outline around group of hexagons

Question

I have a group of hexagons in my hexagonal grid, which I'd like outline with a border.

This is how it looks like so far:

desired output:

I have stored all the cotrner points of each hexagon from that group. I suppose these points can be used to calculate the border around the group later on.

[[{"x":123.39745962155612,"y":260},{"x":101.74682452694516,"y":272.5},{"x":80.0961894323342,"y":260},{"x":80.0961894323342,"y":235},{"x":101.74682452694516,"y":222.5},{"x":123.39745962155612,"y":235}],[{"x":145.0480947161671,"y":222.5},{"x":123.39745962155614,"y":235},{"x":101.74682452694518,"y":222.5},{"x":101.74682452694518,"y":197.5},{"x":123.39745962155614,"y":185},{"x":145.0480947161671,"y":197.5}],[{"x":166.69872981077808,"y":260},{"x":145.0480947161671,"y":272.5},{"x":123.39745962155612,"y":260},{"x":123.39745962155612,"y":235},{"x":145.0480947161671,"y":222.5},{"x":166.69872981077805,"y":235}],[{"x":188.34936490538905,"y":297.5},{"x":166.69872981077808,"y":310},{"x":145.0480947161671,"y":297.5},{"x":145.0480947161671,"y":272.5},{"x":166.69872981077808,"y":260},{"x":188.34936490538902,"y":272.5}],[{"x":188.34936490538905,"y":222.5},{"x":166.69872981077808,"y":235},{"x":145.0480947161671,"y":222.5},{"x":145.0480947161671,"y":197.5},{"x":166.69872981077808,"y":185},{"x":188.34936490538902,"y":197.5}],[{"x":210,"y":260},{"x":188.34936490538902,"y":272.5},{"x":166.69872981077805,"y":260},{"x":166.69872981077805,"y":235},{"x":188.34936490538902,"y":222.5},{"x":209.99999999999997,"y":235}],[{"x":231.65063509461098,"y":297.5},{"x":210,"y":310},{"x":188.34936490538902,"y":297.5},{"x":188.34936490538902,"y":272.5},{"x":210,"y":260},{"x":231.65063509461095,"y":272.5}]]

Also added a live example to see how the grid works so far.

And now I'm trying to figure out how exactly do I determine how the border will be generated.

Now how do I exactly generate the border? Should I just find the center of this group, and then find all the points with the greater distance, and then connect them?

As advised by someone in discussion below, I tried sorting the points by their [X,Y] coordinates and also removed all duplicate coordinates, but it turned into this disaster :/.

Or is there any other technique to achieve this?

How about doing it iteratively? Start with a list of sorted points (by x, then y). Start with the first, draw full border. Add other points one by one, draw full border, calculate overlap of borders with all objects that are already drawn and remove those pieces. — bebbi, Jul 20 '16 at 09:01
added a jsfiddle link to the main post. I have divided the js content into 3 script tags so it's less confusing. — Alexus, Jul 20 '16 at 09:09

score 9 · Answer 1 · answered Jul 20 '16 at 15:21

Here's a simple algorithm:

For each hex H in your brown region, iterate over each of the 6 directions 0 ≤ dir < 6, and set D to be hex_neighbor(H, dir).
If D is green then draw a border between the two.

Caveat: this does not connect the border edges into a single polyline.

I have a live demo with an algorithm that works on any number of regions, as well as an extension to draw curved lines.

score 2 · Answer 2 · answered Jul 21 '16 at 09:20

Thanks Amit, for sharing your knowledge with us. Your algorithm is way more efficient and faster. I have had to make very little amendments to make it work in my example above.

First one, if the hex didn't have a neighbor on one of its direction , mark the direction with null.
The second, take the neighbors with null value to consideration while generating edges.

Otherwise it was leaving gaps if the hex didn't have neighbor on one of their sides.

This a modified function that I'm using to draw the edges:

generateEdges: function( ctx ){
    var edges = [];
    var self = this;
    var neighbor = null;
    self.obs_arr.forEach( function( hex ){
        for( var dir = 0, nb_l = hex.neighbors.length; dir < nb_l; dir++ ){
            neighbor = hex.neighbors[dir];
            if(neighbor == null ||  hex.content != neighbor.content ){
                var p1 = self.point_add( hex.center, self.hex_corner_offset( dir ) );
                var p2 = self.point_add( hex.center, self.hex_corner_offset( (dir+1)%6 ) );
                edges.push( p1, p2 );
            }
        }
    });
    return edges;
},

It all now works perfectly . Thanks a lot Amit for all your help!

outline around group of hexagons

2 Answers2