opengl 鼠标捡选(可漫游,gluPickMatrix)

//参照opengl超级宝典的planets源程序

#include <windows.h>
#include <gl/gl.h>
#include <gl/glu.h>
#include <gl/glut.h>
#include <math.h>

#define glRGB(x, y, z) glColor3ub((GLubyte)x, (GLubyte)y, (GLubyte)z)

#define SUN  1
#define MERCURY 2
#define VENUS 3
#define EARTH 4
#define MARS 5

GLfloat fAspect;

// Called to draw scene
void RenderScene(void)
 {
 // Clear the window with current clearing color
 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

//此处可加gluLookAt()函数

 // Save the matrix state and do the rotations
 glMatrixMode(GL_MODELVIEW);
 glPushMatrix();

 // Translate the whole scene out and into view 
 glTranslatef(0.0f, 0.0f, -300.0f); 

 // Initialize the names stack
 glInitNames();
 glPushName(0);

 
 // Set material color, Yellow
 // Sun
 glRGB(255, 255, 0);
 glLoadName(SUN);
 glutSolidSphere(15.0f, 15, 15);

 // Draw Mercury
 glRGB(128,0,0);
 glPushMatrix();
 glTranslatef(24.0f, 0.0f, 0.0f);
 glLoadName(MERCURY);
 glutSolidSphere(2.0f,15,15);
 glPopMatrix();

 // Draw Venus
 glPushMatrix();
 glRGB(128,128,255);
 glTranslatef(60.0f, 0.0f, 0.0f);
 glLoadName(VENUS);
 glutSolidSphere(4.0f,15,15);
 glPopMatrix();

 // Draw the Earth
 glPushMatrix();
 glRGB(0,0,255);
 glTranslatef(100.0f,0.0f,0.0f);
 glLoadName(EARTH);
 glutSolidSphere(8.0f,15,15);
 glPopMatrix();

 // Draw Mars
 glRGB(255,0,0);
 glPushMatrix();
 glTranslatef(150.0f, 0.0f, 0.0f);
 glLoadName(MARS);
 glutSolidSphere(4.0f,15,15);
 glPopMatrix();

 // Restore the matrix state
 glPopMatrix(); // Modelview matrix

 glutSwapBuffers();
 }

// Present the information on which planet/sun was selected and displayed
void ProcessPlanet(GLuint id)
 {
 switch(id)
  {
  case SUN:
   MessageBox(NULL,"You clicked on the Sun!","Info",MB_OK | MB_ICONEXCLAMATION);
   break;

  case MERCURY:
   MessageBox(NULL,"You clicked on Mercury!","Info",MB_OK | MB_ICONEXCLAMATION);
   break;

  case VENUS:
   MessageBox(NULL,"You clicked on Venus!","Info",MB_OK | MB_ICONEXCLAMATION);
   break;

  case EARTH:
   MessageBox(NULL,"You clicked on Earth!","Info",MB_OK | MB_ICONEXCLAMATION);
   break;

  case MARS:
   MessageBox(NULL,"You clicked on Mars!","Info",MB_OK | MB_ICONEXCLAMATION);
   break;

  default:
   MessageBox(NULL,"Nothing was clicked on!","Error",MB_OK | MB_ICONEXCLAMATION);
   break;
  }
 }

 

// Process the selection, which is triggered by a right mouse
// click at (xPos, yPos).
#define BUFFER_LENGTH 64
void ProcessSelection(int xPos, int yPos)
 {
 // Space for selection buffer
 GLuint selectBuff[BUFFER_LENGTH];

 // Hit counter and viewport storeage
 GLint hits, viewport[4];

 // Setup selection buffer
 glSelectBuffer(BUFFER_LENGTH, selectBuff);
 
 // Get the viewport
 glGetIntegerv(GL_VIEWPORT, viewport);

 // Switch to projection and save the matrix
 glMatrixMode(GL_PROJECTION);
 glPushMatrix();

 // Change render mode
 glRenderMode(GL_SELECT);

 // Establish new clipping volume to be unit cube around
 // mouse cursor point (xPos, yPos) and extending two pixels
 // in the vertical and horzontal direction
 glLoadIdentity();
 gluPickMatrix(xPos, viewport[3] - yPos, 2,2, viewport);

 // Apply perspective matrix
 gluPerspective(45.0f, fAspect, 1.0, 425.0);

 // Draw the scene
 RenderScene();

 // Collect the hits
 hits = glRenderMode(GL_RENDER);

 // If a single hit occured, display the info.
 if(hits  >= 1)
 {
  int choose = selectBuff[3];
  int depth = selectBuff[1];

  for(int i = 0 ; i < hits ; i++)
  {
   if(selectBuff[i*4 + 1] < (GLuint)depth)//获取深度最小的物体(selectBuff是按照ID从小到大排列的)
   {
    choose = selectBuff[i*4 + 3];
    depth  = selectBuff[i*4 + 1];
   }
  }
  
   ProcessPlanet( choose);
  
 }

 // Restore the projection matrix
 glMatrixMode(GL_PROJECTION);
 glPopMatrix();

 // Go back to modelview for normal rendering
 glMatrixMode(GL_MODELVIEW);
 }

 

// Process the mouse click
void MouseCallback(int button, int state, int x, int y)
 {
 if(button == GLUT_LEFT_BUTTON && state == GLUT_DOWN)
  ProcessSelection(x, y);
 }

 

 

void ChangeSize(int w, int h)
 {
 // Prevent a divide by zero
 if(h == 0)
  h = 1;

 // Set Viewport to window dimensions
    glViewport(0, 0, w, h);

 // Calculate aspect ratio of the window
 fAspect = (GLfloat)w/(GLfloat)h;

 // Set the perspective coordinate system
 glMatrixMode(GL_PROJECTION);
 glLoadIdentity();

 // Field of view of 45 degrees, near and far planes 1.0 and 425
 gluPerspective(45.0f, fAspect, 1.0, 425.0);

 // Modelview matrix reset
 glMatrixMode(GL_MODELVIEW);
 glLoadIdentity();
 }

int main(int argc, char* argv[])
 {
 glutInit(&argc, argv);
 glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
 glutInitWindowSize(600,300);
 glutCreateWindow("Pick a Planet");
 glutReshapeFunc(ChangeSize);
 glutMouseFunc(MouseCallback);
 glutDisplayFunc(RenderScene);
 
 glutMainLoop();

 return 0;
 }

注意:
1.ProcessSelection()函数中的gluPerspective(45.0f, fAspect, 1.0, 425.0);的参数必须与ChangeSize()函数内的gluPerspective参数一致,否则会不匹配.
2.gluPickMatrix选出的矩阵数组里的元素是按ID号逐渐增大排列的.