Collision (SweepAndSlide)

[Daniel]

Hello everyone!

I'm trying to use this procedure for collision handling of my fps-camera.
It works nicely in general! But when I try to use it for a FPS-camera on a moving object (a ship), then it fails some times.
The camera is a child of the ship model, so it follows the ships movement, so maybe the sweepAndSlide procedure uses absolute vectors which causes the camera to jump over obstacles when the ship is rolling/pitching?
Any idea what to change to make it work with local vectors?
I do not need the camera to move in the Y direction, only X and Z, so maybe it can be made 2 dimensional?

Kind regards,
Daniel

procedure TForm1.SphereSweepAndSlide(freeform:TGLFreeform;SphereStart:TVector;var Velocity,newPosition:TVector;SphereRadius:Single);
var
  oldPosition, ray:TVector;
  vel,slidedistance:Single;
  intPoint,intNormal:TVector;
  newDirection, newRay,collisionPosition, pointOnSphere,point2OnSphere:TVector;
  i:integer;
  CollisionState:TCollisionState;
  NegNormalizedVelocity:TVector;
begin
  oldPosition:=SphereStart;

  //Direction sphere is moving in
  ray:=VectorSubtract(newPosition,oldPosition);
//  ray:=Velocity;
//  newPosition:=VectorAdd(newPosition,ray);
  //Speed of sphere
  vel:=VectorLength(ray);

  //if the Sphere is not moving, nothing is required
  // else do up to 7 loops

  if vel>0 then
  for i:=0 to 6 do
  begin
    //if an intersection occurs, will need to do further calculations
    if (freeform.OctreeSphereSweepIntersect(oldPosition,ray,vel,SphereRadius,@intPoint,@intNormal)) then
    begin
      if VectorDistance2(oldPosition,intPoint)<=sqr(SphereRadius) then
      begin
        //sphere is intersecting triangle
        intNormal:=VectorScale(VectorSubtract(oldPosition,intPoint),1.0001);
      end
      else
      begin
        //sphere is not intersecting triangle
        //intNormal:=VectorSubtract(oldPosition,intPoint);  //not correct but works okay at small time steps
        //intNormal:=VectorScale(VectorNormalize(intNormal),SphereRadius+0.0001);
        if RayCastSphereIntersect(intPoint,VectorNormalize(VectorNegate(ray)),oldPosition,SphereRadius,PointOnSphere,Point2OnSphere)>0 then
          intNormal:=VectorScale(VectorSubtract(oldPosition,PointOnSphere),1.0001)
          //intNormal:=VectorScale(VectorNormalize(VectorSubtract(oldPosition,PointOnSphere)),SphereRadius+0.001)//VectorDistance(oldPosition,PointOnSphere));
        else
        begin
//          Assert(False);  //this shouldn't happen (this is here for debugging)
          intNormal:=VectorScale(VectorSubtract(oldPosition,intPoint),1.0001);
        end;

      end;

      //calculate position of centre of sphere when collision occurs
      collisionPosition:=VectorAdd(intPoint,intNormal);
      oldPosition:=collisionPosition;

      //calculate distance that wasn't travelled, due to obstacle
      newRay:=VectorSubtract(newPosition,collisionPosition);

      //calculate new direction when a wall is hit (could add bouncing to this)
      newDirection:=VectorCrossProduct(intNormal,VectorCrossProduct(newRay,intNormal));
      if VectorNorm(NewDirection)>0 then
        NormalizeVector(newDirection);

      //calculate distance that it should slide (depends on angle between plane & ray)
      SlideDistance:=vectorDotProduct(newRay,newDirection);
      //still need to implement friction properly
//      if abs(SlideDistance)<10*deltaTime then SlideDistance:=0;
      ScaleVector(newDirection,SlideDistance);

      //calculate new position sphere is heading towards
      newPosition:=VectorAdd(collisionPosition,newDirection);
      ray:=newDirection;
      vel:=VectorLength(ray);

 {     //display arrows for collision normals & slide direction
      if i=0 then
      //  DrawArrows(intPoint,intNormal,Ray, GLArrowLine1, GLArrowLine4)
      else if i=1 then
      //  DrawArrows(intPoint,intNormal,Ray, GLArrowLine2, GLArrowLine5)
      else if i=2 then
       // DrawArrows(intPoint,intNormal,Ray, GLArrowLine3, GLArrowLine6)
      else if i=6 then
      begin
//        caption:=FloatToStr(vectordistance(newPosition,oldPosition));
        newPosition:=oldPosition;
        break;
      end;           }

      //check if very small motion (e.g. when stuck in a corner)
      if vel<1E-10 then//deltaTime then
      begin
        newPosition:=oldPosition;
        break;
      end;

     {
      CollisionState:=TCollisionState.Create();
      CollisionState.Position:=oldPosition;
      CollisionState.Contact.intNormal:=intNormal;
      CollisionState.Contact.intPoint:=intPoint;
      CollisionState.Time:=GetTickCount64();

      CollisionStates.Add(CollisionState);    }

    end
    else //no collision occured, so quit loop
    begin
      Break;
    end;
  end; //end i loop
  Velocity:=Ray;
end;

[Daniel]

Hi gents!

I found my problem as well as a simple solution for the local issue!
First of all I used Scale instead of autoScaling for the model, this seems to have made "holes" in the freeForm.
Secondly I let the collision model stay at postion 0,0,0 and use global position vectors, while my camera onboard the moving ship uses local position vectors. Then when I move onboard the ship, a sphere is moving inside the global collision model and my camera gets it's position from the sphere.
So player local position := collision Spheres global position.

Cheers!