chen

03-21-2006, 12:00 PM

I need to draw a sphere in my project, without using the openGL function, because my project is to implement the openGL graphics pipe-line.

I use this code for drawing the sphere:

typedef vector<Vector3> vectors;

void mygluSphere(float radius, int slices, int stacks)

{

if (slices < 3 &#0124;&#0124; stacks < 2 &#0124;&#0124; radius <= 0.0) {

cout<<"MyGluSphere() - bad parameters";

return;

}

// calculate all the x,y coordinates (at radius 1)

vector<vectors> N(stacks - 1);

int k, s, i;

double z, a, r;

for (k=0; k<stacks-1; ++k) {

N[k].resize(slices);

a = PI * (-0.5 + (1.0 + k) / stacks);

z = sin(a);

r = cos(a);

for (s=0; s<slices; ++s) {

a = PI * 2 * s / slices;

N[k][s].set(cos(a) * r, sin(a) * r, z);

}

}

// bottom triangle fan

myglBegin(MYGL_POLYGON);

myglNormal3f(0.0, 0.0, -1.0);

myglVertex3f(0.0, 0.0, -radius);

for (s=slices; s>=0; --s) {

i = (s == slices) ? 0 : s;

const Vector3& n = N[0][i];

myglNormal3f(n.x, n.y, n.z);

myglVertex3f(n.x * radius, n.y * radius, n.z * radius);

}

myglEnd();

// middle quad strips

for (k=0; k<stacks-2; ++k) {

myglBegin(MYGL_POLYGON);

for (s=slices; s>=0; --s) {

i = (s == slices) ? 0 : s;

const Vector3& n1 = N[k][i];

myglNormal3f(n1.x, n1.y, n1.z);

myglVertex3f(n1.x * radius, n1.y * radius, n1.z * radius);

const Vector3& n2 = N[k + 1][i];

myglNormal3f(n2.x, n2.y, n2.z);

myglVertex3f(n2.x * radius, n2.y * radius, n2.z * radius);

}

myglEnd();

}

// top triangle fan

myglBegin(MYGL_POLYGON);

myglVertex3f(0.0, 0.0, radius);

for (s=0; s<=slices; ++s) {

i = (s == slices) ? 0 : s;

const Vector3& n = N[stacks - 2][i];

myglNormal3f(n.x, n.y, n.z);

myglVertex3f(n.x * radius, n.y * radius, n.z * radius);

}

myglEnd();

}

But when i'm using it, after some rotation operation, some of the sphere's polygons, are hidden.

Can some one check this code and found what is wrong, or perhaps suggest a better one?

Chen

I use this code for drawing the sphere:

typedef vector<Vector3> vectors;

void mygluSphere(float radius, int slices, int stacks)

{

if (slices < 3 &#0124;&#0124; stacks < 2 &#0124;&#0124; radius <= 0.0) {

cout<<"MyGluSphere() - bad parameters";

return;

}

// calculate all the x,y coordinates (at radius 1)

vector<vectors> N(stacks - 1);

int k, s, i;

double z, a, r;

for (k=0; k<stacks-1; ++k) {

N[k].resize(slices);

a = PI * (-0.5 + (1.0 + k) / stacks);

z = sin(a);

r = cos(a);

for (s=0; s<slices; ++s) {

a = PI * 2 * s / slices;

N[k][s].set(cos(a) * r, sin(a) * r, z);

}

}

// bottom triangle fan

myglBegin(MYGL_POLYGON);

myglNormal3f(0.0, 0.0, -1.0);

myglVertex3f(0.0, 0.0, -radius);

for (s=slices; s>=0; --s) {

i = (s == slices) ? 0 : s;

const Vector3& n = N[0][i];

myglNormal3f(n.x, n.y, n.z);

myglVertex3f(n.x * radius, n.y * radius, n.z * radius);

}

myglEnd();

// middle quad strips

for (k=0; k<stacks-2; ++k) {

myglBegin(MYGL_POLYGON);

for (s=slices; s>=0; --s) {

i = (s == slices) ? 0 : s;

const Vector3& n1 = N[k][i];

myglNormal3f(n1.x, n1.y, n1.z);

myglVertex3f(n1.x * radius, n1.y * radius, n1.z * radius);

const Vector3& n2 = N[k + 1][i];

myglNormal3f(n2.x, n2.y, n2.z);

myglVertex3f(n2.x * radius, n2.y * radius, n2.z * radius);

}

myglEnd();

}

// top triangle fan

myglBegin(MYGL_POLYGON);

myglVertex3f(0.0, 0.0, radius);

for (s=0; s<=slices; ++s) {

i = (s == slices) ? 0 : s;

const Vector3& n = N[stacks - 2][i];

myglNormal3f(n.x, n.y, n.z);

myglVertex3f(n.x * radius, n.y * radius, n.z * radius);

}

myglEnd();

}

But when i'm using it, after some rotation operation, some of the sphere's polygons, are hidden.

Can some one check this code and found what is wrong, or perhaps suggest a better one?

Chen