vcglib/wrap/gl/gl_geometry.h

/* Portion of this file were more or less adapted from 
 * freeglut_geometry.c
 *
 * Copyright (c) 1999-2000 Pawel W. Olszta. All Rights Reserved.
 * that was Written by Pawel W. Olszta, <olszta@sourceforge.net>
 */

#include<stdlib.h>
#include<math.h>

/*
 * Compute lookup table of cos and sin values forming a cirle
 *
 * Notes:
 *    It is the responsibility of the caller to free these tables
 *    The size of the table is (n+1) to form a connected loop
 *    The last entry is exactly the same as the first
 *    The sign of n can be flipped to get the reverse loop
 */

static void fghCircleTable(double **sint,double **cost,const int n)
{
    int i;

    /* Table size, the sign of n flips the circle direction */

    const int size = abs(n);

    /* Determine the angle between samples */

    const double angle = 2*M_PI/(double)( ( n == 0 ) ? 1 : n );

    /* Allocate memory for n samples, plus duplicate of first entry at the end */

    *sint = (double *) calloc(sizeof(double), size+1);
    *cost = (double *) calloc(sizeof(double), size+1);

    /* Bail out if memory allocation fails, fgError never returns */

    if (!(*sint) || !(*cost))
    {
        free(*sint);
        free(*cost);
        abort(); //fgError("Failed to allocate memory in fghCircleTable");
    }

    /* Compute cos and sin around the circle */

    (*sint)[0] = 0.0;
    (*cost)[0] = 1.0;

    for (i=1; i<size; i++)
    {
        (*sint)[i] = sin(angle*i);
        (*cost)[i] = cos(angle*i);
    }

    /* Last sample is duplicate of the first */

    (*sint)[size] = (*sint)[0];
    (*cost)[size] = (*cost)[0];
}

/*
 * Draws a solid sphere
 */
void glutSolidSphere(GLdouble radius, GLint slices, GLint stacks)
{
    int i,j;

    /* Adjust z and radius as stacks are drawn. */

    double z0,z1;
    double r0,r1;

    /* Pre-computed circle */

    double *sint1,*cost1;
    double *sint2,*cost2;

  //  FREEGLUT_EXIT_IF_NOT_INITIALISED ( "glutSolidSphere" );

    fghCircleTable(&sint1,&cost1,-slices);
    fghCircleTable(&sint2,&cost2,stacks*2);

    /* The top stack is covered with a triangle fan */

    z0 = 1.0;
    z1 = cost2[(stacks>0)?1:0];
    r0 = 0.0;
    r1 = sint2[(stacks>0)?1:0];

    glBegin(GL_TRIANGLE_FAN);

        glNormal3d(0,0,1);
        glVertex3d(0,0,radius);

        for (j=slices; j>=0; j--)
        {
            glNormal3d(cost1[j]*r1,        sint1[j]*r1,        z1       );
            glVertex3d(cost1[j]*r1*radius, sint1[j]*r1*radius, z1*radius);
        }

    glEnd();

    /* Cover each stack with a quad strip, except the top and bottom stacks */

    for( i=1; i<stacks-1; i++ )
    {
        z0 = z1; z1 = cost2[i+1];
        r0 = r1; r1 = sint2[i+1];

        glBegin(GL_QUAD_STRIP);

            for(j=0; j<=slices; j++)
            {
                glNormal3d(cost1[j]*r1,        sint1[j]*r1,        z1       );
                glVertex3d(cost1[j]*r1*radius, sint1[j]*r1*radius, z1*radius);
                glNormal3d(cost1[j]*r0,        sint1[j]*r0,        z0       );
                glVertex3d(cost1[j]*r0*radius, sint1[j]*r0*radius, z0*radius);
            }

        glEnd();
    }

    /* The bottom stack is covered with a triangle fan */

    z0 = z1;
    r0 = r1;

    glBegin(GL_TRIANGLE_FAN);

        glNormal3d(0,0,-1);
        glVertex3d(0,0,-radius);

        for (j=0; j<=slices; j++)
        {
            glNormal3d(cost1[j]*r0,        sint1[j]*r0,        z0       );
            glVertex3d(cost1[j]*r0*radius, sint1[j]*r0*radius, z0*radius);
        }

    glEnd();

    /* Release sin and cos tables */

    free(sint1);
    free(cost1);
    free(sint2);
    free(cost2);
}

/*
 * Draws a wire sphere
 */
void glutWireSphere(GLdouble radius, GLint slices, GLint stacks)
{
    int i,j;

    /* Adjust z and radius as stacks and slices are drawn. */

    double r;
    double x,y,z;

    /* Pre-computed circle */

    double *sint1,*cost1;
    double *sint2,*cost2;

    //FREEGLUT_EXIT_IF_NOT_INITIALISED ( "glutWireSphere" );

    fghCircleTable(&sint1,&cost1,-slices  );
    fghCircleTable(&sint2,&cost2, stacks*2);

    /* Draw a line loop for each stack */

    for (i=1; i<stacks; i++)
    {
        z = cost2[i];
        r = sint2[i];

        glBegin(GL_LINE_LOOP);

            for(j=0; j<=slices; j++)
            {
                x = cost1[j];
                y = sint1[j];

                glNormal3d(x,y,z);
                glVertex3d(x*r*radius,y*r*radius,z*radius);
            }

        glEnd();
    }

    /* Draw a line loop for each slice */

    for (i=0; i<slices; i++)
    {
        glBegin(GL_LINE_STRIP);

            for(j=0; j<=stacks; j++)
            {
                x = cost1[i]*sint2[j];
                y = sint1[i]*sint2[j];
                z = cost2[j];

                glNormal3d(x,y,z);
                glVertex3d(x*radius,y*radius,z*radius);
            }

        glEnd();
    }

    /* Release sin and cos tables */

    free(sint1);
    free(cost1);
    free(sint2);
    free(cost2);
}