http://blog.csdn.net/qp120291570/article/details/8373896

一、提要

       有一款例子特效軟件叫做particle illution，在影視后期和游戲制作領(lǐng)域都可以用到，相信很多人都接觸過，今天我們用SDL+OpenGL來實現(xiàn)例子效果。

確保你搞定了物理模擬的代碼！

   代碼下載

二、原理簡介

     所謂的例子系統(tǒng)，就是同時控制一大堆類似的對象，這些對象可能是形體，可能是圖片，有著不同的特征（壽命，速度，位置）。有了之前的基礎(chǔ)，我們可以很輕易地搞定今天的東西。

三、代碼清單

首先是粒子的頭文件，我直接寫成結(jié)構(gòu)體了，里面有一些基本的屬性。

/*****************************************************************************
Copyright: 2012, ustc All rights reserved.
contact:k283228391@126.com
File name: particle.h
Description:Partical in opengl.
Author:Silang Quan
Version: 1.0
Date: 2012.12.20
 *****************************************************************************/
#ifndef PARTICLE_H
#define PARTICLE_H
#include "vector3d.h"
typedef struct
{
    float r;
    float g;
    float b;
    float alpha;
}Color;
typedef struct
{
    Vector3D position;
    Vector3D velocity;
    Vector3D acceleration;
    Color color;
    float age;
    float life;
    float size;
}Particle;
#endif // PARTICLE_H

接下來是粒子系統(tǒng)類（類名拼寫錯了*-*）

/*****************************************************************************
Copyright: 2012, ustc All rights reserved.
contact:k283228391@126.com
File name: particalsystem.h
Description:Partical in opengl.
Author:Silang Quan
Version: 1.0
Date: 2012.12.20
 *****************************************************************************/
#ifndef PARTICALSYSTEM_H
#define PARTICALSYSTEM_H
#include <vector>
#include <math.h>
#include <time.h>
#include <stdlib.h>
#include <iostream>
#include <GL/gl.h>
#include <GL/glu.h>
#include "particle.h"
#define PI 3.1415926
using namespace std;
class ParticalSystem
{
    public:
        ParticalSystem();
        ParticalSystem(int _count,float _gravity){ptlCount=_count;gravity=_gravity;};
        void init();
        void simulate(float dt);
        void aging(float dt);
        void applyGravity();
        void kinematics(float dt);
        void render();
        virtual ~ParticalSystem();
    protected:
    private:
    int ptlCount;
    float gravity;
    GLUquadricObj *mySphere;
    vector<Particle> particles;
};
#endif // PARTICALSYSTEM_H

init：做一些例子系統(tǒng)的初始化工作；

aging：計算粒子的年齡；

applyGravity：向粒子施加重力；

kinematics：這個單詞的意思是運動學，所以就是負責管理粒子的加速，位移；

simulate：例子模擬的總負責函數(shù)；

render：渲染粒子；

然后來看函數(shù)是怎么實現(xiàn)的：

/*****************************************************************************
Copyright: 2012, ustc All rights reserved.
contact:k283228391@126.com
File name: particalsystem.Cpp
Description:Partical in opengl.
Author:Silang Quan
Version: 1.0
Date: 2012.12.22
 *****************************************************************************/
#include "particalsystem.h"
ParticalSystem::ParticalSystem()
{
    //ctor
}
ParticalSystem::~ParticalSystem()
{
    //dtor
}
void ParticalSystem::init()
{
    int i;
    srand(unsigned(time(0)));
    Color colors[3]={{0,0,1,1},{1,0,1,1}};
    for(i=0;i<ptlCount;i++)
    {
        //theta =(rand()%361)/360.0* 2*PI;
        Particle tmp={Vector3D(0,0,0),Vector3D(((rand()%50)-26.0f),((rand()%50)-26.0f),((rand()%50)-26.0f)),Vector3D(0,0,0),colors[rand()%2],0.0f,0.5+0.05*(rand()%10),0.3f};
        particles.push_back(tmp);
    }
    mySphere=gluNewQuadric();
}
void ParticalSystem::simulate(float dt)
{
    aging(dt);
    applyGravity();
    kinematics(dt);
}
void ParticalSystem::aging(float dt)
{
    for(vector<Particle>::iterator iter=particles.begin();iter!=particles.end();iter++)
    {
        iter->age+=dt;
        if(iter->age>iter->life)
        {
            iter->position=Vector3D(0,0,0);
            iter->age=0.0;
            iter->velocity=Vector3D(((rand()%30)-15.0f),((rand()%30)-11.0f),((rand()%30)-15.0f));
        }
    }
}
void ParticalSystem::applyGravity()
{
    for(vector<Particle>::iterator iter=particles.begin();iter!=particles.end();iter++)
            iter->acceleration=Vector3D(0,gravity,0);
}
void ParticalSystem::kinematics(float dt)
{
    for(vector<Particle>::iterator iter=particles.begin();iter!=particles.end();iter++)
    {
        iter->position = iter->position+iter->velocity*dt;
        iter->velocity = iter->velocity+iter->acceleration*dt;
    }
}
void ParticalSystem::render()
{
    for(vector<Particle>::iterator iter=particles.begin();iter!=particles.end();iter++)
    {
        float alpha = 1 - iter->age / iter->life;//calculate the alpha value according to the age of particle.
        Vector3D tmp=iter->position;
        glColor4f(iter->color.r,iter->color.g,iter->color.b,alpha);
        glPushMatrix();
        glTranslatef(tmp.x,tmp.y,tmp.z);
        gluSphere(mySphere,iter->size, 32, 16);
        glPopMatrix();
    }
}

首先要在initGL函數(shù)中添加兩句話：

glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

接著初始化一個例子系統(tǒng)，并對例子進行初始化：

ParticalSystem ps;

int main( int argc, char* argv[] )
{
// Color depth in bits of our window.
int flags= SDL_OPENGL|SDL_RESIZABLE;
//Set the SDL
initSDL(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP,flags);
//Set the OpenGL
initGL(SCREEN_WIDTH, SCREEN_HEIGHT );
    ps=ParticalSystem(100,-15.0);
    ps.init();
//main loop
while(true)
{
/* Process incoming events. */
handleEvents( );
ps.simulate(0.01);
/* Draw the screen. */
renderGL( );
}
return 0;
}

然后是渲染函數(shù)：

void renderGL()
{
// Clear the color and depth buffers.
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT );
// We don't want to modify the projection matrix. */
glMatrixMode( GL_MODELVIEW );
glLoadIdentity( );
// Move down the z-axis.
glTranslatef(0.0f,0.0f,-35.0f);
ps.render();
SDL_GL_SwapBuffers( );
}

效果還是不錯的~下面我們來實現(xiàn)一些更棒的效果！

四、動態(tài)模糊和碰撞檢測

動態(tài)模糊的實現(xiàn)比較簡單，主循環(huán)不再每次把整個畫面清空，而是每幀畫一個半透明的黑色長方形，就可以模擬動態(tài)模糊(motion blur)的效果。

將之前的

// Clear the color and depth buffers.
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT );

// Clear the depth buffers.
glClear(GL_DEPTH_BUFFER_BIT );

void ParticalSystem::render()
{
    for(vector<Particle>::iterator iter=particles.begin();iter!=particles.end();iter++)
    {
        float alpha = 1 - iter->age / iter->life;
        Vector3D tmp=iter->position;
        glColor4f(iter->color.r,iter->color.g,iter->color.b,alpha);
        //glColor4f(1.0f, 1.0f, 1.0f, 0.1);
        glPushMatrix();
        glTranslatef(tmp.x,tmp.y,tmp.z);
        gluSphere(mySphere,iter->size, 32, 16);
        glPopMatrix();
    }
    //Motion blue
    glColor4f(0.0f,0.0f,0.0f,0.1);
    glBegin(GL_QUADS);
    glVertex3f(-20.0f  , -20.0f  ,  20.0f  );
    glVertex3f( 20.0f  , -20.0f  ,  20.0f  );
    glVertex3f( 20.0f  ,  20.0f  ,  20.0f  );
    glVertex3f(-20.0f  ,  20.0f  ,  20.0f  );
    glEnd();
}

效果還不錯！

碰撞檢測之前也實現(xiàn)過，在粒子系統(tǒng)里面加檢測函數(shù)就Ok了.

void ParticalSystem::checkBump(float x1,float x2,float y1,float y2)
{
    for(vector<Particle>::iterator iter=particles.begin();iter!=particles.end();iter++)
        {
            if (iter->position.x - iter->size < x1 || iter->position.x +iter->size > x2) iter->velocity.x = -iter->velocity.x;
            if (iter->position.y - iter->size < y1 || iter->position.y + iter->size > y2) iter->velocity.y = -iter->velocity.y;
        }
}

五、交互發(fā)射

這個其實是opengl之外的東西了。我們要用的是SDL的獲取鼠標信息函數(shù)：SDL_GetMouseState(&posX, &posY);

作用就是獲取當前鼠標的位置。

接下來還要做的一件事是寫坐標變換函數(shù)。因為opengl的坐標個SDL窗口的坐標并不是重合的，我們要將鼠標的當前坐標映射到OpenGL的坐標上去。

float posTransX(int posX)
{
    return (posX-400)/20.0;
}
float posTransY(int posY)
{
    return (400-posY)/20.0;
}

坐后要修改一下粒子的simulate函數(shù)。當粒子死亡的時候，他的初始位置設(shè)置為鼠標當前的位置。

void ParticalSystem::aging(float dt,float posX,float posY)
{
    for(vector<Particle>::iterator iter=particles.begin();iter!=particles.end();iter++)
    {
        iter->age+=dt;
        if(iter->age>iter->life)
        {
            iter->position=Vector3D(posX,posY,0);
            iter->age=0.0;
            iter->velocity=Vector3D(((rand()%30)-15.0f),((rand()%30)-11.0f),((rand()%30)-15.0f));
        }
    }
}

六、參考