Hi,

I need to write a flood fill algorithm using C# in Unity, in order to make a simple colour-fill tool similar to the one in MS paint. The user will be presented with a white texture with black line-drawings to be filled. They will pick a colour from a pallet, and click to fill sections of the line-drawing with colour. Black will always represent the boundary colour.

Here is the flood-fill method I have written. The code surrounding the sample is checked and works, but the algorithm seems to only fill one line to the left of the clicked pixel.

It would be great to get some advice on this, either to find out what is wrong with the existing code, or find another method of doing colour-fills. I think it's overflowing the stack.

EDIT: New version of code below, still with same problem:

/ FloodFill function

void FloodFill() {

// TEST - colour the clicked pixel
//_tex.SetPixel( (int)_pixelUV.x, (int)_pixelUV.y, m_fillColour );
//_tex.SetPixel( _pixelX, _pixelY, m_fillColour );


// FLOOD FILL 
// ----------

// Create WestEast
List<Point> m_WestEast;

//get the pixel's colour
Color PC = new Color(_tex.GetPixel(m_StartNode.X, m_StartNode.Y).r, _tex.GetPixel(m_StartNode.X, m_StartNode.Y).g, _tex.GetPixel(m_StartNode.X, m_StartNode.Y).b);

//Record clicked pixel as point
Point node = new Point(m_StartNode.X, m_StartNode.Y);

//if the pixel's colour is boundary colour (black), return.
if(PC == Color.black)
{
    return;
}

//else continue

// Create a list Q[]
m_List = new List<Point>();

//add clicked pixel to Q[]
m_List.Add(node);

//for each element in Q[]
for(int i=0; i<m_List.Count; i++)
{
    //create new WE[] and add Q[n] to it
    m_WestEast = new List<Point>();
    m_WestEast.Add(node);

    //get pixel 1 to left (w) of Q[n]
    Point w = new Point(node.X + 1, node.Y);
    //get colour of w
    Color wCol = new Color(_tex.GetPixel(w.X, w.Y).r, _tex.GetPixel(w.X, w.Y).g, _tex.GetPixel(w.X, w.Y).b);   

    while(wCol != Color.black)
    {   
       //add pixel to WE[] and repeat
       m_WestEast.Add(w);

       //get new w
       w = new Point(w.X + 1, w.Y);

       //get colour of w
       wCol = new Color(_tex.GetPixel(w.X, w.Y).r, _tex.GetPixel(w.X, w.Y).g, _tex.GetPixel(w.X, w.Y).b);    

       //else if colour is boundary colour
         //go to next step
    }

    //get pixel 1 to right (e) of Q[n]
    Point e = new Point(node.X - 1, node.Y);
    //get colour of w
    Color eCol = new Color(_tex.GetPixel(e.X, e.Y).r, _tex.GetPixel(e.X, e.Y).g, _tex.GetPixel(e.X, e.Y).b);   

    while(eCol != Color.black)
    {   
       //add pixel to WE[] and repeat
       m_WestEast.Add(e);

       //get new e
       e = new Point(e.X - 1, e.Y);

       //get colour of e
       eCol = new Color(_tex.GetPixel(e.X, e.Y).r, _tex.GetPixel(e.X, e.Y).g, _tex.GetPixel(e.X, e.Y).b);    

       //else if colour is boundary colour
         //go to next step
    }

    //for each pixel in WE[]
    for(int j=0; j<m_WestEast.Count; j++)
    {
       //set the pixel to replacement colour
       _tex.SetPixel(m_WestEast[j].X, m_WestEast[j].Y, m_fillColour);

       //get pixel 1 to north (n) of Q[n]
       Point n = new Point(m_WestEast[j].X, m_WestEast[j].Y - 1);    

       //get colour of n
       Color nCol = new Color(_tex.GetPixel(n.X, n.Y).r, _tex.GetPixel(n.X, n.Y).g, _tex.GetPixel(n.X, n.Y).b);

       //if colour is not boundary colour
       if(nCol != Color.black)
       {
         //add pixel to Q[]
         m_List.Add(n);
       }

       //get pixel 1 to south (s) of Q[n]
       Point s = new Point(m_WestEast[j].X, m_WestEast[j].Y + 1);    

       //get colour of s
       Color sCol = new Color(_tex.GetPixel(s.X, s.Y).r, _tex.GetPixel(s.X, s.Y).g, _tex.GetPixel(s.X, s.Y).b);

       //if colour is not boundary colour
       if(sCol != Color.black)
       {
         //add pixel to Q[]
         m_List.Add(s);
       }
    }

}

// ----------

}