2D Sliding Collision - How do I do it?

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Mobiius

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Posted: 15th Jul 2015 13:35

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Hello,
Thanks to Humble Bundle, I've just purchased AGK2 and have started my first AGK2 game. (I've used AGK1 since release.)

I'm trying to create a 2d top down scroller, but can't figure out how to implement 2D sliding collision. I have my walls set in a sprite group, but I don't know how to create a sliding collision routine similar to the 3D SphereSlide command.

Does anyone have and pointers/code they can share?

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baxslash

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Posted: 15th Jul 2015 13:47

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Hi Mobiius! Long time no see

You can detect collision or use 2D Physics to simulate it. There aren't any manual commands I have seen for sliding collision. You might be interested as an experienced DBPro user in the 3D collision code which is fully based on sparky's collision. You could:

1-Use hidden 3D objects and 'sparky's'
2-Use 2D physics (I would)
3-Use your own sliding code based on the 2D collision detection code but that would probably take the longest and be hardest to implement

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Mobiius

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Posted: 15th Jul 2015 13:50

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Was hoping to not have to use the physics as it seems overkill for my needs.

I might actually create my own sliding collision code, I've just had a quick think and it should be too difficult.

Gimme 5 minutes.... lol

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Mobiius

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Posted: 15th Jul 2015 14:20 Edited at: 15th Jul 2015 14:50

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Function UpdatePlayer()
   FrameTime# = GetFrameTime()
   If GetDirectionX() <> 0.0 Or GetDirectionY() <> 0.0
      Ang# = ATanFull( GetDirectionX(), GetDirectionY() )
      SetSpriteAngle( Player.SpriteNo, Ang# )

OldX# = GetSpriteXByOffset( Player.SpriteNo ) : OldY# = GetSpriteYByOffset( Player.SpriteNo )
      NewX# = NewXPosition#( OldX#, Ang# + 180.0, ( 4.0 * FrameTime# ) )
      NewY# = NewYPosition#( OldY#, Ang# + 180.0, ( 4.0 * FrameTime# ) )
      
      SetSpritePositionByOffset( Player.SpriteNo, SphereSlide2DX#( OldX#, OldY#, NewX#, NewY# ), SphereSlide2DY#( OldX#, OldY#, NewX#, NewY# ) )
   EndIf
EndFunction
`===============================================================================================
`===============================================================================================
`===============================================================================================
Function SphereSlide2DX#( X1#, Y1#, X2#, Y2# )
      Return# = X2#
      If SpriteRayCast( X1#, Y1#, X2#, Y2# )
         Return# = GetRayCastX()
      EndIf
EndFunction Return#
`===============================================================================================
`===============================================================================================
`===============================================================================================
Function SphereSlide2DY#( X1#, Y1#, X2#, Y2# )
      Return# = Y2#
      If SpriteRayCast( X1#, Y1#, X2#, Y2# )
         Return# = GetRayCastY()
      EndIf
EndFunction Return#

+ Code Snippet

Function UpdatePlayer()
   FrameTime# = GetFrameTime()
   If GetDirectionX() <> 0.0 Or GetDirectionY() <> 0.0
      Ang# = ATanFull( GetDirectionX(), GetDirectionY() )
      SetSpriteAngle( Player.SpriteNo, Ang# )

      OldX# = GetSpriteXByOffset( Player.SpriteNo ) : OldY# = GetSpriteYByOffset( Player.SpriteNo )
      NewX# = NewXPosition#( OldX#, Ang# + 180.0, ( 4.0 * FrameTime# ) )
      NewY# = NewYPosition#( OldY#, Ang# + 180.0, ( 4.0 * FrameTime# ) )
      
      SetSpritePositionByOffset( Player.SpriteNo, SphereSlide2DX#( OldX#, OldY#, NewX#, NewY# ), SphereSlide2DY#( OldX#, OldY#, NewX#, NewY# ) )
   EndIf
EndFunction
`===============================================================================================
`===============================================================================================
`===============================================================================================
Function SphereSlide2DX#( X1#, Y1#, X2#, Y2# )
      Return# = X2#
      If SpriteRayCast( X1#, Y1#, X2#, Y2# )
         Return# = GetRayCastX()
      EndIf
EndFunction Return#
`===============================================================================================
`===============================================================================================
`===============================================================================================
Function SphereSlide2DY#( X1#, Y1#, X2#, Y2# )
      Return# = Y2#
      If SpriteRayCast( X1#, Y1#, X2#, Y2# )
         Return# = GetRayCastY()
      EndIf
EndFunction Return#

Ok, I have this. It makes collision work, but no sliding. I may have to write my own raycasting functions.. Gimme another 5 minutes!

(The above code needs you to create 1 sprite to be your player, stored as Player.SpriteNo.

Type tPlayer
SpriteNo
EndType
Global Player As tPlayer

And a number of sprites set up as a 'wall')

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Mobiius

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Posted: 15th Jul 2015 14:50 Edited at: 15th Jul 2015 14:50

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Function UpdatePlayer()
   FrameTime# = GetFrameTime()
   If GetDirectionX() <> 0.0 Or GetDirectionY() <> 0.0
      SetSpriteAngle( Player.SpriteNo, Ang# + 180.0 )

OldX# = GetSpriteXByOffset( Player.SpriteNo )
      OldY# = GetSpriteYByOffset( Player.SpriteNo )

Speed# = ( 4.0 * Engine.FrameTime# )

XDist# = RayCastX#( OldX#, OldY#, Ang#, Speed#, 2.5 )
      YDist# = RayCastY#( OldX#, OldY#, Ang#, Speed#, 2.5 )

NewX# = NewXPosition#( OldX#, Ang#, XDist# )
      NewY# = NewYPosition#( OldY#, Ang#, YDist# )
      
      SetSpritePositionByOffset( Player.SpriteNo, NewX#, NewY# )

Player.CurrentFrame# = Player.CurrentFrame# + ( 16.0 * Engine.FrameTime# ) : If Player.CurrentFrame# >= 16.0 Then Player.CurrentFrame# = ( Player.CurrentFrame# - 16.0 )
   Else
      Player.CurrentFrame# = CurveValue#( Player.CurrentFrame#, 13.0, 2.5 )
   EndIf
   SetSpriteFrame( Player.SpriteNo, Round( Player.CurrentFrame# ) )
EndFunction
`===============================================================================================
`===============================================================================================
`===============================================================================================
Function RayCastX#( X#, Y#, Ang#, Dist#, Radiius# )
   X2# = NewXPosition#( X#, Ang#, Radiius# )

If SpriteRayCast( X#, Y#, X2#, Y# ) Then Dist# = 0.0
EndFunction Dist#
`===============================================================================================
`===============================================================================================
`===============================================================================================
Function RayCastY#( X#, Y#, Ang#, Dist#, Radiius# )
   Y2# = NewYPosition#( Y#, Ang#, Radiius# )

If SpriteRayCast( X#, Y#, X#, Y2# ) Then Dist# = 0.0
EndFunction Dist#

+ Code Snippet

Function UpdatePlayer()
   FrameTime# = GetFrameTime()
   If GetDirectionX() <> 0.0 Or GetDirectionY() <> 0.0
      SetSpriteAngle( Player.SpriteNo, Ang# + 180.0 )

      OldX# = GetSpriteXByOffset( Player.SpriteNo )
      OldY# = GetSpriteYByOffset( Player.SpriteNo )

      Speed# = ( 4.0 * Engine.FrameTime# )

      XDist# = RayCastX#( OldX#, OldY#, Ang#, Speed#, 2.5 )
      YDist# = RayCastY#( OldX#, OldY#, Ang#, Speed#, 2.5 )

      NewX# = NewXPosition#( OldX#, Ang#, XDist# )
      NewY# = NewYPosition#( OldY#, Ang#, YDist# )
      
      SetSpritePositionByOffset( Player.SpriteNo, NewX#, NewY# )

      Player.CurrentFrame# = Player.CurrentFrame# + ( 16.0 * Engine.FrameTime# ) : If Player.CurrentFrame# >= 16.0 Then Player.CurrentFrame# = ( Player.CurrentFrame# - 16.0 )
   Else
      Player.CurrentFrame# = CurveValue#( Player.CurrentFrame#, 13.0, 2.5 )
   EndIf
   SetSpriteFrame( Player.SpriteNo, Round( Player.CurrentFrame# ) )
EndFunction
`===============================================================================================
`===============================================================================================
`===============================================================================================
Function RayCastX#( X#, Y#, Ang#, Dist#, Radiius# )
   X2# = NewXPosition#( X#, Ang#, Radiius# )

   If SpriteRayCast( X#, Y#, X2#, Y# ) Then Dist# = 0.0
EndFunction Dist#
`===============================================================================================
`===============================================================================================
`===============================================================================================
Function RayCastY#( X#, Y#, Ang#, Dist#, Radiius# )
   Y2# = NewYPosition#( Y#, Ang#, Radiius# )

   If SpriteRayCast( X#, Y#, X#, Y2# ) Then Dist# = 0.0
EndFunction Dist#

2D sliding collision complete. No Physics object required

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baxslash

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Posted: 15th Jul 2015 15:41

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There ya go... good to have you around!

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Mobiius

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Posted: 15th Jul 2015 16:09

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Glad to be back!

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