本文中將對第5篇文章的太陽系模型進行修改，加入一些動畫效果。此外還會加入顯示幀速率的代碼。
加入動畫效果最容易的方法是響應(yīng)WM_TIMER消息，在其消息處理函數(shù)中改變一些參數(shù)值，比如每過多少毫秒就旋轉(zhuǎn)一定的角度，并且重繪場景。
Frame Rate
Frame rate is nothing but the number of frames that can be rendered per second. The higher this rate, the smoother the animation. In order to calculate the frame rate we retrieve the system time (using the Windows multimedia API function timeGetTime()) before the rendering is performed and after the buffer is swapped. The difference between the two values is the elapsed time to render one frame. Thus we can calculate the frame rate for a given application.
1，我們需要調(diào)用timeGetTime（）函數(shù),因此在stdafx.h中加入:
#include <mmsystem.h> // for MM timers (you'll need WINMM.LIB)
并且Link—>Object/library modules中加入winmm.lib
2，為了計算繪制用時，在CCY457OpenGLView.h中加入如下變量：
//For elapsed timing calculations
DWORD m_StartTime, m_ElapsedTime, m_previousElapsedTime;
CString m_WindowTitle; //Window Title
int DayOfYear;
int HourOfDay;
并在構(gòu)造函數(shù)中進行初始化：
CCY457OpenGLView::CCY457OpenGLView()
{
DayOfYear = 1;
HourOfDay = 1;
}
3，為了計算幀速率，修改OnCreate函數(shù)，在其中獲取窗口標(biāo)題，從標(biāo)題中去掉”Untitled”字樣，并啟動定時器；
4，同樣為了計算幀速率，修改OnDraw函數(shù)如下，在其中用glPushMatrix 和 glPopMatrix將RenderScene函數(shù)包裹起來，從而確保動畫會正確運行。在SwapBuffers調(diào)用后我們調(diào)用PostRenderScene來顯示幀速率信息到窗口標(biāo)題。
void CCY457OpenGLView::OnDraw(CDC* pDC)
{
CCY457OpenGLDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
// Get the system time, in milliseconds.
m_ElapsedTime = ::timeGetTime(); // get current time
if ( ElapsedTimeinMSSinceLastRender() < 30 )
return
// Clear out the color & depth buffers
::glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glPushMatrix();
RenderScene();
glPopMatrix();
// Tell OpenGL to flush its pipeline
::glFinish();
// Now Swap the buffers
::SwapBuffers( m_pDC->GetSafeHdc() );
//Perform Post Display Processing
// Only update the title every 15 redraws (this is about
// every 1/2 second)
PostRenderScene();
// the very last thing we do is to save
// the elapsed time, this is used with the
// next elapsed time to calculate the
// elapsed time since a render and the frame rate
m_previousElapsedTime = m_ElapsedTime;
}
4，在CCY457OpenGLView類中加入下述成員函數(shù)，用來顯示幀速率信息到窗口標(biāo)題
//////////////////////////////////////////////////////////////////////////////
// PostRenderScene
// perform post display processing
// The default PostRenderScene places the framerate in the
// view's title. Replace this with your own title if you like.
void CCY457OpenGLView::PostRenderScene( void )
{
// Only update the title every 15 redraws (this is about
// every 1/2 second)
static int updateFrame = 15;
if (16 > ++updateFrame )
return;
updateFrame = 0;
char string[256];
_snprintf( string, 200, "%s ( %d Frames/sec )",
(const char*)m_WindowTitle, FramesPerSecond() );
GetParentFrame()->SetWindowText( string );
}
//////////////////////////////////////////////////////////////////////////////
// FramesPerSecond
// fetch frame rate calculations
int CCY457OpenGLView::FramesPerSecond( void )
{
double eTime = ElapsedTimeinMSSinceLastRender();
if ( 0 == (int)eTime )
return 0;
return (int)(1000/(int)eTime);
}
DWORD ElapsedTimeinMSSinceLastStartup()
{
return(m_ElapsedTime - m_StartTime);
}
DWORD ElapsedTimeinMSSinceLastRender()
{
return(m_ElapsedTime - m_previousElapsedTime);
}
5，在OnTimer函數(shù)中，通過增加變量DayOfYear 和 HourOfDay的值來控制地球和月球的位置，并且調(diào)用InvalidateRect來刷新界面。
void CCY457OpenGLView::OnTimer(UINT nIDEvent)
{
if(DayOfYear < 365)
DayOfYear++;
else
DayOfYear = 1;
if(HourOfDay < 365)
HourOfDay++;
else
HourOfDay = 1;
InvalidateRect(NULL, FALSE);
CView::OnTimer(nIDEvent);
}
6，在RenderScene中加入繪制代碼：
void CCY457OpenGLView::RenderScene ()
{//繪制函數(shù)
glTranslatef(0.0f,0.0f,-5.0f);
//Draw the Sun
glutWireSphere(1.0f,20,20);
//Rotate the Planet in its orbit
glRotatef((GLfloat) (360.0*DayOfYear)/365.0, 0.0f, 1.0f, 0.0f);
glTranslatef(4.0f,0.0f,0.0f);
glPushMatrix();
//Rotate the Planet in its orbit
glRotatef((GLfloat)(360*HourOfDay)/24.0, 0.0f,1.0f,0.0f);
//Draw the Planet
glutWireSphere(0.2f,20,20);
glPopMatrix();
glRotatef((GLfloat) (360.0*12.5*DayOfYear)/365.0, 0.0f, 1.0f, 0.0f);
glTranslatef(0.5f,0.0f,0.0f);
//Draw the Moon
glutWireSphere(0.01f,20,20);
}
原文鏈接：
http://www.cnblogs.com/phinecos/archive/2008/11/05/1327558.html