Colisiones y ATTR
(copiado de algunos hilos de WoS)
Spectrum BASIC includes helper functions to do it for you. SCREEN$(row,column) returns the character at a particular screen location, and ATTR(row,column) returns its colour attributes (128 * flash + 64 * bright + 8 * paper + ink).
Note that SCREEN$ can only recognise characters in the 32-127 range, not graphical characters or user-defined graphics.
Simplest way is to draw things in different colours then use ATTR(y,x) to retrieve the attribute byte. Or it's at PEEK (22528+x+(y*32)).
Just remember for your blank spaces to print them with black INK and PAPER, because an empty space can have a coloured INK and you wouldn't realise.
SCREEN$(y,x) will give you the character at screen location y,x, but it won't recognise UDGs, which are presumably what you'll be using for the graphics. As a workaround there are POKEs that will let you redefine the entire character set instead, whereupon SCREEN$ will work.
ATTR(y,x) will give you the attribute value at location y,x, encoded as (128 * flash setting) + (64 * bright setting) + (8 * paper colour) + (ink colour). Testing this will be faster than doing a SCREEN$ test. Generally though, you might find it faster still to avoid testing the screen directly and instead to keep everything you need to know in variables - for example, storing the maze grid in a two-dimensional array and looking up wall positions in that.
Actually, I don't even use INK, PAPER that much anymore as I switched to using:
POKE 23693,<ATTR>
where 23693 is the ATTR P system variable.
where ATTR is:
INK ( 0 to 7 ) +
PAPER ( 8 * 0 to 7 ) +
BRIGHT ( 64 ) +
FLASH ( 128 )
so if I wanted bright, red paper with yellow ink then I would POKE a value of 86 (6+(8*2)+64) prior to doing any printing.
In fact I define a constant "p" in my program that is equal to 23693 to reduce memory usage.
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