Trent Polack's OpenGL Game Programming Tutorials

Jeff Molofee's OpenGL Windows Tutorial #3
float Get_Location(int coordinate);
void Set_Location(float x, float y, float z);
void Set_Texture(S3DTGA_PTR texture1);
void Set_ParticlesPerSec(unsigned int number);
void Set_Velocity(float xv, float yv, float zv);
void Set_Size(float startsize, float endsize);
void Set_Alpha(float startalpha, float endalpha);
void Set_Speed(float Speed);
void Set_Angle(float half_angle);
void Set_SystemFlag(int flag, bool state);
void Set_Color(float start_red, float start_green, float start_blue, float
end_red, float end_green, float end_blue);
void Set_Life(float seconds);
void Set_Spread(int Spread_Min, int Spread_Max, float Spread_factor);
void Set_Attraction(unsigned int Attraction_Percent);
void Set_Gravity(float xpull, float ypull, float zpull);
bool IsAttracting(void)
{ return attracting; }
bool IsStopped(void)
{ return stopped; }
PARTICLE_SYSTEM();
~PARTICLE_SYSTEM();
};
A little on the big size isn't it. ;) Now, if you'll notice, I made the array of particle public, 'why' you ask? That way you
can check a particle's position in space, and see if it is colliding with anything. A particle demo with collision ranks
up there in the REALLY cool category. Now, instead of going through the variables one by one, I will just go
through the functions, and describe them as I go (because there are quite a bit of them, and to understand their
true meaning, you may have to see them in action to fully understand them). First, lets go through the particle
system's version of the Update function:
bool PARTICLE_SYSTEM::
Update(float time, int flag, float num_to_create)
{
int loop;
unsigned int particles_created;
float time_counter;
float particles_needed=num_to_create;
This is the beginning of the function. Notice the three arguments, I'll talk about the first argument later when we see
the particle engine in action for our demo, but lets talk about the others now. The flag variable can be one of three
things:
● ONLY_CREATE You will be using this one when you want your current system to generate an effect when a
'cause' is triggered. For our demo, for instance, we use it when we generate an explosion, so when the 'e' key
is pressed, this is what we call:
ps1.Update(time, ONLY_CREATE, 500);
This way, we can generate an explosion of 500 particles when the 'e' key is pressed, and we don't have to
update the whole particle system if we don't want to (that would make the user hold down the 'e' key to see
the actual animation).
● ONLY_UPDATE This is what we are going to use for systems that have effects generated dynamically (such
as the explosion effect discussed above), instead of effects that need to be generated constantly (such as
http://nehe.gamedev.net/gametutorials/lesson03.asp (9 of 14) [20/08/2001 22:34:18]