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Ray pick ?

Started by Mythar Apr 5, 2005 at 9:38 AM 6 replies 1.5k views

Original Post

Apr 5, 2005 at 9:38 AM

Hi all, i was trying to add ray picking to my terrain, but i cant get it to work.


  GetTransform(D3DTS_PROJECTION, m);
  GetViewport(vp);

  v.x :=  ( ( ( 2.0 * x ) / vp.Width ) - 1 ) / m._00;
  v.y := -( ( ( 2.0 * y ) / vp.Height ) - 1 ) / m._11;
  v.z :=  1.0;

  GetTransform(D3DTS_VIEW, m2);
  D3DXMatrixInverse( m, nil, m2);

  rayDir.x := v.x*m._00 + v.y*m._10 + v.z*m._20;
  rayDir.y := v.x*m._01 + v.y*m._11 + v.z*m._21;
  rayDir.z := v.x*m._02 + v.y*m._12 + v.z*m._22;
  rayOrigin.x := m._30;
  rayOrigin.y := m._31;
  rayOrigin.z := m._32;

  GetTransform(D3DTS_WORLD, m2);
  D3DXMatrixInverse( m, nil, m2);

  D3DXVec3TransformCoord(rayObjOrigin, rayOrigin, m);
  D3DXVec3TransformNormal(rayObjDir, rayDir, m);
  D3DXVec3Normalize(rayObjDir, rayObjDir);

did I overlook something ?

matthughson

Apr 5, 2005 at 12:58 PM

Since you haven't got a response yet, I'll just post a potentially unhelpful link: Ray Picking.

It's the tutorial I used to get picking working, and aside from some updating from the old D3DMath_ functions, I was able to get things working with no probalems.

So take a look, and maybe you can compare your code to it.

Matt Hughson

Mythar

Author

Mythar

Apr 6, 2005 at 9:26 AM

Thx Matt, this helped.

However I have a few things I would like to be able to do.

First I would like to be able to extract the FOV,NEAR and FAR, directly from
the PROJECTION matrix. (as I would like this to work for any PROJECTION used, how do I do that ? )

The ASPECT I can get by using GetViewport, ( Width / Height ).

2ndly I would need to Transform the p1 and p2 according to the WORLD (model space) matrix.

Lord_Taren

Apr 6, 2005 at 11:00 AM

Here is the function I created to do the ray picking for me. It's written in c#. The function calculates a picking ray based on a set of screen coordinates. I hope this helps. If you have any questions, let me know.

//*****************************************************************************
//* calcPickingRay
//*
//* Calculate a Picking ray based on a set of screen coordinates.
//*****************************************************************************
private rdRay calcPickingRay(System.Int32 x, System.Int32 y)
{
Direct3D.Viewport vp;
DirectX.Matrix proj;

rdRay xTmpRay;

System.Single px = 0.0f;
System.Single py = 0.0f;

//* Get the viewport and the projection matrix
vp = m_dxDevice.Viewport;
proj = m_dxDevice.Transform.Projection;

px = (((2.0f * x) / vp.Width) - 1.0f) / proj.M11;
py = (((-2.0f * y) / vp.Height) + 1.0f) / proj.M22;

xTmpRay = new rdRay();
xTmpRay.origin = new Vector3(0, 0, 0);
xTmpRay.direction = new Vector3(px, py, 1);

return xTmpRay;
}

Here's the definition of rdRay
//*****************************************************************************
//* rdRay
//*
//* A ray contains an origin and a direction.
//*****************************************************************************
public struct rdRay
{
public DirectX.Vector3 origin;
public DirectX.Vector3 direction;
};

matthughson

Apr 6, 2005 at 11:14 AM

Quote:
Original post by Mythar
First I would like to be able to extract the FOV,NEAR and FAR, directly from
the PROJECTION matrix. (as I would like this to work for any PROJECTION used, how do I do that ? )

Hmm, does your FOV and clipping planes change dynaically in game? I don't see why they would (maybe FOV if u have a zoom feature), but if not can't you just save them when you initialize Direct3D?

Quote:
Original post by Mythar
2ndly I would need to Transform the p1 and p2 according to the WORLD (model space) matrix.

I can't seem to find what p1 and p2 represent in that question?

Also, here's my function for creating a ray from a point in pixel space. It's based on a tutorial out there; not sure which one though =(

void pixelToWorld(float x, float y, D3DXVECTOR3 &rayDir, D3DXVECTOR3 &rayOrigin){	// Singletons	CDX_D3DWrapper* pD3DMan		= CDX_D3DWrapper::getInstance();	CDX_Text* pTxtMan			= CDX_Text::getInstance();	CDX_Camera* pCamMan			= CDX_Camera::getInstance();	// Get the screen res	D3DXVECTOR2 v2WindDim		= pD3DMan->getWindowDimensions();	D3DXVECTOR2 v2WindDimHalf	= v2WindDim * 0.5f;	// Get the aspect ration	float fAspect = v2WindDim.x / v2WindDim.y;	D3DXVECTOR3 v;	v.x =  ( ( ( 2.0f * x ) / v2WindDim.x ) - 1 ) / pD3DMan->m_matProj._11;	v.y = -( ( ( 2.0f * y ) / v2WindDim.y ) - 1 ) / pD3DMan->m_matProj._22;	v.z =  1.0f;		D3DXMATRIXA16 m;	D3DXMATRIX matView;	pCamMan->getMatrix(&matView);	D3DXMatrixInverse( &m, NULL, &matView );	// Transform the screen space pick ray into 3D space	rayDir.x  = v.x*m._11 + v.y*m._21 + v.z*m._31;	rayDir.y  = v.x*m._12 + v.y*m._22 + v.z*m._32;	rayDir.z  = v.x*m._13 + v.y*m._23 + v.z*m._33;	rayOrigin.x = m._41;	rayOrigin.y = m._42;	rayOrigin.z = m._43;	D3DXVec3Normalize(&rayDir, &rayDir);}

Let me know how things go!
Matt Hughson

Mythar

Author

Mythar

Apr 7, 2005 at 9:19 AM

OK here is what i got so far.

Method 1:

  GetTransform(D3DTS_PROJECTION, m);  GetViewport(vp);  v.x :=  ( ( ( 2.0 * x ) / vp.Width ) - 1 ) / m._11;  v.y := -( ( ( 2.0 * y ) / vp.Height ) - 1 ) / m._22;  v.z :=  1.0;   GetTransform(D3DTS_VIEW, matView);  D3DXMatrixInverse( m, NULL, matView );  rayDir.x  := v.x*m._11 + v.y*m._21 + v.z*m._31;  rayDir.y  := v.x*m._12 + v.y*m._22 + v.z*m._32;  rayDir.z  := v.x*m._13 + v.y*m._23 + v.z*m._33;  rayOrigin.x := m._41;  rayOrigin.y := m._42;  rayOrigin.z := m._43;

Method 2:

  GetViewport(vp);  ASPECT := vp.Width / vp.Height;  // FOV in rads  dx := tan(FOV*0.5)*(x/(vp.Width*0.5)-1.0)/ASPECT;  dy := tan(FOV*0.5)*(1.0-y/(vp.Height*0.5));  GetTransform(D3DTS_VIEW, matView);  D3DXMatrixInverse( m, NULL, matView );  rayOrigin := Vector(dx*NEAR,dy*NEAR,NEAR);  rayDir := Vector(dx*FAR,dy*FAR,FAR);  VectorMatrixMultiply(rayOrigin,rayOrigin,m);  VectorMatrixMultiply(rayDir,rayDir,m);  rayDir := DirectionVector(rayDir,rayOrigin);

When using M1 : Im forced to use D3DXMatrixPerspectiveFovLH, to make it work.

When using M2 : I can use any projection matrix i want, BUT it only works on "Y", the "x" aspect is not correct (it's too "wide").

I would prefer to use M2, as this gives me more freedom when it comes to the projection matrix.

I usealy create my projection matrix like this :

  c := cos(fov*0.5);  s := sin(fov*0.5);  Q := s/(1.0 - near_plane/far_plane);  ZeroMemory(@m, sizeof(D3DMATRIX));  m._11 := c;  m._22 := c;  m._33 := Q;  m._43 := -Q*near_plane;  m._34 := s;

I now need to figure out why M2 mess up on the "x" aspect ??

Mythar

Author

Mythar

Apr 7, 2005 at 9:58 AM

hmm, it seems there was a bug in the ray pick link (http://www.mvps.org/directx/articles/rayproj.htm) you posted.

That tut. calc. dx as :
dx=tan(FOV*0.5f)*(x/WIDTH_DIV_2-1.0f)/ASPECT

But it seems that it should have been :
dx=tan(FOV*0.5f)*(x/WIDTH_DIV_2-1.0f)

This seems to fix the "x" aspect :)

Now I only need to take the WORLD matrix into account also ?

Instruo

Apr 7, 2005 at 10:08 AM

tag

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