DirectX 2D grid - vb.net

Question

I have been trying to get a 2D grid going. It's for a game map.
Unfortunately, the grid is not as it should be. And I cannot figure out why.
Does anyone have an idea?
Imports Microsoft.DirectX
Imports Microsoft.DirectX.Direct3D
Public Class clsIsometric
'==================================
' SETTINGS
'==================================
Private tile_size As New Point(64, 64) 'Size of one tile in pixels
Private map_size As New Point(25, 25) 'Amount of tiles in total
Private gDevice As Device
Private bufVertex As VertexBuffer
Private bufIndex As IndexBuffer
Private gVertices() As CustomVertex.TransformedColored
Private gIndices() As Integer
'==================================
' CONSTRUCTOR
'==================================
Public Sub New(vDevice As Device)
gDevice = vDevice
End Sub
Public Sub dispose()
bufVertex.Dispose()
bufIndex.Dispose()
bufVertex = Nothing
bufIndex = Nothing
End Sub
'==================================
' RENDERING
'==================================
Public Sub buildMap()
' Recreate buffers to fit the map size
ReDim gVertices((map_size.X + 1) * (map_size.Y + 1)) ' x+1 * y+1
ReDim gIndices(map_size.X * map_size.Y * 6) ' x * y * 6
Dim k As Integer
For cX = 0 To map_size.X - 1 'Rows
For cY = 0 To map_size.Y - 1 'Columns
'VERTEX
k = cX * map_size.X + cY
gVertices(k) = New CustomVertex.TransformedColored(cX * tile_size.X, cY * tile_size.Y, 0, 1, Color.Blue.ToArgb)
Next cY
Next cX
Dim vertexPerCol As Integer = map_size.Y + 1
k = 0
For ccX = 0 To map_size.X - 1
For ccY = 0 To map_size.Y - 1
gIndices(k) = ccX * vertexPerCol + ccY ' 0
gIndices(k + 1) = (ccX + 1) * vertexPerCol + (ccY + 1) ' 1
gIndices(k + 2) = (ccX + 1) * vertexPerCol + ccY ' 2
gIndices(k + 3) = ccX * vertexPerCol + ccY ' 3
gIndices(k + 4) = ccX * vertexPerCol + (ccY + 1) ' 4
gIndices(k + 5) = (ccX + 1) * vertexPerCol + (ccY + 1) ' 5
k += 6 'Each tile has 6 indices. Increase for next tile
Next
Next
bufVertex = New VertexBuffer(GetType(CustomVertex.TransformedColored), gVertices.Length, gDevice, Usage.Dynamic Or Usage.WriteOnly, CustomVertex.TransformedColored.Format, Pool.Default)
bufIndex = New IndexBuffer(GetType(Integer), gIndices.Length, gDevice, Usage.WriteOnly, Pool.Default)
End Sub
Public Sub render()
'RENDER THE MAP
bufVertex.SetData(gVertices, 0, LockFlags.ReadOnly)
bufIndex.SetData(gIndices, 0, LockFlags.None)
gDevice.VertexFormat = CustomVertex.TransformedColored.Format
gDevice.SetStreamSource(0, bufVertex, 0)
gDevice.Indices = bufIndex
gDevice.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, gVertices.Length, 0, CInt(gIndices.Length / 3))
End Sub
End Class
This should output a perfect square grid of 25 by 25 tiles. But the wireframe looks like:
http://i43.tinypic.com/2whf51c.jpg

Answer 1

Your loop which build the vertices seems to end too early, because you have n+1 vertices each row/column. It fills the array only to the forelast column, which leads to a shift in the vertices.
For cX = 0 To map_size.X 'Rows
For cY = 0 To map_size.Y 'Columns
'VERTEX
k = cX * (map_size.X + 1) + cY
gVertices(k) = New CustomVertex.TransformedColored(cX * tile_size.X, cY * tile_size.Y, 0, 1, Color.Blue.ToArgb)
Next cY
Next cX