Help with platform engine

Hello (first post). My name is DoctorN (but seemingly, that name was taken). I am working on a platform engine for my company. At this beginning moment, gameplay will be like an old case of super mairo. However, im at a stump, and can continue no farther unless I get some help. My character can not freely fall on his own, he has to jump in order to fall off the platform (if i jump off of the platform that is). He has to be perfectly alligned on top of the platform if he wishes to jump (so if i spawn him not on the platform, he doesnt fall, nor can he jump, just move left and right). And you'll see in the TimerY_Tick, theres a +113. that is because when he lands, thats the Y coordinate that he must land on (becuase 114 and below is the platform I guess). Can you look and adjust my code to those three things, or at least guide me in the right path? 1.wherever he spawns, hell fall if theres no ground underneath him. 2. there doesnt need to be a precise code where he has to land. thanks. heres the code

Code:

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Public Class Form1

    Dim WithEvents TimerX As New Timer With {.Enabled = True, .Interval = 10}
    Dim WithEvents TimerY As New Timer With {.Enabled = True, .Interval = 10}
    Dim WithEvents TimerGravity As New Timer With {.Enabled = False, .Interval = 100}


    Dim PlayerWidth As Integer = 20
    Dim playerHeight As Integer = 20

    'This is your Player
    Dim playChar As PictureBox
    'This rectangle represente the window,if the player does not intersec with this rectangle
    'it means that it is about to move out of the window
    Dim theBox As Rectangle
    'This rectangle is your floor, if the player intersec with it, it means that it touch the floor
    Dim TheFloor As Rectangle

    'These are your movement variable (Higher the value faster your player goes
    Dim SpeedX As Integer = 0
    Dim SpeedY As Integer = 0
    'This is your gravity Variable, Higher the value, stronger is the gravity
    Dim Gravity As Integer = 1.5
    'This is your jump variable, higher the value, higher is the jump
    'We set the negative value of the speed toward the top of the form, this
    'simplify the math
    Dim JumpSpeed As Integer = -5.6

    Private Sub Form1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown
        Select Case e.KeyCode
            Case Keys.A ' Going toward the left
                playChar.Image = Image.FromFile("C:\Users\Nick Lopez\Documents\Visual Studio 2010\Projects\n_platform\n_platform\Resources\player_walk_2_l.png")
                SpeedX = -1.5
            Case Keys.D ' Going toward the right
                playChar.Image = Image.FromFile("C:\Users\Nick Lopez\Documents\Visual Studio 2010\Projects\n_platform\n_platform\Resources\player_walk_2_r.png")
                SpeedX = 1.5
            Case Keys.W ' Jump
                'Create a test rectangle before jumping to see if the player touch the ground
                Dim Test As Rectangle = New Rectangle(New Point(playChar.Location.X, playChar.Location.Y + 2), playChar.Size)
                'If The test rectangle intersect with the floor, allow the jump
                If Test.IntersectsWith(TheFloor) Then
                    'Perform the jump
                    SpeedY = JumpSpeed
                    'Start the gravite meter
                    TimerGravity.Enabled = True
                End If
        End Select
    End Sub

    Private Sub Form1_KeyUp(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyUp
        Select Case e.KeyCode
            Case Keys.A ' stop moving when the key is release
                playChar.Image = Image.FromFile("C:\Users\Nick Lopez\Documents\Visual Studio 2010\Projects\n_platform\n_platform\Resources\player_stand_l.png")
                SpeedX = 0
            Case Keys.D ' stop moving when the key is release
                playChar.Image = Image.FromFile("C:\Users\Nick Lopez\Documents\Visual Studio 2010\Projects\n_platform\n_platform\Resources\player_stand_r.png")
                SpeedX = 0
        End Select
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ' Set up the rectangle
        Me.Size = New Size(320, 240)
        theBox = New Rectangle(PlayerWidth, playerHeight, Me.ClientSize.Width - (PlayerWidth * 2), Me.ClientSize.Height - (playerHeight * 2))
        playChar = PlayModel
        TheFloor = New Rectangle(33, 140, 233, 156)
        Me.DoubleBuffered = True
    End Sub

    Private Sub TimerX_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles TimerX.Tick
        'Create a test rectangle before moving the player to see if he is about to move out of the screen
        Dim Test As Rectangle = New Rectangle(New Point(playChar.Location.X + SpeedX, playChar.Location.Y), playChar.Size)
        ' If not moving out of the screen then move
        'NB If there is some obstacles, you will also test here if the Test rectangle intersect with the obstacle before moving
        If Test.IntersectsWith(theBox) Then
            playChar.Location = New Point(playChar.Location.X + SpeedX, playChar.Location.Y)
        End If
        'redraw the screen
        Me.Refresh()
    End Sub

    Private Sub TimerY_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles TimerY.Tick
        playChar.Location = New Point(playChar.Location.X, playChar.Location.Y + SpeedY)
        ' if the player touches the floor
        If playChar.Bounds.IntersectsWith(TheFloor) Then
            ' stop the downward movement
            SpeedY = 0
            'replace the player 1 pixel above the floor
            playChar.Location = New Point(playChar.Location.X, levelGround.ClientSize.Height - playerHeight + 113)
            'stop the gravity timer
            TimerGravity.Enabled = False
        End If
        'redraw the screen
        Me.Refresh()
    End Sub

    Private Sub TimerGravity_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles TimerGravity.Tick
        SpeedY += Gravity
    End Sub
End Class

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ive updated the code very slightly but not enough to call it an improvement, please help.

in case the code wasnt formatted properly here:

vb Code:

Public Class Form1
 
    Dim WithEvents TimerX As New Timer With {.Enabled = True, .Interval = 10}
    Dim WithEvents TimerY As New Timer With {.Enabled = True, .Interval = 10}
    Dim WithEvents TimerGravity As New Timer With {.Enabled = False, .Interval = 100}
 
 
    Dim PlayerWidth As Integer = 20
    Dim playerHeight As Integer = 20
 
    'This is your Player
    Dim playChar As PictureBox
    'This rectangle represente the window,if the player does not intersec with this rectangle
    'it means that it is about to move out of the window
    Dim theBox As Rectangle
    'This rectangle is your floor, if the player intersec with it, it means that it touch the floor
    Dim TheFloor As Rectangle
 
    'These are your movement variable (Higher the value faster your player goes
    Dim SpeedX As Integer = 0
    Dim SpeedY As Integer = 0
    'This is your gravity Variable, Higher the value, stronger is the gravity
    Dim Gravity As Integer = 1.5
    'This is your jump variable, higher the value, higher is the jump
    'We set the negative value of the speed toward the top of the form, this
    'simplify the math
    Dim JumpSpeed As Integer = -5.6
 
    Private Sub Form1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown
        Select Case e.KeyCode
            Case Keys.A ' Going toward the left
                playChar.Image = Image.FromFile("C:\Users\Nick Lopez\Documents\Visual Studio 2010\Projects\n_platform\n_platform\Resources\player_walk_2_l.png")
                SpeedX = -1.5
            Case Keys.D ' Going toward the right
                playChar.Image = Image.FromFile("C:\Users\Nick Lopez\Documents\Visual Studio 2010\Projects\n_platform\n_platform\Resources\player_walk_2_r.png")
                SpeedX = 1.5
            Case Keys.W ' Jump
                'Create a test rectangle before jumping to see if the player touch the ground
                Dim Test As Rectangle = New Rectangle(New Point(playChar.Location.X, playChar.Location.Y + 2), playChar.Size)
                'If The test rectangle intersect with the floor, allow the jump
                If Test.IntersectsWith(TheFloor) Then
                    'Perform the jump
                    SpeedY = JumpSpeed
                    'Start the gravite meter
                    TimerGravity.Enabled = True
                End If
        End Select
    End Sub
 
    Private Sub Form1_KeyUp(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyUp
        Select Case e.KeyCode
            Case Keys.A ' stop moving when the key is release
                playChar.Image = Image.FromFile("C:\Users\Nick Lopez\Documents\Visual Studio 2010\Projects\n_platform\n_platform\Resources\player_stand_l.png")
                SpeedX = 0
            Case Keys.D ' stop moving when the key is release
                playChar.Image = Image.FromFile("C:\Users\Nick Lopez\Documents\Visual Studio 2010\Projects\n_platform\n_platform\Resources\player_stand_r.png")
                SpeedX = 0
        End Select
    End Sub
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ' Set up the rectangle
        Me.Size = New Size(320, 240)
        theBox = New Rectangle(PlayerWidth, playerHeight, Me.ClientSize.Width - (PlayerWidth * 2), Me.ClientSize.Height - (playerHeight * 2))
        playChar = PlayModel
        TheFloor = New Rectangle(33, 140, 233, 156)
        Me.DoubleBuffered = True
    End Sub
 
    Private Sub TimerX_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles TimerX.Tick
        'Create a test rectangle before moving the player to see if he is about to move out of the screen
        Dim Test As Rectangle = New Rectangle(New Point(playChar.Location.X + SpeedX, playChar.Location.Y), playChar.Size)
        ' If not moving out of the screen then move
        'NB If there is some obstacles, you will also test here if the Test rectangle intersect with the obstacle before moving
        If Test.IntersectsWith(theBox) Then
            playChar.Location = New Point(playChar.Location.X + SpeedX, playChar.Location.Y)
        End If
        'redraw the screen
        Me.Refresh()
    End Sub
 
    Private Sub TimerY_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles TimerY.Tick
        playChar.Location = New Point(playChar.Location.X, playChar.Location.Y + SpeedY)
        ' if the player touches the floor
        If playChar.Bounds.IntersectsWith(TheFloor) Then
            ' stop the downward movement
            SpeedY = 0
            'replace the player 1 pixel above the floor
            playChar.Location = New Point(playChar.Location.X, levelGround.ClientSize.Height - playerHeight + 113)
            'stop the gravity timer
            TimerGravity.Enabled = False
        End If
        'redraw the screen
        Me.Refresh()
    End Sub
 
    Private Sub TimerGravity_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles TimerGravity.Tick
        SpeedY += Gravity
    End Sub
End Class

I haven't looked at your code (because I know I won't have time to completely understand any of it), but if your character can only fall if he is ON an obstacle that indicates that your logic is wrong.

I haven't got much experience with games, but I would use this approach. I am assuming you've got some kind of game loop that runs every few milliseconds (at least maybe 10 times a second, preferably more). In that loop I would take the following actions:
- Store (a copy of) the bounds of the character in a local variable
- Decrease the Y value of the speed of the character by the amount of gravity (well, increase it, since positive Y is down)
- Change the bounds of the character by his speed (bounds.X += speed.X, bounds.Y += speed.Y)
- Check if the new bounds of the character are inside an obstable (likely; you'd loop through every obstacle, get it's bounds and check if the new bounds are inside these bounds, Rectangle.IntersectsWith or something)
- If they are inside an obstacle, a collision occured, and the new bounds are invalid. Set the new bounds such that the character is standing exactly on the obstacle (bottom of character bounds = top of obstable bounds, maybe with a 1px boundary as long as they don't intersect anymore)
- If they are not inside an obstacle, all is well, just continue
- At the end, assign the new bounds to the character again.


The reason for making a copy of the bounds, changing that copy, and checking for collisions on that copy, is simple. You could just change the character bounds immediately and check for collisions afterwards, but if a collision occurs you'd have to move him back up, and this can cause the character to become stuck in some occasions (he would be colliding, move him back, he's still colliding, then you're stuck). Maybe not in this case, I don't know, but it doesn't hurt to use the copy approach.


As for jumping, when the jump key is pressed you'd first check if the character is standing on an obstacle (you may want to use a simple boolean property for this, which you set to False every iteration of the game loop, and only to True after a collision has occurred and you re-set his position to just above the colliding obstacle). If yes, you set his speed.Y to a certain value. Each game loop iteration this value will be decreased (but still positive) until it reaches zero (peak of jump) and then it goes negative (falling down again).

can someone else help too?

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