This function returns the address in screen memory of the TOP line of the character in print position X-Y. Remember that the next line will be 256 bytes further on, and the 3rd line 256 further again and so forth, for 7 more lines.
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. 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
Examples of use (though more likely to be used as parameters to other screen handling functions):
Print scrAddress(8,15) Print attrAddress(8,15)