《计算机图形学基础》实验2OpenGL实现橡皮筋技术一、实验目的及要求1.掌握橡皮筋技术的实现原理和方法；2.掌握OpenGL的双缓存技术；3.掌握OpenGL中鼠标的使用方法；4.掌握OpenGL中键盘的使用方法；二、实验环境主要是软件开发环境：VC 6.0三、实验内容1、OpenGL中利用鼠标实现橡皮筋技术的例子。

2、OpenGL中利用键盘实现橡皮筋技术的例子。

3、OpenGL实现拾取操作的例子，演示拾取操作的过程，其中拾取窗口的宽度和高度都设置为10。

四、实验结果1、利用鼠标实现橡皮筋技术的结果：2、利于键盘实现橡皮筋技术的结果：3、实现拾取操作的例子结果：五、程序代码1、利用鼠标实现橡皮筋技术#include <gl/glut.h>int iPointNum = 0; //已确定点的数目int x1=0,x2=0,y1=0,y2=0; //确定的点坐标int winWidth = 400, winHeight = 300; //窗口的宽度和高度void Initial(void){glClearColor(1.0f, 1.0f, 1.0f, 1.0f);void ChangeSize(int w, int h){winWidth = w; winHeight = h;glViewport(0, 0, w, h); //指定窗口显示区域glMatrixMode(GL_PROJECTION); //设置投影参数glLoadIdentity();gluOrtho2D(0.0,winWidth,0.0,winHeight);}void Display(void){glClear(GL_COLOR_BUFFER_BIT);glColor3f(1.0f, 0.0f, 0.0f);if(iPointNum >= 1) {glBegin(GL_LINES); //绘制直线段glVertex2i(x1,y1);glVertex2i(x2,y2);glEnd();}glutSwapBuffers(); //交换缓冲区void MousePlot(GLint button, GLint action, GLint xMouse, GLint yMouse){if(button == GLUT_LEFT_BUTTON && action == GLUT_DOWN) {if(iPointNum == 0 || iPointNum == 2){iPointNum = 1;x1 = xMouse; y1 = winHeight - yMouse;}else {iPointNum = 2;x2 = xMouse; y2 = winHeight - yMouse;glutPostRedisplay(); //指定窗口重新绘制}}if(button==GLUT_RIGHT_BUTTON&&action == GLUT_DOWN){ iPointNum = 0;glutPostRedisplay();}}void PassiveMouseMove (GLint xMouse, GLint yMouse){if(iPointNum == 1) {x2 = xMouse;y2 = winHeight - yMouse;glutPostRedisplay();}}int main(int argc, char* argv[]){glutInit(&argc, argv);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); //使用双缓存及RGB模型glutInitWindowSize(400,300);glutInitWindowPosition(100,100);glutCreateWindow("橡皮筋技术");glutDisplayFunc(Display);glutReshapeFunc(ChangeSize); //指定窗口在整形回调函数glutMouseFunc(MousePlot); //指定鼠标响应函数glutPassiveMotionFunc(PassiveMouseMove); //指定鼠标移动响应函数Initial();glutMainLoop();return 0;}2、利于键盘实现橡皮筋技术#include <gl/glut.h>int iPointNum = 0; //已确定点的数目int x1=0,x2=0,y1=0,y2=0; //确定的点坐标int winWidth = 400, winHeight = 300; //窗口的宽度和高度void Initial(void){glClearColor(1.0f, 1.0f, 1.0f, 1.0f);}void ChangeSize(int w, int h){winWidth = w; winHeight = h;glViewport(0, 0, w, h); //指定窗口显示区域glMatrixMode(GL_PROJECTION); //设置投影参数glLoadIdentity();gluOrtho2D(0.0,winWidth,0.0,winHeight);}void Display(void){glClear(GL_COLOR_BUFFER_BIT);glColor3f(1.0f, 0.0f, 0.0f);if(iPointNum >= 1) {glBegin(GL_LINES); //绘制直线段glVertex2i(x1,y1);glVertex2i(x2,y2);glEnd();}glutSwapBuffers(); //交换缓冲区}void PassiveMouseMove (GLint xMouse, GLint yMouse) {if(iPointNum == 1) {x2 = xMouse;y2 = winHeight - yMouse;glutPostRedisplay();}}void Key(unsigned char key, int x, int y){switch(key){case 'p':if(iPointNum == 0 || iPointNum == 2) {iPointNum = 1;x1 = x; y1 = winHeight - y;}else {iPointNum = 2;x2 = x; y2 = winHeight - y;glutPostRedisplay();}break;default: break;}}int main(int argc, char* argv[]){glutInit(&argc, argv);glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); //使用双缓存及RGB模型glutInitWindowSize(400,300);glutInitWindowPosition(100,100);glutCreateWindow("橡皮筋技术");glutDisplayFunc(Display);glutReshapeFunc(ChangeSize); //指定窗口在整形回调函数glutKeyboardFunc(Key); //指定键盘响应函数glutPassiveMotionFunc(PassiveMouseMove); //指定鼠标移动响应函数Initial();glutMainLoop();return 0;}3、实现拾取操作的例子#include <gl/glut.h>#include "stdio.h"const GLint pickSize = 32;int winWidth = 400, winHeight = 300;void Initial(void){glClearColor(1.0f, 1.0f, 1.0f, 1.0f);}void DrawRect(GLenum mode){if(mode == GL_SELECT) glPushName(1); //压入堆栈glColor3f(1.0f,0.0f,0.0f);glRectf(60.0f,50.0f,150.0f,150.0f);if(mode == GL_SELECT) glPushName(2); //压入堆栈glColor3f(0.0f,1.0f,0.0f);glRectf(230.0f,50.0f,330.0f,150.0f);if(mode == GL_SELECT) glPushName(3); //压入堆栈glColor3f(0.0f,0.0f,1.0f);glRectf(140.0f,140.0f,240.0f,240.0f);void ProcessPicks(GLint nPicks, GLuint pickBuffer[]) {GLint i;GLuint name, *ptr;printf("选中的数目为%d个\n",nPicks);ptr=pickBuffer;for(i=0;i<nPicks; i++){name=*ptr; //选中图元在堆栈中的位置ptr+=3; //跳过名字和深度信息ptr+=name-1; //根据位置信息获得选中的图元名字if(*ptr==1) printf("你选择了红色图元\n");if(*ptr==2) printf("你选择了绿色图元\n");if(*ptr==3) printf("你选择了蓝色图元\n");ptr++;}printf("\n\n");}void ChangeSize(int w, int h){winWidth = w;winHeight = h;glViewport(0, 0, w, h);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluOrtho2D(0.0,winWidth,0.0,winHeight);}void Display(void){glClear(GL_COLOR_BUFFER_BIT);DrawRect(GL_RENDER);glFlush();}void MousePlot(GLint button, GLint action, GLint xMouse, GLint yMouse){GLuint pickBuffer[pickSize];GLint nPicks, vp[4];if(button == GLUT_LEFT_BUTTON && action == GLUT_DOWN){glSelectBuffer(pickSize,pickBuffer); //设置选择缓冲区glRenderMode(GL_SELECT); //激活选择模式glInitNames(); //初始化名字堆栈glMatrixMode(GL_PROJECTION);glPushMatrix();glLoadIdentity();glGetIntegerv(GL_VIEWPORT, vp);//定义一个10×10的选择区域gluPickMatrix(GLdouble(xMouse),GLdouble(vp[3]-yMouse),10.0,10.0,vp);gluOrtho2D(0.0,winWidth,0.0,winHeight);DrawRect(GL_SELECT);//恢复投影变换glMatrixMode(GL_PROJECTION);glPopMatrix();glFlush();//获得选择集并输出nPicks = glRenderMode(GL_RENDER);ProcessPicks(nPicks, pickBuffer);glutPostRedisplay();}}int main(int argc, char* argv[]){glutInit(&argc, argv);glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowSize(400,300);glutInitWindowPosition(100,100);glutCreateWindow("拾取操作");glutDisplayFunc(Display);glutReshapeFunc(ChangeSize);glutMouseFunc(MousePlot);Initial();glutMainLoop();return 0;}六、心得体会通常在实验过程中，可以加入自己喜欢的其他东西，不过要保证原本的基本东西没有错误。