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level.asm
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level.asm
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; Constants
screen_ptr = $04
color_ptr = $06
screen_col = $08
screen_ptr_dest = $0a
color_ptr_dest = $0c
COLOR_CHANGE_DELAY = 10
; Variables
ceil_height !byte 0
floor_height !byte 0
message_index !byte 0
current_color !byte 1
current_color_change_delay !byte COLOR_CHANGE_DELAY
level_data !byte 1,2,3,4,5,6,7,8,7,6,5,4,3,2,1
level_index !byte 0
str_message !scr "1amstudios.com ", 0
level_init
ldy #0
+set16im 0, screen_col
level_render_next_col
+set16 screen_base, screen_ptr
+set16im $d800, color_ptr
+add16 screen_ptr, screen_col, screen_ptr ;increment screen row
+add16 color_ptr, screen_col, color_ptr ;increment screen row
inc screen_col
dec current_color_change_delay
bne level_render_col
lda #COLOR_CHANGE_DELAY
sta current_color_change_delay
inc current_color
level_render_col
ldx level_index
lda level_data, x ; load ceiling height
sta ceil_height
tax ; x now holds ceiling height
level_render_ceil
lda #$A0
sta (screen_ptr), y ; output to screen
lda current_color
sta (color_ptr), y ; and color ram
+add16im screen_ptr, 40, screen_ptr ; increment screen row
+add16im color_ptr, 40, color_ptr ; increment color row
dex ; decrement ceiling counter
bne level_render_ceil ; if we're not at the bottom of the ceiling keep rendering the colum
level_skip_ceil
ldx level_index
lda level_data, x ; load floor height
sta floor_height
inx ; increment level data index
cpx #10
bne *+4 ; skip next line if we don't want to wrap to start of level data again
; +4 (2 for bne, 2 for ldx)
ldx #0 ; wrap around level data
stx level_index ; store updated level data index
lda #23 ;
sec
sbc ceil_height
sbc floor_height
tax ; x now holds the number of rows between end of ceiling and start of floor
level_skip_to_floor
lda #$20
sta (screen_ptr), y ; output blank char to screen
+add16im screen_ptr, 40, screen_ptr ; increment screen row
+add16im color_ptr, 40, color_ptr ; increment color row
dex
bne level_skip_to_floor ; keep skipping rows until x == 0
ldx floor_height ; X now holds height of floor
level_render_floor
lda #$A0
sta (screen_ptr), y ; output char to screen
lda current_color
sta (color_ptr), y ; and color ram
+add16im screen_ptr, 40, screen_ptr ; increment screen row
+add16im color_ptr, 40, color_ptr ; increment color row
dex ; decrement floor counter
bne level_render_floor ; if we're not at the bottom of the floor keep rendering the column
; print message at bottom of screen
ldx message_index
lda str_message, x ; output char to screen
sta (screen_ptr), y
lda #1
sta (color_ptr), y ; and color ram
inx
cpx #16
bne *+4 ; jump over next 2 lines if we're not at 16 yet
ldx #0
stx message_index
lda screen_col
cmp #40 ; if we've rendered 40 columns, we're finished
beq level_render_done
jmp level_render_next_col ; and we haven't hit column 30 yet, render the next column
level_render_done
rts ; return from last jsr
level_render_last_col ; this is used to render the rightmost column of the screen when we need
; new data to scroll in
ldy #0
+set16im 39, screen_col
jsr level_render_next_col
rts