// QuickHull seemed like a neat algorithm, and efficient-ish for large input sets.
// My implementation performs an in place reduction using the result array as scratch space.
int
cpConvexHull(int count, cpVect *verts, cpVect *result, int *first, cpFloat tol)
{
if(result){
// Copy the line vertexes into the empty part of the result polyline to use as a scratch buffer.
memcpy(result, verts, count*sizeof(cpVect));
} else {
// If a result array was not specified, reduce the input instead.
result = verts;
}
// Degenerate case, all poins are the same.
int start, end;
cpLoopIndexes(verts, count, &start, &end);
if(start == end){
if(first) (*first) = 0;
return 1;
}
SWAP(result[0], result[start]);
SWAP(result[1], result[end == 0 ? start : end]);
cpVect a = result[0];
cpVect b = result[1];
if(first) (*first) = start;
int resultCount = QHullReduce(tol, result + 2, count - 2, a, b, a, result + 1) + 1;
cpAssertSoft(cpPolyValidate(result, resultCount),
"Internal error: cpConvexHull() and cpPolyValidate() did not agree."
"Please report this error with as much info as you can.");
return resultCount;
}
// QuickHull seemed like a neat algorithm, and efficient-ish for large input sets.
// My implementation performs an in place reduction using the result array as scratch space.
int
cpConvexHull(int count, const cpVect *verts, cpVect *result, int *first, cpFloat tol)
{
if(verts != result){
// Copy the line vertexes into the empty part of the result polyline to use as a scratch buffer.
memcpy(result, verts, count*sizeof(cpVect));
}
// Degenerate case, all points are the same.
int start, end;
cpLoopIndexes(verts, count, &start, &end);
if(start == end){
if(first) (*first) = 0;
return 1;
}
SWAP(result[0], result[start]);
SWAP(result[1], result[end == 0 ? start : end]);
cpVect a = result[0];
cpVect b = result[1];
if(first) (*first) = start;
return QHullReduce(tol, result + 2, count - 2, a, b, a, result + 1) + 1;
}
static int
QHullReduce(cpFloat tol, cpVect *verts, int count, cpVect a, cpVect pivot, cpVect b, cpVect *result)
{
if(count < 0){
return 0;
} else if(count == 0) {
result[0] = pivot;
return 1;
} else {
int left_count = QHullPartition(verts, count, a, pivot, tol);
int index = QHullReduce(tol, verts + 1, left_count - 1, a, verts[0], pivot, result);
result[index++] = pivot;
int right_count = QHullPartition(verts + left_count, count - left_count, pivot, b, tol);
return index + QHullReduce(tol, verts + left_count + 1, right_count - 1, pivot, verts[left_count], b, result + index);
}
}
