Question about collision in 2D - GameCreators Forum

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martianxx

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Joined: 19th Feb 2011

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Posted: 15th Jun 2011 04:27

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Hi I am making a game and am begining to progress, have loaded data into an array that maps my level, used the arrays to map the data, added character with animation that moves from left to right with user input and the level scrolls when the player is in the center of the screen and the level is not at the start or end. The character even jumps and there is some very basic collision in place (to avoid him walking off the screen/level or falling into abyss when he jumps).

However I am now looking at implementing collision so instead of defining values the character can't go outside of (the screen or ground level) the program intuitavley notices colision. I want to do this by readining in bounds of areas into array from a data stetement which I have done since thats the easy part. Now the hard part, making use of the data. I have tried to make a collision check system myslef but after a long time of theorising and playing around without success I started searching around on the forums without much success. I can't see many other people trying to create collisions in this way yet I am sure it's a viable method. While searching I came accross sparky's collision detection. Now the real aim of my question is to ask if sparky's collision detection can be used in 2D as most if not all of the demos and examples seem to be for 3D and if it can how could I use it in conjunction with a data statement similar to the following where 1's represent tiles I want the player to collide with.

+ Code Snippet

Data  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Data  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Data  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Data  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Data  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Data  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Data  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Data  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Data  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
Data  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

If i were to have a quick attempt I would think about reading the array storing the above data and making an object for each entry of 1 (if you can make objects for tiles) and then use the other commands in sparky's detection system to determing when collision occurs.

If any of the veterans out there could give me a point in the right direction I would be most grateful. Thanks in advance. David

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martianxx

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Posted: 15th Jun 2011 19:20

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I haven't gotten any replies yet but I will update you with where I am. As far as I can see sparky's collisions is sued for 3D objects so I can's use unless there is some nifty technique (like loading it into a 3D scenario and making 2D plane objects to be used for collision).

Regardless I have done some drawings to try and get it straight in my mind and decided to try and create sprites ontop of the tiles that I want the character to collide with. I can then use the sprite collision(sprite1, sprite2) function to test if there is a colision with the sprites.

I know how to update the sprites on screen for screenscolling as its very similar to my technique for pasting images onto the screen whilst the level is scrolling. However there is a variable number of bound tiles on screen at anytime as the level scroll and the array I use to store the info about the sprites would need to change as the level scrolls.

Is there any ReDim command for this so I can re dim the array when a new bound tile is found or do I need a sepeare loop to store the values for the array then another loop to input the new values into the array by using UNDIM arrayName(x,y) Dim arrayName(var1, var2) where var 1/2 are the values obtained from the previous loop. If I dont use this technique or a similar one then I would have to create a sprite for every tile on screen which seems un necisary.

Here is the code I am currently using to create sprites for collision on screen, is there a more efficient way? I am sure there is:

type colSprite
    collision As Integer
    x As Integer
    y As Integer
    num As Integer
    imgNum As Integer
EndType

Dim collisionSprites As colSprite

Rem Later in program

Function RenderCollisions(map,x_offset,y_offset)

RemStart x_offset and y_offset are the amount of pixels between the start of the level and the 0,0 origin on the screen. in my program y_offset is always 0 as it is only sidescroller. the x_offset scales with character speed as long as the character is in the middle of the screen RemEnd

ty = y_offset / TileHeight(map) rem tile height and width are both 32
sy = -(y_offset Mod TileHeight(map))

RemStart sy is the amount of pixels of the tile that is only part on screen, starts at minus so the forst "half tile" starts offscreen RemEnd

While sy < SCREEN_HEIGHT
           
      tx = x_offset / TileWidth(map) 
      sx = -(x_offset Mod TileWidth(map))
    
         While sx < SCREEN_WIDTH
                
            bound = GetBounds(map,tx Mod MapWidth(map),ty Mod MapHeight(map))

RemStart GetBounds returns the value stored in the array for bounds which is in turn obtained from a data statement. bounds are greater than 0RemEnd
            
            If bound > 0
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).x = sx
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).y = sy
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).imgNum = 21
            EndIf
            
            If bound <= 0
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).x = -100
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).y = 0
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).imgNum = 21
            EndIf
            
            tx = tx + 1
            sx = sx + TileWidth(map)
                     
         EndWhile
         
         ty = ty + 1
         sy = sy + TileHeight(map)
         
   EndWhile

RemStart I amde a data statement to store numbers 1 to 330 to be used as image numbers as i was getting spite number invalid error and just wanted to be sure, can probably remove this now RemEnd

restore spriteNumbers
            for y = 0 to 15 -1
               for x = 0 to 22 - 1
                  read collisionSprites(x,y).num
               next x
            next y
   
      For y = 0 to 14
         For x = 0 to 21
         If collisionSprites(x,y).x > -99
            sprite collisionSprites(x,y).num, collisionSprites(x,y).x, collisionSprites(x,y).y, collisionSprites(x,y).imgNum
         EndIf
      Next x
   Next y
RemStart the sprites made here can then be used to detect collision RemEnd
EndFunction

+ Code Snippet

type colSprite
    collision As Integer
    x As Integer
    y As Integer
    num As Integer
    imgNum As Integer
EndType

Dim collisionSprites As colSprite

Rem Later in program

Function RenderCollisions(map,x_offset,y_offset)

RemStart x_offset and y_offset are the amount of pixels between the start of the level and the 0,0 origin on the screen. in my program y_offset is always 0 as it is only sidescroller. the x_offset scales with character speed as long as the character is in the middle of the screen RemEnd

ty = y_offset / TileHeight(map) rem tile height and width are both 32
sy = -(y_offset Mod TileHeight(map)) 

RemStart sy is the amount of pixels of the tile that is only part on screen, starts at minus so the forst "half tile" starts offscreen RemEnd

   While sy < SCREEN_HEIGHT
           
      tx = x_offset / TileWidth(map) 
      sx = -(x_offset Mod TileWidth(map))
    
         While sx < SCREEN_WIDTH
                
            bound = GetBounds(map,tx Mod MapWidth(map),ty Mod MapHeight(map))

RemStart GetBounds returns the value stored in the array for bounds which is in turn obtained from a data statement. bounds are greater than 0RemEnd
            
            If bound > 0
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).x = sx
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).y = sy
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).imgNum = 21
            EndIf
            
            If bound <= 0
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).x = -100
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).y = 0
            collisionSprites(tx Mod MapWidth(map), ty Mod MapHeight(map)).imgNum = 21
            EndIf
            
            tx = tx + 1
            sx = sx + TileWidth(map)
                     
         EndWhile
         
         ty = ty + 1
         sy = sy + TileHeight(map)
         
   EndWhile

RemStart I amde a data statement to store numbers 1 to 330 to be used as image numbers as i was getting spite number invalid error and just wanted to be sure, can probably remove this now RemEnd

   restore spriteNumbers
            for y = 0 to 15 -1
               for x = 0 to 22 - 1
                  read collisionSprites(x,y).num
               next x
            next y
   
      For y = 0 to 14
         For x = 0 to 21
         If collisionSprites(x,y).x > -99
            sprite collisionSprites(x,y).num, collisionSprites(x,y).x, collisionSprites(x,y).y, collisionSprites(x,y).imgNum
         EndIf
      Next x
   Next y
RemStart the sprites made here can then be used to detect collision RemEnd
EndFunction

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29 games

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Posted: 15th Jun 2011 21:45 Edited at: 15th Jun 2011 21:52

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Quote: "I haven't gotten any replies yet "

Give us a chance, you only posted yesterday

There are a couple of ways to use data in data statements to create maps and stuff.

In the example below I've used eleven lines and columns of data to represent a grid. I think use a couple of nested "for to next loops" To read this data. When a "1" is read, a green wall is pasted to the screen, with the coordinates being calculated from the x and y values multiplied by the size of the box

Editing the data essentially edits the map.

You can use different values to hold different images, ie 1 is a wall, 2 is plant pot, 3 is a door etc.

I've then used the "sprite hit" command to detect when the player hits the wall and the player will stop.

`use the arrow keys to move the red box
`edit the data to edit the map
`1 indicates a wall sprite

sync on
sync rate 60
hide mouse

`create some images for the sprites
`create a new bitmap to draw the images to
create bitmap 1, 20,20
set current bitmap 1

`use green boxes for the walls
ink rgb(0,250,0),0
box 0,0,20,20
get image 1, 0,0,20,20

`use a red box for the player
ink rgb(250,0,0),0
box 0,0,10,10
get image 2, 0,0,10,10

set current bitmap 0

`read the data from the data block and paste the sprites to the screen
`the 1 to 11 for x and y matches the eleven rows and collumns of the data statements
for y = 1 to 11
	for x = 1 to 11
		read block
		if block = 1
			inc block_num
			sprite block_num,x*20,y*20,1
		endif
	next 10
next x

`player sprite number
ply = block_num + 1

`player starting variable
xply = screen width() / 2 		:`x coordinate
yply = screen height() / 2		:`y coordinate

do
	
	`save the old position
	old_xply = xply
	old_yply = yply
	
	`controls
	if upkey() = 1 then dec yply,2
	if downkey() = 1 then inc yply,2
	if leftkey() = 1 then dec xply,2
	if rightkey() = 1 then inc xply,2
	
	`paste player sprite to the screen
	sprite ply, xply, yply, 2

`collision detection
	for i = 1 to block_num
		if sprite hit(ply, i) = 1
			`if player hits a wall, put the player back to its old coordinates
			xply = old_xply
			yply = old_yply
		endif
	next i

sync

loop

`map data
data 1,1,1,1,0,1,1,1,1,1,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,0
data 1,1,1,0,0,0,0,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,1,1,1,1,1,1,1,0,1,1
data 1,0,0,0,0,1,0,0,0,0,1
data 1,0,0,0,0,0,0,0,0,0,1
data 1,0,0,0,0,1,0,0,0,0,0
data 1,0,1,1,1,1,1,0,1,0,1

+ Code Snippet

`use the arrow keys to move the red box
`edit the data to edit the map
`1 indicates a wall sprite

sync on
sync rate 60
hide mouse

`create some images for the sprites
`create a new bitmap to draw the images to
create bitmap 1, 20,20
set current bitmap 1

`use green boxes for the walls
ink rgb(0,250,0),0
box 0,0,20,20
get image 1, 0,0,20,20

`use a red box for the player
ink rgb(250,0,0),0
box 0,0,10,10
get image 2, 0,0,10,10

set current bitmap 0


`read the data from the data block and paste the sprites to the screen
`the 1 to 11 for x and y matches the eleven rows and collumns of the data statements
for y = 1 to 11
	for x = 1 to 11
		read block
		if block = 1
			inc block_num
			sprite block_num,x*20,y*20,1
		endif
	next 10
next x

`player sprite number
ply = block_num + 1

`player starting variable
xply = screen width() / 2 		:`x coordinate
yply = screen height() / 2		:`y coordinate


do
	
	`save the old position
	old_xply = xply
	old_yply = yply
	
	`controls
	if upkey() = 1 then dec yply,2
	if downkey() = 1 then inc yply,2
	if leftkey() = 1 then dec xply,2
	if rightkey() = 1 then inc xply,2
	
	`paste player sprite to the screen
	sprite ply, xply, yply, 2

	`collision detection
	for i = 1 to block_num
		if sprite hit(ply, i) = 1
			`if player hits a wall, put the player back to its old coordinates
			xply = old_xply
			yply = old_yply
		endif
	next i

	sync

loop

`map data
data 1,1,1,1,0,1,1,1,1,1,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,0
data 1,1,1,0,0,0,0,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,1,1,1,1,1,1,1,0,1,1
data 1,0,0,0,0,1,0,0,0,0,1
data 1,0,0,0,0,0,0,0,0,0,1
data 1,0,0,0,0,1,0,0,0,0,0
data 1,0,1,1,1,1,1,0,1,0,1

Another way of doing this, is to use the data to hold the actual coordinates of all the things on the map. I did this on my "driver 20 parallel line" game on the 20 line challenge board. It's a 3D game but will give you an idea of how to use the data.

Lastly, Sparky's collision only works for 3D objects not 2D sprites. The collision detection and resolution I've used in the above example is very simple. You might want to look at Box 2D, I've never used it and have no idea what it actually does, but someone else might be able to shed some light on it.

I hope this helps.

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martianxx

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Posted: 16th Jun 2011 00:27

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Thanks you for the example.

Quote: "Give us a chance, you only posted yesterday"

Sorry, I didn't mean it in that way. I just wanted to keep you updated on where I was despite any lack of replies.

I think I can take the example you have given me and apply it to my own game. Here is a slightly different version showing how I intend to use the technique.

`use the arrow keys to move the red box
`edit the data to edit the map
`1 indicates a wall sprite

sync on
sync rate 60
hide mouse

`create some images for the sprites
`create a new bitmap to draw the images to
create bitmap 1, 20,20
set current bitmap 1
set image colorkey 0, 250, 0

`use green boxes for the bounds
ink rgb(0,250,0),0
box 0,0,20,20
get image 1, 0,0,20,20

`use a red box for the player
ink rgb(250,0,0),0
box 0,0,10,10
get image 2, 0,0,10,10

`use a yellow box for the map
ink rgb(255,255,0),0
box 0,0,20,20
get image 3, 0,0,20,20

set current bitmap 0

`read the data from the data block and paste the sprites to the screen
`the 1 to 11 for x and y matches the eleven rows and collumns of the data statements
for y = 1 to 11
	for x = 1 to 11
		read block
		if block = 1
			inc block_num
			sprite block_num,x*20,y*20,1
		endif
	next 10
next x

restore map_data
for y = 1 to 11
   for x = 1 to 11
      read map
      if map = 1
         inc map_num
         sprite map_num,x*20,y*20,3
      endif
   next x
next y

`player sprite number
ply = block_num + 1

`player starting variable
xply = 100 `x coordinate
yply = 100 `y coordinate

do
	
	`save the old position
	old_xply = xply
	old_yply = yply
	
	`controls
	if upkey() = 1 then dec yply, 2
	if downkey() = 1 then inc yply, 2
	if leftkey() = 1 then dec xply,2
	if rightkey() = 1 then inc xply,2
	
	`paste player sprite to the screen
	sprite ply, xply, yply, 2

`collision detection
	for i = 1 to map_num
		if sprite hit(ply, i) = 1
			`if player hits a wall, put the player back to its old coordinates
			xply = old_xply
			yply = old_yply
		endif
	next i

sync

loop

map_data:
data 1,1,1,1,0,1,1,1,1,1,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,0
data 1,1,1,0,0,0,0,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,1,1,1,1,1,1,1,0,1,1
data 1,0,0,0,0,1,0,0,0,0,1
data 1,0,0,0,0,0,0,0,0,0,1
data 1,0,0,0,0,1,0,0,0,0,0
data 1,0,1,1,1,1,1,0,1,0,1

+ Code Snippet

`use the arrow keys to move the red box
`edit the data to edit the map
`1 indicates a wall sprite

sync on
sync rate 60
hide mouse

`create some images for the sprites
`create a new bitmap to draw the images to
create bitmap 1, 20,20
set current bitmap 1
set image colorkey 0, 250, 0

`use green boxes for the bounds
ink rgb(0,250,0),0
box 0,0,20,20
get image 1, 0,0,20,20

`use a red box for the player
ink rgb(250,0,0),0
box 0,0,10,10
get image 2, 0,0,10,10

`use a yellow box for the map
ink rgb(255,255,0),0
box 0,0,20,20
get image 3, 0,0,20,20

set current bitmap 0


`read the data from the data block and paste the sprites to the screen
`the 1 to 11 for x and y matches the eleven rows and collumns of the data statements
for y = 1 to 11
	for x = 1 to 11
		read block
		if block = 1
			inc block_num
			sprite block_num,x*20,y*20,1
		endif
	next 10
next x

restore map_data
for y = 1 to 11
   for x = 1 to 11
      read map
      if map = 1
         inc map_num
         sprite map_num,x*20,y*20,3
      endif
   next x
next y

`player sprite number
ply = block_num + 1

`player starting variable
xply = 100 `x coordinate
yply = 100 `y coordinate

do
	
	`save the old position
	old_xply = xply
	old_yply = yply
	
	`controls
	if upkey() = 1 then dec yply, 2
	if downkey() = 1 then inc yply, 2
	if leftkey() = 1 then dec xply,2
	if rightkey() = 1 then inc xply,2
	
	`paste player sprite to the screen
	sprite ply, xply, yply, 2

	`collision detection
	for i = 1 to map_num
		if sprite hit(ply, i) = 1
			`if player hits a wall, put the player back to its old coordinates
			xply = old_xply
			yply = old_yply
		endif
	next i

	sync

loop

map_data:
data 1,1,1,1,0,1,1,1,1,1,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,0
data 1,1,1,0,0,0,0,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,0,0,0,0,0,1,0,0,0,1
data 1,1,1,1,1,1,1,1,0,1,1
data 1,0,0,0,0,1,0,0,0,0,1
data 1,0,0,0,0,0,0,0,0,0,1
data 1,0,0,0,0,1,0,0,0,0,0
data 1,0,1,1,1,1,1,0,1,0,1

As you can see I layer other sprites under the visable ones and make the colour transparent and use the back sprites to test for collision. It's possibly not necessary but for now it's easier to implement (as I dont have to chnage so much of the code I have to paste the visable tiles to the screen). When I have completed this test I can refine the code then making it more efficient I think. Do you think this method will work with a scrolling level where the position of the sprites is being changed constantly? I guess i'll have to see

Thanks. David

Ps. Ill look into that Box 2D but looks like its more for Dark GDK as its in c++. Correct?

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Neuro Fuzzy

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Posted: 16th Jun 2011 04:19 Edited at: 16th Jun 2011 04:24

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Quote: "Ps. Ill look into that Box 2D but looks like its more for Dark GDK as its in c++. Correct? "

There's a commercial plugin for DBPro:
http://www.thegamecreators.com/?m=view_product&id=2257

[edit]
also, I can help with collision stuff, but... most of the stuff I write is a bit math intensive for some people. ex:
http://forum.thegamecreators.com/?m=forum_view&t=179370&b=6

Why does blue text appear every time you are near?

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martianxx

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Posted: 16th Jun 2011 22:10

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Thanks Neuro thats really helpful for getting it stratight in my mind. Actuall after doing maths for a long time t's quite nice to apply that to my programming

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