;----------------------------------------------------- ; ; Bounce a smiley face around the screen ; ; There is small game element to this. Use 'W', 'A', 'S', 'D' ; to move a pointer around the screen. Try and get the pointer on the ; face for a screen flashing effect. ; ; Vic 20 assembly demo by ; Dennis Katsonis, Sep 2020 ; ; This is my first 6502 assembly program. I have a Vic 20 ; but it doens't work. If I can restore it, I'll be able to ; run this on native hardware! ; ; To be run on an unexpanded Vic20 (i.e., no additional memory) ; It may not work at all with memory expansion. ; ; Compile using ca65 ; cl65 -t vic20 -C smilebounce.cfg smilebounce.asm ; ; May not display correctly on NTSC models. ; ; This is public domain code. ;----------------------------------------------------- ; The memory layout of this program is as follows ; $1000 - $17FF : BASIC (Just enough to squeeze in this program) ; $1800 - $1BFF : Screen map (We only need 750 bytes) ; $1C00 - $1FFF : Custom Characters (We only use the first few bytes, ; so the space after this could be used as storage.) bsout=$FFD2 offset=$FB ; Two bytes for offset of SCREENMAP coloffset = $45 ; Current variable name ZP location. Use this space xpos = $FD ypos = $FE deltax = $F9 ; RS-232 tx pointer ZP location. We aren't using this. deltay = $F8 ; We store delta x and y here. sndcnt = $FA scrolltimer = $B7 ; # of characters in filename in ZP location. ; We aren't using this so store scrolltimer currentchar = $B8 ; Current logical file in ZP location. ; We aren't using this so store current char for scrolling text currentscrollcol = $B9 ; Current secondary address in ZP location ; Store scrolling colour text here. blocker_x = $BA blocker_y = $BB blockerchar = $BC ; Zero Page pointers to the music. Because the total number of notes for each ; song is greater than 255, we need to be able to dynamically ; point between song 1 and 2, otherwise if we just point to song 1 and go, ; X will overflow while referencing the second song. song_notes_treble = $0A ; Load/Verify, basic stuff we aren't use song_notes_bass = $0C ; Input buffer pointer for BASIC we aren't using HORIZOFFSET=$9000 VERTOFFSET=$9001 ; 36865 COLSIZE=$9002 ;36866 ROWSIZE=$9003 SCREENMAP=$9005 ROWS=30 COLUMNS=25 VOLUME=36878 SPEAKER1=36876 SPEAKER2=36875 SPEAKER3=36874 SCREENMEM=$1800 COLOURMEM=$9400 SCROLLDELAY=5 PRA = $dc00 ; CIA#1 (Port Register A) PRB = $dc01 ; CIA#1 (Port Register B) DDRA = $dc02 ; CIA#1 (Data Direction Register A) DDRB = $dc03 ; CIA#1 (Data Direction Register B) SCROLLMESSAGELENGTH=$B0-1 O=SCREENMEM+((ROWS-1)*COLUMNS)-1 ; Offsets for grass P=COLOURMEM+((ROWS-1)*COLUMNS)-1 jsr pointsong1 ; Start with the first song. lda 52 ; Save end of basic memory sta old52+1 ;By directly modifying the code that will restore it. lda 56 sta old56+1 lda SCREENMAP sta oldSCREENMAP+1 ; Save current pointer to character set and other VIC lda #24 ; Set end of basic to $1800 ; This gives us only 2K of space to work in! Although very limited by ; todays standards, it is JUST enough for this program. sta 52 lda #24 ; Set end of basic to $1800. This is where our characters ; will be stored sta 56 ; Lower end of basic memory to make room ; for our custom character set. lda #SCROLLDELAY sta scrolltimer sta blocker_y sta blocker_x sta currentscrollcol ; Set colour to same as scroll timer (5) lda #2 sta xpos sta ypos ; Set starting coordinates to 1,1 lda #1 sta deltax sta deltay lda #0 sta sndcnt lda #239 ; 254 is 240 AND 14 ; The 14 refers to the lower three bits, which places the character map at 6144 ; 240 refers to bits 4-7, which with bit 7 of 36866 cleared, places the screen map ; at 7168 ; This gives the screen map enough space for the extended screen size. ; Refer to technical documentation for more info. sta SCREENMAP ; :Point VIC to our own character set lda #14 ; Black background, blue border sta $900F ; Set background/foreground ldx #0 colloop2: lda colors,x sta $9400,x lda colors+$100,x sta $9500,x ; lda colors+$200,x ; sta $9600,x dex bne colloop2 ; Loop over color map and set colours. ; We will only worry about the first 768 bytes. lda COLSIZE sta oldCOLSIZE+1 and #%01111111 sta COLSIZE lda currentsong ; If we have run this program before (by saving 2 here) cmp #2 ; Skip the intro because it is now corrupted beq skipintro jsr waitkey skipintro: sei lda #$20 ldx #$8f stx $9125 ; Set up the timer sta $9126 lda #IrqHandler sta $0315 cli lda #COLUMNS ; This will clear the 7th bit, moving sta COLSIZE ; the location of the screen map to 7168 ($1c00) ; It will also move the colour map to 37888 ($9400) lda ROWSIZE sta oldROWSIZE+1 and #129 ora #(ROWS*2) sta ROWSIZE lda HORIZOFFSET ; save screen information sta oldHORIZOFFSET+1 clc sbc #3 ; Shift screen to the left sta HORIZOFFSET lda VERTOFFSET sta oldVERTOFFSET+1 clc sbc #12 ; Shift screen up sta VERTOFFSET lda #(2*16) ; Set auxillary colour. Multiply by 16 because it is bits 7-4 ; we need to set. sta VOLUME ; Auxillary colour is stored here, it occupies ; the top 4 bits of volume. ; Turn volume up! lda VOLUME ora #15 sta VOLUME ldx #0 copychars: lda smiley,x sta $1C00,x inx cpx #(8*12) ; Copy first 10 characters bne copychars jsr colourtoprow ldx #0 lda #%1100 colloop1: sta $9419,x sta $9500,x sta $9600,x dex bne colloop1 ; Loop over color map and set colours. ; We will only worry about the first 768 bytes. ldx #0 lda #($20+128) ; 09 is the blank space in our character set loop1: sta $1800,x sta $1900,x sta $1A00,x dex bne loop1 ; Loop over character map and set to space ; We will only worry about the first 768 bytes. ldx #25 drawgrass: ; Draw the characters which depict grass. lda #1 ; There are 5 grass characters. sta O,x dex lda #2 sta O,x dex lda #6 sta O,x dex lda #7 sta O,x dex lda #8 sta O,x dex bne drawgrass ldx #30 lda #5 colorgrass: sta P,x dex bne colorgrass colorloop: ; This is the main loop ldx xpos ldy ypos cpx #(COLUMNS-2) ;Last Column beq flipx cpx #0 beq flipx xdone: cpy #(ROWS-3) ;Second last row (grass is on the last row beq flipy cpy #1 beq flipy ydone: jsr adjustxy stx xpos sty ypos jsr drawstars ldx ypos jsr plotchar jsr plotcolour jsr checkkeyboard jsr drawface lda #11 sta blockerchar jsr drawblocker jsr wait ldx ypos jsr plotchar jsr plotcolour jsr eraseface lda #($20+128) sta blockerchar jsr drawblocker jsr checksnd jsr $ffe1 bne colorloop jmp end ;============================================================== ; This will negate DELTAX to switch the X direction of the face. ; ; Clobbers A ;=============================================================== flipx: lda deltax eor #$fe ; Negate all the bits except LSB sta deltax ; Effectively alternating between the values ; of 1 and 254 ; If we add 254, it is effectively the same as subtracting 1 jsr beep jsr colourtoprow jmp xdone ;============================================================== ; This will negate DELTAY to switch the X direction of the face. ; ; Clobbers A ;=============================================================== flipy: lda deltay eor #$fe sta deltay jsr beep jmp ydone ;================================================================== ; Calculates the offset in the COLOURMAP ; Only to the row, not the column. ; ; X = Row ;================================================================== plotcolour: pha txa pha lda #00 sta coloffset lda #$94 sta coloffset+1 beq cendplot ; Add nothing if row 0 cplotitl: clc lda coloffset adc #COLUMNS sta coloffset lda coloffset+1 adc #0 sta coloffset+1 dex bne cplotitl cendplot: pla tax pla rts ;================================================================= ; This calculates the offset of the LINE that we will ; draw on. ; ; X = Row ;================================================================== plotchar: pha txa pha lda #00 sta offset lda #$18 sta offset+1 beq endplot ; Add nothing if row 0 plotitl: clc lda offset adc #COLUMNS sta offset lda offset+1 adc #0 sta offset+1 dex bne plotitl endplot: pla tax pla rts ;================================================================== ; Adjust X and Y positions ;================================================================== adjustxy: clc txa adc deltax ; Add the 'delta x', which would either ; increment or decrement this by 1. tax clc tya adc deltay tay rts ;================================================================= ;Check if a sound is playing. If so, lower the volume ;================================================================= checksnd: lda sndcnt cmp #0 beq skipcheck dec sndcnt bne skipcheck lda #0 STA SPEAKER3 skipcheck: rts ;================================================================== ;Short delay. 4/60th of a second to be exact; ;================================================================== wait: pha lda #0 sta 162 ; Store 0 in the timer register waitl: lda 162 ; Load it. It will increment by one every jiffy ; (1/60th of a second) cmp #2 ; Four jiffies passed? bne waitl pla rts ;==================================================================== ; Start a sound ; checksnd will turn this off eventually. This just starts the sound ; ; Clobbers A ;===================================================================== beep: lda #204 sta SPEAKER3 lda #2 ; This is how many frames before the sound fades out sta sndcnt rts ;====================================================================== ; Routine to draw the face ; Y = X column ; ; Clobbers A and Y ;====================================================================== drawface: clc ldy xpos lda #0 ; Load the PETSCII for a heart. sta (offset),y ; Save the heart at offset + y (which actually holds lda #%1100 sta (coloffset),y ; the X position). tya adc #1 tay lda #3 sta (offset),y lda #%1100 sta (coloffset),y tya adc #24 tay lda #%1100 sta (coloffset),y lda #4 sta (offset),y tya adc #1 tay lda #%1100 sta (coloffset),y lda #5 sta (offset),y rts ;====================================================================== ;Routine to erase the face ;====================================================================== eraseface: clc lda #($20+128) ldy xpos sta (offset),y ; Save the heart at offset + y (which actually holds ; the X position). tya adc #1 tay lda #($20+128) sta (offset),y tya adc #24 tay lda #($20+128) sta (offset),y tya adc #1 tay lda #($20+128) sta (offset),y rts ;=================================================================== ; Print scrolling message at the top of the screen. ; ; Clobbers A ;=================================================================== writemsg: dec scrolltimer bne writeend lda #SCROLLDELAY sta scrolltimer lda textoff pha ; Store text offset tya pha txa pha ldx #0 writemsg2: txa pha ; Save X value (count, screen offset) ldy #>msg ldx #notes ldx #notes2 ldx #notes_song2 ldx #notes2_song2 ldx #