# calculating normal for smooth shading

ummm so what i understand is for the shade model for lighting to be smooth i need to give a normal vector for each vertex…

below is my normal function and then the drawing function with the normal for each vertex…my mesh is made up of QUADS and when i use the following code to draw the light is in triangle shape…

i think the problem is the vertices im passing to normal function…

my each quad is structured as …

mesh[i][0] - lower left
mesh[i][1] - uper left
mesh[i][2] - upper right
mesh[i][3] - lower right

help plz

normal function

``````
void normal (point p1,point p2,point p3,point &normal)
{
point a, b;

// calculate the vectors A and B
// note that v[3] is defined with counterclockwise winding in mind
// a
a.x = p3.x - p2.x;
a.y = p3.y - p2.y;
a.z = p3.z - p2.z;
// b
b.x = p1.x - p2.x;
b.y = p1.y - p2.y;
b.z = p1.z - p2.z;

// calculate the cross product and place the resulting vector
// into the address specified by vertex_t *normal
normal.x = ((a.y * b.z) - (a.z * b.y));
normal.y = ((a.z * b.x) - (a.x * b.z));
normal.z = ((a.x * b.y) - (a.y * b.x));

// normalize
float len = (float)(sqrt((double)((normal.x * normal.x) + (normal.y * normal.y) + (normal.z * normal.z))));

// avoid division by 0
if (len == 0.0f)
len = 1.0f;

// reduce to unit size
normal.x /= len;
normal.y /= len;
normal.z /= len;
}

``````

drawing function

``````
void draw()
{
glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);

point norm;
//sphere2(20,20);
//glPolygonMode(GL_FRONT_AND_BACK ,GL_LINE);

for(int i=0;i<stack;i++){ // base mesh
if(mesh[i][3].y==0){
if(mesh[i][3].y >=0 && mesh[i][3].y <=30)
glColor4f(0,0,1,0.6);

normal(mesh[i][0],mesh[i][1],mesh[i][3],norm);
glNormal3f(norm.x,norm.y,norm.z);
glVertex3i(mesh[i][0].x,mesh[i][0].y,mesh[i][0].z);

normal(mesh[i][1],mesh[i][0],mesh[i][2],norm);
glNormal3f(norm.x,norm.y,norm.z);
glVertex3i(mesh[i][1].x,mesh[i][1].y,mesh[i][1].z);

normal(mesh[i][2],mesh[i][1],mesh[i][3],norm);
glNormal3f(norm.x,norm.y,norm.z);
glVertex3i(mesh[i][2].x,mesh[i][2].y,mesh[i][2].z);

normal(mesh[i][3],mesh[i][0],mesh[i][2],norm);
glNormal3f(norm.x,norm.y,norm.z);
glVertex3i(mesh[i][3].x,mesh[i][3].y,mesh[i][3].z);
glEnd();
}
}

for(int i=0;i<=mesh2count;i++) {  	      // print elevated mesh

glColor3f(0.0,0.6,0.0);
int j=0;
if(i>=41*21 && i<=41*28) {
glMaterialfv(GL_FRONT,GL_AMBIENT_AND_DIFFUSE,mbdiffuse_ambient);
glMaterialfv(GL_FRONT, GL_SPECULAR, mbspecular);
}
normal(mesh[i][0],mesh[i][1],mesh[i][3],norm);
glNormal3f(norm.x,norm.y,norm.z);
glVertex3i(mesh2[i][0].x,mesh2[i][0].y,mesh2[i][0].z);

normal(mesh[i][0],mesh[i][1],mesh[i][2],norm);
glNormal3f(norm.x,norm.y,norm.z);
glVertex3i(mesh2[i][1].x,mesh2[i][1].y,mesh2[i][1].z);

normal(mesh[i][2],mesh[i][1],mesh[i][3],norm);
glNormal3f(norm.x,norm.y,norm.z);
glVertex3i(mesh2[i][2].x,mesh2[i][2].y,mesh2[i][2].z);

normal(mesh[i][0],mesh[i][3],mesh[i][2],norm);
glNormal3f(norm.x,norm.y,norm.z);
glVertex3i(mesh2[i][3].x,mesh2[i][3].y,mesh2[i][3].z);
glEnd();
glMaterialfv(GL_FRONT,GL_AMBIENT_AND_DIFFUSE,mdiffuse_ambient);
glMaterialfv(GL_FRONT, GL_SPECULAR, mspecular);
}
}

``````

thanks
Raza

Hi,

is your question “how to calculate the smooth normal”?

If so, this has a good explanation:
http://www.lighthouse3d.com/opengl/terrain/index.php3?normals

As you can see in the last picture, you basically sum up the face normals for the faces around the vertex, and normalize the result.