Avram Posted April 13, 2011 Share Posted April 13, 2011 This modified version of code by Gauntman allows you to use a joystick to move a text character around the screen. What I'm trying to do now is the assembly-language equivalent of Basic's Locate command but the character you control ploughs through everything. The joystick routines make sure you're not exiting the screen, then (supposedly) locates what's left, right, above, or below you, erases your current position, and then moves you to the new place. *=$4000 begin lda #<scr ; start by calculating look-up tables sta $d0 ; at the same time, we will clear the lda #>scr ; screen sta $d1 ldx #0 c0 lda #0 ; draw a character ldy #39 ; clear a single line c1 ;sta ($d0),y dey bpl c1 lda $d1 ; store address into look-up table sta schi,x lda $d0 sta sclo,x clc ; update zero page to next line adc #40 ; 40 bytes per line sta $d0 bcc c2 inc $d1 c2 inx ; for all 24 lines... cpx #24 bne c0 lda #4 ; set some colors sta 708 ; make ANTIC4 slightly more readable lda #6 sta 709 lda #8 sta 710 lda #<DLIST ; finally, point ANTIC to new display sta 560 lda #>DLIST sta 561 ; Plot a character ldx #20 ; vertical position ldy #20 ; horizontal position lda sclo,x ; set up zero-page address sta $d0 lda schi,x sta $d1 lda #33 ; plot the character sta ($d0),y ; Plot a block ldx #8 ; upper corner ldy #8 lda sclo,x ; set up zero-page addresses sta $d0 lda schi,x sta $d1 inx lda sclo,x sta $d2 lda schi,x sta $d3 lda #34 ; plot the character block... sta ($d0),y ; warning - no boundary testing sta ($d2),y iny sta ($d0),y sta ($d2),y ; Main loop j1 lda $14 wait1 cmp $14 beq wait1 lda 632 ; read joystick left cmp #11 bne right jmp moveleft ; or JSR? right cmp #7 bne up jmp moveright up cmp #14 bne down jmp moveup down cmp #13 beq movedown jmp j1 ; moveleft lda 1536 cmp #0 bne moveleft1 jmp j1 moveleft1 dec 1536 jsr checkchar lda 1538 cmp #0 beq moveleft2 inc 1536 jmp j1 moveleft2 jsr erasechar dec 1536 jmp plotchar ; moveright lda 1536 cmp #39 ;x position too small? bne moveright1 jmp j1 moveright1 jsr erasechar inc 1536 jmp plotchar ; moveup lda 1537 cmp #0 bne moveup1 jmp j1 moveup1 jsr erasechar dec 1537 jmp plotchar ; movedown lda 1537 cmp #22 bne movedown1 jmp j1 movedown1 jsr erasechar inc 1537 jmp plotchar ; return jmp j1 checkchar ; Plot a character ldx 1537 ; vertical position ldy 1536 ; horizontal position lda sclo,x ; set up zero-page address sta $d0 lda schi,x sta $d1 lda ($d0),y ;read character sta 1538 ;store it in 1538 rts erasechar ; Plot a character ldx 1537 ; vertical position ldy 1536 ; horizontal position lda sclo,x ; set up zero-page address sta $d0 lda schi,x sta $d1 lda #0 ; plot the character sta ($d0),y rts plotchar ; Plot a character ldx 1537 ; vertical position ldy 1536 ; horizontal position lda sclo,x ; set up zero-page address sta $d0 lda schi,x sta $d1 lda #33 ; plot the character sta ($d0),y jmp j1 DLIST .byte 112,112,112 ; blank lines .byte 68,<scr,>scr ; 24 lines of ANTIC 4 .byte 4,4,4,4,4,4,4,4,4,4,4,4,4,4,4 .byte 4,4,4,4,4,4,4 .byte 65,<DLIST,>DLIST ; Jump to top *=$5000 ;scr .ds 40*24 ; 960 bytes for screen scr .sbyte "****************************************" .sbyte "* *" .sbyte "* *" .sbyte "* *" .sbyte "* ===============*" .sbyte "* ===============*" .sbyte "* *" .sbyte "* *" .sbyte "* *" .sbyte "* *" .sbyte "* ================ *" .sbyte "* ================ *" .sbyte "* *" .sbyte "* *" .sbyte "* *" .sbyte "* ========== *" .sbyte "* ========== *" .sbyte "* *" .sbyte "* *" .sbyte "* ========== *" .sbyte "* ========== *" .sbyte "* *" .sbyte "****************************************" sclo .ds 24 schi .ds 24 Quote Link to comment Share on other sites More sharing options...
+JAC! Posted April 13, 2011 Share Posted April 13, 2011 (edited) Well, you perform zhe locate check only in one location but not in all four... Tips: - You should definition xpos = 1536, ypos = 1537, instead of using addresses - In the j1 routine, you can ldx ypos and ldy xpos without modifying 1536/1538 an keep them there - Instead of dec/inc 1536/1537 use DEX/INX/DEY/INY to compute the new "target" position without changing the actual value - Write back x/y to xpos/ypos only at the end - Every direction of the stick corresponds to a cleared bit, this version uses LSR to check so also diagonals work - All this is so fast that is easier to save code and always clear/draw the character Example (MADS syntax, ORG instead of start, byte instead of sbyte) org $4000 p1 = $d0 p2 = $d2 xpos = 1536 ypos = 1537 joystick = 1538 begin lda #<scr ; start by calculating look-up tables sta p1 ; at the same time, we will clear the lda #>scr ; screen sta p1+1 ldx #0 c0 lda #0 ; draw a character ldy #39 ; clear a single line c1 ;sta (p1),y dey bpl c1 lda p1+1 ; store address into look-up table sta schi,x lda p1 sta sclo,x clc ; update zero page to next line adc #40 ; 40 bytes per line sta p1 bcc c2 inc p1+1 c2 inx ; for all 24 lines... cpx #24 bne c0 lda #4 ; set some colors sta 708 ; make ANTIC4 slightly more readable lda #6 sta 709 lda #8 sta 710 lda #<DLIST ; finally, point ANTIC to new display sta 560 lda #>DLIST sta 561 ; Plot a character ldx #20 ; vertical position stx xpos ldy #20 ; horizontal position sty ypos lda sclo,x ; set up zero-page address sta p1 lda schi,x sta p1+1 lda #33 ; plot the character sta (p1),y ; Plot a block ldx #8 ; upper corner ldy #8 lda sclo,x ; set up zero-page addresses sta p1 lda schi,x sta p1+1 inx lda sclo,x sta p2 lda schi,x sta p2+1 lda #34 ; plot the character block... sta (p1),y ; warning - no boundary testing sta (p2),y iny sta (p1),y sta (p2),y ; Main loop j1 lda $14 wait1 cmp $14 beq wait1 ldx ypos ldy xpos lda #0 jsr plotchar ;Always erase lda 632 ;read joystick sta joystick ;Shift area for direction bits lsr joystick bcs no_up cpx #0 beq no_stick dex jsr checkchar beq no_up inx no_up lsr joystick bcs no_down cpx #24 beq no_stick inx jsr checkchar beq no_down dex no_down lsr joystick bcs no_left cpy #0 beq no_stick dey jsr checkchar beq no_left iny no_left lsr joystick bcs no_right cpy #39 beq no_stick iny jsr checkchar beq no_right dey no_right no_stick lda #33 jsr plotchar sty xpos stx ypos jmp j1 ; Locate char at (X,Y) into <A> checkchar lda sclo,x ; set up zero-page address sta p1 lda schi,x sta p1+1 lda (p1),y ;read character rts ; Plot a character <A> at (Y,X) plotchar pha lda sclo,x ; set up zero-page address sta p1 lda schi,x sta p1+1 pla sta (p1),y rts DLIST .byte 112,112,112 ; blank lines .byte 68,<scr,>scr ; 24 lines of ANTIC 4 .byte 4,4,4,4,4,4,4,4,4,4,4,4,4,4,4 .byte 4,4,4,4,4,4,4 .byte 65,<DLIST,>DLIST ; Jump to top *=$5000 ;scr .ds 40*24 ; 960 bytes for screen scr .byte "****************************************" .byte "* *" .byte "* *" .byte "* *" .byte "* ===============*" .byte "* ===============*" .byte "* *" .byte "* *" .byte "* *" .byte "* *" .byte "* ================ *" .byte "* ================ *" .byte "* *" .byte "* *" .byte "* *" .byte "* ========== *" .byte "* ========== *" .byte "* *" .byte "* *" .byte "* ========== *" .byte "* ========== *" .byte "* *" .byte "****************************************" sclo .ds 24 schi .ds 24 Edited April 13, 2011 by JAC! Quote Link to comment Share on other sites More sharing options...
Avram Posted April 13, 2011 Author Share Posted April 13, 2011 Very cool - thank-you. Quote Link to comment Share on other sites More sharing options...
Avram Posted April 15, 2011 Author Share Posted April 15, 2011 If I wanted decorative characters that could be passed through and they were restricted to, say, atascii 0-9, what would be the best way to do it? If I subtracted 10 from what's read by the Locate routine and did either a BMI or BPL? Or is there a better way? Quote Link to comment Share on other sites More sharing options...
MaPa Posted April 15, 2011 Share Posted April 15, 2011 I would do compare.. replace BEQ after JSR checkchar with CMP #10 and BCC. Quote Link to comment Share on other sites More sharing options...
+JAC! Posted April 15, 2011 Share Posted April 15, 2011 If the char set should be the same for all movement directions (which I assume), it can be done centrally without changing the rest like this: ; Return <A> <> 0 and Z=0 if not transparent, <A>=0, <Z>=1 if transparent. checkchar lda sclo,x ; set up zero-page address sta p1 lda schi,x sta p1+1 lda (p1),y ;read character beq check_exit ;Z=1 cmp #'0 bcc check_exit ;less then 0, also Z=0 cmp #'9 + 1 ;first char after last transparent one bcs check_exit ;greater then 9, also Z=0 lda #0 ;set Z=1 check_exit rts Quote Link to comment Share on other sites More sharing options...
Avram Posted April 15, 2011 Author Share Posted April 15, 2011 Thanks Jac and MaPa. I'm going to be adding my player-missile routine to this shortly and wanted to get the locate function working before I proceeded. Thanks again! And I should say that I think using software collisions instead of the player hardware collision seems to be the way to go. Quote Link to comment Share on other sites More sharing options...
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