Math Problem

[Dying]

I've got a question for all the math/trig geniuses.

I am attempting to achieve an accurate reflection of velocity when my pawn contacts a surface (angled surfaces included).

I am getting the normal of what i contact.

cNorm=HitNormal.X;

set the new velocity variables to use when getting the angle..

veloX = Velocity.X;
veloZ = Velocity.Z;

then I'm converting my velocity to an angle in radians, and then converting that to degrees(for testing)..

angleInRadians = atan2 (veloZ, veloX);
angleInDegrees = angleInRadians * 180 / PI;

then multiplying the normal by 2 and subtracting the angle to get the new reflected angle and turn it back into a radian..

nAng = cNorm*2-angleInDegrees;
nRad = nAng*PI/180;

I can not find a way to convert radians back into velocity.. so I am trying to get the new reflected velocity from the angle in degrees..

V = Sqrt((veloX*veloX)+(veloZ*veloZ));
velocx= cos(nAng)*V;
velocZ = Sqrt((V*V)-(veloX*veloX));

Finally I set the pawns velocity to equal the new reflected velocity.

Velocity.Z=velocZ;
Velocity.X=velocX;

I am doing something wrong and often get sporadic results..if anyone sees where I am going astray please help by pointing it out or how I should go about doing it.

thank you,
-Dying

[Wormbo]

Are we talking about in=out angles? In that case you might want to try:

Velocity = MirrorVectorByNormal(Velocity, HitNormal);

If you want to factor in dampening, the UT games use variations of the following formula:

    VNorm = (Velocity dot HitNormal) * HitNormal;
    Velocity = -VNorm * DampenFactor + (Velocity - VNorm) * DampenFactorParallel;

The MirrorVectorByNormal function basically does that calculation with the two dampening factors being 1.

[Dying]

Wow I did not know unreal had this! thank you so much wormbo, this saves me alot of time and headaches

[Dying]

hmm wondering if anyone knows why when the angle im bouncing off of is over 60 degrees(so unreal reads it as a wall) the new reflection doesn bounce off correctly.. if the angle is 90 degrees the pawn doesnt bounce off at all, it actually stops and floats up..?

[toxicFork]

Are we talking about in=out angles? In that case you might want to try:

Velocity = MirrorVectorByNormal(Velocity, HitNormal);

Oh god, I didn't see this, so I had to make it on my own. :P

/** Vector reflection of a based on normal vector b*/
function vector rV(Vector a, vector b){
	return 2 * (-a.x * b.x + -a.y * b.y + -a.z * b.z) * b + a;
}

[Dying]

hey toxicFork have you ever had a similar problem where this formula doesn't work if the Normal.X is between 60 to 90 degrees?

[Wormbo]

You really should have looked up available operators and functions.
UnrealWiki: Vector sums up the built-in vector operations, in case you need more.

[toxicFork]

Dying, I don't know, it worked pretty well for me.
Normal.X isn't in degrees btw, paste your code so we can see what's going wrong

[Wormbo]

Well, if you really want to see an angle in a normal vector component, then Normal.X is the cosine of the normal's angle from the YZ plane. For reflections this is an absolutely useless piece of information, though.

[Dying]

ah i figured out my problem, I was only applying the new velocity to the Z velocity when hitting a wall and not the X..

thanks guys, you got my project back on its way to completion