Scratch

Just only allow movement along set intervals (like below).  Alternatively you could "snap to a grid" (there's a wiki article on that), but I'm pretty sure that's not the effect you're looking for.

when gf clicked
forever
if<key [right arrow v] pressed?>
repeat (10)
change x by (1)
end
end
if<key [left arrow v] pressed?>
repeat (10)
change x by (-1)
end
end
if<key [up arrow v] pressed?>
repeat (10)
change y by (1)
end
end
if<key [down arrow v] pressed?>
repeat (10)
change y by (-1)
end
end

Assuming it is top-down, the below script is one way.  If it is more 3-D looking, I'd have a 2-D list with whether a block can be moved through and check that (if that's the case, I can try to give you a script for that).

when gf clicked
forever
if<key [right arrow v] pressed?>
change x by (10)
if<not<touching [wall v]?>>
change x by (-10)
repeat (10)
change x by (1)
end
else
change x by (-10)
end
end
etc.

What do you mean "accurate".  A smaller grid?

I'm not sure exactly what you want.  Do you want a script that returns a sprite's x and y position on the grid?  A script that uses a 2D array for wall collision?

A script that uses a 2D array for wall collision?


The script for a sprite's x and y position on a grid looks something like this:

set [x v] to ((round(((x position)-[horizontal shift])/(tile_size)))+[some number])
set [y v] to ((round(((y position)-[vertical shift])/(tile_size)))+[some other number])

((x-hs)/(tile_size)) + some number

Thinking back on it, "horizontal shift" and "some number" are probably the same number.  I'm away from home visiting relatives right now so I can't confirm it