glm.c

计算机图形学～想必是很多人需要的～在此共享一下

/* glmUnitize: "unitize" a model by translating it to the origin and
 * scaling it to fit in a unit cube around the origin.   Returns the
 * scalefactor used.
 *
 * model - properly initialized GLMmodel structure 
 */
GLfloat
glmUnitize(GLMmodel* model)
{
    GLuint  i;
    GLfloat maxx, minx, maxy, miny, maxz, minz;
    GLfloat cx, cy, cz, w, h, d;
    GLfloat scale;
    
    assert(model);
    assert(model->vertices);
    
    /* get the max/mins */
    maxx = minx = model->vertices[3 + 0];
    maxy = miny = model->vertices[3 + 1];
    maxz = minz = model->vertices[3 + 2];
    for (i = 1; i <= model->numvertices; i++) {
        if (maxx < model->vertices[3 * i + 0])
            maxx = model->vertices[3 * i + 0];
        if (minx > model->vertices[3 * i + 0])
            minx = model->vertices[3 * i + 0];
        
        if (maxy < model->vertices[3 * i + 1])
            maxy = model->vertices[3 * i + 1];
        if (miny > model->vertices[3 * i + 1])
            miny = model->vertices[3 * i + 1];
        
        if (maxz < model->vertices[3 * i + 2])
            maxz = model->vertices[3 * i + 2];
        if (minz > model->vertices[3 * i + 2])
            minz = model->vertices[3 * i + 2];
    }
    
    /* calculate model width, height, and depth */
    w = glmAbs(maxx) + glmAbs(minx);
    h = glmAbs(maxy) + glmAbs(miny);
    d = glmAbs(maxz) + glmAbs(minz);
    
    /* calculate center of the model */
    cx = (maxx + minx) / 2.0;
    cy = (maxy + miny) / 2.0;
    cz = (maxz + minz) / 2.0;
    
    /* calculate unitizing scale factor */
    scale = 2.0 / glmMax(glmMax(w, h), d);
    
    /* translate around center then scale */
    for (i = 1; i <= model->numvertices; i++) {
        model->vertices[3 * i + 0] -= cx;
        model->vertices[3 * i + 1] -= cy;
        model->vertices[3 * i + 2] -= cz;
        model->vertices[3 * i + 0] *= scale;
        model->vertices[3 * i + 1] *= scale;
        model->vertices[3 * i + 2] *= scale;
    }
    
    return scale;
}

/* glmDimensions: Calculates the dimensions (width, height, depth) of
 * a model.
 *
 * model   - initialized GLMmodel structure
 * dimensions - array of 3 GLfloats (GLfloat dimensions[3])
 */
GLvoid
glmDimensions(GLMmodel* model, GLfloat* dimensions)
{
    GLuint i;
    GLfloat maxx, minx, maxy, miny, maxz, minz;
    
    assert(model);
    assert(model->vertices);
    assert(dimensions);
    
    /* get the max/mins */
    maxx = minx = model->vertices[3 + 0];
    maxy = miny = model->vertices[3 + 1];
    maxz = minz = model->vertices[3 + 2];
    for (i = 1; i <= model->numvertices; i++) {
        if (maxx < model->vertices[3 * i + 0])
            maxx = model->vertices[3 * i + 0];
        if (minx > model->vertices[3 * i + 0])
            minx = model->vertices[3 * i + 0];
        
        if (maxy < model->vertices[3 * i + 1])
            maxy = model->vertices[3 * i + 1];
        if (miny > model->vertices[3 * i + 1])
            miny = model->vertices[3 * i + 1];
        
        if (maxz < model->vertices[3 * i + 2])
            maxz = model->vertices[3 * i + 2];
        if (minz > model->vertices[3 * i + 2])
            minz = model->vertices[3 * i + 2];
    }
    
    /* calculate model width, height, and depth */
    dimensions[0] = glmAbs(maxx) + glmAbs(minx);
    dimensions[1] = glmAbs(maxy) + glmAbs(miny);
    dimensions[2] = glmAbs(maxz) + glmAbs(minz);
}

/* glmScale: Scales a model by a given amount.
 * 
 * model - properly initialized GLMmodel structure
 * scale - scalefactor (0.5 = half as large, 2.0 = twice as large)
 */
GLvoid
glmScale(GLMmodel* model, GLfloat scale)
{
    GLuint i;
    
    for (i = 1; i <= model->numvertices; i++) {
        model->vertices[3 * i + 0] *= scale;
        model->vertices[3 * i + 1] *= scale;
        model->vertices[3 * i + 2] *= scale;
    }
}

/* glmReverseWinding: Reverse the polygon winding for all polygons in
 * this model.   Default winding is counter-clockwise.  Also changes
 * the direction of the normals.
 * 
 * model - properly initialized GLMmodel structure 
 */
GLvoid
glmReverseWinding(GLMmodel* model)
{
    GLuint i, swap;
    
    assert(model);
    
    for (i = 0; i < model->numtriangles; i++) {
        swap = T(i).vindices[0];
        T(i).vindices[0] = T(i).vindices[2];
        T(i).vindices[2] = swap;
        
        if (model->numnormals) {
            swap = T(i).nindices[0];
            T(i).nindices[0] = T(i).nindices[2];
            T(i).nindices[2] = swap;
        }
        
        if (model->numtexcoords) {
            swap = T(i).tindices[0];
            T(i).tindices[0] = T(i).tindices[2];
            T(i).tindices[2] = swap;
        }
    }
    
    /* reverse facet normals */
    for (i = 1; i <= model->numfacetnorms; i++) {
        model->facetnorms[3 * i + 0] = -model->facetnorms[3 * i + 0];
        model->facetnorms[3 * i + 1] = -model->facetnorms[3 * i + 1];
        model->facetnorms[3 * i + 2] = -model->facetnorms[3 * i + 2];
    }
    
    /* reverse vertex normals */
    for (i = 1; i <= model->numnormals; i++) {
        model->normals[3 * i + 0] = -model->normals[3 * i + 0];
        model->normals[3 * i + 1] = -model->normals[3 * i + 1];
        model->normals[3 * i + 2] = -model->normals[3 * i + 2];
    }
}

/* glmFacetNormals: Generates facet normals for a model (by taking the
 * cross product of the two vectors derived from the sides of each
 * triangle).  Assumes a counter-clockwise winding.
 *
 * model - initialized GLMmodel structure
 */
GLvoid
glmFacetNormals(GLMmodel* model)
{
    GLuint  i;
    GLfloat u[3];
    GLfloat v[3];
    
    assert(model);
    assert(model->vertices);
    
    /* clobber any old facetnormals */
    if (model->facetnorms)
        free(model->facetnorms);
    
    /* allocate memory for the new facet normals */
    model->numfacetnorms = model->numtriangles;
    model->facetnorms = (GLfloat*)malloc(sizeof(GLfloat) *
                       3 * (model->numfacetnorms + 1));
    
    for (i = 0; i < model->numtriangles; i++) {
        model->triangles[i].findex = i+1;
        
        u[0] = model->vertices[3 * T(i).vindices[1] + 0] -
            model->vertices[3 * T(i).vindices[0] + 0];
        u[1] = model->vertices[3 * T(i).vindices[1] + 1] -
            model->vertices[3 * T(i).vindices[0] + 1];
        u[2] = model->vertices[3 * T(i).vindices[1] + 2] -
            model->vertices[3 * T(i).vindices[0] + 2];
        
        v[0] = model->vertices[3 * T(i).vindices[2] + 0] -
            model->vertices[3 * T(i).vindices[0] + 0];
        v[1] = model->vertices[3 * T(i).vindices[2] + 1] -
            model->vertices[3 * T(i).vindices[0] + 1];
        v[2] = model->vertices[3 * T(i).vindices[2] + 2] -
            model->vertices[3 * T(i).vindices[0] + 2];
        
        glmCross(u, v, &model->facetnorms[3 * (i+1)]);
        glmNormalize(&model->facetnorms[3 * (i+1)]);
    }
}

/* glmVertexNormals: Generates smooth vertex normals for a model.
 * First builds a list of all the triangles each vertex is in.   Then
 * loops through each vertex in the the list averaging all the facet
 * normals of the triangles each vertex is in.   Finally, sets the
 * normal index in the triangle for the vertex to the generated smooth
 * normal.   If the dot product of a facet normal and the facet normal
 * associated with the first triangle in the list of triangles the
 * current vertex is in is greater than the cosine of the angle
 * parameter to the function, that facet normal is not added into the
 * average normal calculation and the corresponding vertex is given
 * the facet normal.  This tends to preserve hard edges.  The angle to
 * use depends on the model, but 90 degrees is usually a good start.
 *
 * model - initialized GLMmodel structure
 * angle - maximum angle (in degrees) to smooth across
 */
GLvoid
glmVertexNormals(GLMmodel* model, GLfloat angle)
{
    GLMnode*    node;
    GLMnode*    tail;
    GLMnode** members;
    GLfloat*    normals;
    GLuint  numnormals;
    GLfloat average[3];
    GLfloat dot, cos_angle;
    GLuint  i, avg;
    
    assert(model);
    assert(model->facetnorms);
    
    /* calculate the cosine of the angle (in degrees) */
    cos_angle = cos(angle * M_PI / 180.0);
    
    /* nuke any previous normals */
    if (model->normals)
        free(model->normals);
    
    /* allocate space for new normals */
    model->numnormals = model->numtriangles * 3; /* 3 normals per triangle */
    model->normals = (GLfloat*)malloc(sizeof(GLfloat)* 3* (model->numnormals+1));
    
    /* allocate a structure that will hold a linked list of triangle
    indices for each vertex */
    members = (GLMnode**)malloc(sizeof(GLMnode*) * (model->numvertices + 1));
    for (i = 1; i <= model->numvertices; i++)
        members[i] = NULL;
    
    /* for every triangle, create a node for each vertex in it */
    for (i = 0; i < model->numtriangles; i++) {
        node = (GLMnode*)malloc(sizeof(GLMnode));
        node->index = i;
        node->next  = members[T(i).vindices[0]];
        members[T(i).vindices[0]] = node;
        
        node = (GLMnode*)malloc(sizeof(GLMnode));
        node->index = i;
        node->next  = members[T(i).vindices[1]];
        members[T(i).vindices[1]] = node;
        
        node = (GLMnode*)malloc(sizeof(GLMnode));
        node->index = i;
        node->next  = members[T(i).vindices[2]];
        members[T(i).vindices[2]] = node;
    }
    
    /* calculate the average normal for each vertex */
    numnormals = 1;
    for (i = 1; i <= model->numvertices; i++) {
    /* calculate an average normal for this vertex by averaging the
        facet normal of every triangle this vertex is in */
        node = members[i];
        if (!node)
            fprintf(stderr, "glmVertexNormals(): vertex w/o a triangle\n");
        average[0] = 0.0; average[1] = 0.0; average[2] = 0.0;
        avg = 0;
        while (node) {
        /* only average if the dot product of the angle between the two
        facet normals is greater than the cosine of the threshold
        angle -- or, said another way, the angle between the two
            facet normals is less than (or equal to) the threshold angle */
            dot = glmDot(&model->facetnorms[3 * T(node->index).findex],
                &model->facetnorms[3 * T(members[i]->index).findex]);
            if (dot > cos_angle) {
                node->averaged = GL_TRUE;
                average[0] += model->facetnorms[3 * T(node->index).findex + 0];
                average[1] += model->facetnorms[3 * T(node->index).findex + 1];
                average[2] += model->facetnorms[3 * T(node->index).findex + 2];
                avg = 1;            /* we averaged at least one normal! */
            } else {
                node->averaged = GL_FALSE;
            }
            node = node->next;
        }
        
        if (avg) {
            /* normalize the averaged normal */
            glmNormalize(average);
            
            /* add the normal to the vertex normals list */
            model->normals[3 * numnormals + 0] = average[0];
            model->normals[3 * numnormals + 1] = average[1];
            model->normals[3 * numnormals + 2] = average[2];
            avg = numnormals;
            numnormals++;
        }
        
        /* set the normal of this vertex in each triangle it is in */
        node = members[i];
        while (node) {
            if (node->averaged) {
                /* if this node was averaged, use the average normal */
                if (T(node->index).vindices[0] == i)
                    T(node->index).nindices[0] = avg;
                else if (T(node->index).vindices[1] == i)
                    T(node->index).nindices[1] = avg;
                else if (T(node->index).vindices[2] == i)
                    T(node->index).nindices[2] = avg;
            } else {
                /* if this node wasn't averaged, use the facet normal */
                model->normals[3 * numnormals + 0] = 
                    model->facetnorms[3 * T(node->index).findex + 0];
                model->normals[3 * numnormals + 1] = 
                    model->facetnorms[3 * T(node->index).findex + 1];
                model->normals[3 * numnormals + 2] = 
                    model->facetnorms[3 * T(node->index).findex + 2];
                if (T(node->index).vindices[0] == i)
                    T(node->index).nindices[0] = numnormals;
                else if (T(node->index).vindices[1] == i)
                    T(node->index).nindices[1] = numnormals;
                else if (T(node->index).vindices[2] == i)
                    T(node->index).nindices[2] = numnormals;
                numnormals++;
            }
            node = node->next;
        }
    }
    
    model->numnormals = numnormals - 1;
    
    /* free the member information */
    for (i = 1; i <= model->numvertices; i++) {
        node = members[i];
        while (node) {
            tail = node;
            node = node->next;
            free(tail);
        }
    }
    free(members);
    
    /* pack the normals array (we previously allocated the maximum
    number of normals that could possibly be created (numtriangles *
    3), so get rid of some of them (usually alot unless none of the
    facet normals were averaged)) */
    normals = model->normals;
    model->normals = (GLfloat*)malloc(sizeof(GLfloat)* 3* (model->numnormals+1));
    for (i = 1; i <= model->numnormals; i++) {
        model->normals[3 * i + 0] = normals[3 * i + 0];
        model->normals[3 * i + 1] = normals[3 * i + 1];
        model->normals[3 * i + 2] = normals[3 * i + 2];