VB.NET - Movement Blocked due to Faulty Collision Detection - vb.net

Question

So, I am making a game for my programming class as part of my final project. I'm just in the planning and experimenting stage at the moment and I decided to get a headstart on graphics and collisions. I first made my program just by experimenting with the Graphics class VB has to offer, instead of using PictureBoxes. Alongside that, I added keyboard input to move an Image around. When I decided to add collision detection through the intersectsWith() method of the Image class, things became weird.
Basically, in my code, the "Player" entity has three different images - which change depending on which way they are facing, which is in turn determined by what key the user presses. Without any collision detection code, the movement and image changing works fine and the image moves about. However, as soon as I add collision detection the player does not move at all, only the way they face changes. This happens even if the player's Image is nowhere near the image I want to test for intersection (a dollar sign). Here's my entire code:
Public Class Form1
Enum DirectionFacing
FORWARDS
BACKWARD
LEFT
RIGHT
End Enum
' Player X position.
Dim pX As Integer = 100
' Player Y position.
Dim pY As Integer = 100
' The direction the player is facing - by default, backward.
Dim dir As DirectionFacing = DirectionFacing.BACKWARD
' The image of the player.
Dim pI As Image = My.Resources.MainCharacter_Forward
' Another image designed to test for collision detection.
Dim dI As Image = My.Resources.DollarSign
Private Sub Form1_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles MyBase.KeyDown
If (e.KeyCode = Keys.W) Then
' If they press W, move forward.
dir = DirectionFacing.FORWARDS
pI = My.Resources.MainCharacter_Forward
movePlayer(DirectionFacing.FORWARDS, 10)
ElseIf (e.KeyCode = Keys.S) Then
' If they press S, move backward.
dir = DirectionFacing.BACKWARD
pI = My.Resources.MainCharacter_Behind
movePlayer(DirectionFacing.BACKWARD, 10)
ElseIf (e.KeyCode = Keys.A) Then
' If they press A, move to the left.
pI = My.Resources.MainCharacter_Side
dir = DirectionFacing.LEFT
movePlayer(DirectionFacing.LEFT, 10)
ElseIf (e.KeyCode = Keys.D) Then
' If they press D, move to the right. To make the player face rightward,
' the image can be flipped.
Dim flipped As Image = My.Resources.MainCharacter_Side
flipped.RotateFlip(RotateFlipType.RotateNoneFlipX)
pI = flipped
dir = DirectionFacing.LEFT
movePlayer(DirectionFacing.RIGHT, 10)
End If
End Sub
' Moves the player by a certain amount AND checks for collisions.
Private Sub movePlayer(dir As DirectionFacing, amount As Integer)
If (dI.GetBounds(GraphicsUnit.Pixel).IntersectsWith(pI.GetBounds(GraphicsUnit.Pixel))) Then
Return
End If
If (dir = DirectionFacing.FORWARDS) Then
pY -= 10
ElseIf (dir = DirectionFacing.BACKWARD) Then
pY += 10
ElseIf (dir = DirectionFacing.LEFT) Then
pX -= 10
ElseIf (dir = DirectionFacing.RIGHT) Then
pX += 10
End If
End Sub
Private Sub draw(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
Dim g As Graphics = e.Graphics()
g.DrawImage(dI, 400, 350)
g.DrawImage(pI, pX, pY)
Me.Invalidate()
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Me.DoubleBuffered = True
End Sub
End Class
Basically, every time I press a key and want the image to move, the image doesn't move at all (even when the Player is nowhere close to the dollar sign), but the direction they are facing still changes. How can I keep the player moving and still stop the player from colliding with another image?

Answer 1

Well, the
If (dI.GetBounds(GraphicsUnit.Pixel).IntersectsWith(pI.GetBounds(GraphicsUnit.Pixel)))
will always return False since the GetBounds method does not return the current location of each rectangle. So they will never intersect, and your drawing scene remains the same.
So let's try to solve this problem.
Enum DirectionFacing
FORWARDS
BACKWARD
LEFT
RIGHT
End Enum
' The image of the player.
Dim pI As New Bitmap(My.Resources.MainCharacter_Forward)
' Another image designed to test for collision detection.
Dim dI As New Bitmap(My.Resources.DollarSign)
'The rectangle of the player's image.
Dim pIrect As New Rectangle(100, 100, pI.Width, pI.Height)
'The static rectangle of the collision's image.
Dim dIrect As New Rectangle(400, 350, dI.Width, dI.Height)
Now the IntersectWith function should work in the movePlayer method:
Private Sub movePlayer(dir As DirectionFacing, amount As Integer)
Dim px = pIrect.X
Dim py = pIrect.Y
Select Case dir
Case DirectionFacing.FORWARDS
py -= amount
Case DirectionFacing.BACKWARD
py += amount
Case DirectionFacing.LEFT
px -= amount
Case DirectionFacing.RIGHT
px += amount
End Select
If Not New Rectangle(px, py, pI.Width, pI.Height).IntersectsWith(dIrect) Then
pIrect = New Rectangle(px, py, pI.Width, pI.Height)
Invalidate()
End If
End Sub
Note that, both px and py variables are now locals because we already have pIrect which includes the currect x and y. We replaced the If statement with Select Case as a better approach I believe. We created a new rectangle to check any possible collision, if not, then we update our pIrect and refresh the drawing.
Besides moving the image through the W S A D keys, you also can make use of the ← ↑ → ↓ keys. To intercept them in the KeyDown event, just override the IsInputKey function as follow:
Protected Overrides Function IsInputKey(keyData As Keys) As Boolean
Select Case keyData And Keys.KeyCode
Case Keys.Left, Keys.Up, Keys.Right, Keys.Down
Return True
Case Else
Return MyBase.IsInputKey(keyData)
End Select
End Function
Thus, the KeyDown event:
Private Sub Form1_KeyDown(sender As Object, e As KeyEventArgs) Handles MyBase.KeyDown
Select Case e.KeyCode
Case Keys.W, Keys.Up
pI?.Dispose()
pI = New Bitmap(My.Resources.MainCharacter_Forward)
movePlayer(DirectionFacing.FORWARDS, 10)
Case Keys.S, Keys.Down
pI?.Dispose()
pI = New Bitmap(My.Resources.MainCharacter_Behind)
movePlayer(DirectionFacing.BACKWARD, 10)
Case Keys.A, Keys.Left
pI?.Dispose()
pI = New Bitmap(My.Resources.MainCharacter_Side)
movePlayer(DirectionFacing.LEFT, 10)
Case Keys.D, Keys.Right
pI?.Dispose()
pI = New Bitmap(My.Resources.MainCharacter_Side)
pI.RotateFlip(RotateFlipType.RotateNoneFlipX)
movePlayer(DirectionFacing.RIGHT, 10)
End Select
End Sub
Again, we replaced the If Then Else statement with Select Case. If you are not supposed to do that, I believe it will be easy for you to revert and use If e.KeyCode = Keys.W OrElse e.KeyCode = Keys.Up Then ....
The Paint routine:
Private Sub draw(sender As Object, e As PaintEventArgs) Handles Me.Paint
Dim g As Graphics = e.Graphics()
g.DrawImage(dI, dIrect)
g.DrawImage(pI, pIrect)
End Sub
Finally, don't forget to clean up:
Private Sub Form1_FormClosed(sender As Object, e As FormClosedEventArgs) Handles Me.FormClosed
pI?.Dispose()
dI?.Dispose()
End Sub
Good luck