Trent Polack's OpenGL Game Programming Tutorials

Jeff Molofee's OpenGL Windows Tutorial #3
// The Emitter Has A Direction. This Is Where We Find It:
random_yaw = (float)(RANDOM_FLOAT*PI*2.0f);
random_pitch= (float)(DEG_TO_RAD(RANDOM_FLOAT*((parent->angle))));
// The Following Code Uses Spherical Coordinates To Randomize
// The Velocity Vector Of The Particle
velocity.vertex[0]=(cosf(random_pitch))*(parent->velocity.vertex[0]);
velocity.vertex[1]=(sinf(random_pitch)*cosf(random_yaw))*(parent-
>velocity.vertex[1]);
velocity.vertex[2]=(sinf(random_pitch)*sinf(random_yaw))*(parent-
>velocity.vertex[2]);
// Velocity At This Point Is Just A Direction (Normalized
// Vector) And Needs To Be Multiplied By The Speed
// Component To Be Legit.
new_speed= ((parent->speed)+(RANDOM_FLOAT*(parent->speed_counter)));
CHECK_RANGE(new_speed, MIN_SPEED, MAX_SPEED);
velocity.vertex[0]*= new_speed;
velocity.vertex[1]*= new_speed;
velocity.vertex[2]*= new_speed;
// Set The Particle's Parent System
Set_ParentSystem(parent);
}
Phew, I am glad that function is over with! For a quick note, CHECK_RANGE is a macro that checks to make sure
that a variable (the first argument) is within a minimum (second argument) and the maximum (last argument)
range. Also, look at these 3 lines:
velocity.vertex[0]=(cosf(random_pitch))*(parent->velocity.vertex[0]);
velocity.vertex[1]=(sinf(random_pitch)*cosf(random_yaw))*(parent-
>velocity.vertex[1]);
velocity.vertex[2]=(sinf(random_pitch)*sinf(random_yaw))*(parent-
>velocity.vertex[2]);
This may be a speed caution, but it also creates the exact effect that we want. I tried using our SIN and COS
tables, but they created explosions that were TOO perfect (it basically created a perfect sphere, instead of a sphere
with 'bumps'). So, sometimes it is necessary to do dynamic calculations.
Next on our list is to show the particle's update function. This function updates the particle that the class currently
represents ONLY (this is all handled within the particle system's update function). Lets go through this function bit
by bit (or, since this is a pretty large function, byte by byte):
bool PARTICLE::
Update(float time_counter)
{
static VERTEX3D attract_location;
static VECTOR3D attract_normal;
This is the start of our update function, we are going to be using the two variables shown here for our particle
attraction calculations (this is one of the FEW special effects that I have included within the engine, and it is for the
particle's attraction to the emitter).
// Age The Particle By The Time Counter
age+= time_counter;
if(age>=dying_age)
http://nehe.gamedev.net/gametutorials/lesson03.asp (5 of 14) [20/08/2001 22:34:18]