// Pivot an edge clockwise around its implicit near vertex.
//
// \ / \ /
// o-------o o-------o
// | | | |
// 2 N | 2 N |
// | | | |
// B V --> B<--E---V
// / \ / \ / \ \
// 1 E \ 1 \
// \ v \ / \ \ /
// A o A o
// | P | | P |
// 0 | 0 |
// | | | |
// o-------o o-------o
// / \ / \
//
// E: edge passed in as parameter
// V: vertex to pivot E around clockwise
// A: old vertex that E is originally pointing at
// B: new vertex that E will now point at
// P: previous face on the counter-clockwise side of E
// N: next face on the clockwise side of E
// 0: outer edge 0 points at A, inner edge 0 points away from A
// 1: outer edge 1 points at B, inner edge 1 points at A, at N before pivot, at P after pivot
// 2: outer edge 2 points away from B
// Note: inner edges point downward, outer edges point upward
private void PivotVertexEdgeForwardUnchecked(int edgeIndex, int twinEdgeIndex, int outerEdgeIndex1, int innerEdgeIndex1)
{
var innerEdgeIndex0 = edgeData[twinEdgeIndex].vNext;
var outerEdgeIndex0 = edgeData[innerEdgeIndex0].twin;
var outerEdgeIndex2 = edgeData[outerEdgeIndex1].fNext;
var prevFaceIndex = edgeData[edgeIndex].face;
var nextFaceIndex = edgeData[twinEdgeIndex].face;
var oldVertexIndex = edgeData[edgeIndex].vertex;
var newVertexIndex = edgeData[outerEdgeIndex1].vertex;
// The edge was pointing at the old vertex, will now point at the new vertex.
edgeData[edgeIndex].vertex = newVertexIndex;
// The second inner edge was pointing at the next face, will now point at the previous face.
edgeData[innerEdgeIndex1].face = prevFaceIndex;
// Remove twin edge from old vertex linked list by skipping over it.
edgeData[outerEdgeIndex1].vNext = innerEdgeIndex0;
// Insert twin edge into new vertex linked list.
edgeData[outerEdgeIndex2].vNext = twinEdgeIndex;
edgeData[twinEdgeIndex].vNext = innerEdgeIndex1;
// Remove second outer edge from next face linked list by skipping over it.
edgeData[edgeIndex].fNext = outerEdgeIndex2;
// Insert second outer edge into the previous face linked list.
edgeData[outerEdgeIndex0].fNext = outerEdgeIndex1;
edgeData[outerEdgeIndex1].fNext = twinEdgeIndex;
// Reroot the vertex and face that just lost edges with edges guaranteed to still belong.
vertexFirstEdgeIndices[oldVertexIndex] = outerEdgeIndex1;
faceFirstEdgeIndices[nextFaceIndex] = edgeIndex;
// Adjust neighbor counts.
vertexNeighborCounts[oldVertexIndex] -= 1;
vertexNeighborCounts[newVertexIndex] += 1;
faceNeighborCounts[nextFaceIndex] -= 1; // Dropping below 0 is undefined behavior; it better not ever happen.
faceNeighborCounts[prevFaceIndex] += 1; // Surpassing 32767 is undefined behavior; it better not ever happen.
// Adjust edge wrap information, coallescing multiple edges together as appropriate.
edgeData[edgeIndex].wrap = EdgeWrapUtility.ModifyTargetVertEdgeRelations(edgeData[edgeIndex].wrap, edgeData[outerEdgeIndex1].wrap); // Edge's target vertex changed, according to Inner Edge 1.
edgeData[twinEdgeIndex].wrap = EdgeWrapUtility.ModifySourceVertEdgeRelations(edgeData[twinEdgeIndex].wrap, edgeData[innerEdgeIndex1].wrap); // Twin Edge's source vertex changed, according to Outer Edge 1.
edgeData[innerEdgeIndex1].wrap = EdgeWrapUtility.ModifyTargetFaceEdgeRelations(edgeData[innerEdgeIndex1].wrap, edgeData[edgeIndex].wrap); // Inner Edge 1's target face changed, according to Twin Edge.
edgeData[outerEdgeIndex1].wrap = EdgeWrapUtility.ModifySourceFaceEdgeRelations(edgeData[outerEdgeIndex1].wrap, edgeData[twinEdgeIndex].wrap); // Outer Edge 1's source face changed, according to Edge.
}
