dos33fsprogs/games/tfv/rotate_intro.s

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;===============================
; rotate intro -- rotate screen
;===============================
rotate_intro:
; init the multiply routines
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; jsr init_multiply_tables
; first copy current screen to background
jsr gr_copy_current_to_offscreen_40x40
lda #0
sta ANGLE
sta SCALE_F
sta FRAMEL
lda #1
sta SCALE_I
rotate_loop:
jsr rotozoom
jsr page_flip
; zoom out
sec
lda SCALE_F
sbc #$10
sta SCALE_F
lda SCALE_I
sbc #$00
sta SCALE_I
dec ANGLE
lda ANGLE
and #$1f
sta ANGLE
; rotate counter-clockwise
cmp #16
beq done_rotate
jmp rotate_loop
done_rotate:
rts
;=========================================================
; gr_copy_current_to_offscreen 40x40
;=========================================================
; Copy draw page to $c00
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; Take image in DRAW_PAGE
; Copy to $c00
; Actually copy lines 0..39
; Don't over-write bottom 4 lines of text
gr_copy_current_to_offscreen_40x40:
ldx #0
gco_40x40_loop:
lda gr_offsets,X
sta OUTL
sta INL
lda gr_offsets+1,X
clc
adc DRAW_PAGE
sta OUTH
lda gr_offsets+1,X
clc
adc #$8
sta INH
ldy #39
gco_40x40_inner:
lda (OUTL),Y
sta (INL),Y
dey
bpl gco_40x40_inner
inx
inx
cpx #40
bne gco_40x40_loop
rts ; 6