OpenGL学习十四：光照1

环境光：那些在环境中进行了充分的散射，无法辨别其方向的光，它似乎来自所有方向
散射光：来自某个方向。因此从它正面照射的表面，看起来更明亮以下。
镜面光：来自特定的方向，并且倾向于从表面的某个特定的方向放射

右图1:环境光 右图2：散射光 右图3：环境光与散射光的混合         创建光源
GLAPI void GLAPIENTRY glLightfv (GLenum light, GLenum pname, const GLfloat *params);

light:对应光源，一般支持0~7号光源
pname:光照信息参数
GL_AMBIENT                    环境光
GL_DIFFUSE                    散射光
GL_SPECULAR                   镜面光
GL_POSITION                   光源位置
GL_CONSTANT_ATTENUATION       常量衰减因子
GL_LINEAR_ATTENUATION         线性衰减因子
GL_QUADRATIC_ATTENUATION      二次衰减因子
params：参数

对于GL_LIGHT0与其他光源默认值不一致GL_LIGHT0的环境光和散射光的默认值是（1,1,1,1）光源位置
GLfloat light_position[] = { x,y,z,w};
glLightfv(GL_LIGHT2, GL_POSITION, light_position);

w=0 为方向性光源
w!=0 为位置性光源
右图1：方向性光源（1,1,1，0）
右图2：位置性光源（1,1,1，1）
右图3：位置性光源（1,1,5，1）     光的衰减
衰减因子=1/k1+k2d+k3d*d
d=光源与顶点之间的距离
k1=GL_CONSTANT_ATTENUATION
k2=GL_LINEAR_ATTENUATION
k3=GL_QUADRATIC_ATTENUATION

说明光的衰减特效要求光源位位置性光源
右图1：光源位置z=5,k1=1
右图2：光源位置z=5,k1=3
   材料属性
GLAPI void GLAPIENTRY glMaterialfv (GLenum face, GLenum pname, const GLfloat *params);

face:GL_FRONT,GL_BACK,GL_FRONT_AND_BACK
pname:GL_AMBIENT                    材料的环境颜色
      GL_DIFFUSE                    材料的散射颜色
      GL_SPECULAR                   材料的镜面颜色
      GL_SHININESS                  镜面指数
      GL_AMBIENT_AND_DIFFUSE        材料的环境和散射颜色
      GL_EMSSION                    材料的发射颜色
      GL_COLOR_INDEXS               颜色索引

球1：
  GLfloat mat_diffuse[] = { 0.1, 0.5, 0.8, 1.0 };
glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);

球2：
   GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, 5);
球3：
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, 180)
球4：
   GLfloat mat_emission[] = {0.3, 0.2, 0.2, 0.0};
   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
   glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);镜面反射
OPENGL允许我们在不存在反射光的情况下通过设置反射材料达到效果，并控制亮点的大小和亮点（GL_SHININESS）其实范围在【0~128】值越小亮度越大 亮点越小发射颜色光
通过GL_EMISSION参数指定RGBA颜色值，可以使物体看上去好像发射这种颜色的光

材料颜色模式
glEnable(GL_COLOR_METERIAL)
glcolor3f(0.5,0.2,0.6);
glColorMeterial(GL_FRONT,GL_AMBIENT)

环境散射衰减光：

#include "header.h" float roar=0.0f; GLfloat attentation[]={1.0}; GLfloat light_position[] = { 1.0, 1.0,1, 0};void init(void) {   GLfloat ambient[] =  { 0.5, 0.5, 0.5, 0.0 };   GLfloat diffuse[] = { 1.0, 0.0, 0.0, 0.0 };   glClearColor (0.0, 0.0, 0.0, 0.0);   glLightfv(GL_LIGHT1, GL_POSITION, light_position);   glLightfv(GL_LIGHT1,GL_AMBIENT,ambient);   glLightfv(GL_LIGHT2, GL_POSITION, light_position);   glLightfv(GL_LIGHT2,GL_DIFFUSE,diffuse);   glLightfv(GL_LIGHT3, GL_POSITION, light_position);   glLightfv(GL_LIGHT3,GL_DIFFUSE,diffuse);   glLightfv(GL_LIGHT3,GL_AMBIENT,ambient);   glLightfv(GL_LIGHT1,GL_CONSTANT_ATTENUATION,attentation);   glLightfv(GL_LIGHT2,GL_CONSTANT_ATTENUATION,attentation);   glLightfv(GL_LIGHT3,GL_CONSTANT_ATTENUATION,attentation);   glEnable(GL_LIGHTING);   glEnable(GL_LIGHT0);   glEnable(GL_DEPTH_TEST);}void display(void){   glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);   glLoadIdentity();    glutSolidSphere(1.0, 16, 16);   glFlush ();}void reshape (int w, int h){   glViewport (0, 0, (GLsizei) w, (GLsizei) h);   glMatrixMode (GL_PROJECTION);   glLoadIdentity();   if (w <= h)      glOrtho (-2.5, 2.5, -2.5*(GLfloat)h/(GLfloat)w,         2.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0);   else      glOrtho (-2.5*(GLfloat)w/(GLfloat)h,         2.5*(GLfloat)w/(GLfloat)h, -2.5, 2.5, -10.0, 10.0);   glMatrixMode(GL_MODELVIEW);   glLoadIdentity();}void keyboard(unsigned char key, int x, int y){   switch (key)    { case '1': glEnable(GL_LIGHTING); glEnable(GL_LIGHT1); glDisable(GL_LIGHT0); glDisable(GL_LIGHT2); glDisable(GL_LIGHT3);     break; case '2': glEnable(GL_LIGHTING); glEnable(GL_LIGHT2); glDisable(GL_LIGHT0); glDisable(GL_LIGHT1); glDisable(GL_LIGHT3); break; case '3': glEnable(GL_LIGHTING); glEnable(GL_LIGHT3); glDisable(GL_LIGHT0); glDisable(GL_LIGHT2); glDisable(GL_LIGHT1); break; case '0': glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); glDisable(GL_LIGHT1); glDisable(GL_LIGHT2); glDisable(GL_LIGHT3); break; case 'A':light_position[0]=1;light_position[1]=1;light_position[2]=1;light_position[3]=0;glLightfv(GL_LIGHT1, GL_POSITION, light_position);glLightfv(GL_LIGHT2, GL_POSITION, light_position);glLightfv(GL_LIGHT3, GL_POSITION, light_position);break; case 'S': light_position[0]=1; light_position[1]=1; light_position[2]=1; light_position[3]=1; glLightfv(GL_LIGHT1, GL_POSITION, light_position); glLightfv(GL_LIGHT2, GL_POSITION, light_position); glLightfv(GL_LIGHT3, GL_POSITION, light_position); break; case 'D': light_position[0]=1; light_position[1]=1; light_position[2]=5; light_position[3]=1; glLightfv(GL_LIGHT1, GL_POSITION, light_position); glLightfv(GL_LIGHT2, GL_POSITION, light_position); glLightfv(GL_LIGHT3, GL_POSITION, light_position); break; case 'Z': light_position[0]=1; light_position[1]=1; light_position[2]=5; light_position[3]=1; glLightfv(GL_LIGHT1, GL_POSITION, light_position); glLightfv(GL_LIGHT2, GL_POSITION, light_position); glLightfv(GL_LIGHT3, GL_POSITION, light_position); attentation[0]=1; glLightfv(GL_LIGHT1,GL_CONSTANT_ATTENUATION,attentation); glLightfv(GL_LIGHT2,GL_CONSTANT_ATTENUATION,attentation); glLightfv(GL_LIGHT3,GL_CONSTANT_ATTENUATION,attentation); break; case 'X': light_position[0]=1; light_position[1]=1; light_position[2]=5; light_position[3]=1; attentation[0]=3; glLightfv(GL_LIGHT1, GL_POSITION, light_position); glLightfv(GL_LIGHT2, GL_POSITION, light_position); glLightfv(GL_LIGHT3, GL_POSITION, light_position); glLightfv(GL_LIGHT1,GL_CONSTANT_ATTENUATION,attentation); glLightfv(GL_LIGHT2,GL_CONSTANT_ATTENUATION,attentation); glLightfv(GL_LIGHT3,GL_CONSTANT_ATTENUATION,attentation); break;   }   glutPostRedisplay();} void rotate(){roar+=0.0001f;glutPostRedisplay();}int main(int argc, char** argv){   glutInit(&argc, argv);   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);   glutInitWindowSize (500, 500);    glutInitWindowPosition (100, 100);   glutCreateWindow (argv[0]);   init ();   glutDisplayFunc(display);    glutReshapeFunc(reshape);   glutKeyboardFunc(keyboard);   glutMainLoop();   return 0;}

移动光源

#include "header.h"static int spin = 0;void init(void) {   glClearColor (0.0, 0.0, 0.0, 0.0);   glShadeModel (GL_SMOOTH);   glEnable(GL_LIGHTING);   glEnable(GL_LIGHT0);   glEnable(GL_DEPTH_TEST);}void display(void){   GLfloat position[] = { 0.0, 0.0, 1.5, 1.0 };   glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);   glPushMatrix ();   gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);   glPushMatrix ();   glRotated ((GLdouble) spin, 1.0, 0.0, 0.0);   glLightfv (GL_LIGHT0, GL_POSITION, position);   glTranslated (0.0, 0.0, 1.5);   glDisable (GL_LIGHTING);   glColor3f (0.0, 1.0, 1.0);   glutWireCube (0.1);   glEnable (GL_LIGHTING);   glPopMatrix ();   glutSolidTorus (0.275, 0.85, 8, 15);   glPopMatrix ();   glFlush ();}void reshape (int w, int h){   glViewport (0, 0, (GLsizei) w, (GLsizei) h);   glMatrixMode (GL_PROJECTION);   glLoadIdentity();   gluPerspective(40.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);   glMatrixMode(GL_MODELVIEW);   glLoadIdentity();}void mouse(int button, int state, int x, int y){   switch (button) {      case GLUT_LEFT_BUTTON:         if (state == GLUT_DOWN) {            spin = (spin + 30) % 360;            glutPostRedisplay();         }         break;      default:         break;   }}void keyboard(unsigned char key, int x, int y){   switch (key) {      case 27:         exit(0);         break;   }}int main(int argc, char** argv){   glutInit(&argc, argv);   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);   glutInitWindowSize (500, 500);    glutInitWindowPosition (100, 100);   glutCreateWindow (argv[0]);   init ();   glutDisplayFunc(display);    glutReshapeFunc(reshape);   glutMouseFunc(mouse);   glutKeyboardFunc(keyboard);   glutMainLoop();   return 0;}

 

光源材料

#include "header.h"void init(void){   GLfloat ambient[] = { 0.0, 0.0, 0.0, 1.0 };   GLfloat diffuse[] = { 1.0, 1.0, 1.0, 1.0 };   GLfloat position[] = { 0.0, 3.0, 2.0, 0.0 };   GLfloat lmodel_ambient[] = { 0.4, 0.4, 0.4, 1.0 };   GLfloat local_view[] = { 0.0 };   glClearColor(0.0, 0.1, 0.1, 0.0);   glEnable(GL_DEPTH_TEST);   glShadeModel(GL_SMOOTH);   glLightfv(GL_LIGHT0, GL_AMBIENT, ambient);   glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuse);   glLightfv(GL_LIGHT0, GL_POSITION, position);   glLightModelfv(GL_LIGHT_MODEL_AMBIENT, lmodel_ambient);   glLightModelfv(GL_LIGHT_MODEL_LOCAL_VIEWER, local_view);   glEnable(GL_LIGHTING);   glEnable(GL_LIGHT0);}void display(void){   GLfloat no_mat[] = { 0.0, 0.0, 0.0, 1.0 };   GLfloat mat_ambient[] = { 0.7, 0.7, 0.7, 1.0 };   GLfloat mat_ambient_color[] = { 0.8, 0.8, 0.2, 1.0 };   GLfloat mat_diffuse[] = { 0.1, 0.5, 0.8, 1.0 };   GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };   GLfloat no_shininess[] = { 0.0 };   GLfloat low_shininess[] = { 5.0 };   GLfloat high_shininess[] = { 100.0 };   GLfloat mat_emission[] = {0.3, 0.2, 0.2, 0.0};   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);   glPushMatrix();   glTranslatef (-3.75, 3.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (-1.25, 3.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);   glMaterialfv(GL_FRONT, GL_SHININESS, low_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (1.25, 3.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);   glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (3.75, 3.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, no_mat);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (-3.75, 0.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (-1.25, 0.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);   glMaterialfv(GL_FRONT, GL_SHININESS, low_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (1.25, 0.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);   glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (3.75, 0.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (-3.75, -3.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (-1.25, -3.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);   glMaterialfv(GL_FRONT, GL_SHININESS, low_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (1.25, -3.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);   glMaterialfv(GL_FRONT, GL_SHININESS, high_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, no_mat);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glPushMatrix();   glTranslatef (3.75, -3.0, 0.0);   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient_color);   glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);   glMaterialfv(GL_FRONT, GL_SPECULAR, no_mat);   glMaterialfv(GL_FRONT, GL_SHININESS, no_shininess);   glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);   glutSolidSphere(1.0, 16, 16);   glPopMatrix();   glFlush();}void reshape(int w, int h){   glViewport(0, 0, w, h);   glMatrixMode(GL_PROJECTION);   glLoadIdentity();   if (w <= (h * 2))      glOrtho (-6.0, 6.0, -3.0*((GLfloat)h*2)/(GLfloat)w,          3.0*((GLfloat)h*2)/(GLfloat)w, -10.0, 10.0);   else      glOrtho (-6.0*(GLfloat)w/((GLfloat)h*2),          6.0*(GLfloat)w/((GLfloat)h*2), -3.0, 3.0, -10.0, 10.0);   glMatrixMode(GL_MODELVIEW);   glLoadIdentity();}void keyboard(unsigned char key, int x, int y){   switch (key) {      case 27:         exit(0);         break;   }}int main(int argc, char** argv){   glutInit(&argc, argv);   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);   glutInitWindowSize (600, 450);   glutCreateWindow(argv[0]);   init();   glutReshapeFunc(reshape);   glutDisplayFunc(display);   glutKeyboardFunc (keyboard);   glutMainLoop();   return 0; }

 

 材料颜色模式

#include "header.h"GLfloat diffuseMaterial[4] = { 0.5, 0.5, 0.5, 1.0 };void init(void) {   GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };   GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };   glClearColor (0.0, 0.0, 0.0, 0.0);   glShadeModel (GL_SMOOTH);   glEnable(GL_DEPTH_TEST);   glMaterialfv(GL_FRONT, GL_DIFFUSE, diffuseMaterial);   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);   glMaterialf(GL_FRONT, GL_SHININESS, 25.0);   glLightfv(GL_LIGHT0, GL_POSITION, light_position);   glEnable(GL_LIGHTING);   glEnable(GL_LIGHT0);   glColorMaterial(GL_FRONT, GL_DIFFUSE);   glEnable(GL_COLOR_MATERIAL);}void display(void){   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);   glutSolidSphere(1.0, 20, 16);   glFlush ();}void reshape (int w, int h){   glViewport (0, 0, (GLsizei) w, (GLsizei) h);   glMatrixMode (GL_PROJECTION);   glLoadIdentity();   if (w <= h)      glOrtho (-1.5, 1.5, -1.5*(GLfloat)h/(GLfloat)w,         1.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0);   else      glOrtho (-1.5*(GLfloat)w/(GLfloat)h,         1.5*(GLfloat)w/(GLfloat)h, -1.5, 1.5, -10.0, 10.0);   glMatrixMode(GL_MODELVIEW);   glLoadIdentity();}void mouse(int button, int state, int x, int y){   switch (button) {      case GLUT_LEFT_BUTTON:         if (state == GLUT_DOWN) {            diffuseMaterial[0] += 0.1;            if (diffuseMaterial[0] > 1.0)               diffuseMaterial[0] = 0.0;            glColor4fv(diffuseMaterial);            glutPostRedisplay();         }         break;      case GLUT_MIDDLE_BUTTON:         if (state == GLUT_DOWN) {            diffuseMaterial[1] += 0.1;            if (diffuseMaterial[1] > 1.0)               diffuseMaterial[1] = 0.0;            glColor4fv(diffuseMaterial);            glutPostRedisplay();         }         break;      case GLUT_RIGHT_BUTTON:         if (state == GLUT_DOWN) {            diffuseMaterial[2] += 0.1;            if (diffuseMaterial[2] > 1.0)               diffuseMaterial[2] = 0.0;            glColor4fv(diffuseMaterial);            glutPostRedisplay();         }         break;      default:         break;   }}void keyboard(unsigned char key, int x, int y){   switch (key) {      case 27:         exit(0);         break;   }}int main(int argc, char** argv){   glutInit(&argc, argv);   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);   glutInitWindowSize (500, 500);    glutInitWindowPosition (100, 100);   glutCreateWindow (argv[0]);   init ();   glutDisplayFunc(display);    glutReshapeFunc(reshape);   glutMouseFunc(mouse);   glutKeyboardFunc(keyboard);   glutMainLoop();   return 0;}