/// <summary>
/// returns a polygon representing the periphery of a square region
/// </summary>
/// <param name="edges">
/// edges within the square region <see cref="List`1"/>
/// </param>
/// <param name="erode_dilate">
/// erosion or dilation level <see cref="System.Int32"/>
/// </param>
/// <param name="perim">
/// returned periphery <see cref="polygon2D"/>
/// </param>
/// <returns>
/// set of edges around the periphery <see cref="List`1"/>
/// </returns>
private static List<List<int>> GetSquarePeriphery(List<int> edges,
int erode_dilate,
ref polygon2D perim)
{
List<List<int>> result = new List<List<int>>();
perim = new polygon2D();
// find the bounding box for all edges
int tx = 99999;
int ty = 99999;
int bx = -99999;
int by = -99999;
for (int i = edges.Count-2; i >= 0; i -= 2)
{
int x = edges[i];
int y = edges[i+1];
if (x < tx) tx = x;
if (y < ty) ty = y;
if (x > bx) bx = x;
if (y > by) by = y;
}
int w = bx - tx;
int h = by - ty;
if ((w > 0) && (h > 0))
{
int[] left = new int[h+1];
int[] right = new int[h+1];
int[] top = new int[w+1];
int[] bottom = new int[w+1];
for (int i = edges.Count - 2; i >= 0; i -= 2)
{
int x = edges[i];
int x2 = x - tx;
int y = edges[i+1];
int y2 = y - ty;
// left side
if ((left[y2] == 0) ||
(x < left[y2]))
left[y2] = x;
// right side
if ((right[y2] == 0) ||
(x > right[y2]))
right[y2] = x;
// top
if ((top[x2] == 0) ||
(y < top[x2]))
top[x2] = y;
// bottom
if ((bottom[x2] == 0) ||
(y > bottom[x2]))
bottom[x2] = y;
}
#if SHOW_TIMINGS
stopwatch timer_best_fit = new stopwatch();
timer_best_fit.Start();
#endif
// find a best fit line for the left side
int best_start = 0;
int best_end = 0;
int hits = BestFitLine(left, ref best_start, ref best_end);
float left_x0 = left[best_start];
float left_y0 = ty + best_start;
float left_x1 = left[best_end];
float left_y1 = ty + best_end;
/*
BestFitLineAverage(left,
ref left_x0, ref left_y0,
ref left_x1, ref left_y1);
left_y0 += ty;
left_y1 += ty;
*/
// find a best fit line for the right side
best_start = 0;
best_end = 0;
hits = BestFitLine(right, ref best_start, ref best_end);
float right_x0 = right[best_start];
float right_y0 = ty + best_start;
float right_x1 = right[best_end];
float right_y1 = ty + best_end;
/*
BestFitLineAverage(right,
ref right_x0, ref right_y0,
ref right_x1, ref right_y1);
right_y0 += ty;
right_y1 += ty;
*/
// find a best fit line for the top side
best_start = 0;
best_end = 0;
hits = BestFitLine(top, ref best_start, ref best_end);
float top_x0 = tx + best_start;
float top_y0 = top[best_start];
float top_x1 = tx + best_end;
float top_y1 = top[best_end];
/*
BestFitLineAverage(top,
ref top_x0, ref top_y0,
ref top_x1, ref top_y1);
top_x0 += tx;
top_x1 += tx;
*/
// find a best fit line for the bottom side
best_start = 0;
best_end = 0;
hits = BestFitLine(bottom, ref best_start, ref best_end);
float bottom_x0 = tx + best_start;
float bottom_y0 = bottom[best_start];
float bottom_x1 = tx + best_end;
float bottom_y1 = bottom[best_end];
/*
BestFitLineAverage(bottom,
ref bottom_x0, ref bottom_y0,
ref bottom_x1, ref bottom_y1);
bottom_x0 += tx;
bottom_x1 += tx;
*/
#if SHOW_TIMINGS
timer_best_fit.Stop();
if (timer_best_fit.time_elapsed_mS > 20)
Console.WriteLine("GetSquarePeriphery: best fit " + timer_best_fit.time_elapsed_mS.ToString() );
#endif
// find the intersection between the left side and the top side
float ix=0;
float iy = 0;
geometry.intersection(left_x1, left_y1, left_x0, left_y0,
top_x1, top_y1, top_x0, top_y0,
ref ix, ref iy);
perim.Add(ix, iy);
// find the intersection between the right side and the top side
ix = 0;
iy = 0;
geometry.intersection(right_x1, right_y1, right_x0, right_y0,
top_x0, top_y0, top_x1, top_y1,
ref ix, ref iy);
perim.Add(ix, iy);
// find the intersection between the right side and the bottom side
ix = 0;
iy = 0;
geometry.intersection(right_x1, right_y1, right_x0, right_y0,
bottom_x0, bottom_y0, bottom_x1, bottom_y1,
ref ix, ref iy);
perim.Add(ix, iy);
// find the intersection between the left side and the bottom side
ix = 0;
iy = 0;
geometry.intersection(left_x1, left_y1, left_x0, left_y0,
bottom_x0, bottom_y0, bottom_x1, bottom_y1,
ref ix, ref iy);
perim.Add(ix, iy);
// left and right
List<int> left_edges = new List<int>();
List<int> right_edges = new List<int>();
for (int y = h; y >= 0; y--)
{
if (left[y] != 0)
{
left_edges.Add(left[y]);
left_edges.Add(ty + y);
}
if (right[y] != 0)
{
right_edges.Add(right[y]);
right_edges.Add(ty + y);
}
}
// top and bottom
List<int> top_edges = new List<int>();
List<int> bottom_edges = new List<int>();
for (int x = w; x >= 0; x--)
{
if (top[x] != 0)
{
top_edges.Add(tx + x);
top_edges.Add(top[x]);
}
if (bottom[x] != 0)
{
bottom_edges.Add(tx + x);
bottom_edges.Add(bottom[x]);
}
}
float aspect_check = perim.getShortestSide() / perim.getLongestSide();
if (aspect_check > 0.2f)
{
result.Add(left_edges);
result.Add(right_edges);
result.Add(top_edges);
result.Add(bottom_edges);
}
else perim = null;
}
// shrink the perimeter according to the erosion/dilation value
if ((perim != null) && (erode_dilate != 0))
{
if (perim.x_points != null)
{
float shrink_percent = (erode_dilate*2) / (perim.getPerimeterLength()/4.0f);
perim = perim.Scale(1.0f - shrink_percent);
}
else perim = null;
}
return(result);
}