Add routine to set ATTR to address

This routine, given a pixel address on the screen in HL will
set the ATTR for it.

Also adds an extra entry point to the SET_ATTR routine.

This routine is in charge of setting the ATTR upon an screen
update operation (PRINT, PLOT, DRAW, CIRCLE).

Now it can be used also by drawing primitives instead of the ROM's one.

Author: boriel

library-asm/attr.asm

@@ -44,6 +44,8 @@ __SET_ATTR:
     PROC 
 
     call __ATTR_ADDR
+
+__SET_ATTR2:  ; Sets attr from ATTR_T to (HL) which points to the scr address
     ld de, (ATTR_T)    ; E = ATTR_T, D = MASK_T
 
     ld a, d
@@ -61,3 +63,17 @@ __SET_ATTR:
     ENDP
 
 
+; Sets the attribute at a given screen pixel address in hl
+; HL contains the address in RAM for a given pixel (not a coordinate)
+SET_PIXEL_ADDR_ATTR:
+    ;; gets ATTR position with offset given in SCREEN_ADDR
+    ld a, h
+    rrca
+    rrca
+    rrca
+    and 3
+    or 18h
+    ld h, a
+    ld de, (SCREEN_ADDR)
+    add hl, de  ;; Final screen addr
+    jp __SET_ATTR2