#include <GL/glut.h>
#include <stdlib.h>
#include<math.h>
#include <iostream>
using namespace std;
int SCREEN_WIDTH = 400; //屏幕尺寸
int SCREEN_HEIGHT = 400;
int posx1 = 150;
int posy1 = 200;
int posx2 = 250;
int posy2 = 200;
int select_point = 0; //1 是第一个点，2是第二个，以此类推
void init()
{ glClearColor(1,1,1,1);}
void draw(GLenum mode)
{ glPointSize(10.0f);
const static GLfloat color_selected[] = {1.0f,0.0f,0.0f};
const static GLfloat color_unselected[] = {0.0f,0.0f,1.0f};
for(int i=1;i<=5;i++)//5个点
{ if (mode == GL_SELECT) glLoadName(i);
glColor3fv( (select_point == i)? color_selected : color_unselected );
glBegin(GL_POINTS);
glVertex2f(i*70,200);
glEnd();
}
}
void display()
{ glClear(GL_COLOR_BUFFER_BIT);
draw(GL_RENDER); //设置渲染模式
glFlush();
}
void reshape(int width, int height)
{ glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0,SCREEN_WIDTH,0,SCREEN_HEIGHT);
glMatrixMode(GL_MODELVIEW);
}
void processHits(GLint hits, GLuint buffer[])
{ unsigned int i;
GLuint name;
for(i=0; i<hits;i++)
{ name = buffer[3+i*4];
select_point = name;//每个选中物体有占用名字栈中4个单位，第4个是物体名字值
cout<<"第"<<name<<"个点"<<endl;
}
}
#define SIZE 500
#define N 10
void mouse(int button, int state, int x, int y)
{ GLuint selectBuffer[SIZE]; //存放物体名称的栈
GLint hits; //存放被选中对象个数
GLint viewport[4]; //存放可视区参数
if( state==GLUT_DOWN && button==GLUT_LEFT_BUTTON) //当鼠标左键按下时
{glGetIntegerv(GL_VIEWPORT,viewport); //获取当前视口坐标参数
glSelectBuffer(SIZE,selectBuffer); //选择名称栈存放被选中的名称
glRenderMode(GL_SELECT); //设置当前为选择模式
glInitNames(); //初始化名称栈
glPushName(0);
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
gluPickMatrix(x,viewport[3]-y,N,N,viewport); //创建用于选择的投影矩阵栈
gluOrtho2D(0,SCREEN_WIDTH,0,SCREEN_HEIGHT); //设置投影方式
draw(GL_SELECT); //绘制场景,选择模式
glPopMatrix();
glFlush();
hits = glRenderMode(GL_RENDER);
glMatrixMode(GL_MODELVIEW);
if(hits > 0) processHits(hits,selectBuffer);
glutPostRedisplay();
}
if( state == GLUT_UP && button == GLUT_LEFT_BUTTON) //当鼠标左键抬起时
{ select_point = 0;
glRenderMode(GL_RENDER);
draw(GL_RENDER);
glutPostRedisplay();
}
}
int main(int argc, char *argv[])
{ glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA| GLUT_DEPTH );
glutInitWindowSize(SCREEN_WIDTH,SCREEN_HEIGHT);
glutInitWindowPosition(0, 0);
glutCreateWindow("图形拾取编程实例");
init();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMouseFunc(mouse);
glutMainLoop();
return 1;
}
9.3.3编程实例－图形拾取