粒子系统

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1. 基本原理

粒子系统由大量的粒子构成，每个粒子有大小，位置以及纹理，另外还有比如颜色，透明度，运动速度，加速度，自旋周期，生命周期等属性

粒子系统随时间不短变换，常经过下面几个变换

1）产生新的粒子

2）更新现有粒子属性

3）删除已经消亡的粒子

4）绘制出粒子

2. 粒子系统设计

1）定义粒子数量，区域，宽度，高度

#define PARTICLE_NUMBER 10000

# define SNOW_SYSTEM_LENGTH_X 20000

#define SNOW_SYSTEM_WIDTH_Z 20000

#define SNOW_SYSTEM_HEIGHT_Y 20000

2）设置顶点结构和顶点格式,粒子系统类

struct POINTVERTEX{

float x,y,z;

float u,v;

};

#define D3DFVF_POINTVERTEX (DEDFVF_XYZ | D3DFVF_TEX1)

CParticleSystem::CParticleSystem(){    m_NumParticles = 0;    m_pParticles = NULL;    m_fSpread = 0.0f;    m_fLifeSpan = 0.0f;    m_fStartSize = 0.0f;    m_fEndSize = 0.0f;    m_fSizeExponent = 0.0f;    m_fStartSpeed = 0.0f;    m_fEndSpeed = 0.0f;    m_fSpeedExponent = 0.0f;    m_fFadeExponent = 0.0f;    m_fRollAmount = 0.0f;    m_fWindFalloff = 0.0f;    m_vPosMul = D3DXVECTOR3( 0, 0, 0 );    m_vDirMul = D3DXVECTOR3( 0, 0, 0 );    m_fCurrentTime = 0.0f;    m_vCenter = D3DXVECTOR3( 0, 0, 0 );    m_fStartTime = 0.0f;    m_vFlashColor = D3DXVECTOR4( 0, 0, 0, 0 );    m_PST = PST_DEFAULT;}

3. 初始化粒子数组

void CParticleSystem::Init(){    for( UINT i = 0; i < m_NumParticles; i++ )    {        m_pParticles[i].vPos.x = RPercent() * m_fSpread;        m_pParticles[i].vPos.y = RPercent() * m_fSpread;        m_pParticles[i].vPos.z = RPercent() * m_fSpread;        m_pParticles[i].vPos.x *= m_vPosMul.x;        m_pParticles[i].vPos.y *= m_vPosMul.y;        m_pParticles[i].vPos.z *= m_vPosMul.z;        m_pParticles[i].vPos += m_vCenter;        m_pParticles[i].vDir.x = RPercent();        m_pParticles[i].vDir.y = fabs( RPercent() );        m_pParticles[i].vDir.z = RPercent();        m_pParticles[i].vDir.x *= m_vDirMul.x;        m_pParticles[i].vDir.y *= m_vDirMul.y;        m_pParticles[i].vDir.z *= m_vDirMul.z;        D3DXVec3Normalize( &m_pParticles[i].vDir, &m_pParticles[i].vDir );        m_pParticles[i].fRadius = m_fStartSize;        m_pParticles[i].fLife = m_fStartTime;        m_pParticles[i].fFade = 0.0f;        m_pParticles[i].fRot = RPercent() * 3.14159f * 2.0f;        float fLerp = RPercent();        D3DXVECTOR4 vColor = m_vColor0 * fLerp + m_vColor1 * ( 1.0f - fLerp );        m_pParticles[i].Color = ( DWORD )( vColor.w * 255.0f ) << 24;        m_pParticles[i].Color |= ( ( DWORD )( vColor.z * 255.0f ) & 255 ) << 16;        m_pParticles[i].Color |= ( ( DWORD )( vColor.y * 255.0f ) & 255 ) << 8;        m_pParticles[i].Color |= ( ( DWORD )( vColor.x * 255.0f ) & 255 );    }    m_bStarted = false;    m_fCurrentTime = m_fStartTime;}

4.更新粒子系统

void CParticleSystem::AdvanceSystem( float fTime, float fElapsedTime, D3DXVECTOR3 vRight, D3DXVECTOR3 vUp,                                     D3DXVECTOR3 vWindVel, D3DXVECTOR3 vGravity ){    if( m_fCurrentTime > 0 )    {        for( UINT i = 0; i < m_NumParticles; i++ )        {            float t = m_pParticles[i].fLife / m_fLifeSpan;            float tm1 = t - 1.0f;            float fSizeLerp = 1.0f - pow( tm1, m_fSizeExponent );            float fSpeedLerp = 1.0f - pow( tm1, m_fSpeedExponent );            float fFadeLerp = 1.0f - pow( tm1, m_fFadeExponent );            float fSize = fSizeLerp * m_fEndSize + ( 1.0f - fSizeLerp ) * m_fStartSize;            float fSpeed = fSpeedLerp * m_fEndSpeed + ( 1.0f - fSpeedLerp ) * m_fStartSpeed;            float fFade = fFadeLerp;            D3DXVECTOR3 vVel = m_pParticles[i].vDir * fSpeed;            float fRot = 0.0f;            float fWindAmt = 1.0f;            vVel += vWindVel * fWindAmt;            m_pParticles[i].vPos += fElapsedTime * vVel;            m_pParticles[i].fRadius = fSize;            m_pParticles[i].fLife += fElapsedTime;            m_pParticles[i].fFade = fFade;            m_pParticles[i].fRot += fRot;            m_pParticles[i].bVisible = true;        }        if( !m_bStarted )        {            m_bStarted = true;        }    }    else    {        for( UINT i = 0; i < m_NumParticles; i++ )        {            m_pParticles[i].bVisible = false;            m_pParticles[i].fLife += fElapsedTime;        }    }    m_fCurrentTime += fElapsedTime;}

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介绍D3D sampler 中 deffer particle ，在射击类游戏中可以有非常绚丽效果，上图

其实呢，原理还是比较容易理解的

1. Alpha Blend

2.diffuse light

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