these fields before submitting!!)
+ * Student name .... Sander van Veen & Taddeus Kroes
+ * Student email ... sandervv@gmail.com & taddeuskroes@hotmail.com
+ * Collegekaart .... 6169676 & 6054129
+ * Date ............ 17.11.2010
  */
 
 #include <stdio.h>

graphics/ass9/source/marching_tetrahedra.c

 /* Computer Graphics, Assignment, Volume rendering with cubes/points/isosurface
  *
- * Student name ....
- * Student email ...
- * Collegekaart ....
- * Date ............
- * Comments ........
- *
- * (always fill in these fields before submitting!!)
+ * Student name .... Sander van Veen & Taddeus Kroes
+ * Student email ... sandervv@gmail.com & taddeuskroes@hotmail.com
+ * Collegekaart .... 6169676 & 6054129
+ * Date ............ 17.11.2010
  */
 
 #include <stdlib.h>
 #include <stdio.h>
 #include <assert.h>
-#include <math.h>
 #include "marching_tetrahedra.h"
 
 /* Compute a linearly interpolated position where an isosurface cuts
@@ -23,13 +19,13 @@ static vec3
 interpolate_points(unsigned char isovalue, vec3 p1, vec3 p2,
 	unsigned char v1, unsigned char v2)
 {
-    //float diff1 = fabsf((float)(isovalue - v1)),
-    //      diff2 = fabsf((float)(isovalue - v2)),
-    //      total = diff1 + diff2;
-	//vec3 v = v3_add(v3_multiply(p1, diff1/total), v3_multiply(p2, diff2/total));
-	
-	vec3 v = v3_add(v3_multiply(p1, 0.5), v3_multiply(p2, 0.5));
+	// Interpolate between v1 and v2 to determine relative coordinates
+	vec3 v = v3_multiply(v3_add(
+		v3_multiply(p1, v2 - isovalue),
+		v3_multiply(p2, isovalue - v1)
+	), 1.0 / (v2 - v1));
 	
+	// Multiply by voxel dimensions for absolute coordinates
 	return v3_create(v.x * sizex, v.y * sizey, v.z * sizez);
 }
 
@@ -59,10 +55,12 @@ generate_tetrahedron_triangles(triangle *triangles, unsigned char isovalue,
 	
 	// Use a 4-bit bitmask to determine the order of "black/white" points of
 	// the tetrahedon. Generate 0, 1 or 2 triangle(s) according to the case.
-	switch( (v[v0] <= isovalue ? 1 : 0) | (v[v1] <= isovalue ? 1<<1 : 0)
-	        | (v[v2] <= isovalue ? 1<<2 : 0) | (v[v3] <= isovalue ? 1<<3 : 0) )
+	switch( (v[v0] <= isovalue ? 1 : 0) | (v[v1] <= isovalue ? 2 : 0)
+	        | (v[v2] <= isovalue ? 4 : 0) | (v[v3] <= isovalue ? 8 : 0) )
 	{
 		case 0x1: case 0xE: // 0001 or 1110
+			// ADD_TRI usage example: interpolate between edges (v0, v1),
+			// (v0, v2) and (v0, v3)
 			ADD_TRI(v0, v1, v0, v2, v0, v3);
 			break;
 		case 0x2: case 0xD: // 0010 or 1101

graphics/ass9/source/questions.txt

+Question 1:
+	What happens for case 0011/1100 when two of the tetrahedron's vertex
+	values are equal to the iso-value of interest and the other two are greater
+	than the iso-value? Is this a bad thing? Hint: think of the kind of output
+	generated in this case.
+
+	In that case, two corners of the same triangle are equal to the tetrahedon
+	vertices that are equal to the isovalue, so an edge of the triangle is
+	exactly on the edge of the tetrahedon between the two equal vertices. In the
+	interpolation function, this means a division by zero (v2 - v1 = 0), which
+	is indeed a bad thing. A solution to this problem would build in an extra
+	check for this kind of cases.
+
+--------------------------------------------------------------------------------
+
+Question 2:
+	We render the iso-surface two-sided here, that is, without back-face culling.
+	But if the iso-surface were to form a closed surface there would be no need
+	for this, as the inside/back-side of the surface would never be visible. So
+	for what situation does marching tetrahedra not produce a closed isosurface?
+
+	For each triangle edge in a tetrahedon, there should be a triangle in one
+	of the neighbouring tetrahedons that shares that edge. Because of the
+	shapes of the tetrahedons, this means that the end points of the edge are
+	the result of interpolation in both tetrahedons (which can be checked in
+	code relatively easily). For example, this situation occurs in a dataset
+	containing a cube or a sphere.
+
+--------------------------------------------------------------------------------
+
+Question 3:
+	What optimizations to the marching tetrahedrons algorithm as described
+	in Section 3 can you think of? Are there computations that are performed
+	redundantly? Is there opportunity for parallel processing?
+
+	- There's plenty of room for parallel processing, since all cells/tetrahedons
+	  are checked independently of eachother.
+	- If we know (by specification) that an isosurface is closed, we can use the
+	  property described in the answer to question 2 by creating an incremental
+	  algorithm that uses already interpolated points in neigbouring tetrahedons
+	  to create a triangle strip, instead of interpolating seperately in each
+	  tetrahedon (note that there is less room for parallel processing in this case).

graphics/ass9/source/volume.c

 /* Computer Graphics, Assignment, Volume rendering with cubes/points/isosurface
  *
- * Student name ....
- * Student email ...
- * Collegekaart ....
- * Date ............
- * Comments ........
- *
- * (always fill in these fields before submitting!!)
+ * Student name .... Sander van Veen & Taddeus Kroes
+ * Student email ... sandervv@gmail.com & taddeuskroes@hotmail.com
+ * Collegekaart .... 6169676 & 6054129
+ * Date ............ 17.11.2010
  */
 
 #include <stdio.h>