Physics - Player moving with platform (Tier 1)

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Funnell7

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Joined: 8th Sep 2011

Location: UK, England

Posted: 1st Mar 2012 14:49

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Hello, I'm currently creating a little platform game... I have created a series of static and moving platforms which the player can jump on. The issue I have is that if the player jumps on the platform which is moving from left to right, the player stays still and the platform moves from underneath him. I need the player to move with the platform... I have tried applying a ridiculous amount of friction, which did kinda work (it was just abit jerky), I was wondering if anyone had any other ideas...

I can throw an example together and post the code if that will help?

Many thanks,

Dan

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baxslash

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Location: Duffield

Posted: 1st Mar 2012 17:35

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How are you controlling the player's movement? If you are setting velocity then that might be the cause. For moving platforms you either:
1-set the player speed using impulse or force
2-add the velocity of your moving platform to your player when he is standing on it

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Funnell7

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Joined: 8th Sep 2011

Location: UK, England

Posted: 2nd Mar 2012 16:08

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Thanks Baxslash, yes, I am currently using Velocity... I have tried to use Impulse and Force, but I cannot stop the sliding effect (as if he's on an ice rink)... What do I need to do to stop the character immediately after releasing the direction? Here is the code I have (no media needed),

SetVirtualResolution(427, 320)
SetOrientationAllowed(1, 0, 0, 0)
SetSyncRate(60, 1)
SetClearColor(0, 0, 0)
SetPrintColor(255, 255, 255)
SetPrintSize(16)

global Sprite1
global Platform
global PlatformX
global PlatformDirection
global Movement

Sprite1 = CreateSprite(Sprite1)
SetSpriteSize(Sprite1, 20, 40)
SetSpriteColor(Sprite1, 255, 0, 0, 255)
SetSpritePosition(Sprite1, 230, 280)
SetSpritePhysicsOn(Sprite1, 2)
SetSpritePhysicsCanRotate(Sprite1, 0)
SetSpritePhysicsFriction(Sprite1, 1)

Platform = CreateSprite(Platform)
SetSpriteSize(Platform, 100, 20)
SetSpriteColor(Platform, 0, 0, 255, 255)
SetSpritePosition(Platform, 190, 240)
SetSpritePhysicsOn(Platform, 3)

SetPhysicsGravity(0, 200)

do
    if GetDirectionX() > 0
        Movement = 100
    elseif GetDirectionX() < 0
        Movement = -100
    else
        Movement = 0
    endif

if GetSpriteX(Sprite1) <= 0 AND Movement < 0
        Movement = 0
        SetSpritePosition(Sprite1, 0, GetSpriteY(Sprite1))
    endif

if GetSpriteX(Sprite1) >= 480 AND Movement > 0
        Movement = 0
        SetSpritePosition(Sprite1, 480, GetSpriteY(Sprite1))
    endif

//SetSpritePhysicsForce(Sprite1, 0, 0, Movement, 0)
    SetSpritePhysicsImpulse(Sprite1, 0, 0, Movement, 0)
    //SetSpritePhysicsVelocitY(Sprite1, Movement, GetSpritePhysicsVelocityY(Sprite1))

if GetRawKeyPressed(32) = 1 OR GetPointerPressed() = 1
        if GetSpritePhysicsVelocityY(Sprite1) = 0.0
            SetSpritePhysicsVelocitY(Sprite1, GetSpritePhysicsVelocityX(Sprite1), -200)
        endif
    endif

PlatformX = GetSpriteX(Platform)

if PlatformX < 100
        PlatformDirection = 0
    elseif PlatformX > 280
        PlatformDirection = 1
    endif

if PlatformDirection = 0
        SetSpritePhysicsVelocity(Platform, 30, 0)
    elseif PlatformDirection = 1
        SetSpritePhysicsVelocity(Platform, -30, 0)
    endif

Sync()
loop

+ Code Snippet

SetVirtualResolution(427, 320)
SetOrientationAllowed(1, 0, 0, 0)
SetSyncRate(60, 1)
SetClearColor(0, 0, 0)
SetPrintColor(255, 255, 255)
SetPrintSize(16)

global Sprite1
global Platform
global PlatformX
global PlatformDirection
global Movement

Sprite1 = CreateSprite(Sprite1)
SetSpriteSize(Sprite1, 20, 40)
SetSpriteColor(Sprite1, 255, 0, 0, 255)
SetSpritePosition(Sprite1, 230, 280)
SetSpritePhysicsOn(Sprite1, 2)
SetSpritePhysicsCanRotate(Sprite1, 0)
SetSpritePhysicsFriction(Sprite1, 1)


Platform = CreateSprite(Platform)
SetSpriteSize(Platform, 100, 20)
SetSpriteColor(Platform, 0, 0, 255, 255)
SetSpritePosition(Platform, 190, 240)
SetSpritePhysicsOn(Platform, 3)

SetPhysicsGravity(0, 200)

do
    if GetDirectionX() > 0
        Movement = 100
    elseif GetDirectionX() < 0
        Movement = -100
    else
        Movement = 0
    endif

    if GetSpriteX(Sprite1) <= 0 AND Movement < 0
        Movement = 0
        SetSpritePosition(Sprite1, 0, GetSpriteY(Sprite1))
    endif

    if GetSpriteX(Sprite1) >= 480 AND Movement > 0
        Movement = 0
        SetSpritePosition(Sprite1, 480, GetSpriteY(Sprite1))
    endif

    //SetSpritePhysicsForce(Sprite1, 0, 0, Movement, 0)
    SetSpritePhysicsImpulse(Sprite1, 0, 0, Movement, 0)
    //SetSpritePhysicsVelocitY(Sprite1, Movement, GetSpritePhysicsVelocityY(Sprite1))

    if GetRawKeyPressed(32) = 1 OR GetPointerPressed() = 1
        if GetSpritePhysicsVelocityY(Sprite1) = 0.0
            SetSpritePhysicsVelocitY(Sprite1, GetSpritePhysicsVelocityX(Sprite1), -200)
        endif
    endif

    PlatformX = GetSpriteX(Platform)

    if PlatformX < 100
        PlatformDirection = 0
    elseif PlatformX > 280
        PlatformDirection = 1
    endif

    if PlatformDirection = 0
        SetSpritePhysicsVelocity(Platform, 30, 0)
    elseif PlatformDirection = 1
        SetSpritePhysicsVelocity(Platform, -30, 0)
    endif

    Sync()
loop

Thanks, as always...

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baxslash

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Joined: 26th Dec 2006

Location: Duffield

Posted: 2nd Mar 2012 16:21

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Here's a simplified solution using your code:

SetVirtualResolution(427, 320)
SetOrientationAllowed(1, 0, 0, 0)
SetSyncRate(60, 1)
SetClearColor(0, 0, 0)
SetPrintColor(255, 255, 255)
SetPrintSize(16)

global Sprite1
global Platform
global PlatformX
global PlatformDirection
global Movement

Sprite1 = CreateSprite(Sprite1)
SetSpriteSize(Sprite1, 20, 40)
SetSpriteColor(Sprite1, 255, 0, 0, 255)
SetSpritePosition(Sprite1, 230, 280)
SetSpritePhysicsOn(Sprite1, 2)
SetSpritePhysicsCanRotate(Sprite1, 0)
rem don't need to edit friction
`SetSpritePhysicsFriction(Sprite1, 1)

Platform = CreateSprite(Platform)
SetSpriteSize(Platform, 100, 20)
SetSpriteColor(Platform, 0, 0, 255, 255)
SetSpritePosition(Platform, 190, 240)
SetSpritePhysicsOn(Platform, 3)
rem put the platform in a group
setSpriteGroup(Platform,1)

SetPhysicsGravity(0, 200)

do
    Movement = GetDirectionX()*100.0
    remstart
    if GetDirectionX() > 0
        Movement = 100
    elseif GetDirectionX() < 0
        Movement = -100
    else
        Movement = 0
    endif

if GetSpriteX(Sprite1) <= 0 AND Movement < 0
        Movement = 0
        SetSpritePosition(Sprite1, 0, GetSpriteY(Sprite1))
    endif

if GetSpriteX(Sprite1) >= 480 AND Movement > 0
        Movement = 0
        SetSpritePosition(Sprite1, 480, GetSpriteY(Sprite1))
    endif
    remend

//SetSpritePhysicsForce(Sprite1, 0, 0, Movement, 0)
    //SetSpritePhysicsImpulse(Sprite1, 0, 0, Movement, 0)
    //SetSpritePhysicsVelocity(Sprite1, Movement, GetSpritePhysicsVelocityY(Sprite1))
    
    rem get current velocity
    x# = getSpriteXbyOffset(Sprite1)
    y# = getSpriteYbyOffset(Sprite1)
    if PhysicsRayCastGroup(1,x#,y#,x#,y#+getSpriteHeight(Sprite1))>0
        ID = getRayCastSpriteID()
        setSpritePhysicsVelocity(Sprite1,Movement+getSpritePhysicsVelocityX(ID),getSpritePhysicsVelocityY(Sprite1))
    else
        SetSpritePhysicsVelocity(Sprite1, Movement, GetSpritePhysicsVelocityY(Sprite1))
    endif

if GetRawKeyPressed(32) = 1 OR GetPointerPressed() = 1
        if GetSpritePhysicsVelocityY(Sprite1) = 0.0
            SetSpritePhysicsVelocitY(Sprite1, Movement+GetSpritePhysicsVelocityX(Sprite1), -200)
        endif
    endif

PlatformX = GetSpriteX(Platform)

if PlatformX < 100
        PlatformDirection = 0
    elseif PlatformX > 280
        PlatformDirection = 1
    endif

if PlatformDirection = 0
        SetSpritePhysicsVelocity(Platform, 30, 0)
    elseif PlatformDirection = 1
        SetSpritePhysicsVelocity(Platform, -30, 0)
    endif

Sync()
loop

+ Code Snippet


SetVirtualResolution(427, 320)
SetOrientationAllowed(1, 0, 0, 0)
SetSyncRate(60, 1)
SetClearColor(0, 0, 0)
SetPrintColor(255, 255, 255)
SetPrintSize(16)

global Sprite1
global Platform
global PlatformX
global PlatformDirection
global Movement

Sprite1 = CreateSprite(Sprite1)
SetSpriteSize(Sprite1, 20, 40)
SetSpriteColor(Sprite1, 255, 0, 0, 255)
SetSpritePosition(Sprite1, 230, 280)
SetSpritePhysicsOn(Sprite1, 2)
SetSpritePhysicsCanRotate(Sprite1, 0)
rem don't need to edit friction
`SetSpritePhysicsFriction(Sprite1, 1)


Platform = CreateSprite(Platform)
SetSpriteSize(Platform, 100, 20)
SetSpriteColor(Platform, 0, 0, 255, 255)
SetSpritePosition(Platform, 190, 240)
SetSpritePhysicsOn(Platform, 3)
rem put the platform in a group
setSpriteGroup(Platform,1)

SetPhysicsGravity(0, 200)

do
    Movement = GetDirectionX()*100.0
    remstart
    if GetDirectionX() > 0
        Movement = 100
    elseif GetDirectionX() < 0
        Movement = -100
    else
        Movement = 0
    endif

    if GetSpriteX(Sprite1) <= 0 AND Movement < 0
        Movement = 0
        SetSpritePosition(Sprite1, 0, GetSpriteY(Sprite1))
    endif

    if GetSpriteX(Sprite1) >= 480 AND Movement > 0
        Movement = 0
        SetSpritePosition(Sprite1, 480, GetSpriteY(Sprite1))
    endif
    remend

    //SetSpritePhysicsForce(Sprite1, 0, 0, Movement, 0)
    //SetSpritePhysicsImpulse(Sprite1, 0, 0, Movement, 0)
    //SetSpritePhysicsVelocity(Sprite1, Movement, GetSpritePhysicsVelocityY(Sprite1))
    
    rem get current velocity
    x# = getSpriteXbyOffset(Sprite1)
    y# = getSpriteYbyOffset(Sprite1)
    if PhysicsRayCastGroup(1,x#,y#,x#,y#+getSpriteHeight(Sprite1))>0
        ID = getRayCastSpriteID()
        setSpritePhysicsVelocity(Sprite1,Movement+getSpritePhysicsVelocityX(ID),getSpritePhysicsVelocityY(Sprite1))
    else
        SetSpritePhysicsVelocity(Sprite1, Movement, GetSpritePhysicsVelocityY(Sprite1))
    endif

    if GetRawKeyPressed(32) = 1 OR GetPointerPressed() = 1
        if GetSpritePhysicsVelocityY(Sprite1) = 0.0
            SetSpritePhysicsVelocitY(Sprite1, Movement+GetSpritePhysicsVelocityX(Sprite1), -200)
        endif
    endif

    PlatformX = GetSpriteX(Platform)

    if PlatformX < 100
        PlatformDirection = 0
    elseif PlatformX > 280
        PlatformDirection = 1
    endif

    if PlatformDirection = 0
        SetSpritePhysicsVelocity(Platform, 30, 0)
    elseif PlatformDirection = 1
        SetSpritePhysicsVelocity(Platform, -30, 0)
    endif

    Sync()
loop

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Funnell7

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Joined: 8th Sep 2011

Location: UK, England

Posted: 2nd Mar 2012 17:01

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Genius... Just so I understand (else I won't learn), is this basically looking for a collision (via RayCast) between the platform and player, and if so, applying the same amount of velocity to both the platform and player?

I think I need to look into RayCasting abit more... Not sure I quite grasp that concept...

Thanks Baxslash, really appreciate it...

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baxslash

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Years of Service

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Joined: 26th Dec 2006

Location: Duffield

Posted: 2nd Mar 2012 17:09

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Ray casting is just like shining a laser from one point to another. It can then tell you:
a-If it hit anything on the way
b-How far away the thing was
c-Its spriteID
etc.

You can also specify a sprite group or even a single sprite to look for along that line.

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