2068 Code Bytes #7

Authors

Lloyd Dreger

Publication

SMUG Bytes

Pub Details

SMUG Bytes v10 n4-7 Volume: 10 Issue: 4-7

Date

August - November 1993

Pages

BASIC Terms

See all articles from SMUG Bytes v10 n4-7

Seventh installment of the Z80 series, presenting the map-cursor and map-editor routine for CONQUEST. Covers PRCURS and PRCUR (cursor initialization and main loop), PIXLOC (screen address from XY coordinates), ATTR (attribute address calculation), PRCHA (print character), INTJOY (joystick-to-cursor translation), TRANS (cursor-to-map coordinate conversion), PUTX (place map element), DOIT (dispatch table using JP(HL)), and four scroll routines (SCROLL L/R/U/D). Full assembly listings.

We continue our discussion of routines from the game Conquest. Up to this point we have discussed in:

Game background music
Sound effects.
General Input routine.
General Menu routine.
Printing of a double wrapping map.
Printing of Graph coordinates.

We continue with a map cursor. Whenever one uses a joystick (for that matter a mouse) to direct the movement of various units one needs a cursor to indicate the desired direction. We use a capitol X for the cursor symbol.

We need to store the screen coordinates of the cursor in two variables called Curx and Cury. The cursor should not run off the map or be allowed to run over the map coordinates which are down the left side and line 22 acrossed the bottom. Therefore, Curx can be from 1 to 31 (in Basic notation) and Cury from o to 21.

The input from this routine not only moves the cursor but also must determine when the joystick button has been pushed as well as interpret all the keyboard commands. Since the keyboard is interpreted differently for the game than in map drawing, 2 different print cursor routines are necessary. The simplest of the two is the one for the map editor which is given below and found in Conquest at 61018.

DOEQU 52388not printed as an EQU; taken from the operand at 61314

CURYEQU 52394not printed as an EQU; taken from the operands at 61023 and 61073

CURXEQU 52395not printed as an EQU; taken from the operand at 61020

MAPCOYEQU 52396not printed as an EQU; taken from the operand at 61274

MAPCOXEQU 52397not printed as an EQU; taken from the operand at 61285

6101862,1PRCURSLD A,1INITILIZE CURX AND CURY

6102050,171,204LD (CURX),A

6102350,170,204LD (CURY),A

61026205,63,236CALL PRMAPP

61029237,75,179,204PRCURLD BC,(CURY)THIS IS THE RETURN FOR REPEATS OF THE ROUTINE IN CASE THE INPUT WAS MERELY A MOVE OF THE CURSOR.

61033205,240,238CALL PIXLOCTRANSLATE THE X AND Y INTO THE FIRST PIXEL OF THE SCREEN FILE.

61036235EX DE,HL

6103762,88LD A,”X”

61039205,18,239CALL PRCHAPRINT THE CURSOR

61042205,255,238CALL ATTR

61045126LD A,(HL)

61046230,248AND 248SAVE THE PAPER COLOR

61048198,7ADD A,7MAKE THE INK WHITE.

61050119LD (HL),A

61051205,184,235CALL GETINP(SEE 2068 CODE BYTES #2 FOR THE ROUTINE.)

61054203,119BIT 6,A

6105632,39JR NZ,KEYBOARDA KEY WAS PRESSED.

61058203,127BIT 7,A

6106040,5JR Z,MOVE

61062205,130,239CALL DOIT

6106524,218JR PRCUR

61067229MOVEPUSH HLOLD ATTR ADDR

61068213PUSH DEOLD SCR ADDR

61069197PUSH BCOLD CUR POSN

61070205,48,239CALL INTJOYCHANGE BC TO NEW POSITION OF CURSOR

61073237,67,170,204LD (CURY),BCSAVE NEW COORDINATES OF CURSOR

61077193POP BC

61078205,90,239CALL TRANS

61081205,26,236CALL PMO

61084126LD A,(HL)ERASE OLD CURSOR

61085209POP DEREPRINT OLD POSITION. SEE #5 AND #6 FOR ROUTINE.

61086205,119,237CALL PRUDG

61089126LD A,(HL)

61090205,254,236CALL FINDAT

61093225POP HL

61094119LD (HL),A

6109524,189JR PRCUR

61097254,99KBCP 99“c”

6109932,5JR NZ,KBF

61101205,167,240CALL CENCURIN EDIT MODE, IT CENTERS MAP ON THE CURSOR. IN GAME MODE, ON THE UNIT TO BE MOVED.

6110424,179JR PRCUR

61106254,102KBFCP 102“f”

6110832,5JR NZ,KBGF,G,T AND V ARE THE 4 SCROLLS

61110205,35,238CALL SCROLL

6111324,170JR PRCUR

61115254,103KBGCP 103“g”

6111732,5JR NZ,KBI

61119205,53,238CALL SCROLR

6112224,161JR PRCUR

61124254,105KBICP 105“i”

6112632,5JR NZ,KBM

61128205,244,246CALL IDENTIFY

6113124,152JR PRCUR

61133254,109KBMCP 109“m”

61135200RET ZM AND Q RETURN

61136254,113CP 113“q”

61138200RET Z

61139254,116CP 116“t”

6114132,5JR NZ,KBV

61143205,78,238CALL SCROLU

6114624,137JR PRCUR

61148254,118KBVCP 118“v”

6115032,5JR NZ,KBA

61152205,63,238CALL SCROLD

6115524,128JR PRCUR

61157254,97KBACP 97“a”

61159194,101,238JP PRCURIF MORE KEYS NEED TO BE READ THEY WOULD BE INSERTED HERE.

61162205,120,240CALL WORLD

61165195,101,238JP PRCUR

BC = COORDINATES FOR PIXLOC & ATTR

61168120PIXLOCLD A,B

61169230,248AND 248

61171198,64ADD A,64

61173103LD H,A

61174120LD A,B

61175230,7AND 7

6117715RRCA

6117815RRCA

6117915RRCA

61180129ADD A,C

61181111LD L,AHL NOW SCREEN FILE ADDRESS OF BC COORDINATES.

61182201RET

61183120ATTRLD A,B

61184203,47SRA A

61186203,47SRA A

61188203,47SRA A

61190198,88ADD A,88

61192103LD H,A

61193120LD A,B

61194230,7AND 7

6119615RRCA

6119715RRCA

6119815RRCA

61199129ADD A,C

61200111LD L,AHL NOW ATTR ADDR OF BC

61201201RET

DE = SCREEN POSN / A = CHARACTER NUMBER

61202197PRACHAPUSH BC

61203229PUSH HL

61204213PUSH DE

6120538,0LD H,0

61207167AND A

6120823RLA

6120923RLA

61210203,20RL H

6121223RLA

61213203,20RL H

61215111LD L,A

61216124LD A,H

61217198,60ADD A,60

61219103LD H,AHL NOW AT PIXELS FOR CHARACTER

612206,8LD B,8

61222126PRCLD A,(HL)

6122318LD (DE),A

6122435INC HL

6122520INC D

6122616,250DJNZ PRC

61228209POP DE

61229225POP HL

61230193POP BC

61231201RET

A = REVERSED BITS FROM JOYSTICK BIT 3= R, 2=L, 1=D, 0=U

61232203,71INTJOYBIT 0,A

6123440,1JR Z,IJ1

612365DEC B

61237203,79IJ1BIT 1,A

6123940,1JR Z,IJ2

612414INC B

61242203,87IJ2BIT 2,A

6124440,1JR Z,IJ3

6124613DEC C

61247203,95IJ3BIT 3,A

6124940,1JR Z,IJ4

6125112INC CNOW CHECK BC TO MAKE SURE NOT OFF SCREEN AS DISCUSSED ABOVE

61252120IJ4LD A,B

61253254,255CP 255

6125532,1JR NZ,IJ5

612575INC B

61258254,22IJ5CP 22

6126032,1JR NZ,IJ6

612624DEC B

61263121IJ6LD A,C

61264254,0CP 0

6126632,1JR NZ,IJ7

6126812INC C

61269254,32IJ7CP 32

61271192RET NZ

6127213DEC C

61273201RET

BC = CURSOR COORDINATES. THIS ROUTINE CONVERTS THE CURSOR COORDINATES INTO THE MAP COORDINATES DEPENDING UPON WHAT IS BEING SHOWN ON THE SCREEN

6127458,172,204TRANSLD A,(MAPCOY)

61277129ADD A,C

61278254,65CP 65

6128056,2JR C,TR

61282214,64SUB 64

6128479TRLD C,A

6128558,173,204LD A,(MAPCOX)

61288128ADD A,B

61289254,65CP 65

6129156,2JR C,TR1

61293214,64SUB 64

6129571LD B,ABC NOW IN MAPCOORDINATES

61296201RET

61297205,90,239PUTXCALL TRANS

61300205,26,236CALL PMO

6130358,26,236LD A,(DO)

61306205,7,241CALL SETST

61309216RET C

61310119LD (HL),A

61311195,63,236JP PRMAPP

THE VARIABLE DO MUST BE SET BEFORE CALLING THIS ROUTINE. 1= PUT SEA, 2= PUT LAND, 3= PUT MOUNTAIN, 4= PUT SHOAL, 5= PUT CITY, 6=BLOTCH SEA, 7= BLOTCH LAND, 8= GROW SEA, 9= GROW LAND

6131458,164,204DOITLD A,(DO)

61317254,0CP 0

61319200RET Z

6132017,158,239LD DE,TABLE

61323254,6CP 6

6132556,9JR C,D1

61327214,5SUB 5

6132938,0LD H,0

61331167AND A

6133223RLA

61333111LD L,A

6133425ADD HL,DE

61335235D1EX DE,HL

6133626LD A,(DE)

61337111LD L,A

6133819INC DE

6133926LD A,(DE)

61340103LD H,A

61341233JP (HL)

61342113,239TABLEDEFW PUTX

61344168,239DEFW BLOTCH

61346168,239DEFW BLOTCH

61348218,240DEFW GROW

61350218,240DEFW GROW

About this transcription

This listing was transcribed from the original scan and checked line by line. The published address column, object-byte column and mnemonics each independently determine the program, so all three were cross-referenced against one another: 190 lines carried both bytes and mnemonics and were fully verified.

9 places were found where the printed columns contradict one another. Which column is at fault is noted line by line; where the evidence does not settle it, that is said plainly:

61029, printed as LD BC,(CURY), should read 237,75,170,204 — the byte column is at fault: CURY is 52394 where the same variable is written at 61023 and read back at 61073, so the third byte should be 170 rather than 179
61039, printed as CALL PRCHA — the bytes reach the right routine; the two columns simply disagree on its name, which is printed PRCHA here and PRACHA at its definition at 61202. Nothing on the page settles which spelling the author intended, and the code is unaffected either way
61056, printed as JR NZ,KEYBOARD, should read JR NZ,KB — the mnemonic column is at fault: the bytes branch to 61097, which the listing labels KB, and no label KEYBOARD appears anywhere in the excerpt
61159, printed as JP PRCUR, should read JP NZ,PRCUR — the mnemonic column is at fault: byte 194 is a conditional JP NZ, and the CP 97 immediately above requires the condition. The unconditional form at 61165 is byte 195
61257, printed as INC B — byte 5 is DEC B, but the printed INC B is what the routine needs, since B holds 255 after the cursor is driven above the top row and has to be brought back to 0. Which column is at fault could not be determined; the same two bytes are used correctly at 61236 and 61241, so this is not a systematic swap
61262, printed as DEC B — the mirror of 61257: byte 4 is INC B where the printed DEC B is what the routine needs to pull the cursor back to row 21. Again the direction could not be determined from the page
61291, printed as JR C,TR1 — the label is missing rather than off-page: the bytes branch to 61295, which is printed here as LD B,A but carries no label. TR1 belongs on that line
61303, printed as LD A,(DO), should read 58,164,204 — the byte column is at fault: DO is 52388 where it is read at 61314, while the operand printed here is 60442, which is the operand of the CALL PMO on the line directly above and appears to have been repeated in error
61325, printed as JR C,D1 — the offset is correct and the label is printed one line early: for DO values below 6 the branch has to land on the LD A,(DE) at 61336 so that DE still points at TABLE, which is what selects the first entry. Landing on the EX DE,HL at 61335, where the listing prints D1, would swap TABLE out of DE

The following could not be resolved from the available scan and are reproduced as printed: 61095. If you have a cleaner copy of this issue, corrections are welcome.

15 symbols and jump targets referenced here are defined outside the published excerpt and could not be verified.

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