大家好,歡迎來(lái)到新的一課,在這一課中我們將擴(kuò)展glCamera類，來(lái)實(shí)現(xiàn)鏡頭光暈的效果。在日常生活中，當(dāng)我們對(duì)著光源看時(shí)，會(huì)發(fā)現(xiàn)強(qiáng)烈的反光。
為了完成這個(gè)效果，我們需要一些數(shù)學(xué)知識(shí)。首先，我們需要一些函數(shù)，用來(lái)檢測(cè)某個(gè)點(diǎn)或球是否在當(dāng)前的視景體內(nèi)。接著我們需要一些紋理作為我們的光暈效果，我們可以把它貼在顯示面上。
在我的上一個(gè)攝像機(jī)類里把下面函數(shù)寫錯(cuò)了，現(xiàn)在修正如下：
 
  

void glCamera::SetPrespective(){ GLfloat Matrix[16];             glVector v;                               
// 根據(jù)當(dāng)前的偏轉(zhuǎn)角旋轉(zhuǎn)視線
glRotatef(m_HeadingDegrees, 0.0f, 1.0f, 0.0f);
glRotatef(m_PitchDegrees, 1.0f, 0.0f, 0.0f);

// 返回模型變換矩陣
glGetFloatv(GL_MODELVIEW_MATRIX, Matrix);

// 獲得視線的方向
m_DirectionVector.i = Matrix[8];
m_DirectionVector.j = Matrix[9];
m_DirectionVector.k = -Matrix[10];

// 重置矩陣
glLoadIdentity();

// 旋轉(zhuǎn)場(chǎng)景
glRotatef(m_PitchDegrees, 1.0f, 0.0f, 0.0f);
glRotatef(m_HeadingDegrees, 0.0f, 1.0f, 0.0f);

// 設(shè)置當(dāng)前攝像機(jī)的位置
v = m_DirectionVector;
v *= m_ForwardVelocity;
m_Position.x += v.i;
m_Position.y += v.j;
m_Position.z += v.k;

// 變換到新的位置
glTranslatef(-m_Position.x, -m_Position.y, -m_Position.z);
}

  
 好了，我們現(xiàn)在開始吧。我將使用4個(gè)對(duì)立的紋理來(lái)制造我們的鏡頭光暈，第一和二個(gè)光暈圖像被放置在光源處，第三和第四個(gè)圖像將根據(jù)視點(diǎn)的位置和方向動(dòng)態(tài)的生成。紋理的圖像如下所示：

Big Glow

   Streaks

 
Glow

   Halo

現(xiàn)在你在頭腦里應(yīng)該有了一個(gè)大慨地圖像了吧。我們來(lái)說(shuō)說(shuō)何時(shí)我們應(yīng)該繪制光暈，一般來(lái)說(shuō)平時(shí)我們是看不見(jiàn)這些光暈的，只有當(dāng)我們對(duì)準(zhǔn)光源的時(shí)候才能看見(jiàn)這些。所以我們首先要獲得視景體的數(shù)據(jù)，下面的函數(shù)可以幫我們完成這個(gè)功能。
 
  

// 獲得當(dāng)前視景體的6個(gè)平面方程的參數(shù)void glCamera::UpdateFrustum(){    GLfloat   clip[16]; GLfloat   proj[16];    GLfloat   modl[16];    GLfloat   t;
//返回投影矩陣
glGetFloatv( GL_PROJECTION_MATRIX, proj );

//返回模型變換矩陣
glGetFloatv( GL_MODELVIEW_MATRIX, modl );

//計(jì)算剪切矩陣，即上面兩個(gè)矩陣的乘積
clip[ 0] = modl[ 0] * proj[ 0] + modl[ 1] * proj[ 4] + modl[ 2] * proj[ 8] + modl[ 3] * proj[12];
clip[ 1] = modl[ 0] * proj[ 1] + modl[ 1] * proj[ 5] + modl[ 2] * proj[ 9] + modl[ 3] * proj[13];
clip[ 2] = modl[ 0] * proj[ 2] + modl[ 1] * proj[ 6] + modl[ 2] * proj[10] + modl[ 3] * proj[14];
clip[ 3] = modl[ 0] * proj[ 3] + modl[ 1] * proj[ 7] + modl[ 2] * proj[11] + modl[ 3] * proj[15];

clip[ 4] = modl[ 4] * proj[ 0] + modl[ 5] * proj[ 4] + modl[ 6] * proj[ 8] + modl[ 7] * proj[12];
clip[ 5] = modl[ 4] * proj[ 1] + modl[ 5] * proj[ 5] + modl[ 6] * proj[ 9] + modl[ 7] * proj[13];
clip[ 6] = modl[ 4] * proj[ 2] + modl[ 5] * proj[ 6] + modl[ 6] * proj[10] + modl[ 7] * proj[14];
clip[ 7] = modl[ 4] * proj[ 3] + modl[ 5] * proj[ 7] + modl[ 6] * proj[11] + modl[ 7] * proj[15];

clip[ 8] = modl[ 8] * proj[ 0] + modl[ 9] * proj[ 4] + modl[10] * proj[ 8] + modl[11] * proj[12];
clip[ 9] = modl[ 8] * proj[ 1] + modl[ 9] * proj[ 5] + modl[10] * proj[ 9] + modl[11] * proj[13];
clip[10] = modl[ 8] * proj[ 2] + modl[ 9] * proj[ 6] + modl[10] * proj[10] + modl[11] * proj[14];
clip[11] = modl[ 8] * proj[ 3] + modl[ 9] * proj[ 7] + modl[10] * proj[11] + modl[11] * proj[15];

clip[12] = modl[12] * proj[ 0] + modl[13] * proj[ 4] + modl[14] * proj[ 8] + modl[15] * proj[12];
clip[13] = modl[12] * proj[ 1] + modl[13] * proj[ 5] + modl[14] * proj[ 9] + modl[15] * proj[13];
clip[14] = modl[12] * proj[ 2] + modl[13] * proj[ 6] + modl[14] * proj[10] + modl[15] * proj[14];
clip[15] = modl[12] * proj[ 3] + modl[13] * proj[ 7] + modl[14] * proj[11] + modl[15] * proj[15];

//提取右面的平面方程系數(shù)
m_Frustum[0][0] = clip[ 3] - clip[ 0];
m_Frustum[0][1] = clip[ 7] - clip[ 4];
m_Frustum[0][2] = clip[11] - clip[ 8];
m_Frustum[0][3] = clip[15] - clip[12];
t = GLfloat(sqrt( m_Frustum[0][0] * m_Frustum[0][0] + m_Frustum[0][1] * m_Frustum[0][1] + m_Frustum[0][2] * m_Frustum[0][2] ));
m_Frustum[0][0] /= t;
m_Frustum[0][1] /= t;
m_Frustum[0][2] /= t;
m_Frustum[0][3] /= t;

//提取左面的平面方程系數(shù)
m_Frustum[1][0] = clip[ 3] + clip[ 0];
m_Frustum[1][1] = clip[ 7] + clip[ 4];
m_Frustum[1][2] = clip[11] + clip[ 8];
m_Frustum[1][3] = clip[15] + clip[12];
t = GLfloat(sqrt( m_Frustum[1][0] * m_Frustum[1][0] + m_Frustum[1][1] * m_Frustum[1][1] + m_Frustum[1][2] * m_Frustum[1][2] ));
m_Frustum[1][0] /= t;
m_Frustum[1][1] /= t;
m_Frustum[1][2] /= t;
m_Frustum[1][3] /= t;

//提取下面的平面方程系數(shù)
m_Frustum[2][0] = clip[ 3] + clip[ 1];
m_Frustum[2][1] = clip[ 7] + clip[ 5];
m_Frustum[2][2] = clip[11] + clip[ 9];
m_Frustum[2][3] = clip[15] + clip[13];
t = GLfloat(sqrt( m_Frustum[2][0] * m_Frustum[2][0] + m_Frustum[2][1] * m_Frustum[2][1] + m_Frustum[2][2] * m_Frustum[2][2] ));
m_Frustum[2][0] /= t;
m_Frustum[2][1] /= t;
m_Frustum[2][2] /= t;
m_Frustum[2][3] /= t;

//提取上面的平面方程系數(shù)
m_Frustum[3][0] = clip[ 3] - clip[ 1];
m_Frustum[3][1] = clip[ 7] - clip[ 5];
m_Frustum[3][2] = clip[11] - clip[ 9];
m_Frustum[3][3] = clip[15] - clip[13];
t = GLfloat(sqrt( m_Frustum[3][0] * m_Frustum[3][0] + m_Frustum[3][1] * m_Frustum[3][1] + m_Frustum[3][2] * m_Frustum[3][2] ));
m_Frustum[3][0] /= t;
m_Frustum[3][1] /= t;
m_Frustum[3][2] /= t;
m_Frustum[3][3] /= t;

//提取遠(yuǎn)面的平面方程系數(shù)
m_Frustum[4][0] = clip[ 3] - clip[ 2];
m_Frustum[4][1] = clip[ 7] - clip[ 6];
m_Frustum[4][2] = clip[11] - clip[10];
m_Frustum[4][3] = clip[15] - clip[14];
t = GLfloat(sqrt( m_Frustum[4][0] * m_Frustum[4][0] + m_Frustum[4][1] * m_Frustum[4][1] + m_Frustum[4][2] * m_Frustum[4][2] ));
m_Frustum[4][0] /= t;
m_Frustum[4][1] /= t;
m_Frustum[4][2] /= t;
m_Frustum[4][3] /= t;

//提取近面的平面方程系數(shù)
m_Frustum[5][0] = clip[ 3] + clip[ 2];
m_Frustum[5][1] = clip[ 7] + clip[ 6];
m_Frustum[5][2] = clip[11] + clip[10];
m_Frustum[5][3] = clip[15] + clip[14];
t = GLfloat(sqrt( m_Frustum[5][0] * m_Frustum[5][0] + m_Frustum[5][1] * m_Frustum[5][1] + m_Frustum[5][2] * m_Frustum[5][2] ));
m_Frustum[5][0] /= t;
m_Frustum[5][1] /= t;
m_Frustum[5][2] /= t;
m_Frustum[5][3] /= t;
}

  
 現(xiàn)在我們可以測(cè)試一個(gè)點(diǎn)或圓是否在視景體內(nèi)了。下面的函數(shù)可以測(cè)試一個(gè)點(diǎn)是否在視景體內(nèi)。 
  

BOOL glCamera::PointInFrustum(glPoint p){ int i; for(i = 0; i < 6; i++) {  if(m_Frustum[i][0] * p.x + m_Frustum[i][1] * p.y + m_Frustum[i][2] * p.z + m_Frustum[i][3] <= 0)  {   return(FALSE);  } } return(TRUE);}

  
 下面的函數(shù)用來(lái)測(cè)試某個(gè)點(diǎn)是否位于當(dāng)前場(chǎng)景物體的前面:
 
  

bool glCamera::IsOccluded(glPoint p){ GLint viewport[4];       GLdouble mvmatrix[16], projmatrix[16];   GLdouble winx, winy, winz;     GLdouble flareZ;       GLfloat bufferZ;      
glGetIntegerv (GL_VIEWPORT, viewport);
glGetDoublev (GL_MODELVIEW_MATRIX, mvmatrix);
glGetDoublev (GL_PROJECTION_MATRIX, projmatrix);

// 返回頂點(diǎn)p在單位立方體中的位置
gluProject(p.x, p.y, p.z, mvmatrix, projmatrix, viewport, &winx, &winy, &winz);
flareZ = winz;

// 讀取點(diǎn)(winx,winy)的深度坐標(biāo)
glReadPixels(winx, winy,1,1,GL_DEPTH_COMPONENT, GL_FLOAT, &bufferZ);

// 如果深度坐標(biāo)小于點(diǎn)的坐標(biāo)，則返回true
if (bufferZ < flareZ)
return true;
//否則返回false
else
return false;
}

  
 我們通過(guò)檢測(cè)光源是否正對(duì)我們的視線來(lái)決定是否繪制光暈，但如果你的視點(diǎn)超過(guò)了光源的位置，則會(huì)發(fā)生看不見(jiàn)光暈的現(xiàn)象。為了避免這種現(xiàn)象，我們?cè)谝苿?dòng)視點(diǎn)的使用，也相應(yīng)的移動(dòng)我們的光源。為了在視點(diǎn)和光源之間繪制多個(gè)光暈，我們需要計(jì)算之間的向量，下面的代碼完成這個(gè)功能： 
  

//下面的函數(shù)完成具體的渲染光暈的任務(wù)void glCamera::RenderLensFlare(){ GLfloat Length = 0.0f;
// 如果我們的光源在我們的視線范圍內(nèi)，則繪制它
if(SphereInFrustum(m_LightSourcePos, 1.0f) == TRUE)
{
vLightSourceToCamera = m_Position - m_LightSourcePos; // 計(jì)算光源到我們視線的距離
Length = vLightSourceToCamera.Magnitude();

//下面三個(gè)函數(shù)計(jì)算光源位置到光暈結(jié)束位置之間的向量
ptIntersect = m_DirectionVector * Length;
ptIntersect += m_Position;
vLightSourceToIntersect = ptIntersect - m_LightSourcePos;
Length = vLightSourceToIntersect.Magnitude();
vLightSourceToIntersect.Normalize();

glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE);
glDisable(GL_DEPTH_TEST);
glEnable(GL_TEXTURE_2D);

  
 首先我們需要找到光源位置和視點(diǎn)位置之間的向量，接下來(lái)我們需要在視線的方向設(shè)置一個(gè)插值點(diǎn)，這個(gè)點(diǎn)的距離必須和光源位置和視點(diǎn)位置之間的距離相等。完成以后，我們找出可以產(chǎn)生光暈的方向，即下圖紅線的方向，在這個(gè)線上我們可以繪制我們的光暈。

  if (!IsOccluded(m_LightSourcePos)) //如果光暈可見(jiàn)  {   // 渲染中間的光暈   RenderBigGlow(0.60f, 0.60f, 0.8f, 1.0f, m_LightSourcePos, 16.0f);   RenderStreaks(0.60f, 0.60f, 0.8f, 1.0f, m_LightSourcePos, 16.0f);   RenderGlow(0.8f, 0.8f, 1.0f, 0.5f, m_LightSourcePos, 3.5f);
//繪制到光暈結(jié)束位置的0.1處的光暈
pt = vLightSourceToIntersect * (Length * 0.1f);
pt += m_LightSourcePos;
RenderGlow(0.9f, 0.6f, 0.4f, 0.5f, pt, 0.6f);

//繪制到光暈結(jié)束位置的0.15處的光暈
pt = vLightSourceToIntersect * (Length * 0.15f);
pt += m_LightSourcePos;
RenderHalo(0.8f, 0.5f, 0.6f, 0.5f, pt, 1.7f);

//繪制到光暈結(jié)束位置的0.175處的光暈
pt = vLightSourceToIntersect * (Length * 0.175f);
pt += m_LightSourcePos;
RenderHalo(0.9f, 0.2f, 0.1f, 0.5f, pt, 0.83f);

//繪制到光暈結(jié)束位置的0.285處的光暈
pt = vLightSourceToIntersect * (Length * 0.285f);
pt += m_LightSourcePos;
RenderHalo(0.7f, 0.7f, 0.4f, 0.5f, pt, 1.6f);

//繪制到光暈結(jié)束位置的0.2755處的光暈
pt = vLightSourceToIntersect * (Length * 0.2755f);
pt += m_LightSourcePos;
RenderGlow(0.9f, 0.9f, 0.2f, 0.5f, pt, 0.8f);

//繪制到光暈結(jié)束位置的0.4755處的光暈
pt = vLightSourceToIntersect * (Length * 0.4775f);
pt += m_LightSourcePos;
RenderGlow(0.93f, 0.82f, 0.73f, 0.5f, pt, 1.0f);

//繪制到光暈結(jié)束位置的0.49處的光暈
pt = vLightSourceToIntersect * (Length * 0.49f);
pt += m_LightSourcePos;
RenderHalo(0.7f, 0.6f, 0.5f, 0.5f, pt, 1.4f);

//繪制到光暈結(jié)束位置的0.65處的光暈
pt = vLightSourceToIntersect * (Length * 0.65f);
pt += m_LightSourcePos;
RenderGlow(0.7f, 0.8f, 0.3f, 0.5f, pt, 1.8f);

//繪制到光暈結(jié)束位置的0.63處的光暈
pt = vLightSourceToIntersect * (Length * 0.63f);
pt += m_LightSourcePos;
RenderGlow(0.4f, 0.3f, 0.2f, 0.5f, pt, 1.4f);

//繪制到光暈結(jié)束位置的0.8處的光暈
pt = vLightSourceToIntersect * (Length * 0.8f);
pt += m_LightSourcePos;
RenderHalo(0.7f, 0.5f, 0.5f, 0.5f, pt, 1.4f);

//繪制到光暈結(jié)束位置的0.7825處的光暈
pt = vLightSourceToIntersect * (Length * 0.7825f);
pt += m_LightSourcePos;
RenderGlow(0.8f, 0.5f, 0.1f, 0.5f, pt, 0.6f);

//繪制到光暈結(jié)束位置的1.0處的光暈
pt = vLightSourceToIntersect * (Length * 1.0f);
pt += m_LightSourcePos;
RenderHalo(0.5f, 0.5f, 0.7f, 0.5f, pt, 1.7f);

//繪制到光暈結(jié)束位置的0.975處的光暈
pt = vLightSourceToIntersect * (Length * 0.975f);
pt += m_LightSourcePos;
RenderGlow(0.4f, 0.1f, 0.9f, 0.5f, pt, 2.0f);

}
glDisable(GL_BLEND );
glEnable(GL_DEPTH_TEST);
glDisable(GL_TEXTURE_2D);
}
}

  
 好了，下面的函數(shù)用來(lái)繪制四種不同的光暈 
  

//繪制Halo形的光暈void glCamera::RenderHalo(GLfloat r, GLfloat g, GLfloat b, GLfloat a, glPoint p, GLfloat scale){ glPoint q[4];  q[0].x = (p.x - scale);            q[0].y = (p.y - scale);              q[1].x = (p.x - scale);            q[1].y = (p.y + scale);              q[2].x = (p.x + scale);            q[2].y = (p.y - scale);              q[3].x = (p.x + scale);            q[3].y = (p.y + scale);              glPushMatrix();              glTranslatef(p.x, p.y, p.z);          glRotatef(-m_HeadingDegrees, 0.0f, 1.0f, 0.0f); glRotatef(-m_PitchDegrees, 1.0f, 0.0f, 0.0f); glBindTexture(GL_TEXTURE_2D, m_HaloTexture);      glColor4f(r, g, b, a);             glBegin(GL_TRIANGLE_STRIP);            glTexCoord2f(0.0f, 0.0f);       glVertex2f(q[0].x, q[0].y);  glTexCoord2f(0.0f, 1.0f);  glVertex2f(q[1].x, q[1].y);  glTexCoord2f(1.0f, 0.0f);  glVertex2f(q[2].x, q[2].y);  glTexCoord2f(1.0f, 1.0f);  glVertex2f(q[3].x, q[3].y); glEnd();           glPopMatrix();             }
//繪制Gloew形的光暈
void glCamera::RenderGlow(GLfloat r, GLfloat g, GLfloat b, GLfloat a, glPoint p, GLfloat scale)
{
glPoint q[4];

q[0].x = (p.x - scale);
q[0].y = (p.y - scale);

q[1].x = (p.x - scale);
q[1].y = (p.y + scale);

q[2].x = (p.x + scale);
q[2].y = (p.y - scale);

q[3].x = (p.x + scale);
q[3].y = (p.y + scale);

glPushMatrix();
glTranslatef(p.x, p.y, p.z);
glRotatef(-m_HeadingDegrees, 0.0f, 1.0f, 0.0f);
glRotatef(-m_PitchDegrees, 1.0f, 0.0f, 0.0f);
glBindTexture(GL_TEXTURE_2D, m_GlowTexture);
glColor4f(r, g, b, a);

glBegin(GL_TRIANGLE_STRIP);
glTexCoord2f(0.0f, 0.0f);
glVertex2f(q[0].x, q[0].y);
glTexCoord2f(0.0f, 1.0f);
glVertex2f(q[1].x, q[1].y);
glTexCoord2f(1.0f, 0.0f);
glVertex2f(q[2].x, q[2].y);
glTexCoord2f(1.0f, 1.0f);
glVertex2f(q[3].x, q[3].y);
glEnd();
glPopMatrix();
}

//繪制BigGlow形的光暈
void glCamera::RenderBigGlow(GLfloat r, GLfloat g, GLfloat b, GLfloat a, glPoint p, GLfloat scale)
{
glPoint q[4];

q[0].x = (p.x - scale);
q[0].y = (p.y - scale);

q[1].x = (p.x - scale);
q[1].y = (p.y + scale);

q[2].x = (p.x + scale);
q[2].y = (p.y - scale);

q[3].x = (p.x + scale);
q[3].y = (p.y + scale);

glPushMatrix();
glTranslatef(p.x, p.y, p.z);
glRotatef(-m_HeadingDegrees, 0.0f, 1.0f, 0.0f);
glRotatef(-m_PitchDegrees, 1.0f, 0.0f, 0.0f);
glBindTexture(GL_TEXTURE_2D, m_BigGlowTexture);
glColor4f(r, g, b, a);

glBegin(GL_TRIANGLE_STRIP);
glTexCoord2f(0.0f, 0.0f);
glVertex2f(q[0].x, q[0].y);
glTexCoord2f(0.0f, 1.0f);
glVertex2f(q[1].x, q[1].y);
glTexCoord2f(1.0f, 0.0f);
glVertex2f(q[2].x, q[2].y);
glTexCoord2f(1.0f, 1.0f);
glVertex2f(q[3].x, q[3].y);
glEnd();
glPopMatrix();
}

//繪制Streaks形的光暈
void glCamera::RenderStreaks(GLfloat r, GLfloat g, GLfloat b, GLfloat a, glPoint p, GLfloat scale)
{
glPoint q[4];

q[0].x = (p.x - scale);
q[0].y = (p.y - scale);

q[1].x = (p.x - scale);
q[1].y = (p.y + scale);

q[2].x = (p.x + scale);
q[2].y = (p.y - scale);

q[3].x = (p.x + scale);
q[3].y = (p.y + scale);

glPushMatrix();
glTranslatef(p.x, p.y, p.z);
glRotatef(-m_HeadingDegrees, 0.0f, 1.0f, 0.0f);
glRotatef(-m_PitchDegrees, 1.0f, 0.0f, 0.0f);
glBindTexture(GL_TEXTURE_2D, m_StreakTexture);
glColor4f(r, g, b, a);

glBegin(GL_TRIANGLE_STRIP);
glTexCoord2f(0.0f, 0.0f);
glVertex2f(q[0].x, q[0].y);
glTexCoord2f(0.0f, 1.0f);
glVertex2f(q[1].x, q[1].y);
glTexCoord2f(1.0f, 0.0f);
glVertex2f(q[2].x, q[2].y);
glTexCoord2f(1.0f, 1.0f);
glVertex2f(q[3].x, q[3].y);
glEnd();
glPopMatrix();
}

  
 你可以使用w,s,a,d變換攝像機(jī)的方向，1，2顯示/關(guān)閉各種信息參數(shù)。C給攝像機(jī)一個(gè)固定的速度，X停止它。

上面就是這個(gè)教程的全部了，所有的問(wèn)題，評(píng)論和抱怨都?xì)g迎。當(dāng)然我不是第一個(gè)作這個(gè)效果的人，下面是其他方面相關(guān)的文章:
http://www.gamedev.net/reference/articles/article874.asp
http://www.gamedev.net/reference/articles/article813.asp
http://www.opengl.org/developers/code/mjktips/lensflare/
http://www.markmorley.com/opengl/frustumculling.html
http://oss.sgi.com/projects/ogl-sample/registry/HP/occlusion_test.txt
http://oss.sgi.com/projects/ogl-sample/registry/NV/occlusion_query.txt