学步园

opengl中的选择基本思路：

1，获得视口信息，指定返回点击记录的数组。

glGetIntegerv (GL_VIEWPORT, viewport);<br /> glSelectBuffer (BUFSIZE, selectBuf);

2，glRenderMode(GL_SELECT)进入选择模式，

3，对名字堆栈进行初始化

glInitNames();<br /> glPushName(-1);

4，利用gluPickMatrix构造拾取矩阵进行选择，

glPushMatrix ();<br /> glLoadIdentity ();<br /> gluPickMatrix((GLdouble) mousex, (GLdouble) (viewport[3] - mousey), 5.0, 5.0, viewport);<br /> gluPerspective(30.0, (GLfloat)g_iWidth/(GLfloat)g_iHeight, 1.0, 20.0);<br /> glMatrixMode(GL_MODELVIEW);<br /> PaintScreen(GL_SELECT);<br /> glPopMatrix ();

鼠标左键拾取cube，为了保证每次只能有一个cube被选中，MouseCB函数中对z值进行比较。保证始终z最小的cube被选择。相应的处理语句：

if(hits)<br /> {<br /> int n = 0;<br /> double minz = selectBuf[1];<br /> for(int i=1; i<hits; i++)<br /> {<br /> if( selectBuf[1+i*4] < minz )<br /> {<br /> n = i;<br /> minz = selectBuf[1+i*4];<br /> }<br /> }<br /> //hit记录第四项为ID编号<br /> cube[selectBuf[3+n*4]].selected = !( cube[selectBuf[3+n*4]].selected );<br /> }

运行效果：

下面是整个cpp：

#include <Windows.h><br /> #include <gl/glut.h></p> <p>const int BUFSIZE = 512;<br /> int g_iWidth = 800;<br /> int g_iHeight = 600;<br /> float g_fAngle = 0;<br /> const GLfloat red[] = { 231/255.0, 36.0/255.0, 46/255.0,1.0};<br /> const GLfloat yellow[] = { 253.0/255.0, 208.0/255.0, 0.0/255., 1.0};</p> <p>class Cube<br /> {<br /> public:<br /> double x,y,z;<br /> bool selected;</p> <p> Cube()<br /> : x(0), y(0), z(0)<br /> , selected(false)<br /> {}</p> <p> void Draw()<br /> {<br /> glPushMatrix();<br /> glTranslated(x, y, z);<br /> if (selected)<br /> glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, red);<br /> else<br /> glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, yellow);</p> <p> glutSolidCube(1.0);<br /> glPopMatrix();<br /> }<br /> };<br /> Cube cube[4];</p> <p>void Init();<br /> void DrawGLScene();<br /> void Reshape(int w, int h);<br /> void KeyBoardCB(unsigned char key, int x, int y);<br /> void MouseCB(int button, int state, int x, int y);</p> <p>void Idle();<br /> void PaintScreen(GLenum mode);</p> <p>int main(int argc, char **argv)<br /> {<br /> glutInit (&argc, argv);<br /> glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);<br /> glutInitWindowSize (800, 600);<br /> glutInitWindowPosition (100, 100);<br /> glutCreateWindow ("OpenGL Select Obj");</p> <p> Init();<br /> glutDisplayFunc ( DrawGLScene );<br /> glutReshapeFunc ( Reshape );</p> <p> glutMouseFunc( MouseCB );<br /> glutKeyboardFunc( KeyBoardCB );<br /> glutIdleFunc( Idle );</p> <p> glutMainLoop ();</p> <p> return 0;<br /> }</p> <p>void Init()<br /> {<br /> glClearColor(84/255.0, 0.0/255.0, 125.0/255.0, 0.0);<br /> glClearDepth(1.0);<br /> glDepthFunc(GL_LESS);<br /> glEnable(GL_DEPTH_TEST);<br /> glShadeModel(GL_SMOOTH); </p> <p> for(int i=0; i<4; i++)<br /> cube[i].x = i*2-3;<br /> }</p> <p>void Reshape(int Width, int Height)<br /> {<br /> glViewport(0, 0, Width, Height);<br /> glMatrixMode(GL_PROJECTION);<br /> glLoadIdentity();<br /> gluPerspective(30.0, (GLfloat)Width/(GLfloat)Height, 1.0, 20.0);<br /> }</p> <p>void DrawGLScene()<br /> {<br /> glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);<br /> glMatrixMode(GL_MODELVIEW);<br /> glLoadIdentity();<br /> gluLookAt(6.0,4.0,10.0,0.0,0.0,0.0,0.0,1.0,0.0);</p> <p> glEnable(GL_DEPTH_TEST);<br /> glEnable(GL_LIGHTING);<br /> glEnable(GL_LIGHT0);</p> <p> PaintScreen(GL_RENDER);</p> <p> glDisable(GL_LIGHT0);<br /> glDisable(GL_LIGHTING);<br /> glDisable(GL_DEPTH_TEST);</p> <p> glutSwapBuffers();<br /> }</p> <p>void PaintScreen(GLenum mode)<br /> {<br /> glPushMatrix();<br /> glRotated( g_fAngle, 0.0, 1.0, 0.0 );<br /> for(int i=0; i<4; i++)<br /> {<br /> if (mode==GL_SELECT)<br /> glLoadName(i);<br /> cube[i].Draw();<br /> }<br /> glPopMatrix();<br /> }</p> <p>void Idle()<br /> {<br /> g_fAngle += 0.5;<br /> if( g_fAngle >= 360 )<br /> g_fAngle = 0;</p> <p> //调用DrawGLScene函数<br /> glutPostRedisplay();<br /> }</p> <p>void KeyBoardCB(unsigned char key, int x, int y)<br /> {<br /> if(key == 27)<br /> exit(0);<br /> }</p> <p>void MouseCB(int button, int state, int mousex, int mousey)<br /> {<br /> if( button != GLUT_LEFT || state != GLUT_DOWN)<br /> return;</p> <p> GLuint selectBuf[BUFSIZE];<br /> GLint hits;<br /> GLint viewport[4];<br /> static bool IsFirst = true;</p> <p> glGetIntegerv (GL_VIEWPORT, viewport);<br /> glSelectBuffer (BUFSIZE, selectBuf);</p> <p> glRenderMode(GL_SELECT); // Enter the SELECT render mode<br /> glInitNames();<br /> glPushName(-1);</p> <p> glMatrixMode (GL_PROJECTION);<br /> glPushMatrix ();<br /> glLoadIdentity ();<br /> gluPickMatrix((GLdouble) mousex, (GLdouble) (viewport[3] - mousey), 5.0, 5.0, viewport);<br /> gluPerspective(30.0, (GLfloat)g_iWidth/(GLfloat)g_iHeight, 1.0, 20.0);<br /> glMatrixMode(GL_MODELVIEW);</p> <p> PaintScreen(GL_SELECT);<br /> glPopMatrix ();<br /> glFlush();</p> <p> hits = glRenderMode (GL_RENDER);</p> <p> glMatrixMode(GL_PROJECTION);<br /> glLoadIdentity();<br /> glViewport(0, 0, g_iWidth, g_iHeight);<br /> gluPerspective(30.0, (GLfloat)g_iWidth/(GLfloat)g_iHeight, 1.0, 20.0);</p> <p> if(hits)<br /> {<br /> int n = 0;<br /> double minz = selectBuf[1];<br /> for(int i=1; i<hits; i++)<br /> {<br /> if( selectBuf[1+i*4] < minz )<br /> {<br /> n = i;<br /> minz = selectBuf[1+i*4];<br /> }<br /> }<br /> //hit记录第四项为ID编号<br /> cube[selectBuf[3+n*4]].selected = !( cube[selectBuf[3+n*4]].selected );<br /> }<br /> //glutPostRedisplay();<br /> }