Screen Scrolling in X and Y on AGK and performance

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mathacka

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Joined: 19th Apr 2013

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Posted: 19th Apr 2013 21:33

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Hi, I understand the idea of screen scrolling, but I'm getting a little confused on the best way to implement it.

I have a starry background that I'm using to create the feel of movement when the player uses a virtual joystick on the screen.

Two things are confusing me, One, It seems like a lot of images on the virtual screen if you're moving left and up to add 3 copy's of a seamless starry background to your screen's virtual screen?

Two, what is best for performance, to delete and reload the sprites, use images instead of sprites, or just copy and hide sprites as the starry background moves?

Could you provide some pseudo-code so I can better make sense of this?

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Marl

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Location: Bradford, UK

Posted: 20th Apr 2013 09:06

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There are a number of ways to approach this and it really depends on what the rest of your game is doing.

In most cases for a starfield, I would tend NOT to scroll the background in the traditional sense, but instead use a background image of a star field and scroll it's texture. That way you only use one sprite and it never needs to be bigger than the screen.

You can use multiple sprites if you want a parallax effect).

I did some samples a while back

http://forum.thegamecreators.com/?m=forum_view&t=194972&b=41

(Though this example is more complex - multiple backgrounds and parallaxing , the actual background is only a few lines and it does use V-Joystick control).

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mathacka

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Posted: 21st Apr 2013 04:53 Edited at: 21st Apr 2013 08:05

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I was able to do what you said with this code:

// Constants
#constant SCREEN = 1

// Globals
global over = 0
global x# = 0
global y# = 0
global x_center = 0
global y_center = 0

// Init Function
game_init()

// Main Loop
do
    game_update()
    game_draw()
    if over = 1
        exit
    endif
loop

// Function: Game Init
Function game_init()

// Setup sprite background
    LoadImage(1, "space_background128.png")
    SetImageWrapU( 1, 1 )
    SetImageWrapV( 1, 1 )
    CreateSprite(SCREEN,1)
    SetSpritePosition(SCREEN,0,0)

// Setup Joystick
    AddVirtualJoystick( 1, 10, 90, 20 )
    SetVirtualJoystickVisible(1,1)

// Setup Print Text Color
    SetPrintColor(0, 0, 0)
EndFunction

// Function: Game Update
Function game_update()
    // Set scrolling background
    SetSpriteUVOffset( SCREEN, x#/100, y#/100 )
    // Check x not 0
    if GetVirtualJoystickX(1) > 0 or GetVirtualJoystickX(1) < 0
        x# = x# + (GetVirtualJoystickX(1)*5)
    endif
    // Check y not 0
    If GetVirtualJoystickY(1) > 0 or GetVirtualJoystickY(1) < 0
        y# = y# + (GetVirtualJoystickY(1)*5)
    Endif
EndFunction

// Function : Game Draw
Function game_draw()
    Print("x: " + Str(x#))
    Print("y: " + Str(y#))
    print("Joystick x: " + str(GetVirtualJoystickX(1)))
    Sync()
EndFunction

+ Code Snippet

// Constants
#constant SCREEN = 1

// Globals
global over = 0
global x# = 0
global y# = 0
global x_center = 0
global y_center = 0

// Init Function
game_init()

// Main Loop
do
    game_update()
    game_draw()
    if over = 1
        exit
    endif
loop

// Function: Game Init
Function game_init()

    // Setup sprite background
    LoadImage(1, "space_background128.png")
    SetImageWrapU( 1, 1 )
    SetImageWrapV( 1, 1 )
    CreateSprite(SCREEN,1)
    SetSpritePosition(SCREEN,0,0)

    // Setup Joystick
    AddVirtualJoystick( 1, 10, 90, 20 )
    SetVirtualJoystickVisible(1,1)

    // Setup Print Text Color
    SetPrintColor(0, 0, 0)
EndFunction

// Function: Game Update
Function game_update()
    // Set scrolling background
    SetSpriteUVOffset( SCREEN, x#/100, y#/100 )
    // Check x not 0
    if GetVirtualJoystickX(1) > 0 or GetVirtualJoystickX(1) < 0
        x# = x# + (GetVirtualJoystickX(1)*5)
    endif
    // Check y not 0
    If GetVirtualJoystickY(1) > 0 or GetVirtualJoystickY(1) < 0
        y# = y# + (GetVirtualJoystickY(1)*5)
    Endif
EndFunction

// Function : Game Draw
Function game_draw()
    Print("x: " + Str(x#))
    Print("y: " + Str(y#))
    print("Joystick x: " + str(GetVirtualJoystickX(1)))
    Sync()
EndFunction

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