opengl 鼠标捡选(可漫游,gluPickMatrix)_pickmatrix glm-优快云博客

该博客介绍了如何使用OpenGL实现鼠标点击选择3D场景中的对象（如太阳系行星），并提供了相应的代码示例。通过gluPickMatrix和gluPerspective进行视口变换和投影，实现精确的鼠标选择。当鼠标点击时，通过ProcessSelection函数处理选择，显示所选物体的信息。此外，还展示了如何处理窗口大小改变以保持正确的透视效果。

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//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.