Has anyone here implemented this test before?
Basically I have run into a case where it does not say there will be collision, but that the same time it it does not say there is collision. However, there is indeed collision.
Here is my scenerio.
Sphere Origin (Base Point) : (1.5, 1.5, 0)
Velocity : (0, -1, 0)
Triangle Normal : (0, 1, 0)
Radius: 1
The next time step (one full second) the sphere will intersect with the triangle plane and there sphere origin should be (1.5, 0.5, 0). However, nothing will report as positive for collision. Does anyone know why?
Triangle:
Vertex One: (4.0f, 0.0f, 4.0f)
Vertex Two: (4.0f, 0.0f, 0.0f)
Vertex Three: (0.0f, 0.0f, 0.0f)
Here is all of my code, in case someone wants to look at it
D3DXVECTOR3 triangleNormal = triangle->GetNormal(); D3DXVECTOR3 triangleOrigin = triangle->GetVertexOne(); D3DXVECTOR3 sphereVelocity = sphere->GetVelocity(); D3DXVECTOR3 p1 = triangle->GetVertexOne(); D3DXVECTOR3 p2 = triangle->GetVertexTwo(); D3DXVECTOR3 p3 = triangle->GetVertexThree(); D3DXVECTOR3 vBasePoint = sphere->GetOrigin(); // Get interval of plane intersection: double t0, t1; bool embeddedInPlane = false; // Calculate the signed distance from sphere // position to triangle plane double signedDistToTrianglePlane; { double nDotOrigin = D3DXVec3Dot(&vBasePoint, &triangleNormal); signedDistToTrianglePlane = nDotOrigin + -(triangleNormal.x*triangleOrigin.x + triangleNormal.y*triangleOrigin.y + triangleNormal.z*triangleOrigin.z); } // cache this as we’re going to use it a few times below: float normalDotVelocity = D3DXVec3Dot(&triangleNormal, &sphereVelocity); // if sphere is travelling parrallel to the plane: if (normalDotVelocity == 0.0f) { if (fabs(signedDistToTrianglePlane) >= 1.0f) { // Sphere is not embedded in plane. // No collision possible: crCollisionResult.enCollisionState = RESTING_CONTACT; return crCollisionResult; } else { // sphere is embedded in plane. // It intersects in the whole range [0..1] crCollisionResult.enCollisionState = HAS_COLLISION; return crCollisionResult; embeddedInPlane = true; t0 = 0.0; t1 = 1.0; } } else { // N dot D is not 0. Calculate intersection interval: t0=(-1.0-signedDistToTrianglePlane)/normalDotVelocity; t1=( 1.0-signedDistToTrianglePlane)/normalDotVelocity; // Swap so t0 < t1 if (t0 > t1) { double temp = t1; t1 = t0; t0 = temp; } // Check that at least one result is within range: if (t0 > 1.0f || t1 < 0.0f) { // Both t values are outside values [0,1] // No collision possible: crCollisionResult.enCollisionState = NO_COLLISION; return crCollisionResult; } // Clamp to [0,1] if (t0 < 0.0) t0 = 0.0; if (t1 < 0.0) t1 = 0.0; if (t0 > 1.0f) t0 = 1.0f; if (t1 > 1.0f) t1 = 1.0f; } // OK, at this point we have two time values t0 and t1 // between which the swept sphere intersects with the // triangle plane. If any collision is to occur it must // happen within this interval. D3DXVECTOR3 collisionPoint; bool foundCollison = false; float t = dElapsedTime; // First we check for the easy case - collision inside // the triangle. If this happens it must be at time t0 // as this is when the sphere rests on the front side // of the triangle plane. Note, this can only happen if // the sphere is not embedded in the triangle plane. if (!embeddedInPlane) { D3DXVECTOR3 planeIntersectionPoint = (vBasePoint - triangleNormal) + t0 * sphereVelocity; if (checkPointInTriangle(planeIntersectionPoint, p1,p2,p3)) { foundCollison = true; t = t0; collisionPoint = planeIntersectionPoint; } } // if we haven’t found a collision already we’ll have to // sweep sphere against points and edges of the triangle. // Note: A collision inside the triangle (the check above) // will always happen before a vertex or edge collision! // This is why we can skip the swept test if the above // gives a collision! if (foundCollison == false) { // some commonly used terms: D3DXVECTOR3 velocity = sphereVelocity; D3DXVECTOR3 base = vBasePoint; float velocitySquaredLength = squaredLength(velocity); float a,b,c; // Params for equation float newT; // For each vertex or edge a quadratic equation have to // be solved. We parameterize this equation as // a*t^2 + b*t + c = 0 and below we calculate the // parameters a,b and c for each test. // Check against points: a = velocitySquaredLength; // P1 D3DXVECTOR3 vBaseMinusP1 = base - p1; b = 2.0*(D3DXVec3Dot(&velocity, &vBaseMinusP1)); c = squaredLength(p1-base) - 1.0; if (getLowestRoot(a,b,c, t, &newT)) { t = newT; foundCollison = true; collisionPoint = p1; } // P2 D3DXVECTOR3 vBaseMinusP2 = base - p2; b = 2.0*(D3DXVec3Dot(&velocity, &vBaseMinusP2)); c = squaredLength(p2-base) - 1.0; if (getLowestRoot(a,b,c, t, &newT)) { t = newT; foundCollison = true; collisionPoint = p2; } // P3 D3DXVECTOR3 vBaseMinusP3 = base - p3; b = 2.0*(D3DXVec3Dot(&velocity, &vBaseMinusP3)); c = squaredLength(p3-base) - 1.0; if (getLowestRoot(a,b,c, t, &newT)) { t = newT; foundCollison = true; collisionPoint = p3; } // Check agains edges: // p1 -> p2: D3DXVECTOR3 edge = p2-p1; D3DXVECTOR3 baseToVertex = p1 - base; float edgeSquaredLength = squaredLength(edge); float edgeDotVelocity = D3DXVec3Dot(&edge, &velocity); float edgeDotBaseToVertex = D3DXVec3Dot(&edge, &baseToVertex); // Calculate parameters for equation a = edgeSquaredLength*-velocitySquaredLength + edgeDotVelocity*edgeDotVelocity; b = edgeSquaredLength*(2.0*D3DXVec3Dot(&velocity, &baseToVertex))-2.0*edgeDotVelocity*edgeDotBaseToVertex; c = edgeSquaredLength*(1.0-squaredLength(baseToVertex))+edgeDotBaseToVertex*edgeDotBaseToVertex; // Does the swept sphere collide against infinite edge? if (getLowestRoot(a,b,c, t, &newT)) { // Check if intersection is within line segment: float f=(edgeDotVelocity*newT-edgeDotBaseToVertex)/edgeSquaredLength; if (f >= 0.0 && f <= 1.0) { // intersection took place within segment. t = newT; foundCollison = true; collisionPoint = p1 + f*edge; } } // p2 -> p3: edge = p3-p2; baseToVertex = p2 - base; edgeSquaredLength = squaredLength(edge); edgeDotVelocity = D3DXVec3Dot(&edge, &velocity); edgeDotBaseToVertex = D3DXVec3Dot(&edge, &baseToVertex); a = edgeSquaredLength*-velocitySquaredLength + edgeDotVelocity*edgeDotVelocity; b = edgeSquaredLength*(2.0f*D3DXVec3Dot(&velocity, &baseToVertex))-2.0*edgeDotVelocity*edgeDotBaseToVertex; c = edgeSquaredLength*(1.0f-squaredLength(baseToVertex))+edgeDotBaseToVertex*edgeDotBaseToVertex; if (getLowestRoot(a,b,c, t, &newT)) { float f=(edgeDotVelocity*newT-edgeDotBaseToVertex)/ edgeSquaredLength; if (f >= 0.0 && f <= 1.0) { t = newT; foundCollison = true; collisionPoint = p2 + f*edge; } } // p3 -> p1: edge = p1-p3; baseToVertex = p3 - base; edgeSquaredLength = squaredLength(edge); edgeDotVelocity = D3DXVec3Dot(&edge, &velocity); edgeDotBaseToVertex = D3DXVec3Dot(&edge, &baseToVertex); a = edgeSquaredLength*-velocitySquaredLength + edgeDotVelocity*edgeDotVelocity; b = edgeSquaredLength*(2.0*D3DXVec3Dot(&velocity, &baseToVertex))-2.0*edgeDotVelocity*edgeDotBaseToVertex; c = edgeSquaredLength*(1.0-squaredLength(baseToVertex))+edgeDotBaseToVertex*edgeDotBaseToVertex; if (getLowestRoot(a,b,c, t, &newT)) { float f=(edgeDotVelocity*newT-edgeDotBaseToVertex)/ edgeSquaredLength; if (f >= 0.0 && f <= 1.0) { t = newT; foundCollison = true; collisionPoint = p3 + f*edge; } } }
