The code below uses an octahedron as a starting 3D shape, ( I found it on the web) and after some tweaking I can't still make it work.
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stddef.h> /* must include for the offsetof macro */
#include <GL/glew.h>
#include <GL/glfw.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <stdlib.h>
#include <vector>
#include <iostream>
using namespace std;
struct XYZ {
GLdouble x;
GLdouble y;
GLdouble z;
};
struct FACET3 {
XYZ p1;
XYZ p2;
XYZ p3;
};
void Normalise(XYZ *p_input)
{
double magnitude = 0;
magnitude = sqrt((p_input->x * p_input->x )+ (p_input->y * p_input->y) + (p_input->z * p_input->z));
p_input->x = p_input->x / magnitude;
p_input->y = p_input->y / magnitude;
p_input->z = p_input->z / magnitude;
}
int CreateNSphere(FACET3 *f,int iterations)
{
int i,it;
double a;
XYZ p[6] = {0,0,1, 0,0,-1, -1,-1,0, 1,-1,0, 1,1,0, -1,1,0};
XYZ pa,pb,pc;
int nt = 0,ntold;
/* Create the level 0 object */
a = 1 / sqrt(2.0);
for (i=0;i<6;i++) {
p[i].x *= a;
p[i].y *= a;
}
f[0].p1 = p[0]; f[0].p2 = p[3]; f[0].p3 = p[4];
f[1].p1 = p[0]; f[1].p2 = p[4]; f[1].p3 = p[5];
f[2].p1 = p[0]; f[2].p2 = p[5]; f[2].p3 = p[2];
f[3].p1 = p[0]; f[3].p2 = p[2]; f[3].p3 = p[3];
f[4].p1 = p[1]; f[4].p2 = p[4]; f[4].p3 = p[3];
f[5].p1 = p[1]; f[5].p2 = p[5]; f[5].p3 = p[4];
f[6].p1 = p[1]; f[6].p2 = p[2]; f[6].p3 = p[5];
f[7].p1 = p[1]; f[7].p2 = p[3]; f[7].p3 = p[2];
nt = 8;
if (iterations < 1)
return(nt);
/* Bisect each edge and move to the surface of a unit sphere */
for (it=0;it<iterations;it++) {
ntold = nt;
for (i=0;i<ntold;i++) {
pa.x = (f[i].p1.x + f[i].p2.x) / 2;
pa.y = (f[i].p1.y + f[i].p2.y) / 2;
pa.z = (f[i].p1.z + f[i].p2.z) / 2;
pb.x = (f[i].p2.x + f[i].p3.x) / 2;
pb.y = (f[i].p2.y + f[i].p3.y) / 2;
pb.z = (f[i].p2.z + f[i].p3.z) / 2;
pc.x = (f[i].p3.x + f[i].p1.x) / 2;
pc.y = (f[i].p3.y + f[i].p1.y) / 2;
pc.z = (f[i].p3.z + f[i].p1.z) / 2;
Normalise(&pa);
Normalise(&pb);
Normalise(&pc);
f[nt].p1 = f[i].p1; f[nt].p2 = pa; f[nt].p3 = pc; nt++;
f[nt].p1 = pa; f[nt].p2 = f[i].p2; f[nt].p3 = pb; nt++;
f[nt].p1 = pb; f[nt].p2 = f[i].p3; f[nt].p3 = pc; nt++;
f[i].p1 = pa;
f[i].p2 = pb;
f[i].p3 = pc;
}
}
return(nt);
}
int main()
{
FACET3 facet[8];
int facets = CreateNSphere(facet, 2);
printf(" Result: %d", facets);
}
When I try to compile it, it returns:
"Segmentation Error"
gdb debugger says:
Program received signal SIGSEGV, Segmentation fault.
0x00000000004011df in CreateNSphere(FACET3*, int) ()
any help?
after compiling with "-g" option "gbd" returned this:
(gdb) run
Starting program: /home/alexander/Graphics/Code-Handouts/tut_3/a.out
Program received signal SIGSEGV, Segmentation fault.
0x00000000004011df in CreateNSphere (f=0x7fffffffdeb0, iterations=2) at sphere_model.cpp:86
86 f[nt].p1 = pb; f[nt].p2 = f[i].p3; f[nt].p3 = pc; nt++;
(gdb) where
#0 0x00000000004011df in CreateNSphere (f=0x7fffffffdeb0, iterations=2) at sphere_model.cpp:86
#1 0x0000000000401303 in main () at sphere_model.cpp:100
(gdb)
For two iterations, you need many more than 8 vertices.
The initial iteration, there are eight vertices.
On iteration one, 24 are added.
On iteration two, it quadruples again.
So you should declare
FACET3 facet[128];
The size of passed array to CreateNSphere()
is 8. Inside CreateNSphere()
you access to yours f
array by nt
index variable which is incremented permanently during the loop. So basically you have memory access violation -- you tries to access f
array out of it's size. When I debuged your sample gdb shown that nt
was 48 when SIGSEGV received.
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