// 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;
}
// Recursively reduce the vertex count on a polyline. Works best for smooth shapes.
// 'tol' is the maximum error for the reduction.
// The reduced polyline will never be farther than this distance from the original polyline.
cpPolyline *
cpPolylineSimplifyCurves(cpPolyline *line, cpFloat tol)
{
cpPolyline *reduced = cpPolylineMake(line->count);
cpFloat min = tol/2.0f;
if(cpPolylineIsClosed(line)){
int start, end;
cpLoopIndexes(line->verts, line->count - 1, &start, &end);
reduced = cpPolylinePush(reduced, line->verts[start]);
reduced = DouglasPeucker(line->verts, reduced, line->count - 1, start, end, min, tol);
reduced = cpPolylinePush(reduced, line->verts[end]);
reduced = DouglasPeucker(line->verts, reduced, line->count - 1, end, start, min, tol);
reduced = cpPolylinePush(reduced, line->verts[start]);
} else {
reduced = cpPolylinePush(reduced, line->verts[0]);
reduced = DouglasPeucker(line->verts, reduced, line->count, 0, line->count - 1, min, tol);
reduced = cpPolylinePush(reduced, line->verts[line->count - 1]);
}
return cpPolylineShrink(reduced);
}
