Strange pixel anomaly - GameCreators Forum

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w0rm

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Posted: 27th Nov 2018 18:32

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I have been trying to build a simple platformer game. I have a strange behavior in drawing where there sometimes is a visible gap between player sprite and platform and sometimes not. I attached screenshot showing the issue.

I have been trying to debug what impact the decimals in sprite position have to this effect but have not found any correlation: the gap can be visible or then not with more or less same same decimals in y-position. I also tried if SetViewOffset has impact on this but the effect is the same when not scrolling the view and when scrolling is enabled.

Any idea what is causing this and is there a way to get rid of this anomaly somehow?

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smallg

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Posted: 27th Nov 2018 18:34

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how are you handling checking the sprite is on the platform or not? i.e. collision shapes? physics? ray casting?

life's one big game
spec= i5 4ghz, 16gb ram, Nvidia 1070ti gpu

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w0rm

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Posted: 27th Nov 2018 18:41

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With collision shapes. No physics involved. I check against all block sprites which are stored in array. The code is likely not most effective at the moment as I have been trying to get this thing to work

+ Code Snippet

	// Vertical collision
	colliding_sprite = PlaceMeeting(player.sprite, player.x, player.y + player.yspd, map_blocks)
	If colliding_sprite <> 0
		While PlaceMeeting(player.sprite, player.x, player.y + signf(player.yspd), map_blocks) = 0
			player.y = player.y + signf(player.yspd)
		EndWhile
		player.yspd = 0
		player.on_ground = TRUE
	EndIf

And the function PlaceMeeting:

+ Code Snippet

Function PlaceMeeting( iSprite1 As Integer, fX As Float, fY As Float, iSprites Ref As Integer[])
	temp_x As Float
	temp_y As Float
	temp_x = GetSpriteX(iSprite1)
	temp_y = GetSpriteY(iSprite1)
	
	SetSpritePosition(iSprite1, fX, fY)
	
	collision As Integer = 0
	i As Integer
	For i = 0 To iSprites.length
		collision = GetSpriteCollision(iSprite1, iSprites[i])
		If collision = 1
			collision = iSprites[i]
			Exit
		EndIf
	Next i
	
	SetSpritePosition(iSprite1, temp_x, temp_y)
	
EndFunction collision

signf function returns either -1,0,1 depending whether given value is negative, zero or positive.

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puzzler2018

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Posted: 27th Nov 2018 18:43 Edited at: 27th Nov 2018 18:44

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You say that your using Decimals - could you perhaps use floats?

Do you have a sample peice of code showing this fault and can have a better solution

EDIT - you read my mind lol - please bear with us for a remedy

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w0rm

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Posted: 27th Nov 2018 19:07

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Also to note that I have the screen (window size) set to 1280x720 and virtual resolution set to 640x360. The sprite and block size is 24x24.

I also tested to not use the virtual resolution but the effect is the same.

But just noted that there's something fishy somewhere as the system reports a collision when trying to move between a hole with height of exactly 1 block (24 pixels) even though sprites are not colliding (attached an image of this).

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puzzler2018

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Posted: 27th Nov 2018 19:09 Edited at: 27th Nov 2018 19:11

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For some reason your code was a little bit exhausting for me

Try this way

// Project: w0rm 
// Created: 2018-11-27

// show all errors
SetErrorMode(2)

// set window properties
SetWindowTitle( "w0rm" )
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

#CONSTANT FALSE=0
#CONSTANT TRUE=1

type _player
	x
	y#
	yspd#
	sprite
	on_ground
endtype
player as _player

player.yspd#=3
player.x=100
player.y#=100
player.sprite=CreateSprite(0)
map_blocks as integer[]

// create a platform 50 across and in centre
for a=0 to 50
	map_blocks.insert(CreateSprite(0))
	SetSpritePosition(map_blocks[a],a*GetSpriteWidth(map_blocks[a]),768/2)
next

do

player.y# = player.y# + signf(player.yspd#)

for collisions=0 to map_blocks.length
		
		if GetSpriteCollision(player.sprite,map_blocks[collisions])
			player.yspd#=0
		endif
		
	next

SetSpritePosition(player.sprite,player.x,player.y#)

Print( ScreenFPS() )
    Sync()
loop

function signf(f#)
	
	if f#<0 then res#=-1
	if f#=0 then res#=0
	if f#>0 then res#=1
	
	
endfunction res#

+ Code Snippet


// Project: w0rm 
// Created: 2018-11-27

// show all errors
SetErrorMode(2)

// set window properties
SetWindowTitle( "w0rm" )
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

#CONSTANT FALSE=0
#CONSTANT TRUE=1

type _player
	x
	y#
	yspd#
	sprite
	on_ground
endtype
player as _player

player.yspd#=3
player.x=100
player.y#=100
player.sprite=CreateSprite(0)
map_blocks as integer[]

// create a platform 50 across and in centre
for a=0 to 50
	map_blocks.insert(CreateSprite(0))
	SetSpritePosition(map_blocks[a],a*GetSpriteWidth(map_blocks[a]),768/2)
next

do

        player.y# = player.y# + signf(player.yspd#)

	for collisions=0 to map_blocks.length
		
		if GetSpriteCollision(player.sprite,map_blocks[collisions])
			player.yspd#=0
		endif
		
	next

		SetSpritePosition(player.sprite,player.x,player.y#)



    Print( ScreenFPS() )
    Sync()
loop

function signf(f#)
	
	if f#<0 then res#=-1
	if f#=0 then res#=0
	if f#>0 then res#=1
	
	
endfunction res#

hope it doesnt mess things up for you - but i find this way works just as well and a little bit shorter in code

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w0rm

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Posted: 27th Nov 2018 19:18

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Thx! I’ll try it in the morning!

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puzzler2018

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Posted: 27th Nov 2018 19:19

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Hope this helps

// Project: w0rm 
// Created: 2018-11-27

// show all errors
SetErrorMode(2)

// set window properties
SetWindowTitle( "w0rm" )
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

#CONSTANT FALSE=0
#CONSTANT TRUE=1

type _player
	x
	y#
	yspd#
	sprite
	on_ground
endtype
player as _player

player.yspd#=1
player.x=100
player.y#=100
player.sprite=CreateSprite(0)
SetSpriteSize(player.sprite,10,10)
SetSpriteColor(player.sprite,255,255,0,255)
map_blocks as integer[]

for a=0 to 400
	map_blocks.insert(CreateSprite(0))
	SetSpriteSize(map_blocks[a],10,10)
	SetSpriteColor(map_blocks[a],255,0,0,255)
	SetSpritePosition(map_blocks[a],random(0,1024),random(0,768))
next

do

for collisions=0 to map_blocks.length
		
		if GetSpriteCollision(player.sprite,map_blocks[collisions])
			player.yspd#=0
		endif
		
	next
        player.y# = player.y# + signf(player.yspd#)

SetSpritePosition(player.sprite,player.x,player.y#)

Print( ScreenFPS() )
    Sync()
loop

function signf(f#)
	
	if f#<0 then res#=-1
	if f#=0 then res#=0
	if f#>0 then res#=1
	
	
endfunction res#

+ Code Snippet


// Project: w0rm 
// Created: 2018-11-27

// show all errors
SetErrorMode(2)

// set window properties
SetWindowTitle( "w0rm" )
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

#CONSTANT FALSE=0
#CONSTANT TRUE=1

type _player
	x
	y#
	yspd#
	sprite
	on_ground
endtype
player as _player

player.yspd#=1
player.x=100
player.y#=100
player.sprite=CreateSprite(0)
SetSpriteSize(player.sprite,10,10)
SetSpriteColor(player.sprite,255,255,0,255)
map_blocks as integer[]


for a=0 to 400
	map_blocks.insert(CreateSprite(0))
	SetSpriteSize(map_blocks[a],10,10)
	SetSpriteColor(map_blocks[a],255,0,0,255)
	SetSpritePosition(map_blocks[a],random(0,1024),random(0,768))
next

do


	for collisions=0 to map_blocks.length
		
		if GetSpriteCollision(player.sprite,map_blocks[collisions])
			player.yspd#=0
		endif
		
	next
        player.y# = player.y# + signf(player.yspd#)

		SetSpritePosition(player.sprite,player.x,player.y#)



    Print( ScreenFPS() )
    Sync()
loop

function signf(f#)
	
	if f#<0 then res#=-1
	if f#=0 then res#=0
	if f#>0 then res#=1
	
	
endfunction res#

Sorry to redesign your existing though...

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smallg

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Posted: 27th Nov 2018 20:16

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ok it is because you're moving in 1 increments (integers) during the collision checks but you could start less than 1 above the platform due to falling / moving in floats.
if puzzler's solution doesn't help you likely want to check when the collision happens and then move in smaller amounts till it is more precise to where you want it (or use the physics and let it work out the point of impact).

something like this (press space to reset the cube to a new random height to fall from)

// show all errors
SetErrorMode(2)
 
// set window properties
SetWindowTitle( "Steering test" )
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

cube = CreateSprite(0)
SetSpriteSize(cube,100,100)
temp# = Random2(1,2)
		temp# = temp# * 0.1
		startingY# = 190+temp#
		SetSpritePositionByOffset(cube,512,startingY#)
SetSpriteShape(cube,2)
SetSpriteColor(cube,255,0,0,255)

ground = createSprite(0)
SetSpriteSize(ground,1000,100)
SetSpritePositionByOffset(ground,512,305)
SetSpriteShape(ground,2)
do
	if GetRawKeyState(32)
		temp# = Random2(1,50)
		temp# = temp# * 0.1
		startingY# = 190+temp#
		SetSpritePositionByOffset(cube,512,startingY#)
	endif
	print(temp#)
	Print("starting Y = "+str(startingY#))
	if GetRawKeyReleased(27) then end 
	if GetSpriteCollision(cube,ground) = 0
		SetSpritePosition(cube,GetSpriteX(cube),GetSpriteY(cube)+1)
	endif
	while GetSpriteCollision(cube,ground) = 1
		SetSpritePosition(cube,GetSpriteX(cube),GetSpriteY(cube)-0.01)
	endwhile
	Print("cube y = "+str(GetSpriteY(cube)))
	sync()
loop

+ Code Snippet

// show all errors
SetErrorMode(2)
 
// set window properties
SetWindowTitle( "Steering test" )
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

cube = CreateSprite(0)
SetSpriteSize(cube,100,100)
temp# = Random2(1,2)
		temp# = temp# * 0.1
		startingY# = 190+temp#
		SetSpritePositionByOffset(cube,512,startingY#)
SetSpriteShape(cube,2)
SetSpriteColor(cube,255,0,0,255)

ground = createSprite(0)
SetSpriteSize(ground,1000,100)
SetSpritePositionByOffset(ground,512,305)
SetSpriteShape(ground,2)
do
	if GetRawKeyState(32)
		temp# = Random2(1,50)
		temp# = temp# * 0.1
		startingY# = 190+temp#
		SetSpritePositionByOffset(cube,512,startingY#)
	endif
	print(temp#)
	Print("starting Y = "+str(startingY#))
	if GetRawKeyReleased(27) then end 
	if GetSpriteCollision(cube,ground) = 0
		SetSpritePosition(cube,GetSpriteX(cube),GetSpriteY(cube)+1)
	endif
	while GetSpriteCollision(cube,ground) = 1
		SetSpritePosition(cube,GetSpriteX(cube),GetSpriteY(cube)-0.01)
	endwhile
	Print("cube y = "+str(GetSpriteY(cube)))
	sync()
loop

life's one big game
spec= i5 4ghz, 16gb ram, Nvidia 1070ti gpu

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w0rm

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Posted: 28th Nov 2018 11:17 Edited at: 28th Nov 2018 12:11

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Thx guys for your support!!

Indeed the fact smallg pointed out seems to be the reason. If I add the rounding to y-position after collision the player aligns perfectly with the grid and tiles.

+ Code Snippet

	If colliding_sprite <> 0
		//SetSpriteColor(colliding_sprite,0,255,0,255)
		While PlaceMeeting(player.sprite, player.x, player.y + signf(player.yspd), map_blocks) = 0
			player.y = player.y + signf(player.yspd)
		EndWhile
**		player.y = Round(player.y)
		player.yspd = 0
		player.on_ground = TRUE
	EndIf

However this leads to a problem with horizontal collision checking as the system thinks player collides with tiles directly below it and therefore can't move horizontally. For example player is located on the first possible row with y-coordinate being 0 with ground below starting at y-coordinate of 24 (see the attached picture). Could it be that the GetSpriteCollision-function reports collision when the shapes are next to each other but not overlapping (the y-coordinate of the player box shape in the example is from 0 to 23 and for the ground tiles below the player 24-47).

Lifting up the player by one pixel (decreasing the y-coordinate by 1) for horizontal collision checking fixes this behavior. So the workaround could be to do that and decrease the height of the player collision shape by 1 pixel. However somehow I don't get the logic how the GetSpriteCollision reports collisions...

I don't know if the physics based collision checking could work better / more easily?

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w0rm

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Posted: 28th Nov 2018 17:50 Edited at: 28th Nov 2018 17:51

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Hmm, somehow this seems to be related to on how the default collision shape works.

Adding the following when creating player sprite seems to fix the odd behavior. After this there's no more this mysterious gap appearing randomly with the original code and player is also able to move between holes of size 1 block (24x24 pixels).

+ Code Snippet

SetSpriteOffset( player.sprite, 0, 0 )
SetSpriteShapeBox( player.sprite, 0, 0, 23, 23, 0, 0 )

If I change the above to

+ Code Snippet

SetSpriteOffset( player.sprite, 0, 0 )
SetSpriteShapeBox( player.sprite, 0, 0, 24, 24, 0, 0 )

I get exactly the same strange behavior as without it: random gap between player and ground, not able to run through holes of size 24x24 pixels (exactly the size of the player sprite and block sprite).

However I find it hard to believe that the default shape logic would be off by 1 pixel?

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puzzler2018

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Posted: 28th Nov 2018 17:56 Edited at: 28th Nov 2018 17:56

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Perhaps aybe its due to having it starting at 0

0-23 = 24 pixels
0-24 = 25 pixels

Maybe

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AppGameKit Classic Chat / Strange pixel anomaly

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