模型视图矩阵和投影矩阵：webgl笔记(6)

GetClientRect(m_Hwnd,&rct); intm_view_width = rct.right- rct.left; intm_view_height = rct.bottom - rct.top; glViewport(0,0,m_view_width,m_view_height); float nearz =5.0; float farz =80000;

float AspectRatio =float(m_view_height)/ float(m_view_width); float ViewAngleH =90 * (PI / 180);//90度

float ViewAngleV = atan(tan(ViewAngleH/2) * AspectRatio)* 2; glMatrixMode(GL_PROJECTION); glLoadIdentity(); GLfloatm[16];

::ZeroMemory(m,16*sizeof(float));

//////m[8],m[9]=0表示对称视椎体即gluPerspective/////////// m[0] = 1.0 /tan(ViewAngleV / 2); m[5] = m[0]*AspectRatio;

m[10] = -(farz +nearz) / (farz - nearz); m[11] = -1;

m[14] = - 2 * farz *nearz / (farz - nearz); glMultMatrixf(m);

glMatrixMode(GL_MODELVIEW);

glLoadIdentity(); }

void OpenGlCom::draw() {

glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glPushMatrix();

glDepthFunc(GL_LEQUAL); glEnable(GL_DEPTH_TEST); glBegin(GL_TRIANGLE_FAN);

glTranslatef(0, 0,10.0f);//往视点方向平移10单位显示更大 glColor3f(0.8f, 0.8f, 0.6f); glVertex3f(0,0,-20); glVertex3f(30,20,-40); glVertex3f(40,10,-30); glPopMatrix(); }

我们看看在gluPerspective图形有什么变化呢 将ReSize()改成： {

RECTrct ;

GetClientRect(m_Hwnd,&rct); intm_view_width = rct.right- rct.left; intm_view_height = rct.bottom - rct.top; glViewport(0,0,m_view_width,m_view_height); glMatrixMode(GL_PROJECTION); glLoadIdentity();

floatfAspect = float(m_view_width) / float(m_view_height); gluPerspective(90.0,fAspect, 5.0, 80000.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); }

接下来，再试试看glFrustum()实现的效果：

将ReSize()改成： {

RECTrct ;

GetClientRect(m_Hwnd,&rct); intm_view_width = rct.right- rct.left; intm_view_height = rct.bottom - rct.top; glViewport(0,0,m_view_width,m_view_height); glMatrixMode(GL_PROJECTION); glLoadIdentity();

GLdouble left =-nearz*tan(ViewAngleV/2); GLdouble right =nearz*tan(ViewAngleV/2); GLdouble bottom =-nearz*tan(ViewAngleH/2); GLdouble top =nearz*tan(ViewAngleH/2);

glFrustum(left,right,bottom,top,nearz,farz); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); }

从三幅图中可以看出图形位置是一样的，这就验证了我们的矩阵是正确的！