glm.c

计算机图形学～想必是很多人需要的～在此共享一下

/*    
      glm.c
      Nate Robins, 1997, 2000
      [e-mail], http://www.pobox.com/~nate
 
      Wavefront OBJ model file format reader/writer/manipulator.

      Includes routines for generating smooth normals with
      preservation of edges, welding redundant vertices & texture
      coordinate generation (spheremap and planar projections) + more.
  
*/


#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "glm.h"


#define T(x) (model->triangles[(x)])


/* _GLMnode: general purpose node */
typedef struct _GLMnode {
    GLuint         index;
    GLboolean      averaged;
    struct _GLMnode* next;
} GLMnode;


/* glmMax: returns the maximum of two floats */
static GLfloat
glmMax(GLfloat a, GLfloat b) 
{
    if (b > a)
        return b;
    return a;
}

/* glmAbs: returns the absolute value of a float */
static GLfloat
glmAbs(GLfloat f)
{
    if (f < 0)
        return -f;
    return f;
}

/* glmDot: compute the dot product of two vectors
 *
 * u - array of 3 GLfloats (GLfloat u[3])
 * v - array of 3 GLfloats (GLfloat v[3])
 */
static GLfloat
glmDot(GLfloat* u, GLfloat* v)
{
    assert(u); assert(v);
    
    return u[0]*v[0] + u[1]*v[1] + u[2]*v[2];
}

/* glmCross: compute the cross product of two vectors
 *
 * u - array of 3 GLfloats (GLfloat u[3])
 * v - array of 3 GLfloats (GLfloat v[3])
 * n - array of 3 GLfloats (GLfloat n[3]) to return the cross product in
 */
static GLvoid
glmCross(GLfloat* u, GLfloat* v, GLfloat* n)
{
    assert(u); assert(v); assert(n);
    
    n[0] = u[1]*v[2] - u[2]*v[1];
    n[1] = u[2]*v[0] - u[0]*v[2];
    n[2] = u[0]*v[1] - u[1]*v[0];
}

/* glmNormalize: normalize a vector
 *
 * v - array of 3 GLfloats (GLfloat v[3]) to be normalized
 */
static GLvoid
glmNormalize(GLfloat* v)
{
    GLfloat l;
    
    assert(v);
    
    l = (GLfloat)sqrt(v[0]*v[0] + v[1]*v[1] + v[2]*v[2]);
    v[0] /= l;
    v[1] /= l;
    v[2] /= l;
}

/* glmEqual: compares two vectors and returns GL_TRUE if they are
 * equal (within a certain threshold) or GL_FALSE if not. An epsilon
 * that works fairly well is 0.000001.
 *
 * u - array of 3 GLfloats (GLfloat u[3])
 * v - array of 3 GLfloats (GLfloat v[3]) 
 */
static GLboolean
glmEqual(GLfloat* u, GLfloat* v, GLfloat epsilon)
{
    if (glmAbs(u[0] - v[0]) < epsilon &&
        glmAbs(u[1] - v[1]) < epsilon &&
        glmAbs(u[2] - v[2]) < epsilon) 
    {
        return GL_TRUE;
    }
    return GL_FALSE;
}

/* glmWeldVectors: eliminate (weld) vectors that are within an
 * epsilon of each other.
 *
 * vectors     - array of GLfloat[3]'s to be welded
 * numvectors - number of GLfloat[3]'s in vectors
 * epsilon     - maximum difference between vectors 
 *
 */
GLfloat*
glmWeldVectors(GLfloat* vectors, GLuint* numvectors, GLfloat epsilon)
{
    GLfloat* copies;
    GLuint   copied;
    GLuint   i, j;
    
    copies = (GLfloat*)malloc(sizeof(GLfloat) * 3 * (*numvectors + 1));
    memcpy(copies, vectors, (sizeof(GLfloat) * 3 * (*numvectors + 1)));
    
    copied = 1;
    for (i = 1; i <= *numvectors; i++) {
        for (j = 1; j <= copied; j++) {
            if (glmEqual(&vectors[3 * i], &copies[3 * j], epsilon)) {
                goto duplicate;
            }
        }
        
        /* must not be any duplicates -- add to the copies array */
        copies[3 * copied + 0] = vectors[3 * i + 0];
        copies[3 * copied + 1] = vectors[3 * i + 1];
        copies[3 * copied + 2] = vectors[3 * i + 2];
        j = copied;             /* pass this along for below */
        copied++;
        
duplicate:
/* set the first component of this vector to point at the correct
        index into the new copies array */
        vectors[3 * i + 0] = (GLfloat)j;
    }
    
    *numvectors = copied-1;
    return copies;
}

/* glmFindGroup: Find a group in the model */
GLMgroup*
glmFindGroup(GLMmodel* model, char* name)
{
    GLMgroup* group;
    
    assert(model);
    
    group = model->groups;
    while(group) {
        if (!strcmp(name, group->name))
            break;
        group = group->next;
    }
    
    return group;
}

/* glmAddGroup: Add a group to the model */
GLMgroup*
glmAddGroup(GLMmodel* model, char* name)
{
    GLMgroup* group;
    
    group = glmFindGroup(model, name);
    if (!group) {
        group = (GLMgroup*)malloc(sizeof(GLMgroup));
        group->name = strdup(name);
        group->material = 0;
        group->numtriangles = 0;
        group->triangles = NULL;
        group->next = model->groups;
        model->groups = group;
        model->numgroups++;
    }
    
    return group;
}

/* glmFindGroup: Find a material in the model */
GLuint
glmFindMaterial(GLMmodel* model, char* name)
{
    GLuint i;
    
    /* XXX doing a linear search on a string key'd list is pretty lame,
    but it works and is fast enough for now. */
    for (i = 0; i < model->nummaterials; i++) {
        if (!strcmp(model->materials[i].name, name))
            goto found;
    }
    
    /* didn't find the name, so print a warning and return the default
    material (0). */
    printf("glmFindMaterial():  can't find material \"%s\".\n", name);
    i = 0;
    
found:
    return i;
}


/* glmDirName: return the directory given a path
 *
 * path - filesystem path
 *
 * NOTE: the return value should be free'd.
 */
static char*
glmDirName(char* path)
{
    char* dir;
    char* s;
    
    dir = strdup(path);
    
    s = strrchr(dir, '/');
    if (s)
        s[1] = '\0';
    else
        dir[0] = '\0';
    
    return dir;
}


/* glmReadMTL: read a wavefront material library file
 *
 * model - properly initialized GLMmodel structure
 * name  - name of the material library
 */
static GLvoid
glmReadMTL(GLMmodel* model, char* name)
{
    FILE* file;
    char* dir;
    char* filename;
    char    buf[128];
    GLuint nummaterials, i;
    
    dir = glmDirName(model->pathname);
    filename = (char*)malloc(sizeof(char) * (strlen(dir) + strlen(name) + 1));
    strcpy(filename, dir);
    strcat(filename, name);
    free(dir);
    
    file = fopen(filename, "r");
    if (!file) {
        fprintf(stderr, "glmReadMTL() failed: can't open material file \"%s\".\n",
            filename);
        exit(1);
    }
    free(filename);
    
    /* count the number of materials in the file */
    nummaterials = 1;
    while(fscanf(file, "%s", buf) != EOF) {
        switch(buf[0]) {
        case '#':               /* comment */
            /* eat up rest of line */
            fgets(buf, sizeof(buf), file);
            break;
        case 'n':               /* newmtl */
            fgets(buf, sizeof(buf), file);
            nummaterials++;
            sscanf(buf, "%s %s", buf, buf);
            break;
        default:
            /* eat up rest of line */
            fgets(buf, sizeof(buf), file);
            break;
        }
    }
    
    rewind(file);
    
    model->materials = (GLMmaterial*)malloc(sizeof(GLMmaterial) * nummaterials);
    model->nummaterials = nummaterials;
    
    /* set the default material */
    for (i = 0; i < nummaterials; i++) {
        model->materials[i].name = NULL;
        model->materials[i].shininess = 65.0;
        model->materials[i].diffuse[0] = 0.8;
        model->materials[i].diffuse[1] = 0.8;
        model->materials[i].diffuse[2] = 0.8;
        model->materials[i].diffuse[3] = 1.0;
        model->materials[i].ambient[0] = 0.2;
        model->materials[i].ambient[1] = 0.2;
        model->materials[i].ambient[2] = 0.2;
        model->materials[i].ambient[3] = 1.0;
        model->materials[i].specular[0] = 0.0;
        model->materials[i].specular[1] = 0.0;
        model->materials[i].specular[2] = 0.0;
        model->materials[i].specular[3] = 1.0;
    }
    model->materials[0].name = strdup("default");
    
    /* now, read in the data */
    nummaterials = 0;
    while(fscanf(file, "%s", buf) != EOF) {
        switch(buf[0]) {
        case '#':               /* comment */
            /* eat up rest of line */
            fgets(buf, sizeof(buf), file);
            break;
        case 'n':               /* newmtl */
            fgets(buf, sizeof(buf), file);
            sscanf(buf, "%s %s", buf, buf);
            nummaterials++;
            model->materials[nummaterials].name = strdup(buf);
            break;
        case 'N':
            fscanf(file, "%f", &model->materials[nummaterials].shininess);
            /* wavefront shininess is from [0, 1000], so scale for OpenGL */
            model->materials[nummaterials].shininess /= 1000.0;
            model->materials[nummaterials].shininess *= 128.0;
            break;
        case 'K':
            switch(buf[1]) {
            case 'd':
                fscanf(file, "%f %f %f",
                    &model->materials[nummaterials].diffuse[0],
                    &model->materials[nummaterials].diffuse[1],
                    &model->materials[nummaterials].diffuse[2]);
                break;
            case 's':
                fscanf(file, "%f %f %f",
                    &model->materials[nummaterials].specular[0],
                    &model->materials[nummaterials].specular[1],
                    &model->materials[nummaterials].specular[2]);
                break;
            case 'a':
                fscanf(file, "%f %f %f",
                    &model->materials[nummaterials].ambient[0],
                    &model->materials[nummaterials].ambient[1],
                    &model->materials[nummaterials].ambient[2]);
                break;
            default:
                /* eat up rest of line */
                fgets(buf, sizeof(buf), file);
                break;
            }
            break;
            default:
                /* eat up rest of line */
                fgets(buf, sizeof(buf), file);
                break;
        }
    }
}

/* glmWriteMTL: write a wavefront material library file
 *
 * model   - properly initialized GLMmodel structure
 * modelpath  - pathname of the model being written
 * mtllibname - name of the material library to be written
 */
static GLvoid
glmWriteMTL(GLMmodel* model, char* modelpath, char* mtllibname)
{