骨骼動畫入門—-BVH檔案的載入和播放

閱讀本文的基礎

1 c++

2 OpenGL

3 圖形學的基本概念

 

骨骼動畫基本概念概括

  傳統的幀動畫將模型中的點的座標資訊存取為一幀，播放下一幀時，就讀取下一幀的全部點的新的座標資訊。這樣的方式浪費了很大的空間，而且模型之間的層級關係無法體現，不利於和情境以及其他模型的互動。

 骨骼動畫也是一幀一幀的，但是每一幀存取的資料不是座標資訊，而是層級結構中，子節點相對父親節點的平移和旋轉資訊。遞迴畫出層級結構是很容易實現的。

這樣存取克服了幀動畫的缺點。骨骼動畫的缺點是實現複雜，新資料產生需要一定的時間。

 選取BVH檔案格式作為入門是不錯的選擇，因為這個格式的簡單，不含有其他資訊，只含有動作資料，讓你化繁為簡，一目瞭然的理解骨骼動畫的演算法。

 

BVH檔案格式

細節1 每行的最後有一個斷行符號符和一個分行符號，用16進位觀察會很明顯的發現

部分一 層級結構資訊

用文字檔開啟後，一目瞭然的會出現一棵樹的結構。

offset 表示當前節點相對於父節點的位置資訊

channels 表示對下面motion資料的解釋 除父節點外 channels都有三個資訊（ 父節點為六個） 對應了子節點對父節點的旋轉量 這些資料放在motion中

部分二 motion資料

有多少幀 就有多少行資料

在每一幀中，也就是每一行中，資料的前3項為根節點的位移資訊

其餘資料三個為一組代表旋轉資訊，和層級中的對應順序為： 文字檔中從上到下channels出現的順序

也就是這個層級樹先序遍曆的順序

細節2 End節點沒有這些旋轉的資訊 root中有這些資訊

 

說明：一組的3個資料中 要根據channels中的資訊來解析

例如 當channels 中為 Xrotation Zrotation Yrotation

操作時就要

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 指向當前的旋轉資訊組

細節3 offset 後的資料之間和channels後的解釋資訊間可能為空白格也可能為tab

強烈建議用16進位查看器看多個檔案 這樣對檔案的具體格式將會有清晰的認識 避免不必要的錯誤碼的編寫

 

下面是代碼和注釋

#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;//根節點stack<BVHJoint*> father;//載入時用到的棧 根據前序構建樹BVHJoint* currentNode;//載入時當前的節點unsigned char* p;//載入時讀buffer的當前位置unsigned jointCount;//節點的數量包括rootunsigned frameCount;//幀數unsigned currentFrame;//當前幀float **frameData;//存取motion資料的二維數組

float frameTime;//float *pFrame;//繪製使用的當前motion資訊位置

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;//三個值表示距離父節點的位移量BVHJoint * child[CHILDSIZE];int childNum;unsigned char name[NAMESIZE];unsigned char flags;//記錄了channels 所代表的含義};//-------------------------------------------------------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;}//------------------------------------------------------//-------------------------------------------------------//根據當前p指向的名字構建一個節點，讀取檔案的buffer時 //必須通過這個函數來產生新節點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;//為了吃掉一個斷行符號符！！p++;return node;}//------------------------------------------------------//獲得每個節點的通道資訊，採用1，2，3，5，6，7表示6種可能的情況unsigned char BVH::getFlags(){return (unsigned char)((*p - 'X' + 1)*1 + (*(p+10) - 'X' + 1)*2 + (*(p+20) - 'X' + 1)*4 - 10);}//------------------------------------------------------//載入一個檔案，產生BVH的一棵樹形結構和motion旋轉資訊的二位元組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;}//擷取檔案長度int iStart = ftell(f);fseek(f,0,SEEK_END);int iEnd = ftell(f);rewind(f);int iFileSize =  iEnd -iStart;//結束擷取長度資訊//分配檔案長的動態數組unsigned char *buffer = new unsigned char[iFileSize]; if(!buffer){printf("mem alloc failed!!\n");return false;}//載入檔案到bufferif(fread(buffer,1,iFileSize,f)!=(unsigned)iFileSize){printf("failed!!\n");delete []buffer;return false;}//驗證檔案是否為BVHconst char * fileheader = "HIERARCHY";p = buffer;for(int i = 0; i < 9 ; i++ ){if( *p != fileheader[i]){delete []buffer;return false;}p++;}//驗證檔案結束//載入根節點名字p += 7;root = newNode();//保持棧頂元素和當前節點同步father.push(root);currentNode = root;//載入根節點的位移offset資訊 這裡的offset資訊和joint不同需要特化處理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;//結束offset資訊的載入//跳到*rotation 位置 越過根節點的位移通道量 這裡認為root是固定的XYZ位移模式while(*p != 'r') p++;p--;//獲得根節點的旋轉通道資訊root->flags = getFlags();p += 30;//結束載入根節點//根據字元流的首字元 構建狀態處理邏輯 載入子節點int counter = 1; //大括弧的數量 初始化為1因為根節點之後已經有了一個for(bool running = true; running ; ){//檔案格式出錯才會這樣if(*p == 0){ delete []buffer;clear();return 0;}//根據首字母 分髮狀態處理switch(*p){case 13://斷行符號case '\n'://換行case ' ':case '':p++;break;case '{':processLeftBrace();counter++;break;case '}':processRightBrace();//判斷層級資料載入是否結束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);//結束載入 層級關係的資料while(*p++ != '\n');// 現在 p 指向了真正的motion資料// 先分配空間frameData = new float*[frameCount];if(frameData == nullptr) {delete []buffer;clear();return false;}//每一幀的資料包括3個root節點的平移資料 和所有節點的旋轉資料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;}}// 開始載入 motion 的資料// 細節:每一幀的資料為一行 每個資料之間有一個空格或tab //行最後有一個空格或tab然後是一個斷行符號符和一個分行符號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++;//跳過空格或tab}//跳過斷行符號和分行符號p+=2;}//載入motion資料結束//載入全部資料結束delete []buffer;fclose(f);return true;}//------------------------------------------------------bool BVH::processLeftBrace(){//棧中存放了一系列的父節點 棧頂為當前節點，father.push(currentNode);p++;return true;}//------------------------------------------------------bool BVH::processRightBrace(){//棧頂為當前節點所以一定要先出棧（被debug1）father.pop();//保持當前節點和棧頂元素同步if(!father.empty())currentNode = father.top();p++;return true;}//------------------------------------------------------bool BVH::processJoint(){p += 6;BVHJoint *node = newNode();//發現一個子節點添加父子關係if(!currentNode->addChild(node))return false;currentNode = node;//馬上會處理‘｛’ 使得棧頂與當前節點同步return true;}//------------------------------------------------------//由於offset在這裡的檔案格式不太統一 所以需要注意 因為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 將根據三個roation前面的三個大寫字母判斷通道的格式bool BVH::processChannels(){p += 11;currentNode->flags = getFlags();p += 30;return true;}//------------------------------------------------------bool BVH::processEnd(){//其實和joint節點的處理是一樣的 就是 p+=4 這裡前進的不同p += 4;BVHJoint *node = newNode();if(!currentNode->addChild(node))return false;currentNode = node;return true;}//-----------------------------------------------------//繪製骨骼 root節點還是多了處理void BVH::draw(){pFrame = frameData[currentFrame];root->x = pFrame[0];root->y = pFrame[1];root->z = pFrame[2];pFrame += 3;drawRecursive(root);}//-----------------------------------------------------//繪製函數的核心 遞迴的繪製 void BVH::drawRecursive(BVHJoint* r){glPushMatrix();//要先平移後旋轉（被debug3）//平移 根據父節點空間glTranslatef(r->x,r->y,r->z);//根據motion中的資訊和節點的通道類型進行旋轉roateSpace(r->flags);//畫出點glutSolidSphere(1.0f,20,16);//遞迴繪製子節點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分葉節點時不能前進 因為它沒有旋轉資訊（被debug2）//pFrame初始化為當前幀root節點的旋轉資訊//每旋轉一個節點的空間後 自動+3跳到下一個節點的旋轉資訊//說明： BVH 存放旋轉的資訊按照檔案中從上到下channel出現的順序儲存//就是遞迴遍曆時的前序周遊順序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;}//------------------------------------------------------//將載入好的層級資訊列印出來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;}