/// <summary>
/// Can we place this Feature at the provided position?
///
/// </summary>
/// <returns><c>true</c>, if the Feature could be placed, <c>false</c> otherwise.</returns>
/// <param name="placedSections">The grid, containing all the Sections we wish to avoid.</param>
/// <param name="gridPosition">The grid position we want to place the Feature at.</param>
/// <param name="localPosition">The location of the Section we want to place at "gridPosition".</param>
/// <param name="rotation">Rotation.</param>
public bool CanPlace(ReadOnlyGrid placedSections, Vector2Int gridPosition, Vector2Int localPosition, int rotation)
{
foreach (Vector2Int sectionPosition in Elements.Keys)
{
// Shift this Section's position over by the offset, "localPosition".
// This places "localPosition" at (0, 0).
// Then rotate the point by the provided rotation.
//
// Because "localPosition" is provided in the same coordinates as "sectionPosition",
// the resulting position is already normalized.
Vector2Int rotatedPoint = Rotate(sectionPosition - localPosition, rotation);
if (placedSections[gridPosition + rotatedPoint] != null)
{
return(false);
}
}
return(true);
}
public bool CanPlace(ReadOnlyGrid placedSections, Configuration configuration)
{
return(CanPlace(placedSections, configuration.gridPosition, configuration.localPosition, configuration.rotation));
}
/// <summary>
/// Returns a list of valid configurations at the provided grid position.
///
/// A configuration is uniquely defined by the grid position, the local position (which
/// represents the specific Section we place at the adjacent grid position), and the
/// rotation used. Additional information is provided to aid in selecting an interesting
/// configuration in generation (such as the direction we connected in).
///
/// A configuration is considered valid if every Section within this Feature can be
/// placed onto the Grid without overlapping any existing Grid Sections.
///
///
///
/// TODO find some way to optimize this, if it's possible to do so. Maybe a cache of recently checked
/// positions, placed in the CanConnect method? This would amortize O(n^2) checks into O(n)? unique
/// lookups, but O(n^2) comparisons still.
///
/// Another idea: statically maintain a list of "internal" Sections within each Feature, and ignore those
/// as seed positions within the CheckPlacement method. The thinking being internal points would never have
/// any external ability to connect. Theoretically still O(n^2) (case study: space-filling curves have n^2
/// surface area and take up n^2 space), but in practice, most Features are likely to have a linear exposed
/// area.
///
/// Tangent from the above idea. Space filling curves like the spiral or comb have O(n^2) surface area, but
/// need "thin" or "small" connection points to be satisfied. Because we try to place Features off of a single
/// Section, we aren't being smart about how it can connect, so we allow bad cases like this. If we take the
/// neighboring e.g. 2-3 Sections in the Grid, we can try fitting small polygons within the Feature instead of
/// individual Sections. If the small polygon is logarithmic in size [width * height = O(log^2(n))], then the
/// "gaps" in the space filling curve must be at least logarithmic as well [O(sqrt(log^2(n))) == O(log(n))]. This
/// might mean that the worst-case behavior is avoided, because the large gaps might force the number of Sections
/// to be O(n log n) instead of O(n^2).
///
/// Another idea: Change the iteration order of the CanPlace method to check nearby Sections first, to
/// increase the likelihood of breaking out early when checking for overlaps. Or check Grid sections near
/// the bounding box? Some heuristics might be faster than others.
///
/// Another idea: Do a bounding box check first, if there's a way to do a cheap check in the global grid.
///
/// Another idea: Keep track if this Feature has rotational symmetry (either 2 way or 4 way). If so, we can
/// memoize the different rotation checks for up to 4x speedup in 4-way rotationally symmetrical cases.
///
/// </summary>
/// <returns>A List containing all valid configurations found.</returns>
/// <param name="placedSections">The grid, containing the positions of Sections already placed.</param>
/// <param name="gridPosition">The position in the grid we want to place the Feature at.</param>
public List <Configuration> CanConnect(ReadOnlyGrid placedSections, Vector2Int gridPosition)
{
Section?maybeGridSection = placedSections[gridPosition];
if (maybeGridSection == null)
{
// Empty Section is invalid, we always need to be passed in a full one.
return(new List <Configuration>());
}
Section gridSection = maybeGridSection.Value;
// A cache of the configurations we've seen while trying to place this Feature.
//
// Two configurations are considered equal if their gridPosition+localPosition and rotation are equal.
//
// This provides up to 4x speedup. Can be achieved with dense Features (approaching filled square
// or a checkerboard pattern).
//
// Motivating 2x2 Feature example: checking if the top-right corner can be placed North of a given
// Section is equivalent to checking if the bottom-left corner can be placed West of the same Section.
// With larger dense Features, Sections away from the edges will produce up to 4 duplicate placement checks.
Dictionary <Configuration, bool> cache = new Dictionary <Configuration, bool>();
// Build up all possible valid configurations we'll return
List <Configuration> toReturn = new List <Configuration>();
// Try to place the Feature at all adjacent grid positions
CheckPlacements(gridPosition + Vector2Int.up);
CheckPlacements(gridPosition + Vector2Int.right);
CheckPlacements(gridPosition + Vector2Int.down);
CheckPlacements(gridPosition + Vector2Int.left);
return(toReturn);
// Checks all possible configurations of placing this Feature down at
// a given grid position. Add them to the returning list
void CheckPlacements(Vector2Int pos)
{
// If the provided input position already has a Section, then trivially
// any Section we try to place here will conflict. So we return early.
if (placedSections[pos] != null)
{
return;
}
// Else try every possible local position.
foreach (KeyValuePair <Vector2Int, Section> element in Elements)
{
// And every possible rotational variant for each.
for (int rot = 0; rot < 4; rot++)
{
Configuration configuration = new Configuration(pos, element.Key, rot);
// Have we already tried this configuration? Check the cache.
if (!cache.TryGetValue(configuration, out bool canPlace))
{
// If it's not in there, compute it manually and add it.
canPlace = CanPlace(placedSections, configuration);
cache[configuration] = canPlace;
}
else
{
Debug.Log("Cache hit!");
}
// If the configuration is valid (no overlaps w/ grid), add it
if (canPlace)
{
toReturn.Add(configuration);
}
}
}
}
}
