| // Copyright 2005 Google Inc. All Rights Reserved. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS-IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| // |
| |
| #ifndef S2_S2COORDS_INTERNAL_H_ |
| #define S2_S2COORDS_INTERNAL_H_ |
| // Author: ericv@google.com (Eric Veach) |
| |
| namespace S2 { |
| namespace internal { |
| |
| // The canonical Hilbert traversal order looks like an inverted 'U': |
| // the subcells are visited in the order (0,0), (0,1), (1,1), (1,0). |
| // The following tables encode the traversal order for various |
| // orientations of the Hilbert curve (axes swapped and/or directions |
| // of the axes reversed). |
| |
| // Together these flags define a cell orientation. If 'kSwapMask' |
| // is true, then canonical traversal order is flipped around the |
| // diagonal (i.e. i and j are swapped with each other). If |
| // 'kInvertMask' is true, then the traversal order is rotated by 180 |
| // degrees (i.e. the bits of i and j are inverted, or equivalently, |
| // the axis directions are reversed). |
| int constexpr kSwapMask = 0x01; |
| int constexpr kInvertMask = 0x02; |
| |
| // kIJtoPos[orientation][ij] -> pos |
| // |
| // Given a cell orientation and the (i,j)-index of a subcell (0=(0,0), |
| // 1=(0,1), 2=(1,0), 3=(1,1)), return the order in which this subcell is |
| // visited by the Hilbert curve (a position in the range [0..3]). |
| extern int const kIJtoPos[4][4]; |
| |
| // kPosToIJ[orientation][pos] -> ij |
| // |
| // Return the (i,j) index of the subcell at the given position 'pos' in the |
| // Hilbert curve traversal order with the given orientation. This is the |
| // inverse of the previous table: |
| // |
| // kPosToIJ[r][kIJtoPos[r][ij]] == ij |
| extern int const kPosToIJ[4][4]; |
| |
| // kPosToOrientation[pos] -> orientation_modifier |
| // |
| // Return a modifier indicating how the orientation of the child subcell |
| // with the given traversal position [0..3] is related to the orientation |
| // of the parent cell. The modifier should be XOR-ed with the parent |
| // orientation to obtain the curve orientation in the child. |
| extern int const kPosToOrientation[4]; |
| |
| // The U,V,W axes for each face. |
| extern double const kFaceUVWAxes[6][3][3]; |
| |
| // The precomputed neighbors of each face (see GetUVWFace). |
| extern int const kFaceUVWFaces[6][3][2]; |
| |
| } // namespace internal |
| } // namespace S2 |
| |
| #endif // S2_S2COORDS_INTERNAL_H_ |
