OPENGL多视口

提要OpenGL视口（Viewport）可以看作是窗口中OpenGL的绘制输出区域，可以通过一条简单的glViewport命令设置。一般的OpenGL教程都是单视口，即整个窗口为惟一的一个视口，Nehe的OpenGL教程是我最早见到涉及多视口的。与单视口程序相比，多视口程序的变化主要是：（一）多视口程序不能在窗口resize/reshape时直接调用glViewport，而应该在此时记下窗口大小，然后在绘制场景时多次调用glViewport设置每个视口的位置和大小；（二）对于每个视口，应分别调用glMatrixMode(GL_PROJECTION)和glMatrixMode(GL_MODELVIEW)以设置投影和建模矩阵。多视口的最常见的应用，就是3DMax中的多视口建模，每一个观察口都从不同的方向去观察模型，从而很方便地去获取模型当前的状态。还有就是赛车游戏中的后视镜等等.具体实现的思路就是对每个视口进行独立的渲染。函数解析下面是需要调用到的一些OpenGL的函数。glLoadIdentity()重置当前指定的矩阵为单位矩阵.glViewport(GLint x,GLint y,GLsizei width,GLsizei height)在窗口中定义一个像素矩形，最终将图像映射到这个矩形中。void gluOrtho2D(GLdouble left,GLdouble right,GLdouble bottom,GLdouble top)建立了一个可视的二位平面区域。这个和用glOrtho函数的当near=0，far=1时效果是一样。void gluPerspective(GLdouble fovy, GLdouble aspect,GLdouble zNear,GLdouble zFar)这个函数指定了观察的视景体（frustum为锥台的意思，通常译为视景体）在世界坐标系中的具体大小，一般而言，其中的参数aspect应该与窗口的宽高比大小相同。void glScissor(GLint x,GLint y,GLsizei width,GLsizei height)设置一个裁剪窗口，前两个参数为窗口左下角位置，后两个参数是窗口的宽度和高度。使用前一定要glEnable(GL_SCISSOR_TEST);代码实现实现一：void renderGL() glClear (GL_COLOR_BUFFER_BIT); glLoadIdentity(); / 重置模型观察矩阵 for (int loop=0; loop4; loop+) / 循环绘制4个视口 if (loop=0) / 绘制左上角的视口 / 设置视口区域 glViewport (0, window_height/2, window_width/2, window_height/2); glMatrixMode (GL_PROJECTION); glLoadIdentity (); gluOrtho2D(0, window_width/2, window_height/2, 0); if (loop=1) / 绘制右上角视口 glViewport (window_width/2, window_height/2, window_width/2, window_height/2); glMatrixMode (GL_PROJECTION); glLoadIdentity (); gluPerspective( 45.0, 1.0f, 0.1f, 500.0 ); if (loop=2) / 绘制右下角视口 glViewport (window_width/2, 0, window_width/2, window_height/2); glMatrixMode (GL_PROJECTION); glLoadIdentity (); gluPerspective( 45.0, 1.0f, 0.1f, 500.0 ); if (loop=3) / 绘制左下角视口 glViewport (0, 0, window_width/2, window_height/2); glMatrixMode (GL_PROJECTION); glLoadIdentity (); gluPerspective( 45.0, 1.0f, 0.1f, 500.0 ); glMatrixMode (GL_MODELVIEW); glLoadIdentity (); glClear (GL_DEPTH_BUFFER_BIT); if (loop=0) / 绘制左上角的视图 glBegin(GL_QUADS); glColor3f(1.0f,0.0f,0.0f); / 设置当前色为红色 glVertex2i(window_width/2, 0 ); glColor3f(0.0f,1.0f,0.0f); / 设置当前色为绿色 glVertex2i(0, 0 ); glColor3f(0.0f,1.0f,1.0f); / 设置当前色为蓝色 glVertex2i(0, window_height/2); glColor3f(1.0f,1.0f,0.0f); / 设置当前色为红色 glVertex2i(window_width/2, window_height/2); glEnd(); if (loop=1) / 绘制右上角的视图 glColor3f(1.0f,0.0f,1.0f); glTranslatef(0.0f,0.0f,-9.0f); glRotatef(rtri,1.0,1.0,0.0); glBegin(GL_TRIANGLES); / 绘制三角形 glVertex3f( 0.0f, 1.0f, 0.0f); / 上顶点 glVertex3f(-1.0f,-1.0f, 0.0f); / 左下 glVertex3f( 1.0f,-1.0f, 0.0f); / 右下 glEnd(); / 三角形绘制结束 if (loop=2) / 绘制右下角的视图 glTranslatef(0.0f,0.0f,-2.0f); glRotatef(-45.0f,1.0f,0.0f,0.0f); glRotatef(rtri,0.0f,0.0f,1.0f); glBegin(GL_QUADS); glColor3f(1.0f,0.0f,0.0f); glVertex3f( 0.5f, 0.5f, 0.0f); glColor3f(0.0f,1.0f,0.0f); glVertex3f(-0.5f, 0.5f, 0.0f); glColor3f(0.0f,0.0f,1.0f); glVertex3f(-0.5f, -1.0f, 0.0f); glColor3f(0.0f,0.0f,0.0f); glVertex3f( 0.5f, -1.0f, 0.0f); glEnd(); if (loop=3) / 绘制左下角的视图 glColor3f(0.0f,0.0f,0.0f); glTranslatef(0.0f,0.0f,-4.0f); glRotatef(-rtri/2,1.0f,0.0f,0.0f); glRotatef(-rtri/2,0.0f,1.0f,0.0f); glRotatef(-rquad/2,0.0f,0.0f,1.0f); glBegin(GL_QUADS); glColor3f(1.0f,0.0f,0.0f); glVertex3f( 0.5f, 0.5f, 0.0f); glColor3f(0.0f,1.0f,0.0f); glVertex3f(-0.3f, 0.5f, 0.0f); glColor3f(0.0f,0.0f,1.0