440 lines
8.8 KiB
ArmAsm
440 lines
8.8 KiB
ArmAsm
;===========
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; CONSTANTS
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;===========
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NUMSTARS EQU 16
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; Plan:
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; Ship at rest 0 - 4
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; Flash 5
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; Ship at warp 25
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; Crazy background
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; Ship moves off
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; Back to stars
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; Rasterbars+credits
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; Done
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;=====================
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;=====================
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;=====================
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; Starfield Demo
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;=====================
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;=====================
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;=====================
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starfield_demo:
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;================================
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; Clear screen and setup graphics
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;================================
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jsr clear_screens_notext ; clear top/bottom of page 0/1
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jsr set_gr_page0
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bit FULLGR
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;===============
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; Init Variables
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;===============
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lda #0 ; 2
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sta DRAW_PAGE ; 3
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sta RANDOM_POINTER ; 3
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; always multiply with low byte as zero
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sta NUM2L ; 3
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sta FRAME_COUNT
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ldy #(NUMSTARS-1) ; 2
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init_stars:
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jsr random_star ; 6
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dey ; 2
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bpl init_stars ; 2nt/3
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;===========================
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;===========================
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; Main Loop
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;===========================
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;===========================
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starfield_loop:
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;===============
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; clear screen
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;===============
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jsr clear_all ; 6+
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; 6047
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;===============
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; draw the stars
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;===============
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jsr draw_stars
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;================
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; draw the ship
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;================
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lda #>ship_forward
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sta INH
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lda #<ship_forward
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sta INL
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lda #15
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sta XPOS
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lda #30
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sta YPOS
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jsr put_sprite
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;==================
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; flip pages
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;==================
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jsr page_flip ; 6
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inc FRAME_COUNT
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lda FRAME_COUNT
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cmp #$ff
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beq done_stars
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;==================
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; loop
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;==================
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jmp starfield_loop ; 3
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done_stars:
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rts
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;=====================
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;=====================
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;=====================
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; Starfield Credits
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;=====================
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;=====================
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;=====================
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starfield_credits:
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;================================
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; Clear screen and setup graphics
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;================================
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jsr clear_screens ; clear top/bottom of page 0/1
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jsr set_gr_page0
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lda #0 ; 2
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sta DRAW_PAGE
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jsr credits_draw_text_background
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lda #4 ; 2
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sta DRAW_PAGE
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jsr credits_draw_text_background
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;===============
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; Init Variables
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;===============
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lda #0 ; 2
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sta DRAW_PAGE ; 3
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sta RANDOM_POINTER ; 3
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sta SCREEN_Y
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; always multiply with low byte as zero
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sta NUM2L ; 3
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sta FRAME_COUNT
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sta YY ; which credit
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sta LOOP ; delay loop
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lda #>credits ; load credits pointer
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sta OUTH
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lda #<credits
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sta OUTL
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; Initialize stars
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ldy #(NUMSTARS-1) ; 2
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init_stars2:
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jsr random_star ; 6
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dey ; 2
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bpl init_stars2 ; 2nt/3
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; Initialize the credits
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jsr init_credits
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;===========================
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;===========================
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; StarCredits Loop
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;===========================
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;===========================
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starcredits_loop:
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;===============
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; clear screen
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;===============
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jsr clear_top ; 6+
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;===============
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; draw the stars
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;===============
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jsr draw_stars
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;====================
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; draw the rasterbars
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;====================
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jsr draw_rasters
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;====================
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; draw the credits
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;====================
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jsr draw_credits
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jsr credits_draw_bottom
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;==================
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; flip pages
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;==================
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jsr page_flip ; 6
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inc FRAME_COUNT
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lda YY
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cmp #15 ; NUMBER OF CREDITS
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beq done_star_credits
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;==================
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; loop
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;==================
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jmp starcredits_loop ; 3
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done_star_credits:
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rts
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;======================================================
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;======================================================
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; draw stars
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;======================================================
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;======================================================
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; draws stars
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draw_stars:
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; start at 15 and count down (rather than 0 and count up)
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ldx #(NUMSTARS-1) ; 2
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draw_stars_loop:
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stx XX ; 3
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;================
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; calculate color
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;================
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lda #$ff ; want if z<16, color = 5 ; 2
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sta COLOR ; if 16<z<32 color = 13 ; 3
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; if 32<z<64 color = 15
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lda star_z,X ; 4
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tay ; put star_z[i] in X for later ; 2
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cmp #32 ; 2
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bpl done_color ; 2nt/3
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cmp #16 ; 15 -1 16 0 17 1 ; 2
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bpl second_color ; 2nt/3
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lda #$55 ; 2
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sta COLOR ; 3
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jmp done_color ; 3
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second_color:
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lda #$dd ; 2
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sta COLOR ; 3
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done_color:
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; calculate x value, stars[i].x/stars[i].z
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; put 1/stars[i].z in NUM1H:NUM1L and multiply
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lda z_table,Y ; 4
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sta NUM1L ; F ; 3
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; adjust spacez for 58+
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; all this logic to avoid having a 128 byte table of mostly zero
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lda #0 ; I ; 2
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clc ; 2
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cpy #60 ; 59 -1 60 0 61 1 ; 2
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bmi no_adjust ; 2nt/3
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adc #1 ; 60, 61 = 1 ; 2
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cpy #62 ; 61 -1 62 0 63 1 ; 2
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bmi no_adjust ; 2nt/3
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adc #1 ; 62 = 2 ; 2
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cpy #63 ; 62 = -1 63 = 0 64 = not possible ; 2
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bne no_adjust ; 2nt/3
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adc #2 ; 63 = 4 ; 2
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no_adjust:
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sta NUM1H ; store int part of spacez ; 3
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; load stars[i].x into NUM2H:NUM2L
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; NUM2L is always zero
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ldy XX ; 3
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lda star_x,Y ; 4
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sta NUM2H ; 3
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sec ; don't reuse old values ; 2
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jsr multiply ; 6+?
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; integer result in X
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txa ; 2
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clc ; 2
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adc #20 ; center on screen ; 2
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sta XPOS ; save for later ; 3
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; calculate y value, stars[i].y/stars[i].z
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; 1/stars[i].z is still in NUM1H:NUM1L
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ldy XX ; reload index ; 3
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lda star_y,Y ; load integer part of star_ ; 4
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sta NUM2H ; 3
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clc ; reuse old values ; 2
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jsr multiply ; 6+
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; integer result in X
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txa ; 2
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clc ; 2
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adc #20 ; center the value ; 2
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tay ; Y is YPOS ; 2
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sty YPOS ; put Y value in Y to plot ; 3
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;============================
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; Check Limits
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;============================
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bmi new_star ; 2nt/3
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y_limit_smc:
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cpy #40 ; 2
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bpl new_star ; if < 0 or > 40 then done ; 2nt/3
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lda XPOS ; 3
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bmi new_star ; 2nt/3
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cmp #40 ; 2
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bpl new_star ; if < 0 or > 40 then done ; 2nt/3
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; FIXME: sort out all of these jumps to be more efficient
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bmi plot_star ; 2
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new_star:
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ldy XX ; 3
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jsr random_star ; 6
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jmp plot_star_continue ; 3
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plot_star:
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jsr plot ; 6
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plot_star_continue:
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;==============================
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ldx XX ; 3
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dex ; 2
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bmi move_stars ; 2nt/3
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bpl draw_stars_loop ; 2nt/3
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;=============================
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; Move stars
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move_stars:
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ldy #(NUMSTARS-1) ; 2
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move_stars_loop:
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; increment z
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clc ; if z >= 64 new star ; 2
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lda star_z,Y ; 4
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adc #1 ; 2
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sta star_z,Y ; 4
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and #64 ; 2
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beq move_loop_skip ; 2nt/3
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jsr random_star ; new random star ; 6
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move_loop_skip:
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dey ; 2
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bpl move_stars_loop ; 2nt/3
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rts
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;==================================================
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;==================================================
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; Random Star
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;==================================================
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;==================================================
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; star number in Y
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; FIXME: increment at end?
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; X trashed
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random_star:
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; random x location
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ldx RANDOM_POINTER ; 3
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lda random_table,X ; 4
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sta star_x,Y ; 5
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inx ; 2
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; random y location
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lda random_table,X ; 4
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sta star_y,Y ; 5
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inx ; 2
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; random z location
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lda random_table,X ; 4
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and #$3f ; 2
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sta star_z,Y ; 5
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inx ; 2
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stx RANDOM_POINTER ; 3
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rts ; 6
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;======================
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; some "random" numbers
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;======================
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random_table:
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.byte 103,198,105,115, 81,255, 74,236, 41,205,186,171,242,251,227, 70
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.byte 124,194, 84,248, 27,232,231,141,118, 90, 46 ,99, 51,159,201,154
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.byte 102, 50, 13,183, 49, 88,163, 90, 37, 93, 5, 23, 88,233, 94,212
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.byte 171,178,205,198,155,180, 84, 17, 14,130,116, 65, 33, 61,220,135
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.byte 112,233, 62,161, 65,225,252,103, 62, 1,126,151,234,220,107,150
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.byte 143, 56, 92, 42,236,176, 59,251, 50,175, 60, 84,236, 24,219, 92
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.byte 2, 26,254, 67,251,250,170, 58,251, 41,209,230, 5, 60,124,148
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.byte 117,216,190, 97,137,249, 92,187,168,153, 15,149,177,235,241,179
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.byte 5,239,247, 0,233,161, 58,229,202, 11,203,208, 72, 71,100,189
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.byte 31, 35, 30,168, 28,123,100,197, 20,115, 90,197, 94, 75,121, 99
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.byte 59,112,100, 36, 17,158, 9,220,170,212,172,242, 27, 16,175, 59
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.byte 51,205,227, 80, 72, 71, 21, 92,187,111, 34, 25,186,155,125,245
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.byte 11,225, 26, 28,127, 35,248, 41,248,164, 27, 19,181,202, 78,232
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.byte 152, 50, 56,224,121, 77, 61, 52,188, 95, 78,119,250,203,108, 5
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.byte 172,134, 33, 43,170, 26, 85,162,190,112,181,115, 59, 4, 92,211
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.byte 54,148,179,175,226,240,228,158, 79, 50, 21, 73,253,130, 78,169
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z_table:
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; 1/16.0 - 1/12.25
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.byte $10,$10,$10,$10,$11,$11,$11,$11,$12,$12,$12,$13,$13,$14,$14,$14
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; 1/12.0 - 1/8.25
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.byte $15,$15,$16,$16,$17,$17,$18,$18,$19,$1A,$1A,$1B,$1C,$1D,$1E,$1F
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; 1/8.0 - 1/4.25
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.byte $20,$21,$22,$23,$24,$25,$27,$28,$2A,$2C,$2E,$30,$33,$35,$38,$3C
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; 1/4.0 - 1/0.25
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.byte $40,$44,$49,$4E,$55,$5D,$66,$71,$80,$92,$AA,$CC,$00,$55,$00,$00
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