649 lines
14 KiB
NASM
649 lines
14 KiB
NASM
; -----------------------------------------------------------
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; common.asm - routines shared by the states: screen drawing,
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; text printing, input, RNG and the rabbit sprite positioning
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; -----------------------------------------------------------
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; ---- clear screen RAM, fill color RAM with black ----
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clear_screen:
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ldx #0
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cls_loop:
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lda #$20 ; space
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sta SCREEN,x
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sta SCREEN+$100,x
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sta SCREEN+$200,x
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sta SCREEN+$2e8,x
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lda #BLACK
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sta COLRAM,x
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sta COLRAM+$100,x
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sta COLRAM+$200,x
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sta COLRAM+$2e8,x
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inx
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bne cls_loop
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rts
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; ---- print a text line: txtlo/hi, prow, pcol, pcolor, plen ----
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print_text:
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ldx prow
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lda mul40lo,x
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clc
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adc pcol
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sta scrlo
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sta collo
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lda mul40hi,x
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adc #>SCREEN ; carry still valid from the low-byte add
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sta scrhi
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clc
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adc #$d4 ; COLRAM - SCREEN high byte distance
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sta colhi
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ldy #0
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pt_loop:
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lda (txtlo),y
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sta (scrlo),y
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lda pcolor
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sta (collo),y
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iny
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cpy plen
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bne pt_loop
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rts
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; ---- set scrlo/hi + collo/hi to the start of char row X ----
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row_ptr:
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lda mul40lo,x
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sta scrlo
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sta collo
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lda mul40hi,x
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clc
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adc #>SCREEN
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sta scrhi
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clc
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adc #$d4 ; COLRAM - SCREEN high byte distance
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sta colhi
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rts
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; ---- the road: grey surface between two painted edge lines,
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; from the horizon apex down to the screen corners, then the
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; trees along both shoulders ----
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draw_road:
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ldx #0
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dr_loop:
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stx drtmp
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jsr road_row
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ldx drtmp
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inx
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cpx #19
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bne dr_loop
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jmp draw_trees
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; ---- redraw road row drtmp (0-18, char row 6+drtmp):
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; edge chars + grey fill; also erases text printed over it ----
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road_row:
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lda drtmp
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clc
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adc #6 ; road runs from char row 6 to row 24
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tax
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jsr row_ptr
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lda #19 ; left edge: one column left per row
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sec
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sbc drtmp
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tay
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sty drleft
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lda #$4e ; '/' diagonal
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sta (scrlo),y
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lda #COL_EDGE
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sta (collo),y
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lda #20 ; right edge: one column right per row
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clc
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adc drtmp
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tay
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lda #$4d ; '\' diagonal
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sta (scrlo),y
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lda #COL_EDGE
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sta (collo),y
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dey ; fill the surface between the edges
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rr_fill:
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cpy drleft
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beq rr_done
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lda #$a0 ; inverse space: solid block
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sta (scrlo),y
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lda #COL_ROAD
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sta (collo),y
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dey
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jmp rr_fill
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rr_done:
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rts
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; ---- the roadside trees ----
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draw_trees:
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lda #0
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sta ttidx
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dt_loop:
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ldx ttidx
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lda tree_tbl,x
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sta trow
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lda tree_tbl+1,x
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sta tcol
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jsr draw_tree
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inc ttidx
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inc ttidx
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lda ttidx
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cmp #NTREES*2
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bne dt_loop
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rts
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; ---- one tree: crown of balls on trow, top ball above,
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; trunk below (trow/tcol = middle row, left column) ----
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draw_tree:
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ldx trow
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dex
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jsr row_ptr
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ldy tcol
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iny
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jsr tree_ball
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ldx trow
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jsr row_ptr
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ldy tcol
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jsr tree_ball
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iny
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jsr tree_ball
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iny
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jsr tree_ball
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ldx trow
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inx
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jsr row_ptr
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ldy tcol
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iny
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lda #$5d ; trunk
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sta (scrlo),y
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lda #BROWN
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sta (collo),y
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rts
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tree_ball:
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lda #$51 ; foliage ball
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sta (scrlo),y
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lda #LGREEN
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sta (collo),y
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rts
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NTREES = 6
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tree_tbl: ; middle row, left column - far trees sit
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!byte 9, 4 ; higher and closer to the road
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!byte 14, 6
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!byte 19, 3
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!byte 8, 31
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!byte 12, 34
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!byte 17, 36
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; ---- input ----
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; read joystick port 2 merged with the a/d keys,
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; return active-high bits in A and joyb
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read_joy:
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lda #$ff ; deselect every keyboard column first
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sta CIA1_PA
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lda CIA1_PA
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eor #$ff
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and #$1f
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sta joyb
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lda #$fd ; 'a' = left: keyboard column 1, row bit 2
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sta CIA1_PA
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lda CIA1_PB
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and #$04
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bne rj_noleft
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lda joyb
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ora #JOY_LEFT
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sta joyb
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rj_noleft:
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lda #$fb ; 'd' = right: keyboard column 2, row bit 2
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sta CIA1_PA
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lda CIA1_PB
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and #$04
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bne rj_noright
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lda joyb
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ora #JOY_RIGHT
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sta joyb
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rj_noright:
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lda joyb
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rts
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; read joystick port 1 merged with the j/l keys (player 2),
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; return active-high bits in A and joyb2
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read_joy2:
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lda #$ff ; no column selected: port B = joystick 1
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sta CIA1_PA
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lda CIA1_PB
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eor #$ff
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and #$1f
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sta joyb2
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and #$0f ; a held direction grounds the same port B
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bne rj2_done ; lines the key rows use: skip the scan
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lda #$ef ; 'j' = left: keyboard column 4, row bit 2
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sta CIA1_PA
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lda CIA1_PB
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and #$04
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bne rj2_noleft
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lda joyb2
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ora #JOY_LEFT
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sta joyb2
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rj2_noleft:
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lda #$df ; 'l' = right: keyboard column 5, row bit 2
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sta CIA1_PA
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lda CIA1_PB
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and #$04
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bne rj2_done
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lda joyb2
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ora #JOY_RIGHT
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sta joyb2
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rj2_done:
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lda joyb2
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rts
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; fire on either stick or space held? returns A != 0 when pressed
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start_pressed:
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jsr read_joy
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and #JOY_FIRE
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bne sp_done
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lda #$ff ; deselect the columns: port B = joystick 1
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sta CIA1_PA
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lda CIA1_PB
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eor #$ff
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and #JOY_FIRE
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bne sp_done
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lda #$7f ; space: keyboard column 7, row bit 4
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sta CIA1_PA
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lda CIA1_PB
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and #$10
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eor #$10
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sp_done:
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rts
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; edge-detected start: A = 1 only on the frame fire/space goes down
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start_edge:
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jsr start_pressed
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beq se_up
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lda fheld
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bne se_no
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lda #1
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sta fheld
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rts ; A = 1: fresh press
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se_up:
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lda #0
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sta fheld
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se_no:
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lda #0
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rts
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; ---- RNG: 8-bit LFSR stirred with the free-running CIA timer
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; (the timer counts every cycle, so call timing = entropy) ----
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rand8:
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lda seed
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asl
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bcc r8_tap
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eor #$1d
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r8_tap:
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eor CIA1_TA
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sta seed
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rts
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; random lane 0-4
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rand5:
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jsr rand8
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and #7
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cmp #LANES
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bcs rand5 ; every retry steps the LFSR, so it terminates
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rts
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; ---- write the per-frame sprite register shadows ----
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write_shadows:
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lda en_sh
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sta SPR_EN
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lda msb_sh
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sta SPR_MSBX
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lda xex_sh
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sta SPR_XEX
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lda yex_sh
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sta SPR_YEX
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rts
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; ============================================================
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; rab_pos - place rabbit slot X on hardware sprite X+1
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; reads r_thi/r_lane, picks size stage + hop frame, writes
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; the position registers and ORs the shadow bits; keeps X
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; ============================================================
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rab_pos:
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stx rslot
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lda r_thi,x
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sta rt
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lda r_lane,x
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sta rlane
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; hop offset: 8-entry wave, one hop per 64 t units
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lda rt
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lsr
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lsr
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lsr
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and #7
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tay
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lda hoptab,y
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sta rhop
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; animation frame 0-3
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lda rt
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lsr
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lsr
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lsr
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lsr
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and #3
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sta rfrm
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lda #0
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sta rexp
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lda rt
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cmp #T_BIG
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bcs rp_big
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; -- far: small frames --
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lda #SPRP_SMALL
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clc
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adc rfrm
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sta rptr
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lda #12
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sta ranchor
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jmp rp_y
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rp_big:
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; -- near: big frames, stronger hop --
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lda #SPRP_BIG
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clc
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adc rfrm
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sta rptr
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asl rhop
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lda #12
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sta ranchor
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lda rt
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cmp #T_EXP
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bcc rp_y
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; -- closest: the same frames double-sized --
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lda #1
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sta rexp
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lda #24
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sta ranchor
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rp_y:
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; sprite y: feet ride the perspective line (art bottom row)
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ldy rt
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lda ytab,y
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sec
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sbc rhop
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sec
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sbc #21
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ldx rexp
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beq rp_ydone
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sec
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sbc #21 ; expanded sprite is 42 tall
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rp_ydone:
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sta ry
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; x center = ROAD_CX +/- lane offset on the t^2 curve
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ldy rt
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lda offtab,y
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sta roff
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lda #ROAD_CX
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sta rxlo
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lda #0
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sta rxhi
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ldy rlane
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cpy #2
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beq rp_xdone ; middle lane: stay on the center line
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bcs rp_right
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lda roff ; lanes 0-1: left of center
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cpy #1
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bne rp_lfull
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lsr ; lane 1 fans out half as far
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rp_lfull:
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sta rtmp
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lda rxlo
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sec
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sbc rtmp ; max offset is 107, never underflows
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sta rxlo
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jmp rp_xdone
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rp_right:
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lda roff ; lanes 3-4: right of center
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cpy #3
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bne rp_rfull
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lsr
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rp_rfull:
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sta rtmp
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lda rxlo
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clc
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adc rtmp
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sta rxlo
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lda rxhi
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adc #0
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sta rxhi
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rp_xdone:
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; sprite left edge = center - anchor (16 bit)
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lda rxlo
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sec
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sbc ranchor
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sta rxlo
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lda rxhi
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sbc #0
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sta rxhi
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; ---- write the hardware registers + shadow bits ----
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ldx rslot
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ldy sprxreg,x
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lda rxlo
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sta SPRPOS,y
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lda ry
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sta SPRPOS+1,y
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lda rptr
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sta SPRPTR+1,x
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lda sprbit,x
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ora en_sh
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sta en_sh
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lda rxhi
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beq rp_nomsb
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lda sprbit,x
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ora msb_sh
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sta msb_sh
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rp_nomsb:
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lda rexp
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beq rp_done
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lda sprbit,x
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ora xex_sh
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sta xex_sh
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lda sprbit,x
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ora yex_sh
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sta yex_sh
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rp_done:
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rts
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; ---- draw a text line with big 3x5 block letters ----
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; txtlo/hi = text (screen codes), bigrow/bigcol = top-left cell,
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; bigcolor = color, biglen = char count; each letter is 3 cells
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; wide + 1 gap, 5 cells tall
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draw_big:
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lda #0
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sta bigi
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db_char:
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ldy bigi
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lda (txtlo),y
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cmp #$20 ; space: leave the cell empty
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beq db_next
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tax
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lda bigmap,x ; screen code -> glyph index
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sta glyphbase
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asl ; glyph base = index * 5
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asl
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clc
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adc glyphbase
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sta glyphbase
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lda bigi ; cell x = bigcol + charindex * 4
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asl
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asl
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clc
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adc bigcol
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sta charx
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lda #0
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sta rowidx
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db_row:
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lda bigrow ; row pointers from the row*40 tables
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clc
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adc rowidx
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tax
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lda mul40lo,x
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sta scrlo
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sta collo
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lda mul40hi,x
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clc
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adc #>SCREEN
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sta scrhi
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clc
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adc #$d4
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sta colhi
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lda glyphbase
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clc
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adc rowidx
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tax
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lda bigglyphs,x
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asl ; 3-bit pattern up to bits 7-5
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asl
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asl
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asl
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asl
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sta curbits
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ldy charx
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lda #3
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sta bitcnt
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db_bit:
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asl curbits ; leftmost pixel first
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bcc db_nobit
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lda #$a0 ; inverse space = solid block
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sta (scrlo),y
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lda bigcolor
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sta (collo),y
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db_nobit:
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iny
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dec bitcnt
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bne db_bit
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inc rowidx
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lda rowidx
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cmp #5
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bne db_row
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db_next:
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inc bigi
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lda bigi
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cmp biglen
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beq db_done
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jmp db_char ; too far for a relative branch
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db_done:
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rts
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; ---- shared tables ----
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; row * 40 lookup tables (25 rows)
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mul40lo:
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!byte $00, $28, $50, $78, $a0, $c8, $f0, $18, $40, $68
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!byte $90, $b8, $e0, $08, $30, $58, $80, $a8, $d0, $f8
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!byte $20, $48, $70, $98, $c0
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mul40hi:
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!byte $00, $00, $00, $00, $00, $00, $00, $01, $01, $01
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!byte $01, $01, $01, $02, $02, $02, $02, $02, $02, $02
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!byte $03, $03, $03, $03, $03
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; 3x5 block font for the big title (5 bytes per glyph,
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; low 3 bits used, MSB side = left)
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bigglyphs:
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!byte 0, 0, 0, 0, 0 ; 0 space
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!byte 2, 5, 7, 5, 5 ; 1 A
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!byte 3, 4, 4, 4, 3 ; 2 C
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!byte 6, 5, 5, 5, 6 ; 3 D
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!byte 7, 4, 6, 4, 7 ; 4 E
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!byte 7, 4, 6, 4, 4 ; 5 F
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!byte 7, 2, 2, 2, 7 ; 6 I
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!byte 4, 4, 4, 4, 7 ; 7 L
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!byte 5, 7, 7, 5, 5 ; 8 M
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!byte 6, 5, 5, 5, 5 ; 9 N
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!byte 7, 5, 5, 5, 7 ; 10 O
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!byte 6, 5, 6, 4, 4 ; 11 P
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!byte 6, 5, 6, 5, 5 ; 12 R
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!byte 3, 4, 2, 1, 6 ; 13 S
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!byte 7, 2, 2, 2, 2 ; 14 T
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!byte 5, 5, 2, 2, 2 ; 15 Y
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!byte 3, 4, 5, 5, 7 ; 16 G
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!byte 6, 5, 6, 5, 6 ; 17 B
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!byte 5, 5, 5, 5, 2 ; 18 V
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bigmap: ; screen code (a=1..z=26) -> glyph index
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!byte 0 ; (unused)
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!byte 1, 17, 2, 3, 4, 5, 16, 0, 6, 0 ; a-j
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!byte 0, 7, 8, 9, 10, 11, 0, 12, 13, 14 ; k-t
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!byte 0, 18, 0, 0, 15, 0 ; u-z
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; ---- texts (screen codes) ----
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txt_score: !scr "score"
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txt_miss: !scr "miss"
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txt_rabbit: !scr "rabbit"
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txt_scooter: !scr "scooter"
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txt_1p: !scr "single player"
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txt_2p: !scr "multiplayer"
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txt_info: !scr "p1: joystick 2 or a/d"
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txt_info2: !scr "p2: joystick 1 or j/l"
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txt_ttgname: !scr "teletype games"
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txt_presents:!scr "presents"
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txt_over: !scr "game over"
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txt_return: !scr "fire = return"
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txt_blank: !fill 19, $20
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washtbl: ; gold glow ramp (16 entries, cyclic)
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!byte $09, $02, $08, $0a, $07, $07, $01, $01
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!byte $01, $01, $07, $07, $0a, $08, $02, $09
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; ---- shared variables ----
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framectr: !byte 0 ; frame counter, incremented by the main loop
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washphase: !byte 0 ; gold wash offset on the intro letters
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bg_top: !byte COL_SKY ; background color above / below the
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bg_bot: !byte COL_GRASS ; horizon raster split
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seed: !byte $a7 ; rand8 LFSR state
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fheld: !byte 0 ; fire/space edge detection state
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joyb: !byte 0 ; player 1 input bits from read_joy
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joyb2: !byte 0 ; player 2 input bits from read_joy2
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mp_mode: !byte 0 ; 0 = single player, 1 = multiplayer
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k12held: !byte 0 ; menu '1'/'2' key edge detection state
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en_sh: !byte 0 ; per-frame sprite register shadows
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msb_sh: !byte 0
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xex_sh: !byte 0
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yex_sh: !byte 0
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prow: !byte 0 ; print_text: row, column, color, length
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pcol: !byte 0
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pcolor: !byte 0
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plen: !byte 0
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bigrow: !byte 0 ; draw_big: row, column, color, length
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bigcol: !byte 0
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bigcolor: !byte 0
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biglen: !byte 0
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bigi: !byte 0 ; draw_big internals
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glyphbase: !byte 0
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charx: !byte 0
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rowidx: !byte 0
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bitcnt: !byte 0
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curbits: !byte 0
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drtmp: !byte 0 ; draw_road internals
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drleft: !byte 0
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ttidx: !byte 0 ; draw_trees internals
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trow: !byte 0
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tcol: !byte 0
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rslot: !byte 0 ; rab_pos internals
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rt: !byte 0
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rlane: !byte 0
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rhop: !byte 0
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rfrm: !byte 0
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rexp: !byte 0
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rptr: !byte 0
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ranchor: !byte 0
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roff: !byte 0
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rxlo: !byte 0
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rxhi: !byte 0
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ry: !byte 0
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rtmp: !byte 0
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rtmp2: !byte 0
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