;----------------------------------------------
; SPRITE MIRRORING
; Eduardo A. Robsy Petrus [22/04/2005]
; (c) Karoshi Corporation, 2005
;----------------------------------------------
; Horizontal and vertical mirroring routines
; for 16x16 sized sprites in VRAM.
;----------------------------------------------
; - Does not use temporary RAM, only the stack.
; - Total assembled size: 110 bytes.
; - Requires the .BIOS directive to be used and
; BIOS routines available in page 0.
; - Requires SPRTBL label to point to VRAM
; sprite pattern table (BIOS default: 3800h).
;----------------------------------------------
; PROs: Reliable, does not use a RAM buffer.
; CONs: Not very fast, not very compact.
;----------------------------------------------

;----------------------------------------------
SPRITE_H_MIRROR:
; Horizontal sprite mirroring
;----------------------------------------------
; Input: A=original sprite number
; B=mirrored sprite number
; Output: none
; Modifies: AF,BC,DE,HL,EI
;----------------------------------------------
; Calculate original sprite address
call MULT32
ld a,b
ld bc,SPRTBL
add hl,bc
; Store original address in DE
ex de,hl
; Calculate mirrored sprite address
call MULT32
add hl,bc
; Store in HL and save into the stack
push hl
; Adjust HL to second part
ld bc,16
add hl,bc
; Copy and invert second half
call @@COPY16
; Copy and invert first half
pop hl
call @@COPY16
; Done
ret
; Copy and inverts 16 bytes of VRAM (DE->HL)
@@COPY16:
ld b,16
; Copy loop
@@COPY:
; Read byte
ex de,hl
call RDVRM
; Invert byte
push bc
push hl
ld b,8
@@INVERT:
rla
ld l,a
ld a,c
rra
ld c,a
ld a,l
djnz @@INVERT
ld a,c
pop hl
pop bc
; Write byte
ex de,hl
call WRTVRM
; Increase pointers
inc de
inc hl
djnz @@COPY
; Done
ret
;----------------------------------------------

;----------------------------------------------
SPRITE_V_MIRROR:
; Vertical sprite mirroring
;----------------------------------------------
; Input: A=original sprite number
; B=mirrored sprite number
; Output: none
; Modifies: AF,BC,DE,HL,EI
;----------------------------------------------
; Original address
; (ORIGINAL_NUM*32)+SPRITE_TABLE
call MULT32
ld a,b
ld bc,SPRTBL
add hl,bc
; Store original address in DE
ex de,hl
call MULT32
add hl,bc
; Push into stack
push hl
ld bc,15
add hl,bc
call @@COPY16
pop hl
ld bc,31
add hl,bc
call @@COPY16
ret
; DE->HL 16 bytes, VRAM
@@COPY16:
ld b,16
@@COPY:
ex de,hl
call RDVRM
ex de,hl
call WRTVRM
inc de
dec hl
djnz @@COPY
ret
;----------------------------------------------

;----------------------------------------------
MULT32:
; Support function
;----------------------------------------------
; Input: A=value
; Output: HL=value*32
; Modifies: HL
;----------------------------------------------
ld l,a
ld h,0
add hl,hl
add hl,hl
add hl,hl
add hl,hl
add hl,hl
ret
;----------------------------------------------