What's wrong with this code? [SOLVED]

[hothead]

I have no problems getting the ball to wrap to the other side of the screen, but now I'm trying to get it to bounce like it does in a Breakout-type game. The code snippet below doesn't work, the ball just sticks to the bottom of the screen.

NOTE: Right now I'm testing the code in a command button's click procedure inside a practice program, just to see if I can get it working.

Private Sub Command1_Click()
    Dim T1 As Long, T2 As Long
    myBackBuffer = CreateCompatibleDC(GetDC(0))
    myBufferBMP = CreateCompatibleBitmap(GetDC(0), 320, 256)
    SelectObject myBackBuffer, myBufferBMP
    BitBlt myBackBuffer, 0, 0, 320, 256, 0, 0, 0, vbWhiteness
    mySprite = LoadGraphicDC(App.Path & "\sprite1.bmp")
    mySprite1 = LoadGraphicDC(App.Path & "\mask.bmp")
    cmdTest.Enabled = False
    T2 = GetTickCount
    Do
        DoEvents
        T1 = GetTickCount
        If (T1 - T2) >= 0.15 Then
            BitBlt myBackBuffer, SpriteX - 1, SpriteY - 1, 32, 32, 0, 0, 0, vbBlackness
            BitBlt myBackBuffer, SpriteX - 1, SpriteY - 1, 32, 32, 0, 0, 0, vbSrcAnd
            BitBlt myBackBuffer, SpriteX, SpriteY, 32, 32, mySprite, 0, 0, vbSrcAnd
            BitBlt myBackBuffer, SpriteX, SpriteY, 32, 32, mySprite1, 0, 0, vbSrcPaint
            BitBlt Me.hdc, 0, 0, 320, 256, myBackBuffer, 0, 0, vbSrcCopy
            SpriteX = SpriteX + 1
            SpriteY = SpriteY + 1
            T2 = GetTickCount
        End If
        If SpriteX = 320 Then
            SpriteX = SpriteX - 1
            SpriteY = SpriteY - 1
        ElseIf SpriteY = 256 Then
            SpriteX = SpriteX - 1
            SpriteY = SpriteY - 1
        End If
    Loop
End Sub

The code works fine when I take it out of the If SpriteX = 320/If SpriteY = 256 statements, so it must be the correct code.

[SLH]

I suggest having 2 lines that add the ball's velocity, then have seperate if statements that alter the ball's velocity. The way you're doing it is that if the ball goes out of bounds it moves back, but then just moves fowards again because you alter the balls position, not it's veolcity. Try something like this:

'Somewhere out of loop set SpriteXVeolcity and SpriteYVelocity to 1 (or whatever)
SpriteX = SpriteX + SpriteXVelocity
SpriteY = SpriteY + SpriteYVelocity
If SpriteX >= 360 Then SpriteXVelocity = -abs(SpriteXVelocity)
If SpriteY >= 256 Then SpriteYVelocity = -abs(SpriteYVelocity)

[DiGiTaIErRoR]

I'd suggest organizing it all in a type.

Private Type tSprite
 X as Single
 Y as Single
 Vx as Single
 Vy as Single
End Type
 
Private Sprite as tSprite

[hothead]

Originally posted by SLH
I suggest having 2 lines that add the ball's velocity, then have seperate if statements that alter the ball's velocity. The way you're doing it is that if the ball goes out of bounds it moves back, but then just moves fowards again because you alter the balls position, not it's veolcity. Try something like this:

'Somewhere out of loop set SpriteXVeolcity and SpriteYVelocity to 1 (or whatever)
SpriteX = SpriteX + SpriteXVelocity
SpriteY = SpriteY + SpriteYVelocity
If SpriteX >= 360 Then SpriteXVelocity = -abs(SpriteXVelocity)
If SpriteY >= 256 Then SpriteYVelocity = -abs(SpriteYVelocity)

At first I wasn't sure what you were talking about, but I experimented with it a bit, and found I could change the direction at which the ball travels by tweaking the values of SpriteXVelocity and SpriteYVelocity, which is kinda cool!

However, it still doesn't bounce when it hits the sides. It still sticks to the bottom.

[DiGiTaIErRoR]

Private Type tSprite
 X as Single
 Y as Single
 Vx as Single
 Vy as Single
End Type
 
Private Sprite as tSprite
 
Private Sub Command1_Click()
    Dim T1 As Long, T2 As Long
    myBackBuffer = CreateCompatibleDC(GetDC(0))
    myBufferBMP = CreateCompatibleBitmap(GetDC(0), 320, 256)
    SelectObject myBackBuffer, myBufferBMP
    BitBlt myBackBuffer, 0, 0, 320, 256, 0, 0, 0, vbWhiteness
    mySprite = LoadGraphicDC(App.Path & "\sprite1.bmp")
    mySprite1 = LoadGraphicDC(App.Path & "\mask.bmp")
    cmdTest.Enabled = False
    T2 = GetTickCount
    Do
        DoEvents
        T1 = GetTickCount
        If (T1 - T2) >= 0.15 Then
            BitBlt myBackBuffer, Sprite.X - 1, Sprite.Y - 1, 32, 32, 0, 0, 0, vbBlackness
            BitBlt myBackBuffer, Sprite.X - 1, Sprite.Y - 1, 32, 32, 0, 0, 0, vbSrcAnd
            BitBlt myBackBuffer, Sprite.X, Sprite.Y, 32, 32, mySprite, 0, 0, vbSrcAnd
            BitBlt myBackBuffer, Sprite.X, Sprite.Y, 32, 32, mySprite1, 0, 0, vbSrcPaint
            BitBlt Me.hdc, 0, 0, 320, 256, myBackBuffer, 0, 0, vbSrcCopy
            Sprite.X = Sprite.X + Sprite.Vx
            Sprite.Y = Sprite.Y + Sprite.Vy
            T2 = GetTickCount
        End If
        If Sprite.X >= 320 Then Sprite.Vx = -1
        If Sprite.Y >= 256 Then Sprite.Vy = -1
        If Sprite.X =< 0 Then Sprite.Vx = 1
        If Sprite.Y =< 0 Then Sprite.Vy = 1
        End If
    Loop
End Sub

[hothead]

Ok, I got it working real good now, but apparently the ball is leaving a little trail behind. This trail appears to be invisible at the default values, but as I increase the values (to get more speed out of the game) I see this trail more the higher the speed goes.

It looks like a chevron trail. Perhaps I'm missing some BitBlt data, or I didn't create my masks correctly?

NOTE: The code is now a function called MoveBall, and this is the code as it appears:

Private Function MoveBall()
    Dim T1 As Long, T2 As Long
    Sprite.Vx = 1.5
    Sprite.Vy = 1.5
    myBackBuffer = CreateCompatibleDC(GetDC(0))
    myBufferBMP = CreateCompatibleBitmap(Picture1.hdc, 344, 392)
    SelectObject myBackBuffer, myBufferBMP
    BitBlt myBackBuffer, 0, 0, 344, 392, 0, 0, 0, vbWhiteness
    mySprite = LoadGraphicDC(App.Path & "\sprite1.bmp")
    mySprite1 = LoadGraphicDC(App.Path & "\mask.bmp")
    T2 = GetTickCount
    Do
        DoEvents
        T1 = GetTickCount
        If (T1 - T2) >= 0.15 Then
            BitBlt myBackBuffer, Sprite.X - 1, Sprite.Y - 1, 32, 32, 0, 0, 0, vbBlackness
            BitBlt myBackBuffer, Sprite.X - 1, Sprite.Y - 1, 32, 32, 0, 0, 0, vbSrcAnd
            BitBlt myBackBuffer, Sprite.X, Sprite.Y, 32, 32, mySprite, 0, 0, vbSrcAnd
            BitBlt myBackBuffer, Sprite.X, Sprite.Y, 32, 32, mySprite1, 0, 0, vbSrcPaint
            BitBlt Me.hdc, 0, 0, 344, 392, myBackBuffer, 0, 0, vbSrcCopy
            Sprite.X = Sprite.X + Sprite.Vx
            Sprite.Y = Sprite.Y + Sprite.Vy
            T2 = GetTickCount
        End If
        If Sprite.X >= 344 Then Sprite.Vx = -1.5
        If Sprite.Y >= 392 Then Sprite.Vy = -1.5
        If Sprite.X <= 0 Then Sprite.Vx = 1.5
        If Sprite.Y <= 0 Then Sprite.Vy = 1.5
    Loop
End Function

[DiGiTaIErRoR]

Could be your screen's refresh rate.