Imports Microsoft.Xna.Framework
Imports Microsoft.Xna.Framework.Input
Imports Microsoft.Xna.Framework.Graphics
Imports System.Runtime.InteropServices

Public Class Game
    Inherits Microsoft.Xna.Framework.Game

#Region "Strutture aggiuntive"
    Private Shared DoubleSize As Byte = Marshal.SizeOf(GetType(Double))

    Private Structure VertexPositionNormalColor
        Public Position As Vector3
        Public Normal As Vector3
        Public Color As Color

        Public Shared SizeInBytes As Int16 = 7 * 4
        Public Shared VertexElements() As VertexElement = New VertexElement() _
        { _
            New VertexElement(0, 0, VertexElementFormat.Vector3, _
                VertexElementMethod.Default, _
                VertexElementUsage.Position, 0), _
            New VertexElement(0, DoubleSize * 3, _
                VertexElementFormat.Color, _
                VertexElementMethod.Default, _
                VertexElementUsage.Color, 0), _
            New VertexElement(0, DoubleSize * 4, _
                VertexElementFormat.Vector3, _
                VertexElementMethod.Default, _
                VertexElementUsage.Normal, 0) _
        }
    End Structure

#End Region

#Region "Variabili globali"

    Private AppPath As String = _
        My.Application.Info.DirectoryPath

    Private Graphics As GraphicsDeviceManager

    Private Shader As Effect
    Private Vertices() As VertexPositionNormalColor
    Private Indices() As Int32
    Private VBuffer As VertexBuffer
    Private IBuffer As IndexBuffer
    Private VDeclaration As VertexDeclaration

    Private ViewMatrix As Matrix
    Private ProjectionMatrix As Matrix
    Private WorldMatrix As Matrix

    Private DX, DZ As Single
    Private Angle As Single

    Private HeightData(,) As Single
    Private Const MinHeight As Single = 0
    Private Const MaxHeight As Single = 30
    Private TerrainWidth, TerrainLength As Int32
#End Region

#Region "Funzioni utili"

    Private Function GetEffect(ByVal FileName As String) As Effect
        Dim CompEffect As CompiledEffect = _
            Effect.CompileEffectFromFile(FileName, _
            Nothing, Nothing, _
            CompilerOptions.None, _
            TargetPlatform.Windows)

        Return New Effect(Me.GraphicsDevice, _
            CompEffect.GetEffectCode, _
            CompilerOptions.None, Nothing)
    End Function

    Private Function GetTexture(ByVal FileName As String)
        Return Texture2D.FromFile(Me.GraphicsDevice, FileName)
    End Function

#End Region

#Region "Caricamento Heightmap"
    Private Sub LoadHeightMap(ByVal HeightMap As Texture2D)
        TerrainWidth = HeightMap.Width
        TerrainLength = HeightMap.Height '2D!

        Dim Colors(TerrainWidth * TerrainLength - 1) As Color
        HeightMap.GetData(Colors)

        For I As Int32 = 0 To TerrainWidth - 1
            ReDim HeightData(I, TerrainLength - 1)
        Next

        For X As Int32 = 0 To TerrainWidth - 1
            For Z As Int32 = 0 To TerrainLength - 1
                HeightData(X, Z) = MinHeight + _
                    (Colors(X + Z * TerrainWidth).R / 255) * _
                    (MaxHeight - MinHeight)
            Next
        Next

        VDeclaration = New VertexDeclaration(Me.GraphicsDevice, _
            VertexPositionNormalColor.VertexElements)
    End Sub

    Private Sub SetVertices()
        ReDim Vertices(TerrainWidth * TerrainLength - 1)

        Dim Strip As Single = (MaxHeight - MinHeight) / 4
        For X As Int32 = 0 To TerrainWidth - 1
            For Z As Int32 = 0 To TerrainLength - 1
                With Vertices(X + Z * TerrainWidth)
                    Dim Y As Single = HeightData(X, Z)

                    .Position = New Vector3(X, Y, -Z)

                    If Y <= MinHeight + Strip Then
                        .Color = Color.LightBlue
                    ElseIf (Y > MinHeight + Strip) And _
                        (Y <= MinHeight + Strip * 2) Then
                        .Color = New Color(115, 171, 58)
                    ElseIf (Y > MinHeight + Strip * 2) And _
                        (Y <= MinHeight + Strip * 3) Then
                        .Color = New Color(125, 85, 49)
                    Else
                        .Color = Color.White
                    End If
                End With
            Next
        Next
    End Sub

    Private Sub SetIndices()
        ReDim Indices((TerrainWidth - 1) * (TerrainLength - 1) * 6 - 1)

        Dim Counter As Int32 = 0

        For X As Int32 = 0 To TerrainWidth - 2
            For Z As Int32 = 0 To TerrainLength - 2
                Dim LowerLeft As Int16 = X + Z * TerrainWidth
                Dim LowerRight As Int16 = (X + 1) + Z * TerrainWidth
                Dim TopLeft As Int16 = X + (Z + 1) * TerrainWidth
                Dim TopRight As Int16 = (X + 1) + (Z + 1) * TerrainWidth

                Indices(Counter) = TopLeft
                Indices(Counter + 1) = LowerRight
                Indices(Counter + 2) = LowerLeft
                Counter += 3

                Indices(Counter) = TopLeft
                Indices(Counter + 1) = TopRight
                Indices(Counter + 2) = LowerRight
                Counter += 3
            Next
        Next
    End Sub

    Private Sub SetNormals()
        For I As Int32 = 0 To Vertices.Length - 1
            Vertices(I).Normal = New Vector3(0, 0, 0)
        Next

        For I As Int16 = 0 To (Indices.Length / 3) - 1
            Dim Index1 As Int16 = Indices(I * 3)
            Dim Index2 As Int16 = Indices(I * 3 + 1)
            Dim Index3 As Int16 = Indices(I * 3 + 2)

            Dim Side1 As Vector3 = _
                Vertices(Index1).Position - Vertices(Index3).Position
            Dim Side2 As Vector3 = _
                Vertices(Index1).Position - Vertices(Index2).Position
            Dim Normal As Vector3 = Vector3.Cross(Side1, Side2)

            Vertices(Index1).Normal += Normal
            Vertices(Index2).Normal += Normal
            Vertices(Index3).Normal += Normal
        Next

        For Each V As VertexPositionNormalColor In Vertices
            V.Normal.Normalize()
        Next
    End Sub
    
    Private Sub CopyToBuffer()
        VBuffer = New VertexBuffer(Me.GraphicsDevice, _
            Vertices.Length * VertexPositionNormalColor.SizeInBytes, _
            BufferUsage.WriteOnly)
        VBuffer.SetData(Vertices)

        IBuffer = New IndexBuffer(Me.GraphicsDevice, _
            GetType(Int32), Indices.Length, BufferUsage.WriteOnly)
        IBuffer.SetData(Indices)

        Me.GraphicsDevice.Indices = IBuffer
        Me.GraphicsDevice.Vertices(0).SetSource( _
            VBuffer, 0, VertexPositionNormalColor.SizeInBytes)
    End Sub
    
#End Region

#Region "Gestione risorse"

    Sub New()
        Me.Graphics = New GraphicsDeviceManager(Me)
        Me.Content.RootDirectory = "content"
    End Sub

    Protected Overrides Sub Initialize()
        MyBase.Initialize()
    End Sub

    Protected Overrides Sub LoadContent()
        Shader = GetEffect(AppPath & "\SimpleShader.fx")
        LoadHeightMap(GetTexture(AppPath & "\HeightMap.bmp"))
        SetVertices()
        SetIndices()
        SetNormals()
        CopyToBuffer()

        ViewMatrix = Matrix.CreateLookAt( _
            New Vector3(70, 100, -70), _
            New Vector3(0, 0, 0), _
            New Vector3(0, 1, 0))

        ProjectionMatrix = Matrix.CreatePerspectiveFieldOfView( _
            MathHelper.PiOver4, _
            Me.GraphicsDevice.Viewport.AspectRatio, _
            1, 500)

        MyBase.LoadContent()
    End Sub

    Protected Overrides Sub UnloadContent()
        MyBase.UnloadContent()
    End Sub

#End Region

#Region "Aggiornamento mondo 3D"

    Protected Overrides Sub Update(ByVal GameTime As GameTime)
        Angle += MathHelper.Pi / 600

        MyBase.Update(GameTime)
    End Sub

    Protected Overrides Sub Draw(ByVal gameTime As GameTime)
        Me.Graphics.GraphicsDevice.Clear(Color.CornflowerBlue)

        Shader.CurrentTechnique = Shader.Techniques("ColoredPlus")

        Shader.Parameters("View").SetValue(ViewMatrix)
        Shader.Parameters("Projection").SetValue(ProjectionMatrix)
        Shader.Parameters("World").SetValue( _
            Matrix.CreateTranslation( _
            New Vector3(-TerrainWidth / 2, 0, TerrainLength / 2)) * _
            Matrix.CreateRotationY(Angle))

        Dim LightDirection As New Vector3(-0.27, 0.33, -0.86)
        LightDirection = Vector3.Transform(LightDirection, _
            Matrix.CreateRotationY(Angle))
        LightDirection.Normalize()
        Shader.Parameters("LightEnabled").SetValue(True)
        Shader.Parameters("LightDirection").SetValue(LightDirection)
        Shader.Parameters("AmbientFactor").SetValue(0.1F)

        Shader.Begin()
        For Each Pass As EffectPass In Shader.CurrentTechnique.Passes
            Pass.Begin()
            With Me.GraphicsDevice
                .VertexDeclaration = VDeclaration
                Me.GraphicsDevice.DrawIndexedPrimitives( _
                    PrimitiveType.TriangleList, 0, 0, _
                    Vertices.Length, 0, Indices.Length / 3)
            End With
            Pass.End()
        Next
        Shader.End()

        MyBase.Draw(gameTime)
    End Sub
#End Region
End Class