Help on collission detection fro a paltformer.

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Dextro

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Posted: 13th Feb 2007 05:09

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Hello.
I've been trying to come up with some formulas for collision detection between a sprite and a tile, but I haven't figured out how to do it in an effective manner.
Anyone got some knowledge about this? I will greatly appreciate it.
Thanks.

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Dextro

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Posted: 13th Feb 2007 15:41

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Ok, I have an idea that may work.
Basically, my idea consists on checking if the pixel below the player belongs to a solid tile, which is defined in a second array apart from my map array.

+ Code Snippet

if collision_layer(int(x1#/32), roundup((y1#+1)/32)) = solid
    velocity_y = 0
else
    velocity_y = velocity_y + gravity
endif

y1# is the y position of the player.
x1# the x position of the player.
roundup is a function for rounding numbers upwards.
For left and right collision I would use the same function, only changing x1# parameters.

Would this work?

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Zergei

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Posted: 13th Feb 2007 20:13

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Thats the main idea, work it out good enough and you'll have your collision ready.
A tip, if you're gonna use shaped tiles, say for example a ramp, if the tile returned was a shaped one, go to the array wich stores information regarding that, and other shaped tiles. What information?, well, for example that at X position within that tile corresponds Y. Get the idea?, when your in the tile, at x=4 (example, and that 4 is within the tile, not regarding the screen/world/whatever...), the height/y ther would be, say, 2... and at x=7 , y=5... and well thats pretty much it.

If this of no use, well, it'll leave the record for others to read. If you know of a better way of doing it, then please state it and let me test it...

Further on my stuff at...

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Dextro

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Posted: 13th Feb 2007 23:27

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Nope, I can't get it to work.
I used a UDT for each tile, keeping it's x,y and image/mask.
Anyone got any ideas on how to check for y collision with a tile?

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Dextro

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Posted: 14th Feb 2007 00:04

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As simple as

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if layermap(roundup(x1#/32), int(y1/32)+2).image = 2
		jumping = 0
		y1 = layermap(roundup(x1#/32), int(y1/32)).y
      endif

Duh to myself

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Thc03

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Posted: 27th Feb 2007 03:10 Edited at: 27th Feb 2007 03:15

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Look at this:

rem collision between a sprite and a tile
type coordinate
   x as float
   y as float
   xRay as float
   yRay as float
endtype

sprite as coordinate
tile as coordinate

intObstacleValue = 100
sprite.x = 2
sprite.y = 3
tile.x = 10
tile.y = 10
dim tilesOnScreen(20, 15)
for y = 1 to 15
   for x = 1 to 20
      tileOnScreen(x, y) = (..(x <> tile.x) and ..(y <> tile.y)) * intObstacleValue
      rem this will return 0 when not both the conditions are true, so every tile will value 0 but not the tile(10, 10), wich will value 100
   next x
next y

do
   cls
   input()
   collision()
   drawTileAndSprite()
   sync
loop

function collision()
   rem this is a distance-based collision check, for arbitrary placed tiles and sprites
   absY = abs(sprite.y - tile.y)
   absX = abs(sprite.x - tile.x)
   xDistance = (sprite.yRay + tile.yRay)
   yDistance = (sprite.xRay + tile.xRay)
   onXAxis = absY <= tile.yRay
   onYAxis = absX <= tile.xRay
   xContact = absX <= xDistance
   yContact = absY <= yDistance
   xCollision = onYAxis and xContact
   yCollision = onXAxis and yContact
   if xCollision
      rem put events here
   endif
   if yCollision
      rem put events here
   endif
endfunction

function moveInTiles(xStep as integer, yStep as integer)
   xNext = int(sprite.x + xStep)
   yNext = int(sprite.y + yStep)
   if tilesOnScreen(xNext, yNext) <> intObstacleValue
      sprite.x = sprite.x + xStep
      sprite.y = sprite.y + yNext
   endif
endfunction

function drawTileAndSprite()
   ellipse int(sprite.x), int(sprite.y), int(sprite.xRay), int(sprite.yRay)
   box int(tile.x - tile.xRay), int(tile.y - tile.yRay), int(tile.x + tile.xRay), int(tile.y + tile.yRay)
endfunction

function input()
   onTheX = (rightkey() - leftkey()) * 0.25
   onTheY = (downkey() - upkey()) * 0.25
   moveInTiles(onTheX, onTheY)
endfunction

+ Code Snippet

rem collision between a sprite and a tile
type coordinate
   x as float
   y as float
   xRay as float
   yRay as float
endtype

sprite as coordinate
tile as coordinate

intObstacleValue = 100
sprite.x = 2
sprite.y = 3
tile.x = 10
tile.y = 10
dim tilesOnScreen(20, 15)
for y = 1 to 15
   for x = 1 to 20
      tileOnScreen(x, y) = (..(x <> tile.x) and ..(y <> tile.y)) * intObstacleValue
      rem this will return 0 when not both the conditions are true, so every tile will value 0 but not the tile(10, 10), wich will value 100
   next x
next y

do
   cls
   input()
   collision()
   drawTileAndSprite()
   sync
loop

function collision()
   rem this is a distance-based collision check, for arbitrary placed tiles and sprites
   absY = abs(sprite.y - tile.y)
   absX = abs(sprite.x - tile.x)
   xDistance = (sprite.yRay + tile.yRay)
   yDistance = (sprite.xRay + tile.xRay)
   onXAxis = absY <= tile.yRay
   onYAxis = absX <= tile.xRay
   xContact = absX <= xDistance
   yContact = absY <= yDistance
   xCollision = onYAxis and xContact
   yCollision = onXAxis and yContact
   if xCollision
      rem put events here
   endif
   if yCollision
      rem put events here
   endif
endfunction

function moveInTiles(xStep as integer, yStep as integer)
   xNext = int(sprite.x + xStep)
   yNext = int(sprite.y + yStep)
   if tilesOnScreen(xNext, yNext) <> intObstacleValue
      sprite.x = sprite.x + xStep
      sprite.y = sprite.y + yNext
   endif
endfunction

function drawTileAndSprite()
   ellipse int(sprite.x), int(sprite.y), int(sprite.xRay), int(sprite.yRay)
   box int(tile.x - tile.xRay), int(tile.y - tile.yRay), int(tile.x + tile.xRay), int(tile.y + tile.yRay)
endfunction

function input()
   onTheX = (rightkey() - leftkey()) * 0.25
   onTheY = (downkey() - upkey()) * 0.25
   moveInTiles(onTheX, onTheY)
endfunction

Bye, Berserk.
.

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aluseus GOD

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Joined: 19th Mar 2007

Location: I\'m here. Now I\'m there. I keep moving

Posted: 27th Mar 2007 20:51

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even better yet...

+ Code Snippet

For tile = 1 to tiles
if sprite collision (1,tile)
(code here)
endif
Next tile

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2D All the way! / Help on collission detection fro a paltformer.