#include "ti83plus.inc"
    .org $9d95-2
    .db $bb,$6d
    bcall(_grbufclr)
    pop bc
    ld hl,31
    push hl
    push hl
    push bc
    ld hl,31

_cx .equ 0
_cy .equ 1
_x .equ 2
_y .equ 3
_err .equ 4
_rmask .equ 5
_lmask .equ 6
_off .equ 7
_ptr .equ 8

;###############################
;draw filled circle
FilledCircle:
    di
    ld ix,cx
    ld (ix+_x),l
    xor a
    ld (y),a
    ld (off),a
    sub l
    ld (err),a
    pop hl
    pop bc
    ex (sp),hl
    ld (ix+_cx),c
    ld (ix+_cy),l

    ld a,l
    sub (ix+_x)
    jr nc,+_
    xor a
_:
    ld l,a
    ld a,c
    ;A=cx, L=cy-x
    call GetPtrMask
    ld (rmask),a
    ld (lmask),a
    ld (ptr),hl

Main:
    call RotLMask
    bcall(_grBufCpy)
    call RotRMask
    bcall(_grBufCpy)
SkipRotate:
    ld a,(x)
    dec a
    sub (ix+_y)
    jp c,End
    ld a,(err)
    inc (ix+_y)
    add a,(ix+_y)
    ;inc (ix+_y)
    add a,(ix+_y)
    ld (err),a
    bit 7,a
    jp nz,Main
        ;draw chunks
    call DrawLChunk
    bcall(_grBufCpy)
    call DrawRChunk
    bcall(_grBufCpy)
        ;change left mask
    ld a,(lmask)
    rlca
    jr nc,+_
    ld a,%00000001
    ld (lmask),a
    inc (ix+_off)
    ld hl,(ptr)
    dec hl
    ld (ptr),hl
    jr ++_
_:
    ld b,a
    ld a,(lmask)
    cpl
    and b
    ld (lmask),a
_:      ;change right mask
    ld a,(rmask)
    rrca
    jr nc,+_
    ld a,%10000000
    inc (ix+_off)
    ld (rmask),a
    jr ++_
_:
    ld b,a
    ld a,(rmask)
    cpl
    and b
    ld (rmask),a
_:
    ld a,(x)
    dec a
    sub (ix+_y)
    jp c,End
        ;draw left vertical
    ld a,(cy)
    sub (ix+_y)
    ld l,a
    ld a,(y)
    add a,a
    inc a
    ld d,a
    ld a,(cx)
    sub (ix+_x)
    call GetPtrMask
    ld c,a
    ld b,d
    call DrawVertLoop
    bcall(_grBufCpy)
        ;draw right vertical
    ld a,(cy)
    sub (ix+_y)
    ld l,a
    ld a,(y)
    add a,a
    inc a
    ld d,a
    ld a,(cx)
    add a,(ix+_x)
    call GetPtrMask
    ld c,a
    ld b,d
    call DrawVertLoop
    bcall(_grBufCpy)
        ;sub x
    ld a,(err)
    ;dec (ix+_x)
    sub (ix+_x)
    dec (ix+_x)
    sub (ix+_x)
    ld (err),a
    ld hl,(ptr)
    ld de,12
    add hl,de
    ld (ptr),hl
    jp SkipRotate
End:
    ei
    ret

GetPtrMask:
    ld h,0
    ld b,h
    ld c,l
    add hl,hl
    add hl,bc
    add hl,hl
    add hl,hl
    ld c,a
    srl c
    srl c
    srl c
    add hl,bc
    ld bc,plotsscreen
    add hl,bc
    and 7
    ld b,a
    ld a,$80
    ret z
_:
    rrca
    djnz -_
    ret


RotLMask:
    ld a,(lmask)
    rlca
    jr nc,+_
    call DrawLChunk
    ld a,%00000001
    ld (lmask),a
    ld hl,(ptr)
    dec hl
    ld (ptr),hl
    inc (ix+_off)
    ret
_:
    ld hl,lmask
    or (hl)
    ld (hl),a
    ret

DrawLChunk:
    ld c,(ix+_lmask)
    ld a,(off)
    or a
    jr nz,+_
    ld a,(rmask)
    and c
    xor c
    ld c,a
_:
    ld hl,(ptr)
    ld a,(x)
    add a,a
    inc a
    ld b,a
    jp DrawVertLoop
    ret

RotRMask:
    ld a,(rmask)
    rrca
    jr nc,+_
    call DrawRChunk
    ld a,%10000000
    ld (rmask),a
    inc (ix+_off)
    ret
_:
    ld hl,rmask
    or (hl)
    ld (hl),a
    ret

DrawRChunk:
    ld c,(ix+_rmask)
    ld a,(off)
    or a
    jr nz,+_
    ld a,(lmask)
    and c
    xor (ix+_lmask)
    ld (lmask),a
_:
    ld hl,(ptr)
    ld e,(ix+_off)
    ld d,0
    add hl,de
    ld a,(x)
    add a,a
    inc a
    ld b,a
    jp DrawVertLoop

DrawVertLoop:
        ;in: B = height, C=mask, HL = pointer
        ;destroys: A, B, DE, HL
        ld de,12
_:
        ld a,(hl)
        xor c
        ld (hl), a
        add hl,de
        djnz -_
        ret



cx:
    .db 0
cy:
    .db 0
x:
    .db 0
y:
    .db 0
err:
    .db 0
rmask:
    .db 0
lmask:
    .db 0
off:
    .db 0
ptr:
    .dw 0