Reading, storing and writing screen values

[oblo]

Hi all

I'm starting to learn how to manipulate screen directly at memory address level. Right now, I'm messing with this code

Code:

rem screen values
paper 0: border 0: ink 7: cls
dim conta as byte
dim x,y,n,adres,dirb as uinteger


bucle:

y=RND*10
x=RND*32
adres=0
POKE attrAddress(x,y),RND*256

Print at 10,0; "X="; x; " - "; "Y="; y;
print at 11,0; "Attrib address is.......: "; attrAddress(x,y);
print at 12,0; "Attrib value is.........: "; PEEK attrAddress(x,y);
print at 13,0; "The 8 screen addresses..: "

for conta=0 to 7
        poke scrAddress(x,y)+adres,RND*256
        print scrAddress(x,y)+adres;","; PEEK (scrAddress(x,y)+adres)
        adres=adres+256
next conta

pause 0

cls

goto bucle


rem funciones

FUNCTION scrAddress(x AS UBYTE, y AS UBYTE) AS UINTEGER
ASM
; This FUNCTION returns the address into HL of the screen address
; x,y in character grid notation.
; Original CODE was extracted by BloodBaz

         ; x Arrives in A, y is in stack.
         AND     31
         ld      l,a
         ld      a,(IX+7) ; Y value
         ld      d,a
         AND     24
         add     a,64
         ld      h,a
         ld      a,d
         AND     7
         rrca
         rrca
         rrca
         OR      l
         ld      l,a
              
END ASM
END FUNCTION



FUNCTION attrAddress (x AS UBYTE, y AS UBYTE) AS UINTEGER
'This function returns the memory address of the Character Position
'x,y in the attribute screen memory.
'Adapted from code by Jonathan Cauldwell.
'Rebuilt for ZX BASIC by Britlion from NA_TH_AN's fourspriter, with permission.

ASM

         ld      a,(IX+7)  ;ypos
         rrca
         rrca
         rrca              ; Multiply by 32
         ld      l,a       ; Pass TO L
         AND     3         ; Mask with 00000011
         add     a,88      ; 88 * 256 = 22528 - start of attributes.
         ld      h,a       ; Put it in the High BYTE
         ld      a,l       ; We get y value *32
         AND     224       ; Mask with 11100000
         ld      l,a       ; Put it in L
         ld      a,(IX+5)  ; xpos
         add     a,l       ; Add it TO the Low BYTE
         ld      l,a       ; Put it back in L, AND we're done. HL=Address.
END ASM
END FUNCTION

Questions are:

- Are there any better options to read and write given a X and Y coordinates?
- What is the best way to storage screen memory addresses and their values? Integer (for addresses) and Ubyte (for values) arrays, right?

Thanks and regards