[RESOLVED] [VB6] - Building games with API functions

[Jacob Roman]

(Continued from above post) Also just to let ya know, if the collision isn't a sprite and its a tile in a tile engine, I do something differently but with the same algorithm. Most people would make the fatal mistake of looping through the whole map one tile at a time to check if a collision took place with the sprite. But if your map is gigantic in size, this would be sluggish. The faster way would be to check all 9 sides of the sprite to see if it collided into the tile surrounding it. Why check all 9 sides and not just the sprite itself? Cause if you are approaching the walls at an angle or move into a corner, you end up going through the walls! So for example, if you use rigid body collision, you do this, assuming you got a tile engine going:

Public Function Collision_Detection() As Boolean
    
    Dim Vertex_List(4) As Vector
    Dim Vertex_List2(4) As Vector
    Dim Boundry(8) As Vector
    Dim Position As Vector
    Dim I As Long
    
    Vertex_List(0) = Vector_New(0, 0)
    Vertex_List(1) = Vector_New(TILE_SIZE, 0)
    Vertex_List(2) = Vector_New(TILE_SIZE, TILE_SIZE)
    Vertex_List(3) = Vector_New(0, TILE_SIZE)
    
    Vertex_List2(0) = Vector_New(0, 0)
    Vertex_List2(1) = Vector_New(TILE_SIZE, 0)
    Vertex_List2(2) = Vector_New(TILE_SIZE, TILE_SIZE)
    Vertex_List2(3) = Vector_New(0, TILE_SIZE)
    
    With Player
    
        Boundry(0).X = .Coordinates.X - 1: Boundry(0).Y = .Coordinates.Y
        Boundry(1).X = .Coordinates.X:     Boundry(1).Y = .Coordinates.Y - 1
        Boundry(2).X = .Coordinates.X + 1: Boundry(2).Y = .Coordinates.Y
        Boundry(3).X = .Coordinates.X:     Boundry(3).Y = .Coordinates.Y + 1
        Boundry(4).X = .Coordinates.X:     Boundry(4).Y = .Coordinates.Y
        Boundry(5).X = .Coordinates.X - 1:     Boundry(5).Y = .Coordinates.Y - 1
        Boundry(6).X = .Coordinates.X + 1:     Boundry(6).Y = .Coordinates.Y - 1
        Boundry(7).X = .Coordinates.X - 1:      Boundry(7).Y = .Coordinates.Y + 1
        Boundry(8).X = .Coordinates.X + 1:     Boundry(8).Y = .Coordinates.Y + 1
    
        For I = 0 To 8
            If Boundry(I).X <= 0 Then Boundry(I).X = 0
            If Boundry(I).Y <= 0 Then Boundry(I).Y = 0
            If Boundry(I).X >= Map.Width - 1 Then Boundry(I).X = Map.Width - 1
            If Boundry(I).Y >= Map.Height - 1 Then Boundry(I).Y = Map.Height - 1
        
            Position.X = Map.Collision_Map.Vertex_List(Boundry(I).X, Boundry(I).Y).X
            Position.Y = Map.Collision_Map.Vertex_List(Boundry(I).X, Boundry(I).Y).Y
            .Collided = Collide(Vertex_List2(), Vertex_List(), 4, 4, Vector_Subtract(.Position, Position), .NColl, .DColl)
            
            If .Collided = True Then
                If Map.Collision_Map.Response(Boundry(I).X, Boundry(I).Y) = COLLISION_WALL Then
                    Collision_Detection = True
                    .Position = Vector_Subtract(.Position, Vector_Multiply2(.NColl, (.DColl * 1.01)))
                End If
            End If
        Next I
        
    End With
 
end function

with sprite coordinates being the tile position of where the sprite is at on the map. To convert a position into tile coordinates you do this:

Public Sub Convert_Position_To_Coordinates(Sprite As Sprite_Type)
 
    Sprite.Coordinates.X = Int(Sprite.Position.X / TILE_SIZE)
    Sprite.Coordinates.Y = Int(Sprite.Position.Y / TILE_SIZE)
 
End Sub

For Box to Box however, its similar but a little different for collision response:

Public Function Collision_Detection2(ByVal Overlap As Long)
 
    Const NO_COLLISION As Long = 0
    Const COL_LEFT As Long = 1
    Const COL_RIGHT As Long = 2
    Const COL_UP As Long = 3
    Const COL_DOWN As Long = 4
 
    Dim Boundry(8) As Vector
    Dim Side As Long
    Dim I As Long
 
    With Player
    
        Boundry(0).X = .Coordinates.X - 1: Boundry(0).Y = .Coordinates.Y
        Boundry(1).X = .Coordinates.X:     Boundry(1).Y = .Coordinates.Y - 1
        Boundry(2).X = .Coordinates.X + 1: Boundry(2).Y = .Coordinates.Y
        Boundry(3).X = .Coordinates.X:     Boundry(3).Y = .Coordinates.Y + 1
        Boundry(4).X = .Coordinates.X:     Boundry(4).Y = .Coordinates.Y
        Boundry(5).X = .Coordinates.X - 1:     Boundry(5).Y = .Coordinates.Y - 1
        Boundry(6).X = .Coordinates.X + 1:     Boundry(6).Y = .Coordinates.Y - 1
        Boundry(7).X = .Coordinates.X - 1:      Boundry(7).Y = .Coordinates.Y + 1
        Boundry(8).X = .Coordinates.X + 1:     Boundry(8).Y = .Coordinates.Y + 1
        
        For I = 0 To 8
        
            If Boundry(I).X <= 0 Then Boundry(I).X = 0
            If Boundry(I).Y <= 0 Then Boundry(I).Y = 0
            If Boundry(I).X >= Map.Width - 1 Then Boundry(I).X = Map.Width - 1
            If Boundry(I).Y >= Map.Height - 1 Then Boundry(I).Y = Map.Height - 1
 
            Side = Collision_Box_To_Box2(Player.Position.X, Player.Position.Y, TILE_SIZE, TILE_SIZE, Boundry(I).X * TILE_SIZE, Boundry(I).Y * TILE_SIZE, TILE_SIZE, TILE_SIZE)
            
            If Side <> 0 Then
                If Map.Collision_Map.Response(Boundry(I).X, Boundry(I).Y) = COLLISION_WALL Then
                    Collision_Detection2 = True
                    .Collided = True
                    Select Case Side
                        Case COL_LEFT: .Position.X = .Position.X + Overlap
                        Case COL_RIGHT:: .Position.X = .Position.X - Overlap
                        Case COL_UP:: .Position.Y = .Position.Y + Overlap
                        Case COL_DOWN:: .Position.Y = .Position.Y - Overlap
                    End Select
                End If
            End If
            
        Next I
        
    End With
    
End Function

Heres a project I uploaded for ya. Although it's an AStar sample I'm working on, it has the tile collision code I was talking about. Have fun