; Stardodger By Stewart C. Russell ; Z80 Assembly Version ; Standard AMSDOS Equates gra_initialise equ &bbba gra_move_abs equ &bbc0 gra_move_rel equ &bbc3 gra_line_rel equ &bbf9 gra_set_pen equ &bbde gra_test_rel equ &bbf3 gra_wr_char equ &bbfc scr_initialise equ &bbff scr_set_ink equ &bc32 scr_set_border equ &bc38 scr_set_mode equ &bc0e km_initialise equ &bb00 km_read_key equ &bb1b km_test_key equ &bb1e txt_initialise equ &bb4e txt_output equ &bb5a txt_set_cursor equ &bb75 kl_time_set equ &bd10 kl_time_please equ &bd0d org &5000 .start call su ; The game itself call su ; Set up colours, etc. .oloop call tiscr ; Print title screen .loop1 call drawscr1 ; Draw screen box call plot ; Plot stars ld de,2 ld hl,200 call gra_move_abs ; Move to start position .contscr call shift ; Test if SHIFT is pressed ld a,3 call haudon ; 0.01 second delay ld a,(dy) ; Get result of SHIFT test cp 4 ; Should it go up? jr nz,down ; Draw it down if it isn't ld hl,4 ld de,4 call gra_line_rel ; Draw line upwards .doline call test ; Have we hit anything? ld a,(col) ; Get result of collision test cp 1 ; Is it white? jr z,lost ; If it is, end game cp 3 ; Have we hit the gap? jr z,next ; If so, go to next screen jr contscr ; Continue the screen if neither .lost call losscr ; Print 'You Goofed' etc... ld a,1 ld (scr),a ; First screen number = 1 ld hl,5 ld (q),hl ; First no. of starts = 5 ld a,4 ld (dy),a ; Initial direction = up jr oloop ; Go back to start of outer loop .next call wonscr ; Print 'Well Done' etc... jr loop1 ; Go to the next screen .down ld hl,-4 ld de,4 call gra_line_rel ; Draw line downwards jr doline ; Draws the lines for the playing screen .drawscr1 ld a,1 call scr_set_mode ; MODE 1 ld a,1 call gra_set_pen ; GRAPHICS PEN 1 ld de,629 ld hl,0 call gra_line_rel ; DRAWR 629,0 ld de,0 ld hl,170 call gra_line_rel ; DRAWR 0,170 ld de,0 ld hl,60 call gra_move_rel ; MOVER 0,60 ld de,0 ld hl,169 call gra_line_rel ; DRAWR 0,169 ld de,-629 ld hl,0 call gra_line_rel ; DRAWR -629,0 ld de,0 ld hl,-399 call gra_line_rel ; DRAWR 0,-399 ld de,0 ld hl,2 call gra_move_rel ; MOVER 0,2 ld de,627 ld hl,0 call gra_line_rel ; DRAWR 627,0 ld de,0 ld hl,168 call gra_line_rel ; DRAWR 0,168 ld de,0 ld hl,60 call gra_move_rel ; MOVER 0,60 ld de,0 ld hl,167 call gra_line_rel ; DRAWR 0,167 ld de,-625 ld hl,0 call gra_line_rel ; DRAWR -625,0 ld de,0 ld hl,-399 call gra_line_rel ; DRAWR 0,-399 ld a,3 call gra_set_pen ; GRAPHICS PEN 3 ld de,637 ld hl,0 call gra_move_abs ; MOVE 637,0 ld de,0 ld hl,400 call gra_line_rel ; DRAWR 0,400 ld de,2 ld hl,0 call gra_move_rel ; MOVER 2,0 ld de,0 ld hl,-400 call gra_line_rel ; DRAWR 0,-400 ld a,1 call gra_set_pen ; GRAPHICS PEN 1 ret ; Returns A = 0 and NC if no key ; key no. and C if ok .keyvalid or a ; Clear carry flag call km_read_key ret c ; Return if we have a key xor a ; Clear accumulator to 0 ret ; Prints string addressed by DE at text position H,L ; String must end with zero byte .prts push af push hl push de ; Save AF, HL & DE registers call txt_set_cursor ; Set cursor to H,L pop de ; Get string address .pl ld a,(de) ; Get character inc de ; Increment string pointer or a ; Is character zero? jr z,pret ; Go to pret if it is call txt_output ; Print it jr pl ; Loop to start of routine .pret pop hl pop af ; Restore HL & AF registers ret ; Pauses until a key is pressed .waitkey push af .w call keyvalid ; Loop while key pressed jr c,w ; to clear buffer .u call keyvalid jr nc,u ; Loop until key pressed pop af ret ; Pauses for A/300ths of a second .haudon push de push hl push af ld de,0 ld hl,0 call kl_time_set ; Reset clock pop af ; Get pause length .tl call kl_time_please ; Get time cp l ; Is it equal to value in A? jr nz,tl ; Loop while it isn't pop hl pop de ret ; Get SHIFT state and return 4 or -4 in (dy) .shift push af push hl push bc ld a,21 call km_test_key ; Has SHIFT been pressed? jr nz,yep ; If so, go to yep ld a,-4 .nup ld (dy),a ; Store value of key test pop bc pop hl pop af ret .yep ld a,4 ; Positive line increment jr nup ; Prints 'Press any key to continue' at 8,25 .waitmess ld hl,&0819 ld de,paktc call prts ret ; Print the title screen .tiscr ld a,1 call scr_set_mode ; MODE 1 ld hl,&1001 ld de,sdr call prts ; Print title ld hl,&0105 ld de,avoi call prts ; Print instructions 1 ld hl,&0906 ld de,wond call prts ; Print instructions 2 ld hl,&0c0d ld de,uses call prts ; Print key to use call waitmess call waitkey ; Wait for a keypress ; Prints A in HEX .prta push af push bc ld b,2 ; Loop counter for two nibbles ld c,a ; Store A rra rra rra rra .gnyb and &f ; Get nibble cp &a ; Is it > = 10? jr nc,hex ; If so, go to hex add a,&30 ; convert to ASCII char 0-9 .prn call txt_output ; Print it ld a,c djnz gnyb ; Act on lower nibble pop bc pop af ret .hex add a,&37 ; Convert to ASCII char A-F jr prn ; Test point relative (2,dy/2) and returns in (col) .test push bc push de push hl ld a,(dy) ; Get player's line direction cp 4 ; Is the line currently going up? jr nz,n4 ; Go to n4 if it isn't ld hl,2 ; Use relative co-ords (2,2) for ld de,2 ; test if going up. .ctest push hl call gra_test_rel ; Test point relative to line end ld (col),a ; Store INK result pop hl call nhl ; Negate HL value ld de,-2 ; Move graphics cursor back call gra_move_rel ; to original position. pop hl pop de pop bc ret .n4 ld hl,-2 ld de,2 ; Use reletive co-ords (2,-2) jr ctest ; for test if going up ; Negate HL value .nhl push af ld a,h cpl ld h,a ; Complement H ld a,l neg ld l,a ; Negate L pop af ret ; Prints success screen .wonscr ld a,1 call scr_set_mode ; MODE 1 ld hl,&1001 ld de,well call prts ; PRINT "Well Done" ld hl,&090d ld de,stan call prts ; Print next screen message ld a,(scr) ; Get next screen number call prta ; Print screen number in HEX call waitmess call waitkey ; Press any key to continue ret ; Prints lose screen .losscr ld a,1 call scr_set_mode ; MODE 1 ld hl,&1001 ld de,youg call prts ; PRINT "You Goofed" ld hl,&040d ld de,numb call prts ; Print number completed message ld a,(scr) ; Get no. of next screen dec a dec a ; Reduce it to screens completed call prta ; Print no. of screens completed call waitmess call waitkey ; Press any key to continue ret ; Returns a psuedo-random integer in HL .random push af push bc ld hl,(seed) ; Get seed push hl ; Save it onto stack add hl,hl add hl,hl add hl,hl add hl,hl add hl,hl add hl,hl add hl,hl add hl,hl ; HL = seed x 256 pop bc ; get original seed add hl,bc ; Add seed to (seed x 256) ld bc,41 add hl,bc ; Add 41 to result for fun of it! ld a,r ; Get value of memory refresh add l ; Add low byte of random result ld l,a ; Return this value to HL pop bc ; Restore BC adc hl,bc ; Add BC to HL (fiddle factor) ld (seed),hl ; Store result for later use pop af ; Restore AF ret ; Remainder routine, returns HL = HL mod DE .rem or a ; Clear carry flag sbc hl,de ; Is DE > HL? add hl,de ; restore HL ret c ; Return if DE > HL sbc hl,de ; HL = HL - DE (-0 in carry flag) jr rem ; Recurse to start ; Plots the relevant number of asterixs ; Keeps track of screen no. and no. of stars ; in scr (byte) and q (word) respectively. .plot push af push bc push de push hl ld hl,(q) ; Get number of asterisks .pltlp push hl ; Save loop counter call random ; Get random number in HL ld de,561 call rem ; HL = HL mod 561 ld de,50 ; Add 50 to it to allow for add hl,de ; initial reaction time push hl ; Save x co-ord call random ; Get random number for y co-ord ld de,361 call rem ; HL = HL mod 361 ld de,20 add hl,de ; Add 20 for tidyness pop de call gra_move_abs ; Move to the random position ld a,'*' call gra_wr_char ; Write a * at that position pop hl ; Get loop counter dec hl ; Decrement it ld a,h or l ; Is it zero? jr nz,pltlp ; Loop if not ld a,(scr) ; Get screen no. inc a ; Increment screen no. ld (scr),a ; Restore new screen no. ld hl,(q) ; Get number of asterisks inc hl inc hl inc hl inc hl inc hl ld (q),hl ; Set no. of stars (scr x 5) pop hl pop de pop bc pop af ret ; Set up MODE, colours, etc... .su ld a,1 call scr_set_mode ; MODE 1 call txt_initialise call km_initialise call gra_initialise call scr_initialise xor a ld b,a ld c,a call scr_set_ink ; INK 0,0,0 ld a,1 ld b,26 ld c,b call scr_set_ink ; INK 1,26,26 ld a,3 ld b,0 ld c,b call scr_set_ink ; INK 3,0,0 xor a ld b,a ld c,a call scr_set_border ; BORDER 0,0 ret ; Static variables and strings .dy defb 4 .col defb 0 .scr defb 1 .paktc defm 'Press any key to continue.',0 .sdr defm 'Stardodger',0 .avoi defm 'Avoid the killer Asterisqs, and seek the',0 .wond defm 'wondrous Nextscreen Gap.',0 .uses defm 'Use SHIFT to climb',0 .well defm 'Well Done!',0 .stan defm 'Stand by for screen ',0 .youg defm 'You Goofed',0 .numb defm 'Number of screens completed = ',0 .seed defw &abcd .q defw 5

Stardodger III - the assembler version Author : Stewart Russell Publisher : Amstrad Computer User November 1988 Stewart Russell shows you how to program the same game three times in three very different languages BCPL produced a game that would be fast enough for anyone, but was about 10K long. This seemed quite excessive, so a non-singing, non-dancing compact game in Z80 code was developed in assembly language. Assembly language programming is quite a different kettle of fish from Basic or BCPL, with absolutely no safety net provided for the unwary. Simple housekeeping tasks such as printing a string have to be written by the author and these can frequently prove to be the most difficult bits. Again, the Basic Stardodger served as the template for this model, with slight differences. The screen numbers in this version are printed in hexadecimal simply because a hex routine is shorter to write than a decimal one. Reasonable care has been taken that each routine does not corrupt registers unnecessarily. This wastes space in the form of PUSHes and POPs, but the approach is preferable to a possible system crash. The random routine and the screen drawing routine could both be made shorter, but they work, this being of the utmost importance. Results of tests were not generally returned in registers but in memory locations, because it is all too easy to corrupt a register by mistake. The listing was produced using the Maxam rom, so the long label names may cause problems for ADAM, Devpac, Zapp and Code Machine users, but are there to increase readability. Check your manuals to see how label names should be entered into your particular assembler. Your reward for all of this effort? A paltry 937 bytes of code. This can be saved by hopping into Basic and typing: +----------------------------------+ | SAVE"STARDOJ",B,&5000,&3A9,&5000 | +----------------------------------+ Some People may find this Assembler version a bit fast. Remedy this by changing part of the START subroutine from LD A,3:CALL HAUDON to LD A,value:CALL HAUDON where value can take any value from zero to 255 - 3 (default),4,5 or 6 (very slow) are the best ones to use. HAUDON, incidentally, is Glaswegian for "hold on". Conclusions ----------- If there has to be a conclusive winner in the general niceness stakes, BCPL would take it by a short head. It was as simple as the Basic version to write, yet ran as quickly as the Assembly version. Its only drawback was the length of the object file produced. Producing the Assembly version was certainly challenging, but the effort involved doesn't really justify the result. Although coming last in the race, Basic provided the slow, good-natured workhorse from which the tetchy thoroughbreds were descended. My current record on both the BCPL and the Assembly versions is Screen 11. I've made it through Screen 19 on the Basic one. Can you get further? Go forth, and dodge them stars! A comparison of the main routines +-------------------------------------------------------------------+ | | Basic | BBPL | Assembly | |---------------------------+---------+---------+-------------------| | Routine | lines | procs | procs | | initialisation | 20-70 | start | su | | Print title screen | 90-170 | start | tiscr | | Draw game screen | 180-450 | drawscr | drawscr1, plot | | Main game logic | 470-530 | start | start | | Print game over screen | 550-600 | start | losscr | | Print success screen | 620-680 | start | wonscr | | Wait for keypress routine | 700-760 | waitkey | waitmess, waitkey | +-------------------------------------------------------------------+