[opengl]弹簧质点模型的opengl实现

实现了一种基于弹簧质点模型的布料仿真程序

论文见：http://wenku.baidu.com/link?url=8rBDraTsWTtTL8cFU0vjhXMyv4RF0npjeizz2CQQI4DvvTrxsN3bNOK91_1jRw7TuVadHuds5VnWzQ8CxP0QSOcY6sEUMKUib44crkbil0K

 

对于超弹问题，依然没能很好地解决，希望大神给予指导

#ifndef GLUT_DISABLE_ATEXIT_HACK
#define GLUT_DISABLE_ATEXIT_HACK
#endif
#define GLEW_STATIC
#include <GL/glew.h>
#include <GL/wglew.h>
#include <GL/freeglut.h>
#include <vector>
#include<cstring>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp> //for matrices
#include <glm/gtc/type_ptr.hpp>
//undefine if u want to use the default bending constraint of pbd
#include<iostream>
using namespace std;
//using namespace glm;

GLfloat rtx = 0.0f, rty = 0.0f, rtz = 0.0;
GLfloat sim_step = 0.1;

glm::vec3 Up=glm::vec3(0,1,0), Right, viewDir;
const int GRID_SIZE=10;  //地板砖边长
GLdouble MV[16];
GLint viewport[4];
GLdouble PP[16];
bool isfix[1000];
int dist = -23;

//椭球参数
int iStacks = 30;
int iSlices = 30;
float fRadius = 1;
//float exp1 = 1e-3;

const int numX = 20, numY=20; //一行有numx+1个点
const int total_points = (numX+1)*(numY+1); //总点数
//布料顶点位置 速度
const int fck = 10000;
glm::vec3 Pos[total_points];
glm::vec3 Veloc[total_points];
glm::vec3 force[total_points];
int size = 4;
float hsize = size/2.0f;
float currentTime,newTime,startTime;

const float mass = 1.0/total_points;
const glm::vec3 gvat = glm::vec3(0,-9.8,0);  //重力加速度
const float Spring_K = 2.5;  //弹性系数
const float len0 = 4.0/numX; //单边长度
const float tolera = 1.08;   //弹性限度

void initGL()
{
    //初始化顶点位置
	memset(Pos,0,sizeof(Pos));
	memset(Veloc,0,sizeof(Veloc));
	memset(force,0,sizeof(force));
    //fill in positions
    int count1 = 0;
    int u = numX + 1;
    int v = numY + 1;
	for(int j=0;j<=numY;j++) {
		for(int i=0;i<=numX;i++) {
            Pos[count1++] = glm::vec3( ((float(i)/(u-1)) *2-1)* hsize, size+1, ((float(j)/(v-1) )* size));
			printf("(%.1lf ,%.1lf)",((float(i)/(u-1)) *2-1)* hsize,((float(j)/(v-1) )* size));
		}printf("\n");
		//悬挂点为X[0] 和 X[numX]
	}
	memset(isfix,0,sizeof(isfix));
	isfix[0] = isfix[numX] = 1;

	//处理时间
	startTime = (float)glutGet(GLUT_ELAPSED_TIME);
	cout<<startTime<<"ddddddddddd\n";
	currentTime = startTime;
}

void DrawGrid()
{
	glBegin(GL_LINES);
	glColor3f(0.5f, 0.5f, 0.5f);
	for(int i=-GRID_SIZE;i<=GRID_SIZE;i++)
	{
		glVertex3f((float)i,0,(float)-GRID_SIZE);
		glVertex3f((float)i,0,(float)GRID_SIZE);

		glVertex3f((float)-GRID_SIZE,0,(float)i);
		glVertex3f((float)GRID_SIZE,0,(float)i);
	}
	glEnd();
}

void drawTextile(){
	//draw polygons
	int k = 0;
    glBegin(GL_LINES);
    glColor3f(1,1,1);
	for(int i = 0;i <= numX;i ++){
        for(int j = 0;j <= numY;j ++){
//                cout<<i<<" "<<j<<";";
            if(j != numX){
                glm::vec3 p1 = Pos[k];
                glm::vec3 p2 = Pos[k+1];
                glVertex3f(p1.x,p1.y,p1.z);
                glVertex3f(p2.x,p2.y,p2.z);
//                printf("add %d %d\n",k,k+1);
            }
            if(i != numY){
                glm::vec3 p1 = Pos[k];
                glm::vec3 p2 = Pos[k+numX+1];
                glVertex3f(p1.x,p1.y,p1.z);
                glVertex3f(p2.x,p2.y,p2.z);
            }
            k++;
        }
//        cout<<endl;
	}
    glEnd();

    glPointSize(3);
    glBegin(GL_POINTS);
    glColor3f(1,0,0);
	for(size_t i = 0;i < total_points;i ++){
        glm::vec3 p = Pos[i];
		glVertex3f(p.x,p.y,p.z);
	}
    glEnd();
}

void OnRender(void)
{
    glClear(GL_COLOR_BUFFER_BIT| GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    //设置视角
	glTranslatef(0,0,dist);
	glRotatef(15,1,0,0);
	//做出地面
    DrawGrid();
    drawTextile();
//    drawblock();
    glutSwapBuffers();
}
//求出b点对a点的作用力
glm::vec3 SpringForce(int a, int b, int is){
    float inilen;
    if(is == 1)inilen = len0;
    if(is == 2) inilen = len0 * 2;
    if(is == 3) inilen = len0 * 1.414213;
    glm::vec3 res = glm::vec3(0);
    glm::vec3 tmp = Pos[b] - Pos[a];
    float dis = glm::length(tmp);
    res = tmp/dis;
    res *= (dis - inilen);
    res *= Spring_K;
    return res;
}
void ComputeForces(){
    //重力
	for(size_t i=0;i<total_points;i++) {
		force[i] = glm::vec3(0);
		if(!isfix[i])
            force[i] += mass * gvat;
	}
	int i,j,k = 0;
    //结构弹簧 上下左右
    for(i = 0;i <= numY;i++){
        for(j = 0;j <= numX;j ++){
            if(i!=0){//上
                force[k] += SpringForce(k, k - numX - 1, 1);
            }
            if(j!=numX){//右
                force[k] += SpringForce(k, k+1, 1);
            }
            if(i!=numY){//下
                force[k] += SpringForce(k, k + numX + 1, 1);
            }
            if(j!=0){//左
                force[k] += SpringForce(k, k - 1, 1);
            }
            k++;
        }
    }
    //柔性弹簧
    k = 0;
    for(i = 0;i <= numY;i++){
        for(j = 0;j <= numX;j ++){
            if(i>1){//上
                force[k] += SpringForce(k, k - 2*numX - 2, 2);
            }
            if(j<numX-1){//右
                force[k] += SpringForce(k, k+2, 2);
            }
            if(i<numY-1){//下
                force[k] += SpringForce(k, k + 2*numX + 2, 2);
            }
            if(j>1){//左
                force[k] += SpringForce(k, k - 2, 2);
            }
            k++;
        }
    }
    //剪切弹簧
    k = 0;
    for(i = 0;i <= numY;i ++){
        for(j = 0;j <= numX;j ++){
            if(i>0&&j>0){  //左上
                force[k] += SpringForce(k, k - numX - 2, 3);
            }
            if(i>0&&j<numX){  //右上
                force[k] += SpringForce(k, k - numX, 3);
            }
            if(i<numY&&j<numX){  //右下
                force[k] += SpringForce(k, k + numX + 2, 3);
            }
            if(i<numY&&j>0){   //坐下
                force[k] += SpringForce(k, k + numX, 3);
            }
            k ++;
        }
    }
}

void CalcPos(){  //计算新的位置
    newTime = (float) glutGet(GLUT_ELAPSED_TIME);
	float frameTime = newTime-currentTime;
	frameTime/=1000;
	currentTime = newTime;
	glm::vec3 acc = glm::vec3(0);
    //得到的frame就是间隔时间 毫秒
    for(size_t i = 0;i <= total_points;i ++){
        if(isfix[i])continue;
        acc = force[i] / mass;  //得到加速度向量
        Veloc[i] *= 0.98;
        Veloc[i] = Veloc[i] + acc*frameTime;  //得到新的速度值
        Pos[i] = Pos[i] + Veloc[i] * frameTime;
    }
}

void gao(int a,int b,int is){  //直线弹簧 要考虑是否是isfix！
    glm::vec3 tmp = Pos[b] - Pos[a];
    float dis = glm::length(tmp);
    float inilen;
    if(is == 1)inilen = len0;
    if(is == 2) inilen = len0 * 2;
    if(is == 3) inilen = len0 * 1.414213;
    inilen *= tolera;
    if(dis<=inilen)return;
    glm::vec3 tmp1 = tmp*(inilen/dis);
    if(isfix[a]&&isfix[b]){
        return;
    }else if(isfix[a]){
        Pos[b] = Pos[a] + tmp1;
    }else if(isfix[b]){
        Pos[a] = Pos[b] - tmp1;
    }else{
        glm::vec3 mid = (Pos[a] + Pos[b]) * 0.5f;
        Pos[a] = mid - tmp1 * 0.5f;
        Pos[b] = mid + tmp1 * 0.5f;
    }
}

//限制每一根弹簧长度
void DynamicConstrain(){
	int i,j,k = 0;
    for(i = 0;i <= numY;i++){
        for(j = 0;j <= numX;j ++){
            if(j!=numX){//右
                gao(k,k+1,1);
            }
            if(i!=numY){//下
                gao(k,k + numX + 1,1);
            }


            if(j<numX-1){//右二
                gao(k,k + 2, 2);
            }
            if(i<numY-1){//下二
                gao(k, k + 2*numX + 2, 2);
            }


            if(i<numY&&j<numX){  //右下
                gao(k,  k + numX + 2, 3);
            }
            if(i<numY&&j>0){   //左下
                gao(k, k + numX, 3);
            }
            k++;
        }
    }
}
void StepPhysics(){
    ComputeForces();
    CalcPos();
    glutPostRedisplay();
//    DynamicConstrain();
    Sleep(5);
}


void OnReshape(int nw, int nh) {
	glViewport(0,0,nw, nh);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluPerspective(60, (GLfloat)nw / (GLfloat)nh, 1.f, 100.0f);

	glGetIntegerv(GL_VIEWPORT, viewport);
	glGetDoublev(GL_PROJECTION_MATRIX, PP);

	glMatrixMode(GL_MODELVIEW);
}
int main(int argc, char * argv[])
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
    glutInitWindowSize(1024, 1024);
    glutCreateWindow("Mass-Spring Model");

    initGL();
    glutDisplayFunc(OnRender);
    //指定窗口形状变化时的回调函数
	glutReshapeFunc(OnReshape);
	//指定程序空闲时调用函数
    glutIdleFunc(StepPhysics);
    glEnable(GL_DEPTH_TEST);

    glutMainLoop();
    return 0;
}

 实现效果