Move a sprite continuously toward choosen 2d point

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Timshark

16

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Joined: 30th Jun 2007

Location: Oslo, Norway

Posted: 11th Nov 2017 19:25

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Hi

I want to move a sprite toward a choosen 2d point. But I want it to continue and not stop at the point.
I've found the example of moving toward a mouse clicked point but I just want it to continue past the clicked point in a set speed.

How is this done

Tim

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Conjured Entertainment

AGK Developer

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Joined: 12th Sep 2005

Location: Nirvana

Posted: 12th Nov 2017 00:07 Edited at: 12th Nov 2017 00:23

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SetSpritePosition(spriteID, GetSpriteX(spriteID)+1, GetSpriteY(spriteID))

That is one way, where that is moving the sprite on its X axis 1 pixel each cycle.

Of course that could be any number you want, and you could do the same for the Y axis if you wanted.

If you Know the fixed value for Y then you could just use that like...

SetSpritePosition(spriteID, GetSpriteX(spriteID)+1, 200)

But the first example just reads whatever it currently is already set to in case it has already been adjusted by something else.

You can do a -1 instead of +1 to move the other direction, and you want to have some kind of limit, so putting that in an IF statement that checks the position would be best.

That way you will not keep moving it until it gets out of bounds and causes an error.

In your case you would have a couple of variables that are representing the fixed point you want to move to for the X and Y.

Then, the IF statement(s) would compare the sprite's current X & Y positions to the desired location variables and then increment or decrement the position accordingly.

+ Code Snippet


If GetSpriteX(1) < desired_x 
   move_it = 1
else 
   move_it = -1
endif

do
   if GetSpriteX(1) > 0 and GetSpriteX(1) < 700
        SetSpritePosition(1, GetSpriteX(1)+move_it, GetSpriteY(1))
   endif
  sync()
loop

That limits it between 0 and 700 so you will not go out of bounds, so if the desired_x is 100 or 400 and you current position is 200, then it will move you in that direction and beyond it, but still stay in the limits.

Hope this makes sense and helps, and I am sure someone else will now tell you a better way to do it.

Coding things my way since 1981 -- Currently using AppGameKit V2 Tier 1

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easter bunny

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Joined: 20th Nov 2012

Playing: Dota 2

Posted: 12th Nov 2017 00:46 Edited at: 12th Nov 2017 00:47

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I'd do it like this:

type vec2
  x as float
  y as float
endtype

start as vec2
end as vec2
direction as vec2

speed as float
obj as integer

//assume start.x/start.y is set to the initial position of the sprite
//assume end.x/end.y are set to the position you want to move the sprite towards
//set speed to the number of pixels per frame you want to move the sprite at
//set obj to the spriteID that you want to move

//first set the direction vector to point from the start to the end
direction.x=end.x-start.x
direction.y=end.y-start.y
//now normalise the vector by dividing both axis's by the length of the vector
//This will make both components <=1 such that x+y=1/ The length is found by pythagoras's theorem (c^2=a^2+b^2)
len as float
len=(sqrt((direction.x*direction.x)+(direction.y*direction.y)))
direction.x=direction.x/len
direction.y=direction.y/len

//direction is now a normalised vector pointing from the initial start point to the end point
//You can move the sprite along this line by x=x+(direction.x*speed),y=y+(direction.y*speed)
//eg
SetSpritePosition(obj, GetSpriteX(obj)+(direction.x*speed), GetSpriteY(obj)+(direction.y*speed))

+ Code Snippet

type vec2
  x as float
  y as float
endtype

start as vec2
end as vec2
direction as vec2

speed as float
obj as integer

//assume start.x/start.y is set to the initial position of the sprite
//assume end.x/end.y are set to the position you want to move the sprite towards
//set speed to the number of pixels per frame you want to move the sprite at
//set obj to the spriteID that you want to move

//first set the direction vector to point from the start to the end
direction.x=end.x-start.x
direction.y=end.y-start.y
//now normalise the vector by dividing both axis's by the length of the vector
//This will make both components <=1 such that x+y=1/ The length is found by pythagoras's theorem (c^2=a^2+b^2)
len as float
len=(sqrt((direction.x*direction.x)+(direction.y*direction.y)))
direction.x=direction.x/len
direction.y=direction.y/len

//direction is now a normalised vector pointing from the initial start point to the end point
//You can move the sprite along this line by x=x+(direction.x*speed),y=y+(direction.y*speed)
//eg
SetSpritePosition(obj, GetSpriteX(obj)+(direction.x*speed), GetSpriteY(obj)+(direction.y*speed))

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smallg

Valued Member

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Joined: 8th Dec 2005

Location: steam

Posted: 12th Nov 2017 15:39

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// Project: onwards 
// Created: 2017-11-12

// show all errors
SetErrorMode(2)

// set window properties
SetWindowTitle( "onwards" )
SetWindowSize( 1024, 768, 0 )
SetWindowAllowResize( 1 ) // allow the user to resize the window

// set display properties
SetVirtualResolution( 1024, 768 ) // doesn't have to match the window
SetOrientationAllowed( 1, 1, 1, 1 ) // allow both portrait and landscape on mobile devices
SetSyncRate( 30, 0 ) // 30fps instead of 60 to save battery
SetScissor( 0,0,0,0 ) // use the maximum available screen space, no black borders
UseNewDefaultFonts( 1 ) // since version 2.0.22 we can use nicer default fonts

ball = CreateSprite(0)
SetSpritePositionByOffset(ball,512,386)
do
	if GetPointerReleased()
		pointSprite(ball,GetPointerX(),GetPointerY())
		clicked = 1
	endif
	if GetSpriteExists(ball) and clicked = 1
		moveSpriteForward(ball,4)
	endif
   
   if GetRawKeyReleased(27) = 1 then end

Print( ScreenFPS() )
    Sync()
loop

function pointSprite(spriteID,x#,y#)
    rem get display data
    dx# = x#-getSpriteXbyOffset(spriteID)
    dy# = y#-getSpriteYbyOffset(spriteID)
    setSpriteAngle(spriteID,atanfull(dx#,dy#)-90)
endfunction

function moveSpriteForward(spriteID, amount#)
    rem get display data
    dw# = getVirtualWidth()
    dh# = getVirtualHeight()
    aspect# = (dw# / dh#)
    if aspect# = 1.0
        aspect# = getDisplayAspect()
    else
        aspect# = 1.0
    endif
    a# = getSpriteAngle(spriteID)
    x# = getSpriteXbyOffset(spriteID)
    y# = getSpriteYbyOffset(spriteID)
    setSpritePositionByOffset(spriteID,x#+cos(a#)*amount#,y#+sin(a#)*amount#*aspect#)
endfunction

+ Code Snippet

// Project: onwards 
// Created: 2017-11-12

// show all errors
SetErrorMode(2)

// set window properties
SetWindowTitle( "onwards" )
SetWindowSize( 1024, 768, 0 )
SetWindowAllowResize( 1 ) // allow the user to resize the window

// set display properties
SetVirtualResolution( 1024, 768 ) // doesn't have to match the window
SetOrientationAllowed( 1, 1, 1, 1 ) // allow both portrait and landscape on mobile devices
SetSyncRate( 30, 0 ) // 30fps instead of 60 to save battery
SetScissor( 0,0,0,0 ) // use the maximum available screen space, no black borders
UseNewDefaultFonts( 1 ) // since version 2.0.22 we can use nicer default fonts

ball = CreateSprite(0)
SetSpritePositionByOffset(ball,512,386)
do
	if GetPointerReleased()
		pointSprite(ball,GetPointerX(),GetPointerY())
		clicked = 1
	endif
	if GetSpriteExists(ball) and clicked = 1
		moveSpriteForward(ball,4)
	endif
   
   if GetRawKeyReleased(27) = 1 then end 

    Print( ScreenFPS() )
    Sync()
loop

function pointSprite(spriteID,x#,y#)
    rem get display data
    dx# = x#-getSpriteXbyOffset(spriteID)
    dy# = y#-getSpriteYbyOffset(spriteID)
    setSpriteAngle(spriteID,atanfull(dx#,dy#)-90)
endfunction

function moveSpriteForward(spriteID, amount#)
    rem get display data
    dw# = getVirtualWidth()
    dh# = getVirtualHeight()
    aspect# = (dw# / dh#)
    if aspect# = 1.0
        aspect# = getDisplayAspect()
    else
        aspect# = 1.0
    endif
    a# = getSpriteAngle(spriteID)
    x# = getSpriteXbyOffset(spriteID)
    y# = getSpriteYbyOffset(spriteID)
    setSpritePositionByOffset(spriteID,x#+cos(a#)*amount#,y#+sin(a#)*amount#*aspect#)
endfunction

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Timshark

16

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Joined: 30th Jun 2007

Location: Oslo, Norway

Posted: 12th Nov 2017 17:30

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Easter Bunny

Thanks, that´s exactly what I need.

It was the len and direction calculations I was looking for

Great Help

Tim

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