math help

[Cloud9_]

What do I need to know for the following?

I am trying to build a particle system with various effects. I have a fireworks like explosion, but trying to get a 'cone' effect is a little rougher for me right now.

I want to be able to pass the direction of the cone (between 1 and 360 degrees) the intensity of the particles (how fast they shoot out of the emitter), and the degree of the cone mouth (for example, the particles can be shot anywhere from 10 degrees to 25 degrees from the emitter)

I am using XNA right now, so I have a position vector, and velocity vector, how would I come up with the velocity vector? Tried a few things but not sure what type of math is involved

Can anyone point me in the right direction?

[Cloud9_]

Think i got it;

        
private static Vector2 SetParticleVelocity(float direction, float directionRange, float speed)
        {

            speed = RNG.GetRandomFloat(.01f, speed);

            return new Vector2(
                speed * (float)Math.Sin(RNG.GetRandomFloat(direction, directionRange)),
                speed * (float)Math.Cos(RNG.GetRandomFloat(direction, directionRange)));

an amendment to the code, to get it to behave more like I wanted to;

private static Vector2 SetParticleVelocity(float direction, float directionRange, float speed)
        {
            direction = MathHelper.ToRadians(direction);
            directionRange = MathHelper.ToRadians(directionRange);

            float randomDirection = RNG.GetRandomFloat(direction - (directionRange / 2), direction + (directionRange / 2));

            speed = RNG.GetRandomFloat(.01f, speed);            

            return new Vector2(
                (float)Math.Sin(randomDirection) * speed,
                (float)Math.Cos(randomDirection) * speed);
        }

This way you can tell it what direction you want to fire, and also how big the cone you want to fire. The first method, you had to specify the first line and the 2nd line and it will fire particles between the two.

I guess the next step is to make an enum to make it easier to fire "Up, Right, Down, Left, Up/Right, Up/Left" etc etc

[Szlia]

I am not sure what you want to do, but currently the particle distribution is homogenous in the angle, so depending on what you are trying to do, it might look better if there is a higher particle density in the middle. There are probably dozens of clever way to code that, but here is a brute force dumb way to do it I think:

float randomDirection = RNG.GetRandomFloat(direction - (directionRange / 2) + RNG.GetRandomFloat(0, directionRange/2), direction + (directionRange / 2)- RNG.GetRandomFloat(0, directionRange/2));

[Cloud9_]

Originally Posted by Szlia

I am not sure what you want to do, but currently the particle distribution is homogenous in the angle, so dpeneding on what you are trying to do, it might look better if there is a higher particle density in the middle. There are probably dozens of clever way to code that, but here is a brute force dumb way to do it I think:

float randomDirection = RNG.GetRandomFloat(direction - (directionRange / 2) + RNG.GetRandomFloat(0, directionRange/2), direction + (directionRange / 2)- RNG.GetRandomFloat(0, directionRange/2));

I'll plug that in when I get home from work in a few hours... thanks