Help with raycast

[KingSnail]

Can someone please share some code of your ray cast function if you are using directx,
I have been stuck on this problem for months, tried a million different ways of making rays, nothing works

[Julio Jerez]

If you post the function you wrote to inteface with the Raycast, I may be able to help you out?

Basically it is a matter of setting a call back and douns soem trival vetor scaling.

[Stucuk]

It shouldn't make any difference if you are using Direct X or OpenGL. All you basically do is give it 2 3D coordinates. As long as you use only one type of coordinate system for the Rays as well as the actual collisions themself, it should work fine. You should be able to just copy and paste the raycast part of a newton tutorial and modify it.

The following is an example of the code im using:

Prefilter/Filter Callbacks

Code: Select all

function RayPrefilterCallback(const body : PNewtonBody; const collision : PNewtonCollision; userData : Pointer) : cardinal; cdecl;
begin
 Result := 1;
end;

var
PickedParam : Float;
PickedBody  : PNewtonBody;

function RayFilterCallback( const body : PNewtonBody; const hitNormal: PFloat; collisionID : Int; userData: Pointer; intersetParam: Float ) : Float; cdecl;
begin
 if intersetParam < PickedParam then
 begin
  PickedParam := intersetParam;
  PickedBody  := body;
 end;
 Result := intersetParam;
end;

RayCast

Code: Select all

PickedBody  := Nil;
PickedParam := 1.1;
NewtonWorldRayCast(World,Point1,Point2,@RayFilterCallback,Nil,@RayPrefilterCallback);

[KingSnail]

I tried using the tutorial it uses gluunproject, I tried the directx version of it D3DXVec3Unproject, I dont really understand it, it needs a world matrix of something? The way I understand it is I have a world matrix for every object in the world.
So does that mean I need to loop through all my objects? confused :S

I also tried just using simple vectors to plug into the newton raycasting function

D3DXVECTOR3 p0(10.0f, 5.0f, 0.0f);
D3DXVECTOR3 p1(10.0f, 5.0f, 1000.0f);

Those are both in global space ? I think, I draw them like this in the world just by making a line using those 2 vertices.

It clearly intersects a body:



But it doesnt detect that its a mass 1 object.
The way I filter it is that the level walls have mass 0 and all objects are above 0, here is my filter

Code: Select all

static unsigned RayCastPrefilter (const NewtonBody* body,  const NewtonCollision* collision, void* userData)
{
   //if(NewtonCollisionIsTriggerVolume(collision))return 0;

   dFloat mass;
   dFloat Ixx;
   dFloat Iyy;
   dFloat Izz;
   NewtonBodyGetMassMatrix (body, &mass, &Ixx, &Iyy, &Izz);

   extern float Display;
   Display = mass; //Prints to the screen, the mass, so if it says 1 then theres a collision with a chair, if 0 then its level

   return (mass > 0.0f) ? 1 : 0;
}


I also tried using the code from http://www.toymaker.info/Games/html/picking.html, Doesnt seem to give me any results either.

Sometimes I do see a 1 and I get happy but its not where my ray is drawn.

[Julio Jerez]

I think we are getting confused here.

You said that you have a problem with ray casting, but by your description it seemes you are having problems
tryin to pick an object from the screen by shooting a ray from the cursor to the back of the frame buffer.

Basically your problem is that you do not know how to transform the points from screen space to world space. Is this correct?
we need to clarify the problem so that the solution is effective.

ther are two problems. Picking and ray casting.
I can help you with both. But first I need to kknow if the ray casting is wroking at all.
if you place a box in the world in hard code position (say teh origin) and you racy cast from pointe you know will interset the Box does the ray Works?

[Stucuk]

Your RayCastPrefilter is flawd. The prefilter will be sent everything that it collides with, so if your line goes through both a wall and a chair then the display float may say 0 even if it passes through a chair (Assuming the Wall is found last). Your code should be more like the following, with Display set to 0 before the NewtonWorldRaycast is called.

Code: Select all

if (mass > 0.0f) Display = mass; //Prints to the screen, the mass, so if it says 1 then theres a collision with a chair, if 0 then its level

[KingSnail]

Thanks for replies, Stucuk you were right, it was flawed, I corrected it how you said, now what seems to happen is that
simple collision shapes like balls and cones trigger using those 2 points I said in earlier post, but the chair still does not trigger,
the chair is a compound collision. Weird

Julio: Thanks for help also, I did what you said after I fixed my filter and everything works except... for the damn compound collision, I cant figure out why because everything works as it should.
So I need to somehow fix that and also cast the ray from center of the screen outward, not just at origin

-Edit: also the chair as a convex hull collision works, just not compound collision chair

[Julio Jerez]

Good to here you are getting some result,
Ray cast should work with all all collision shapes, even compound.

[KingSnail]

I cant get the compound collision to be detected by ray, Any tips on what to do?

[Stucuk]

Have you implemented a debug display that can draw the collision shapes on the screen so you can be sure that everything is setup right?

[Julio Jerez]

debug display is your best friend when thongs do not look liek the should.

My guess is tha teh shape are not where you think they are.

[KingSnail]

I have debug shapes, everything is perfect. and performs as it should, just cant think of what to try anymore

[JernejL]

There were some versions of 2.x releases where raycasting did not work properly in some situations, make sure you have the latest one.

If this is a bug i suggest you make a test case demo for Julio.

[Julio Jerez]

yes that is right, makw sure you hav eteh later version.

and if you can send me a test demo I can debug it for you.