internal override RayHitTestParameters RayFromViewportPoint(Point p, Size viewSize, Rect3D boundingRect, out double distanceAdjustment) { // The camera may be animating. Take a snapshot of the current value // and get the property values we need. (Window OS #992662) Point3D position = Position; Vector3D lookDirection = LookDirection; Vector3D upDirection = UpDirection; Transform3D transform = Transform; double zn = NearPlaneDistance; double zf = FarPlaneDistance; double fov = M3DUtil.DegreesToRadians(FieldOfView); // // Compute rayParameters // // Find the point on the projection plane in post-projective space where // the viewport maps to a 2x2 square from (-1,1)-(1,-1). Point np = M3DUtil.GetNormalizedPoint(p, viewSize); // Note: h and w are 1/2 of the inverse of the width/height ratios: // // h = 1/(heightDepthRatio) * (1/2) // w = 1/(widthDepthRatio) * (1/2) // // Computation for h is a bit different than what you will find in // D3DXMatrixPerspectiveFovRH because we have a horizontal rather // than vertical FoV. double aspectRatio = M3DUtil.GetAspectRatio(viewSize); double halfWidthDepthRatio = Math.Tan(fov / 2); double h = aspectRatio / halfWidthDepthRatio; double w = 1 / halfWidthDepthRatio; // To get from projective space to camera space we apply the // width/height ratios to find our normalized point at 1 unit // in front of the camera. (1 is convenient, but has no other // special significance.) See note above about the construction // of w and h. Vector3D rayDirection = new Vector3D(np.X / w, np.Y / h, -1); // Apply the inverse of the view matrix to our rayDirection vector // to convert it from camera to world space. // // NOTE: Because our construction of the ray assumes that the // viewMatrix translates the position to the origin we pass // null for the Camera.Transform below and account for it // later. Matrix3D viewMatrix = CreateViewMatrix(/* trasform = */ null, ref position, ref lookDirection, ref upDirection); Matrix3D invView = viewMatrix; invView.Invert(); invView.MultiplyVector(ref rayDirection); // The we have the ray direction, now we need the origin. The camera's // position would work except that we would intersect geometry between // the camera plane and the near plane so instead we must find the // point on the project plane where the ray (position, rayDirection) // intersect (Windows OS #1005064): // // | _.> p = camera position // rd _+" ld = camera look direction // .-" |ro pp = projection plane // _.-" | rd = ray direction // p +"--------+---> ro = desired ray origin on pp // ld | // pp // // Above we constructed the direction such that it's length projects to // 1 unit on the lookDirection vector. // // // rd _.> // .-" rd = unnormalized rayDirection // _.-" ld = normalized lookDirection (length = 1) // -"---------> // ld // // So to find the desired rayOrigin on the projection plane we simply do: Point3D rayOrigin = position + zn * rayDirection; rayDirection.Normalize(); // Account for the Camera.Transform we ignored during ray construction above. if (transform != null && transform != Transform3D.Identity) { Matrix3D m = transform.Value; m.MultiplyPoint(ref rayOrigin); m.MultiplyVector(ref rayDirection); PrependInverseTransform(m, ref viewMatrix); } RayHitTestParameters rayParameters = new RayHitTestParameters(rayOrigin, rayDirection); // // Compute HitTestProjectionMatrix // Matrix3D projectionMatrix = GetProjectionMatrix(aspectRatio, zn, zf); // The projectionMatrix takes camera-space 3D points into normalized clip // space. // The viewportMatrix will take normalized clip space into // viewport coordinates, with an additional 2D translation // to put the ray at the rayOrigin. Matrix3D viewportMatrix = new Matrix3D(); viewportMatrix.TranslatePrepend(new Vector3D(-p.X, viewSize.Height - p.Y, 0)); viewportMatrix.ScalePrepend(new Vector3D(viewSize.Width / 2, -viewSize.Height / 2, 1)); viewportMatrix.TranslatePrepend(new Vector3D(1, 1, 0)); // `First world-to-camera, then camera's projection, then normalized clip space to viewport. rayParameters.HitTestProjectionMatrix = viewMatrix * projectionMatrix * viewportMatrix; // // Perspective camera doesn't allow negative NearPlanes, so there's // not much point in adjusting the ray origin. Hence, the // distanceAdjustment remains 0. // distanceAdjustment = 0.0; return(rayParameters); }
internal override RayHitTestParameters RayFromViewportPoint(Point p, Size viewSize, Rect3D boundingRect, out double distanceAdjustment) { // The camera may be animating. Take a snapshot of the current value // and get the property values we need. (Window OS #992662) Point3D position = Position; Vector3D lookDirection = LookDirection; Vector3D upDirection = UpDirection; double zn = NearPlaneDistance; double zf = FarPlaneDistance; double width = Width; // // Compute rayParameters // // Find the point on the projection plane in post-projective space where // the viewport maps to a 2x2 square from (-1,1)-(1,-1). Point np = M3DUtil.GetNormalizedPoint(p, viewSize); double aspectRatio = M3DUtil.GetAspectRatio(viewSize); double w = width; double h = w / aspectRatio; // Direction is always perpendicular to the viewing surface. Vector3D direction = new Vector3D(0, 0, -1); // Apply the inverse of the view matrix to our ray. Matrix3D viewMatrix = CreateViewMatrix(Transform, ref position, ref lookDirection, ref upDirection); Matrix3D invView = viewMatrix; invView.Invert(); // We construct our ray such that the origin resides on the near // plane. If our near plane is too far from our the bounding box // of our scene then the results will be inaccurate. (e.g., // OrthographicCameras permit negative near planes, so the near // plane could be at -Inf.) // // However, it is permissable to move the near plane nearer to // the scene bounds without changing what the ray intersects. // If the near plane is sufficiently far from the scene bounds // we make this adjustment below to increase precision. Rect3D transformedBoundingBox = M3DUtil.ComputeTransformedAxisAlignedBoundingBox( ref boundingRect, ref viewMatrix); // DANGER: The NearPlaneDistance property is specified as a // distance from the camera position along the // LookDirection with (Near < Far). // // However, when we transform our scene bounds so that // the camera is aligned with the negative Z-axis the // relationship inverts (Near > Far) as illustrated // below: // // NearPlane Y FarPlane // | ^ | // | | | // | | (rect.Z + rect.SizeZ) | // | | o____ | // | | | | | // | | | | | // | | ____o | // | | (rect.Z) | // | Camera -> | // +Z <----------+----------------------------> -Z // | 0 | // // It is surprising, but its the "far" side of the // transformed scene bounds that determines the near // plane distance. double zn2 = -AddEpsilon(transformedBoundingBox.Z + transformedBoundingBox.SizeZ); if (zn2 > zn) { // // Our near plane is far from our children. Construct a new // near plane that's closer. Note that this will modify our // distance computations, so we have to be sure to adjust our // distances appropriately. // distanceAdjustment = zn2 - zn; zn = zn2; } else { // // Our near plane is either close to or in front of our // children, so let's keep it -- no distance adjustment needed. // distanceAdjustment = 0.0; } // Our origin is the point normalized to the front of our viewing volume. // To find our origin's x/y we just need to scale the normalize point by our // width/height. In camera space we are looking down the negative Z axis // so we just set Z to be -zn which puts us on the projection plane // (Windows OS #1005064). Point3D origin = new Point3D(np.X * (w / 2), np.Y * (h / 2), -zn); invView.MultiplyPoint(ref origin); invView.MultiplyVector(ref direction); RayHitTestParameters rayParameters = new RayHitTestParameters(origin, direction); // // Compute HitTestProjectionMatrix // Matrix3D projectionMatrix = GetProjectionMatrix(aspectRatio, zn, zf); // The projectionMatrix takes camera-space 3D points into normalized clip // space. // The viewportMatrix will take normalized clip space into // viewport coordinates, with an additional 2D translation // to put the ray at the origin. Matrix3D viewportMatrix = new Matrix3D(); viewportMatrix.TranslatePrepend(new Vector3D(-p.X, viewSize.Height - p.Y, 0)); viewportMatrix.ScalePrepend(new Vector3D(viewSize.Width / 2, -viewSize.Height / 2, 1)); viewportMatrix.TranslatePrepend(new Vector3D(1, 1, 0)); // `First world-to-camera, then camera's projection, then normalized clip space to viewport. rayParameters.HitTestProjectionMatrix = viewMatrix * projectionMatrix * viewportMatrix; return(rayParameters); }