Flood fill algorithm for Visual Basic [duplicate] - vb.net

Question

I am an amateur in Visual Basic. I am attempting to recreate the game of Go, and I have created the board and am able to place stones on the intersections of the grid.
I now want to start capturing stones which are surrounded. I have looked online and found that flood fill is the best way to go about this. However, I have looked online for days, and I can't find anything that I can use, or manipulate to create this. I do not understand any other programming language, so I cannot use bits of code from Java, etc. And the bits of information for Visual Basic I have found do not make much sense to me as I am still a beginner.
I have attempted to start it by myself, starting off small with the situation of "If one stone were to be captured". I have two representations for the board, one is declared as "grid", and the other as "placed_stone".
"Grid" is the actual board where the users click to place their stones. placed_stone is a copy of this board, but I have used "0", "1" and "2" to represent empty, black and white respectively. I am using Windows Forms to recreate this game. This is the segment of code I have written for capturing the stones:
Private Sub Panel1_Click(sender As Object, e As EventArgs) Handles Panel1.Click
Dim board As Panel = DirectCast(sender, Panel)
' Figure out where the user clicked: min = 0, max = (gridsize - 1)
Dim pt As Point = board.PointToClient(Cursor.Position)
Dim colWidth As Integer = (1 / (GridSize + 1)) * board.Size.Width
Dim rowHeight As Integer = (1 / (GridSize + 1)) * board.Size.Height
Dim gridPosition As New Point(Math.Min(Math.Max((pt.X / colWidth) - 1, 0), GridSize - 1), Math.Min(Math.Max((pt.Y / rowHeight) - 1, 0), GridSize - 1))
Dim newcoordsx As Integer
Dim newcoordsy As Integer
' Now do something with gridPosition:
If Not Grid(gridPosition.X)(gridPosition.Y).HasValue Then 'If gird(x,y) is empty
illegalmovelbl.Hide() ' Hides the "Illegal Move" Label
If cp = True Then ' If current player is Black
This is the part where I got stuck and realised that the coding for every situation will take too long. I managed to write up the code for one situation:
newcoordsx = gridPosition.X + 1
If placed_stone(newcoordsx, gridPosition.Y) = 2 Then
newcoordsy = gridPosition.Y + 1
If placed_stone(newcoordsx, newcoordsy) = 1 Then
newcoordsy = gridPosition.Y - 1
If placed_stone(newcoordsx, newcoordsy) = 1 Then
newcoordsx = gridPosition.X + 2
If placed_stone(newcoordsx, gridPosition.Y) = 1 Then
newcoordsx = gridPosition.X + 1
Grid(gridPosition.X)(gridPosition.Y) = True 'Place a black stone at Grid(x,y)
Grid(newcoordsx)(gridPosition.Y) = Nothing
placed_stone(newcoordsx, gridPosition.Y) = 0
pass = False
cp = False
passbtn.BackColor = Color.White 'The passbutton changes colour to white
passbtn.ForeColor = Color.Black 'The passbutton font changes colour to black
End If
End If
End If
End If
'Grid(gridPosition.X)(gridPosition.Y) = True ' Place a black stone at Grid(x,y)
'placed_stone(gridPosition.X, gridPosition.Y) = 1
'pass = False
'cp = False
'passbtn.BackColor = Color.White ' The passbutton changes colour to white
'passbtn.ForeColor = Color.Black ' The passbutton font changes colour to black
ElseIf cp = False Then ' If current player is White
Grid(gridPosition.X)(gridPosition.Y) = False ' Place a white stone at Grid(x,y)
placed_stone(gridPosition.X, gridPosition.Y) = 2
pass = False
cp = True
passbtn.BackColor = Color.Black ' The passbutton changes colour to black
passbtn.ForeColor = Color.White ' The passbutton font changes colour to white
End If
ElseIf Grid(gridPosition.X)(gridPosition.Y).HasValue Then ' If gird(x,y) isn't empty
illegalmovelbl.Show() ' Shows the "Illegal Move" Label
MsgBox("Place your stone in a vacant point") ' Displays error message
End If
board.Invalidate() ' Force the board to redraw itself
End Sub
I have tried to use Wikipedia's algorithm on flood fill, and I understand the logic of how it works, but I just don't know how to program it in Visual Basic.
Flood-fill (node, target-color, replacement-color):
1. If target-color is equal to replacement-color, return.
2. If the color of node is not equal to target-color, return.
3. Set the color of node to replacement-color.
4. Perform Flood-fill (one step to the south of node, target-color, replacement-color).
Perform Flood-fill (one step to the north of node, target-color, replacement-color).
Perform Flood-fill (one step to the west of node, target-color, replacement-color).
Perform Flood-fill (one step to the east of node, target-color, replacement-color).
5. Return.
Of course, in Go, instead of colouring in the area, you have to remove the stones when capturing, and you don't start the flood fill from the stone you just placed to capture, you start from the closest stone you wish to capture.
Can you please explain how to use flood fill in Visual Basic in an easy way and how to implement it to this game of Go?
If anyone would like to look at the whole code, please let me know. I would appreciate any suggestions!

Answer 1

I'm not familiar with the rules/game-play of the game Go, so I'm not sure exactly what you are attempting to accomplish, but if you believe that a flood-fill type of algorithm is what you need, then I can at least offer some advice in how you could do that. The primary thing that your code needs is to be broken down into more granular methods. What are the steps that you are attempting to perform when the panel is clicked? Surely it's not just one thing. There are many different things going on--each of which could be performed by a separate dedicated method. For instance, if you had a method like this:
Private Function GetGridPosition(board As Panel, cursorPosition As Point) As Point
Dim pt As Point = board.PointToClient(Cursor.Position)
Dim colWidth As Integer = (1 / (GridSize + 1)) * board.Size.Width
Dim rowHeight As Integer = (1 / (GridSize + 1)) * board.Size.Height
Return New Point(Math.Min(Math.Max((pt.X / colWidth) - 1, 0), GridSize - 1), Math.Min(Math.Max((pt.Y / rowHeight) - 1, 0), GridSize - 1))
End Function
Then, in the Panel1_Click event handler, you could simplify the beginning of the code considerably, like this:
Private Sub Panel1_Click(sender As Object, e As EventArgs) Handles Panel1.Click
Dim board As Panel = DirectCast(sender, Panel)
Dim gridPosition As Point = GetGridPosition(board, Cursor.Position)
' ...
Sure, that makes the code more organized and easier to read, but that doesn't get you any closer to a flood fill algorithm, right? Well, yes, that's mostly true, but organization and readability are worthy goals in their own right, so lets continue anyway... The next step we need to perform is to make the player's move, and then, if the move was successful, we need to switch to the other player. So, let's first create the method to switch players:
Private Sub SwitchPlayer()
pass = False
cp = Not cp
passbtn.BackColor = GetPlayerForeColor(cp)
passbtn.ForeColor = GetPlayerBackColor(cp)
End Sub
Private Function GetPlayerForeColor(player as Boolean) As Color
If player Then
Return Color.White
Else
Return Color.Black
End If
End Function
Private Function GetPlayerBackColor(player as Boolean) As Color
If player Then
Return Color.Black
Else
Return Color.White
End If
End Function
You'll notice that I snuck (Chrome auto-spell tells me that isn't a word, but my American upbringing begs to differ) a couple other methods in there while I was at it. I'm sure their purpose is obvious. But stop right there. It's obvious? You'll notice that the comments are gone, yet the meaning of the code is still obvious. That's what we mean by self-documenting code. Comments are great when they're necessary, but it's even better when they aren't necessary at all.
So, pretend for now we have a method like this:
Private Function MakeMove(gridPosition As Grid, player As Boolean) As Boolean
' return true if the move was successful
End Function
Then the whole Panel1_Click event handler could look like this:
Private Sub Panel1_Click(sender As Object, e As EventArgs) Handles Panel1.Click
Dim board As Panel = DirectCast(sender, Panel)
Dim gridPosition As Point = GetGridPosition(board, Cursor.Position)
If MakeMove(gridPosition, cp) Then
SwitchPlayer()
Else
ShowIllegalMoveMessage()
End If
End Sub
Private Sub ShowIllegalMoveMessage()
illegalmovelbl.Show() 'Shows the "Illegal Move" Label
MsgBox("Place your stone in a vacant point") 'Displays error message
End Sub
Ok, so now we're getting to the meat of it. So, what are the steps that need to be taken when a move is being made? Well, I don't know, because I don't know the game. I leave that exercise up to you, but, if your inclinations are correct, and you need some kind of flood fill algorithm, then that probably means that you need some kind of PlaceStone action which can be repeated over and over again, so that should be its own method:
Private Sub PlaceStone(gridPosition As Point, player As Boolean)
' Do something
End Sub
Obviously the Do something is the key part of all this, and it's the one part that I can't help you with. But, if it's going to be a flood fill algorithm, I can give you a really big hint. Among all the other stuff it's going to do in there, it's going to be calling PlaceStone again, passing it a different grid position (one of the surrounding positions). So for instance, something like this:
Private Sub PlaceStone(gridPosition As Point, player As Boolean)
Dim north As Position = GetNorthPosition(gridPosition)
If Floodable(north, player) Then
PlaceStone(north, player)
End If
' ...
End Sub
When a method calls itself, like that, we call it recursion. But, until you start splitting your code up into dedicated little methods, each with its own encapsulated task, then you can't really add recursion. So, first get organized, then add recursion.