2D platformer collision - GameCreators Forum

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xxelixx

15

Years of Service

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Joined: 6th Dec 2008

Location: CodeLand

Posted: 2nd Oct 2011 22:24

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I am having a little trouble with my collision. My player disappears when you walk on the ground. Any help is appreciated.

Rem ***** Main Source File *****
Sync On : Sync rate 30
set display mode 640, 480, 32

gosub setup
gosub mapSetup

Do
	While game = 1
	
	gosub player_Control
	
	sync
	Endwhile
Loop

setup: ///////////////Main setup
game as Integer
jump as Integer
playerSpr as Integer
playerXPos# as Float
playerYPos# as Float
oldXPos# as Float
oldYPos# as Float
grav# as Float
chktimer as Integer
fall As integer

tileNum as Integer

Dim map(20,15)

game = 1
playerSpr = 9999
grav# = 1.2
tileNum = 1

return ///////////////End Main setup

mapSetup: ////////////Map

Box 0, 0, 32, 32, rgb(0, 100, 100), rgb(0, 100, 0), rgb(0, 100, 100), rgb(0, 100, 0)
    Get Image 1, 0, 0, 32, 32
    
    Box 33, 0, 65, 64, rgb(100,0,0), rgb(120,0,0), rgb(100, 0,0), rgb(120,0,0)
    Get image 2, 33, 0, 65, 64

For y = 1 to 15
        For x = 1 to 20
            
            Read A
            If A = 1
                Sprite tileNum, groundX, groundY, 1
                map(x, y) = 1
                inc tileNum
            EndIf
            If A = 2
                Sprite playerSpr, groundX, groundY, 2
            EndIf
            
            groundX = groundX + 32
        Next x
        groundX = 0
        groundY = groundY + 32
    Next y

return ///////////////End of map setup

player_Control: ////////////Player controller
	playerXPos# = sprite x(playerSpr)
	playerYPos# = sprite y(playerSpr)
	oldXPos# = sprite x(playerSpr)
	oldYPos# = sprite y(playerSpr)
	
	If keystate(32) = 1
		inc playerXPos#, 2.0
	endIf
	
	If keystate(30) = 1
		dec playerXPos#, 1.5
	endIf
	
	playerYPos# = playerYPos# + 1
	//////////////////////////////////////////////////////////////Collision
	for c = 1 to tileNum - 1
	
		fall = scanY(playerSpr, c)
		
		If sprite collision(playerSpr, c)
			playerXPos# = scanX(playerSpr, c, oldXPos#)
		endIf
		
		If fall = 0
			playerYPos# = oldYPos# - 1
		EndIf
		
	Next c
	////////////////////////////////////////////////////////////////////////
	sprite playerSpr, playerXPos#, playerYPos#, 2
	
return //////////////End player control

function scanY(player, tile)////////////////////////////////   scanY
	falling as integer
	playerTop = sprite y(player)
    playerBase = findSprBase(player)
    
    tileTop = sprite y(tile)
    tileBase = findSprBase(tile)
	
	falling = 1
	
	If sprite collision(player, tile)
		If playerTop <= tileBase
			If playerBase - 6 >= tileBase
				falling = 1
			endIf
		EndIf
	
		If playerBase >= tileTop
			If playerTop + 6 <= tileTop
				falling = 0
			EndIf
		EndIf
	endIf
endFunction falling

function scanX(spr, tile, sprx)//////////////////////////////  scanX
	playerwidth = sprite x(spr) + sprite width(spr)
	tilewidth = sprite x(tile) + sprite width(tile)
	playerBase = findSprBase(spr)
	tileBase = findSprBase(tile)
	
	//Right Collision
	If playerwidth >= sprite x(tile)
		If sprite x(spr) <= sprite x(tile) - 6	
			newX = sprx
		endIf
	EndIf
			
	//Left Collision
	If sprite x(spr) <= (tilewidth)
		If playerwidth >= tilewidth + 6
			newX = sprx
		EndIf
	EndIf
	
endfunction newX

function findSprBase(spr)
	spriteBase = sprite y(spr) + sprite height(spr)
endfunction spriteBase

//Map Setup\\
//Will load from txt files later.\\
Data 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1
Data 1,0,0,2,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,1,0,1,0,1,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,0,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,1
Data 1,0,1,1,1,1,0,0,0,0,0,1,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,1,1,1,0,0,0,0,0,0,0,0,0,0
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1
Data 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1

+ Code Snippet

Rem ***** Main Source File *****
Sync On : Sync rate 30
set display mode 640, 480, 32

gosub setup
gosub mapSetup

Do
	While game = 1
	
	gosub player_Control
	
	sync
	Endwhile
Loop

setup: ///////////////Main setup
game as Integer
jump as Integer
playerSpr as Integer
playerXPos# as Float
playerYPos# as Float
oldXPos# as Float
oldYPos# as Float
grav# as Float
chktimer as Integer
fall As integer

tileNum as Integer

Dim map(20,15)

game = 1
playerSpr = 9999
grav# = 1.2
tileNum = 1

return ///////////////End Main setup

mapSetup: ////////////Map

    Box 0, 0, 32, 32, rgb(0, 100, 100), rgb(0, 100, 0), rgb(0, 100, 100), rgb(0, 100, 0)
    Get Image 1, 0, 0, 32, 32
    
    Box 33, 0, 65, 64, rgb(100,0,0), rgb(120,0,0), rgb(100, 0,0), rgb(120,0,0)
    Get image 2, 33, 0, 65, 64

    For y = 1 to 15
        For x = 1 to 20
            
            Read A
            If A = 1
                Sprite tileNum, groundX, groundY, 1
                map(x, y) = 1
                inc tileNum
            EndIf
            If A = 2
                Sprite playerSpr, groundX, groundY, 2
            EndIf
            
            groundX = groundX + 32
        Next x
        groundX = 0
        groundY = groundY + 32
    Next y

return ///////////////End of map setup

player_Control: ////////////Player controller
	playerXPos# = sprite x(playerSpr)
	playerYPos# = sprite y(playerSpr)
	oldXPos# = sprite x(playerSpr)
	oldYPos# = sprite y(playerSpr)
	
	If keystate(32) = 1
		inc playerXPos#, 2.0
	endIf
	
	If keystate(30) = 1
		dec playerXPos#, 1.5
	endIf
	
	playerYPos# = playerYPos# + 1
	//////////////////////////////////////////////////////////////Collision
	for c = 1 to tileNum - 1
	
		fall = scanY(playerSpr, c)
		
		If sprite collision(playerSpr, c)
			playerXPos# = scanX(playerSpr, c, oldXPos#)
		endIf
		
		If fall = 0
			playerYPos# = oldYPos# - 1
		EndIf
		
	Next c
	////////////////////////////////////////////////////////////////////////
	sprite playerSpr, playerXPos#, playerYPos#, 2
	
return //////////////End player control

function scanY(player, tile)////////////////////////////////   scanY
	falling as integer
	playerTop = sprite y(player)
    playerBase = findSprBase(player)
    
    tileTop = sprite y(tile)
    tileBase = findSprBase(tile)
	
	falling = 1
	
	If sprite collision(player, tile)
		If playerTop <= tileBase
			If playerBase - 6 >= tileBase
				falling = 1
			endIf
		EndIf
	
		If playerBase >= tileTop
			If playerTop + 6 <= tileTop
				falling = 0
			EndIf
		EndIf
	endIf
endFunction falling

function scanX(spr, tile, sprx)//////////////////////////////  scanX
	playerwidth = sprite x(spr) + sprite width(spr)
	tilewidth = sprite x(tile) + sprite width(tile)
	playerBase = findSprBase(spr)
	tileBase = findSprBase(tile)
	
	//Right Collision
	If playerwidth >= sprite x(tile)
		If sprite x(spr) <= sprite x(tile) - 6	
			newX = sprx
		endIf
	EndIf
			
	//Left Collision
	If sprite x(spr) <= (tilewidth)
		If playerwidth >= tilewidth + 6
			newX = sprx
		EndIf
	EndIf
	
endfunction newX

function findSprBase(spr)
	spriteBase = sprite y(spr) + sprite height(spr)
endfunction spriteBase

//Map Setup\\
//Will load from txt files later.\\
Data 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1
Data 1,0,0,2,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,1,0,1,0,1,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,0,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,1
Data 1,0,1,1,1,1,0,0,0,0,0,1,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,1,1,1,0,0,0,0,0,0,0,0,0,0
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1
Data 1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1
Data 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1

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29 games

19

Years of Service

User Offline

Joined: 23rd Nov 2005

Location: not entirely sure

Posted: 3rd Oct 2011 00:41

Link

Hi xxelixx, I think I've solved your immediate question.

When I ran your code the following happened:

Player box would fall onto the green platform. When I moved left or right, the player box would go so far and then position itself and the far left of the screen and slowly move upward until it dispeared off the top of the screen.

I'm guessing this is what you mean by "My player disappears when you walk on the ground".

Ok then, for the player box to be on the far left of the screen the boxes x coordinate must have been set to zero for some reason.

Looking at the function "scanX", if a horizontal collision has occured then you reposition the player sprite at its old position. In this case "newX = sprx".

However, newX can only equal sprx if the conditions of the if statements are met. If the conditions of the if statment are not met then newX = 0.

For some reason, the conditions of the if statements were not being met so newX was being set to zero. This sets the player's x position to zero, which just so happens to put the player box in the left most had wall of green sprites.

When you deal with falling, if the player box hits the ground you then position the player box to the old y coordinate plus 1 pixel.

When the player box has been put into the left hand wall, there is constant collision and the box moves up and eventually off the screen.

The way I got around this was to modify the scanX function by setting newX to the player's current x coordinate before the if statements.

+ Code Snippet

function scanX(spr, tile, sprx)//////////////////////////////  scanX
	playerwidth = sprite x(spr) + sprite width(spr)
	tilewidth = sprite x(tile) + sprite width(tile)
	playerBase = findSprBase(spr)
	tileBase = findSprBase(tile)


	`this sets a default value for the x coordinate in case no collision has occured
	`without this line the defaut value of newX = 0 therefore if the conditions in the following
	`if statements are not met the player's x coordinate will be set to zero.
	newX = sprite x(spr)
	
	//Right Collision
	If playerwidth >= sprite x(tile)
		If sprite x(spr) <= sprite x(tile) - 6	
			newX = sprx
		endIf
	EndIf
			
	//Left Collision
	If sprite x(spr) <= (tilewidth)
		If playerwidth >= tilewidth + 6
			newX = sprx
		EndIf
	EndIf
	
endfunction newX

I have to admit, I don't know what:

If sprite x(spr) <= sprite x(tile) - 6

and

If playerwidth >= tilewidth + 6

actually do. I think this may be where the real problem lies as when I took them out, this achieved the same effect as putting in the line "newX = sprite x(spr)". You might want to have a look at this.

The other issue with the collision code is that when the player is touching the side of a green tile, the player box starts to move upward. Moving sideways into a green tile is being treated as if the player has fallen on it, i.e. move the player up 1 pixel. I also noticed that when this happens the player can not move horizontally so they are completely stuck. This means that the player can not fall through any of the gaps in the platform.

I think what you need to do is to first check whether the collision is horizontal or vetical (i.e. has the player moved sideways into a green tile or have they fallen on top of it) and then work out what they new coordinates are based on how the player has collided with the map.

One other thing, you seem to be mixing up floats and integer which, while it doesn't seem to be affecting the running of you, is something you may want to sort out.

Hope this helps and let us know if you sort out the collision or not.

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