Monday, January 29, 2007

Simple Particle Rendering.

Particles are really nice to see. usually we can see particle effects in most computer games . They appear as water fountain , flame, wind,sand, etc. It has infinite scope.  Actully we can create anything using particles.. But it will depends on the speed of computer.

In this page i am trying to create a simple particle engine , which renders a water fountain. So what is a particle ? the first answer coming to my mind is it is a point , but this is not fully correct. It can be represented as a point , or triangle , or polygon etc. This will depends on the application which we are writing. For the creation of water fountain we can assume the following attributes for a particle.

It is represented a single point . (GL_POINT in opengl )
it has 3 dimensions.
if follows gravity rules.  ( if we are using gravity).
it has a specific acceleration in all directions. ( 3 directions , x , y z).

 Above are the basic things to keep in mind. So now we can create a structure like this

struct Particles

   double xPos,yPos,zPos; 
   double xAcc; // xAcc is a constant one.
   double yAcc; // this is a diminishing one due to the gravity. 
   double zAcc; // For the timebeing this is zero.
 #define XACC .05
int        YACC 1.0

now we can create a bunch of particles by declaring an array of Particles.
Particles fountain[MAX_NUMS];

 Now we need to design in which way one particle travels. it can be like this in a X-Y plane ( now no depth)

        o  o
    o         o
  o             o
o               o

so for simulating the movement of a single particle we need to make changes on both x , y .we can keep the x acceleration as constant number ( Particles::xAcc) . If u look the image more closely it can be seen that the acceleration in y direction is more compared to X ,  it is also decreasing due to gravity.

 so we can do it like this, For each particle particle[i].x += XACC ( constant) , and particle[i].y += particle[i].yAcc; so initially this particle[i].yAcc is initialized to 1. after each rendering this will be decreased by the amount of gravity , like  particle[i].yAcc-=gravity; so when the yAcc becomes -ve we will get a falling effect.

 If a particles y value is  -ve and x value is +ve it means that , that particles is falled down to ground. so we need to again reinitialize it position to zero , again sets its acceleration and gravity to the predefined value...

Till now we have drawn only particles in 2d space, ie we haven't changed the z value. we can do that by giving rotating about y axis. The pseudo code is shown below..

For(int i = 0; i < TOT_PARTICLE;i++)

       for(int j = 10; j < 360 ; j+=90)    

              glRoate(j degrees in y axis);
              Apply colors or textures.
              ChangeAccleration(particle[i]); // here we are changing the accleration in both y and x direction

Now it is complete I am attaching a sample screen shot which i did with this idea. Hopes this may give some good starting for beginners who want to learn particles.