opengl 学习的的好东西--明白各种参数意义

/* glm.c Nate Robins, 1997, 2000 [email protected], 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),