Direction Vector to Plane Calculation

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Hello, I have a question about calculating a direction vector based on the plane my player is standing on. I was planning on using the plane's normal and 90 degrees to that to calculate the direction vector on the plane the player is standing on. _________ <--- this planes normal is 0,1,0 ..../ .../ ../ <--- this planes normal is 0,.5,.5 ./ / How do I get the direction vector to calculate perpendicular to the planes normal? I'd like to adjust the direction vector with the vector resulting from this calulation. Should I use some algebra and find the vector based on a dot value and a vector? My rendering engine works great as long as the surface planes are flat. I tried using the cross product of a right vector and the planes normal but that didn't work to well. Player stair stepped up the smooth plane. Camera bounced up and down a bit. Is there an industry norm that I should be using? Thanks in advance for your reply. I still get a little camera bounce with this code as well and the player digs into the plane at the top of the plane. Here's a code snippet of what I have:
if (gsPlayer.playerState == PLAYER_FORWARD )
{
gsPlayer.m_Dir.x = gcCamera.m_LookAt.x;
gsPlayer.m_Dir.y = gcCamera.m_LookAt.y;
gsPlayer.m_Dir.z = gcCamera.m_LookAt.z;

gsPlayer.m_Velocity.x = VELOCITY;
gsPlayer.m_Velocity.z = VELOCITY;

for (x=0; x &lt; MAX_PLANE_COUNT; x++)
{
if (gsPlane[x].isActive == 1 )
{
gcCollision.PlayerToPlane(&gsPlayer, &gsPlane[x]);
}
}
if ( gcCollision.dPlaneHit )
{
if ( (gcCollision.dot_d &lt; 0.50f) && (gcCollision.dot_d &gt; 0.00f))
{
// gravity change player going up a plane
gsPlayer.m_Velocity.y = -GRAVITY;

gsPlayer.m_Dir.x = gcCollision.dPlaneNormal.x;
gsPlayer.m_Dir.y -= gcCollision.dPlaneNormal.y;
gsPlayer.m_Dir.z = gcCollision.dPlaneNormal.z;
gcMath.VectNormalize(&gsPlayer.m_Dir, &gsPlayer.m_Dir);
}
}

//additional plane checking for other plane collisions


One final note, there is no bounce of the camera when the forward vector of the camera is at (0,0,-1). Player just goes up the plane a little slower than when on a level plane. [Edited by - HackSaw220 on November 16, 2006 10:32:10 PM]

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First, use [ code ] and [ source ] tags for source code. (they do slightly different things).

Quote:
 Hello, I have a question about calculating a direction vector based on the plane my player is standing on. I was planning on using the plane's normal and 90 degrees to that to calculate the direction vector on the plane the player is standing on.

There is no "the direction vector of the plane". Planes are two-dimensional.

Maybe I just don't understand what it is you are trying to do.

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I'm trying to get my player to clip properly on a plane that is sloped.
So, if you are looking straight ahead on a flat plane the plane is level.

If you are going up a hill there is a slope.

Moving forward is the direction vector so this vector's Y value (and the two others x and z ) would need to be adjusted so the player goes upward and have gravity applied at the same time so they don't go flying up into the air.

I'm just looking for a way to adjust the players direction vector parallel to the plane they are standing on along with the direction the camera is orientated.

Perhaps when I calculate the planes normal I should keep track of the two vectors I cross to get the normal? Then use those to determine a vector to adjust the players direction vector?

Did I just answer my own question? O-o

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(plane_normal ^ walking_direction) ^ plane_normal
or
plane_normal ^ (plane_normal ^ walking_direction)

^ is vector cross product,

I might be wrong about the order of the cross product but I seems to remember something like that works.

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Thanks, I think thats what I've been looking for.

Looks like that would work to adjust the Y.

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Still bouncing. Using the planes y normal seems to work.

I think it's bouncing is due to the gravity stuff I'm doing. Looks like the player breaks through the plane and then get's pushed back up out of it and that gets rendered as it's happening.

Thanks for the help.

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Often enough, you can get away with moving the player in the direction he's facing, paying no attention to collisions, then apply gravity and floor-bounding afterwards to reposition him.

If the player is under the constant downwards acceleration of gravity, and is, each frame, checked against the plane by something along the lines of:
float ground_y = GroundY(player.x, player.z);if (player.y < ground_y) player.y = ground_y
then there's no need to mess about with directional derivatives and cross-products.

Regards

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Took an alternative approach. Little more CPU intensive but works for both flat ground planes and angled. Works real smooth too. There is a slight camera bounce when up against a wall but it's barely noticeable unless you are really looking for it. I'm merely popping the player back up out of the ground plane.

	gsPlayer.m_Velocity.y = 0;	gsPlayer.m_Dir.y = 0;	int inPlane = 1;	for (x = 0; x < MAX_PLANE_COUNT; x++)	{		gsPlayer.m_Velocity.y = GRAVITY;		gsPlayer.m_Dir.y = -1.0f;		if (gsPlane[x].isActive == 1 )		{			gcCollision.PlayerToPlane(&gsPlayer, &gsPlane[x]);			if ( gcCollision.dPlaneHit )			{				while (inPlane)				{					gsPlayer.m_Dir.y = 1.0f;					gsPlayer.m_Velocity.y = 0.125f;					gcPlayer.UpdatePosition(&gsPlayer);					gcCollision.dPlaneHit = 0;					gcCollision.PlayerToPlane(&gsPlayer, &gsPlane[x]);					if (!gcCollision.dPlaneHit)					{						gsPlayer.m_Velocity.y = 0.0f;						break;					}				}			}		}	}

Now if I could just get my darn camera to work decent I'll be good to go.

Thanks for all the input. :-)

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