骨骼动画入门----BVH文件的载入和播放

阅读本文的基础

1 c++

2 OpenGL

3 图形学的基本概念

 

骨骼动画基本概念概括

  传统的帧动画将模型中的点的坐标信息存取为一帧，播放下一帧时，就读取下一帧的全部点的新的坐标信息。这样的方式浪费了很大的空间，而且模型之间的层级关系无法体现，不利于和场景以及其他模型的交互。

 骨骼动画也是一帧一帧的，但是每一帧存取的数据不是坐标信息，而是层级结构中，子节点相对父亲节点的平移和旋转信息。递归画出层级结构是很容易实现的。

这样存取克服了帧动画的缺点。骨骼动画的缺点是实现复杂，新数据生成需要一定的时间。

 选取BVH文件格式作为入门是不错的选择，因为这个格式的简单，不含有其他信息，只含有动作数据，让你化繁为简，一目了然的理解骨骼动画的算法。

 

BVH文件格式

细节1 每行的最后有一个回车符和一个换行符，用16进制观察会很明显的发现

部分一 层级结构信息

用文本文件打开后，一目了然的会出现一棵树的结构。

offset 表示当前节点相对于父节点的位置信息

channels 表示对下面motion数据的解释 除父节点外 channels都有三个信息（ 父节点为六个） 对应了子节点对父节点的旋转量 这些数据放在motion中

部分二 motion数据

有多少帧 就有多少行数据

在每一帧中，也就是每一行中，数据的前3项为根节点的位移信息

其余数据三个为一组代表旋转信息，和层级中的对应顺序为： 文本文件中从上到下channels出现的顺序

也就是这个层级树先序遍历的顺序

细节2 End节点没有这些旋转的信息 root中有这些信息

 

说明：一组的3个数据中 要根据channels中的信息来解析

例如 当channels 中为 Xrotation Zrotation Yrotation

操作时就要

glRotatef(pFrame[0],1.0f,0.0f,0.0f);
glRotatef(pFrame[1],0.0f,0.0f,1.0f);
glRotatef(pFrame[2],0.0f,1.0f,0.0f);

pFrame 指向当前的旋转信息组

细节3 offset 后的数据之间和channels后的解释信息间可能为空格也可能为tab

强烈建议用16进制查看器看多个文件 这样对文件的具体格式将会有清晰的认识 避免不必要的错误代码的编写

 

下面是代码和注释

#ifndef __BVH_H__#define __BVH_H__#include <stack>using namespace std;class BVHJoint;class BVH{public:BVH();~BVH();void clear();bool loadFile(const char * pfile);void print();void setCurrentFrame(unsigned c);void draw();unsigned getFrameCount();void addFrame();private:BVHJoint * root;//根节点stack<BVHJoint*> father;//载入时用到的栈 根据前序构建树BVHJoint* currentNode;//载入时当前的节点unsigned char* p;//载入时读buffer的当前位置unsigned jointCount;//节点的数量包括rootunsigned frameCount;//帧数unsigned currentFrame;//当前帧float **frameData;//存取motion数据的二维数组

float frameTime;//float *pFrame;//绘制使用的当前motion信息位置

void drawRecursive(BVHJoint * r);void roateSpace(unsigned char);void deleteRecursive(BVHJoint* r);bool processLeftBrace();bool processRightBrace();bool processJoint();bool processOffset();bool processChannels();bool processEnd();unsigned char getFlags();BVHJoint * newNode();void printRecursive(BVHJoint* r,int n);};#endif

 

#include <cassert>#include <cstdio>#include <cstdlib>#include <gl/glut.h>#include "BVH.h"enum { CHILDSIZE = 16 ,NAMESIZE = 24};enum { ZYX = 1, YZX = 2, ZXY = 3, XZY = 5, YXZ = 6, XYZ = 7};//------------------------------------------------------class BVHJoint{public:friend class BVH;BVHJoint():x(0),y(0),z(0),childNum(0),flags(0){name[0] = 0;}bool addChild(BVHJoint* pc){assert(childNum != NAMESIZE);child[childNum] = pc;childNum++;return true;}BVHJoint* getChild(int i){assert( i>=0 && i<CHILDSIZE);return child[i];}private:float x;float y;float z;//三个值表示距离父节点的偏移量BVHJoint * child[CHILDSIZE];int childNum;unsigned char name[NAMESIZE];unsigned char flags;//记录了channels 所代表的含义};//-------------------------------------------------------BVH::BVH():currentNode(nullptr),p(nullptr),root(nullptr),frameCount(0),frameData(nullptr),pFrame(nullptr),frameTime(1),jointCount(1),currentFrame(0){}//------------------------------------------------------BVH::~BVH(){clear();}//------------------------------------------------------void BVH::deleteRecursive(BVHJoint* r){for(int i = 0; i < r->childNum; i++){deleteRecursive(r->getChild(i));}delete r;}//------------------------------------------------------void BVH:: clear(){currentNode = nullptr;p = nullptr;while(!father.empty()) father.pop();frameTime = 1;for(unsigned int i = 0; i < frameCount; i++)delete []frameData[i];delete []frameData;frameData = nullptr;pFrame = nullptr;frameCount = 0;currentFrame = 0;jointCount = 1;if(root != nullptr){deleteRecursive(root);}root = nullptr;}//------------------------------------------------------//-------------------------------------------------------//根据当前p指向的名字构建一个节点，读取文件的buffer时 //必须通过这个函数来产生新节点BVHJoint* BVH:: newNode(){BVHJoint * node = new BVHJoint();int i;for(i = 0; i < NAMESIZE && *p != '\n';i++){node->name[i] = *p;p++;}if(i == NAMESIZE) --i;node->name[i-1] = 0;//为了吃掉一个回车符！！p++;return node;}//------------------------------------------------------//获得每个节点的通道信息，采用1，2，3，5，6，7表示6种可能的情况unsigned char BVH::getFlags(){return (unsigned char)((*p - 'X' + 1)*1 + (*(p+10) - 'X' + 1)*2 + (*(p+20) - 'X' + 1)*4 - 10);}//------------------------------------------------------//载入一个文件，生成BVH的一棵树形结构和motion旋转信息的二位数组bool BVH::loadFile(const char* pfile){if(pfile == 0)return false;FILE *f;if(!(f = fopen(pfile,"rb"))){printf("file load failed!\n");return false;}//获取文件长度int iStart = ftell(f);fseek(f,0,SEEK_END);int iEnd = ftell(f);rewind(f);int iFileSize =  iEnd -iStart;//结束获取长度信息//分配文件长的动态数组unsigned char *buffer = new unsigned char[iFileSize]; if(!buffer){printf("mem alloc failed!!\n");return false;}//载入文件到bufferif(fread(buffer,1,iFileSize,f)!=(unsigned)iFileSize){printf("failed!!\n");delete []buffer;return false;}//验证文件是否为BVHconst char * fileheader = "HIERARCHY";p = buffer;for(int i = 0; i < 9 ; i++ ){if( *p != fileheader[i]){delete []buffer;return false;}p++;}//验证文件结束//载入根节点名字p += 7;root = newNode();//保持栈顶元素和当前节点同步father.push(root);currentNode = root;//载入根节点的偏移offset信息 这里的offset信息和joint不同需要特化处理while(*p != 'O') p++;p += 7;root->x = (float)atof((char*)p);p += 5;if(*p == ' ') p++;root->y = (float)atof((char*)p);p += 5;if(*p == ' ') p++;root->z = (float)atof((char*)p);p += 5;//结束offset信息的载入//跳到*rotation 位置 越过根节点的位移通道量 这里认为root是固定的XYZ位移模式while(*p != 'r') p++;p--;//获得根节点的旋转通道信息root->flags = getFlags();p += 30;//结束载入根节点//根据字符流的首字符 构建状态处理逻辑 载入子节点int counter = 1; //大括号的数量 初始化为1因为根节点之后已经有了一个for(bool running = true; running ; ){//文件格式出错才会这样if(*p == 0){ delete []buffer;clear();return 0;}//根据首字母 分发状态处理switch(*p){case 13://回车case '\n'://换行case ' ':case '':p++;break;case '{':processLeftBrace();counter++;break;case '}':processRightBrace();//判断层级数据载入是否结束counter--;if(counter == 0) running = false;break;case 'J':jointCount++;processJoint();break;case 'O':processOffset();break;case 'C':processChannels();break;case 'E':processEnd();break;default:printf("_%c_ _%d_ file format error!! \n",*p,*p);delete []buffer;clear();return false;}}while(*p!= 'F') p++;p += 8;frameCount = (unsigned)atoi((char *)p);while(*p != 'F') p++;p += 12;frameTime = (float)atof((char*)p);//结束载入 层级关系的数据while(*p++ != '\n');// 现在 p 指向了真正的motion数据// 先分配空间frameData = new float*[frameCount];if(frameData == nullptr) {delete []buffer;clear();return false;}//每一帧的数据包括3个root节点的平移数据 和所有节点的旋转数据if(jointCount == 1){delete []buffer;clear();return false;}int dataCount = jointCount*3 + 3;//printf("dataCount is : %d\n", dataCount );for(unsigned int i = 0; i < frameCount; i++){frameData[i] = new float[dataCount];if(frameData == nullptr){delete []buffer;clear();return false;}}// 开始载入 motion 的数据// 细节:每一帧的数据为一行 每个数据之间有一个空格或tab //行最后有一个空格或tab然后是一个回车符和一个换行符for(unsigned int i = 0; i < frameCount; i++){for(int j = 0; j < dataCount; j++){frameData[i][j] = (float)atof((char*)p);p += 8;while(*p != ' ' && *p != '') p++;p++;//跳过空格或tab}//跳过回车和换行符p+=2;}//载入motion数据结束//载入全部数据结束delete []buffer;fclose(f);return true;}//------------------------------------------------------bool BVH::processLeftBrace(){//栈中存放了一系列的父节点 栈顶为当前节点，father.push(currentNode);p++;return true;}//------------------------------------------------------bool BVH::processRightBrace(){//栈顶为当前节点所以一定要先出栈（被debug1）father.pop();//保持当前节点和栈顶元素同步if(!father.empty())currentNode = father.top();p++;return true;}//------------------------------------------------------bool BVH::processJoint(){p += 6;BVHJoint *node = newNode();//发现一个子节点添加父子关系if(!currentNode->addChild(node))return false;currentNode = node;//马上会处理‘｛’ 使得栈顶与当前节点同步return true;}//------------------------------------------------------//由于offset在这里的文件格式不太统一 所以需要注意 因为root的offset格式特殊bool BVH::processOffset(){p += 7;currentNode->x = atof((const char *)p);p += 8;while(*p != ' ' && *p != '' ) p++;p++;currentNode->y = atof((const char *)p);p += 8;while(*p != ' ' && *p != '' ) p++;p++;currentNode->z = atof((const char *)p);while(*p++ != '\n');return true;}//------------------------------------------------------//getFlags 将根据三个roation前面的三个大写字母判断通道的格式bool BVH::processChannels(){p += 11;currentNode->flags = getFlags();p += 30;return true;}//------------------------------------------------------bool BVH::processEnd(){//其实和joint节点的处理是一样的 就是 p+=4 这里前进的不同p += 4;BVHJoint *node = newNode();if(!currentNode->addChild(node))return false;currentNode = node;return true;}//-----------------------------------------------------//绘制骨骼 root节点还是多了处理void BVH::draw(){pFrame = frameData[currentFrame];root->x = pFrame[0];root->y = pFrame[1];root->z = pFrame[2];pFrame += 3;drawRecursive(root);}//-----------------------------------------------------//绘制函数的核心 递归的绘制 void BVH::drawRecursive(BVHJoint* r){glPushMatrix();//要先平移后旋转（被debug3）//平移 根据父节点空间glTranslatef(r->x,r->y,r->z);//根据motion中的信息和节点的通道类型进行旋转roateSpace(r->flags);//画出点glutSolidSphere(1.0f,20,16);//递归绘制子节点for(int i = 0; i < r->childNum; i++){drawRecursive(r->getChild(i));} glPopMatrix();}//-----------------------------------------------------void BVH::roateSpace(unsigned char flags){//enum {ZYX = 1, YZX = 2,ZXY = 3,XZY = 5,YXZ = 6,XYZ = 7};switch (flags){case ZYX:glRotatef(pFrame[0],0.0f,0.0f,1.0f);glRotatef(pFrame[1],0.0f,1.0f,0.0f);glRotatef(pFrame[2],1.0f,0.0f,0.0f);break;case YZX:glRotatef(pFrame[0],0.0f,1.0f,0.0f);glRotatef(pFrame[1],0.0f,0.0f,1.0f);glRotatef(pFrame[2],1.0f,0.0f,0.0f);break;case ZXY:glRotatef(pFrame[0],0.0f,0.0f,1.0f);glRotatef(pFrame[1],1.0f,0.0f,0.0f);glRotatef(pFrame[2],0.0f,1.0f,0.0f);break;case XZY:glRotatef(pFrame[0],1.0f,0.0f,0.0f);glRotatef(pFrame[1],0.0f,0.0f,1.0f);glRotatef(pFrame[2],0.0f,1.0f,0.0f);break;case YXZ:glRotatef(pFrame[0],0.0f,1.0f,0.0f);glRotatef(pFrame[1],1.0f,0.0f,0.0f);glRotatef(pFrame[2],0.0f,0.0f,1.0f);break;case XYZ:glRotatef(pFrame[0],1.0f,0.0f,0.0f);glRotatef(pFrame[1],0.0f,1.0f,0.0f);glRotatef(pFrame[2],0.0f,0.0f,1.0f);break;default:break;}//End叶节点时不能前进 因为它没有旋转信息（被debug2）//pFrame初始化为当前帧root节点的旋转信息//每旋转一个节点的空间后 自动+3跳到下一个节点的旋转信息//说明： BVH 存放旋转的信息按照文件中从上到下channel出现的顺序存储//就是递归遍历时的前序周游顺序if(flags != 0) pFrame+=3;}//----------------------------------------------------unsigned BVH::getFrameCount(){return frameCount;}//-----------------------------------------------------void BVH::addFrame(){currentFrame ++;if(currentFrame == frameCount) currentFrame = 0;}//-----------------------------------------------------void BVH::setCurrentFrame(unsigned c){assert(c>=0&&c<frameCount);currentFrame = c;}//------------------------------------------------------//将载入好的层级信息打印出来void BVH::printRecursive(BVHJoint* r,int n){for(int i = 0; i < n; i++) printf(" -"); printf("%s",r->name);printf(" ： %f,%f,%f -%d- ",r->x,r->y,r->z,r->flags);switch(r->flags){case 1:printf("zyx");break;case 2:printf("yzx");break;case 3:printf("zxy");break;case 5:printf("xzy");break;case 6:printf("yxz");break;case 7:printf("xyz");break;default:break;}printf("\n");for(int i = 0; i < r->childNum ; i++){printRecursive(r->getChild(i) , n+1);}}//------------------------------------------------------void BVH::print(){printRecursive(root , 0);//int datacount = jointCount*3+3;//for(int j= 0 ; j < frameCount; j++)//{//printf("frame %d:\n",j);//for(int i = 0; i < datacount; i++)//printf("%f ",frameData[j][i]);//printf("\n");//}}//------------------------------------------------------

#include <cstdio>#include <cstdlib>#include <gl/glut.h>#include "BVH.h"BVH model;float R = 200.0f;float angle = 10;void init(){glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );glEnable(GL_DEPTH_TEST);GLfloat position[] = {0.0f,0.0f,1.0f,1.0f};glLightfv(GL_LIGHT0,GL_POSITION,position);glEnable(GL_LIGHTING);glEnable(GL_LIGHT0);glLineWidth(3.0f);glColor3f(0.0f,1.0f,0.0f);model.loadFile("sexy.bvh");model.print();}void uninit(){}void display(){glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );glLoadIdentity();gluLookAt( R*cos(angle), 20, R*sin(angle), 0, 20, 0, 0, 1, 0 );model.draw();glBegin(GL_QUADS);glVertex3f(-100,-10,100);glVertex3f(100,-10,100);glVertex3f(100,-10,-100);glVertex3f(-100,-10,-100);glEnd();glutSwapBuffers();}void reshape( int w, int h ){glViewport( 0, 0, GLsizei( w ), GLsizei( h ) );glMatrixMode( GL_PROJECTION );glLoadIdentity();gluPerspective( 45, ( GLdouble ) w / ( GLdouble ) h, 1.0f, 1000.0f );glMatrixMode( GL_MODELVIEW );glLoadIdentity();gluLookAt( R*cos(angle), 0, R*sin(angle), 0, 0, 0, 0, 1, 0 );}void keyboard( unsigned char key, int x, int y ){switch( key  ){case 27:exit( 0 );case 'a':case 'A':angle += 0.1;if(angle >= 360.0f) angle = 0;break;case 'd':case 'D':angle -= 0.1;if(angle <=0.0f) angle = 359.9f;break;case 'w':case 'W':model.addFrame();}glutPostRedisplay();}int main( int argc, char *argv[] ){glutInit( &argc, argv );glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH );glutInitWindowPosition( 300, 75 );glutInitWindowSize( 600, 600 );glutCreateWindow( "OpenGL  Test" );init();glutReshapeFunc( reshape );glutKeyboardFunc( keyboard );glutDisplayFunc( display );//glutIdleFunc(display);glutMainLoop();uninit();return 0;}