Creating a sphere

OpenGL OpenGL: Basic Coding
1

Hello,

I have created a sphere.I have actually modified a code taken from elsewhere.I am viewing the sphere with Polygon mode set to GL_LINE.I have enabled culling and set the culling to back face.I am getting a non-uniform sphere.I have attached the output.


#define GLEW_STATIC
#include <stdio.h>
#include <stdlib.h>
#include <gl/glew.h>
#include <glfw.h>
#include <math.h>


#define space 10
#define  vertexcount (180/space)*(360/space)*2



const double PI=3.1415926535897;

 struct Vertices
{
	double x;
	double y;
	double z;
} vertex [vertexcount];

void init(void)
{
	int glewinitialize;

	glClearColor(0.0,0.0,0.0,0.0);
	glClearDepth(1.0);
	glShadeModel(GL_SMOOTH);
		
	

    glewinitialize=glewInit();
	if(glewinitialize==GLEW_OK)
	{
		printf("GLEW is available
");
	}
	
}

void GLFWCALL reshape(int width,int height)
{

	glViewport(0,0,500,500);
   glMatrixMode(GL_PROJECTION);
    
   glLoadIdentity();
 
 gluPerspective(60.0,width/height,0.1,100.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
 
   gluLookAt(0.0,0.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0);
}


void createsphere(int R,int H,int K,int Z)
{
	int n;
	int a;
	int b;
	int debug=0;
	int d=0;
	double A;
	double B;


	n=0;
	for(b=0;b<=180-space;b+=space)
	{
		for(a=0;a<=360-space;a+=space)
		{
			
			vertex[n].x=R*(sin((a*PI)/180))*(sin((b*PI)/180))-H;
			vertex[n].z=R*(cos((b*PI)/180))*(sin((a*PI)/180))-Z;
			vertex[n].y=R*(cos((a*PI)/180))-K;
			n++;

			vertex[n].x=R*(sin((a*PI)/180))*(sin(((b+space)*PI)/180))-H;
			vertex[n].z=R*(cos(((b+space)*PI)/180))*(sin((a*PI)/180))-Z;
			vertex[n].y=R*(cos((a*PI)/180))-K;
		
			n++;
          
			}
	}
}

void displaysphere(double R)
{
	int b;
	GLfloat mat[16];
        glScalef(0.0125*R,0.0125*R,0.0125*R);
        glGetFloatv(GL_MODELVIEW_MATRIX,mat);
	glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
	
	glBegin(GL_TRIANGLE_STRIP);
	for(b=0;b<=vertexcount;b++)
	{
		glVertex3f(vertex[b].x,vertex[b].y,vertex[b].z);
	}
	
	glEnd();


	
}
void display(void)
{
	
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
	glColor3f(1.0,0.5,0.0);
	
  	glEnable(GL_CULL_FACE);
    glCullFace(GL_BACK);
    glPushMatrix();
	 glTranslatef(0.0,0.0,-10.0);
	glColor3f(1.0,0.5,0.0);
	createsphere(20,0,0,0);
	displaysphere(15);
    glPopMatrix();
	
    glPushMatrix();
	glColor3f(0.0,1.0,0.0);
	createsphere(20,0,0,0);
	glTranslatef(10.0,10.0,-50.0);
	//displaysphere(10);
	glPopMatrix();
	
    glfwSwapBuffers();
}
int main(int argc,char** argv)
{
 
	int wndstate,wndopenstate;
	
	wndstate=glfwInit();
	
	if(wndstate==1)
	{
		wndopenstate=glfwOpenWindow(640,480,0,0,0,0,4,0,GLFW_WINDOW);
		
		if(wndopenstate==0)
		{

			glfwTerminate();
		}
		else
		{
			glfwSetWindowTitle("Hello Opengl");
			glfwSetWindowPos(30,30);
			init();
			glfwSetWindowSizeCallback(reshape);
			
			while(1)
			{
				display();
				 if(glfwGetKey(GLFW_KEY_ESC))
	             {
		             glfwTerminate();
		
	             }
                
			}
		}
	}

	glfwTerminate();
	return 0;
 
  }

I had taken this code from some other references in which culling was enabled.

Why am I getting an output like this?Where is the mistake

2

Also how do i calculate the normal for this sphere?

3

Simple subtract the vertex position from the sphere’s center and normalize this vector.

4

Hello,
The non uniformity in the rendering of the sphere was due to perspective projection.I have calculated the normal but it looks faceted.How do i get a smooth surface?
-swetha

5

You must be using the face normal as the vertex normal.
For a vertex v, find all the faces containing vertex v and then average their normals. Then use this average normal as the vertex normal.

6

Using glColor to assign colors means that you are not using lighting. Lighting must be used to do smooth shading. Without lighting your sphere would just look like a filled in circle. How about posting a picture of what you have now with glPolygonMode to to GL_FILL instead of GL_LINES.