algorithm name for island polygons between non overlapping objects

Question

I am looking for algorithm name and could not identify which algorithm is it. My task is,

Given: 1.Size(Width,Height) of a parent container 2.Position (X,Y) and size(Width,Height) for a number of rectangular and square particles which cannot overlap each other and can fit inside the container

Task: Find the empty polygon points in either counter-clockwise or clockwise when the user clicks on an empty spot

What I have tried is,

1.I took a starting point around the empty spot

2.Start with left direction

3.I checked for nearest particle to the left side of the point's Y-axis and above the point's X-axis. If found add the right bottom point of the found particle (x,particle_Y+particle_Height) and turn downwards

4.get particle to the left of the point. If found add the left bottom point of the particle (particle_X.y) and continue left.

5.if left has reached zero find nearest downward particle and add the top left point (x,particle_Y) and continue right.

6.if there is an upward particle next to it, add the top left (x particle_Y) and continue up.

7.1f not found, another if: find the top particle adjacent to the point which ends farther but has next point in between, add the top right (particle_X+particle_Width,y) of the particle and continue up.

8.If none of the above, turn down and continue downward search.

My code

https://pastebin.com/2cnMb67G

while ((islandCurrentX != islandStartX || islandCurrentY != islandStartY) && count < 500)
                                                {
                                                    int tempIslandX = (islandCurrentX == -1 ? islandStartX : islandCurrentX);
                                                    int tempIslandY = (islandCurrentY == -1 ? islandStartY : islandCurrentY);
                                                    //break;
                                                    count++;

But if I follow this, after I reach bottom part of the empty part, it again goes counterclockwise rather than clockwise. What algorithm should I search the internet? One more thing, I looked for connected components algorithm which is for pixel wise datatable. But I have position and size datatable. If I convert it to pixel wise, my windows form (C#) will become slow during search. (need to search on each click). Thanks in advance

Answer 1

Thanks for spending your valuable times. I have made it by changing the successive directions after each movement. https://pastebin.com/dNrHFn5W

(starts with)

List<Point> points = new List<Point>();
DataRow[] drNearestTop = dtCurrentPattern.Select("Starting_Y+Image_Length<" + controlRelatedCoords.Y + " and Starting_X<=" + controlRelatedCoords.X + " and Starting_X+Image_Width>=" + controlRelatedCoords.X + "");

Regards