Bouncy

Wrote a Z80 Assembly script to allow a sprite to move pixel by pixel around a screen, which can be challenging with the ZX Spectrum due to it's graphics configuration and memory layout.

001 0000 DEVICE ZXSPECTRUM48 002 0000 org $8000 003 8000 004 8000 C3 32 80 jp start 005 8003 XPOS = 21 ; take value between 0 and 265 decimal 006 8003 YPOS = 21 ; take vale between 0 and 168 decimal 007 8003 008 8003 009 8003 COUNTER = $8; 010 8003 DELAYVALUE = %00001010 011 8003 012 8003 bitmap: 013 8003 3C db %00111100 014 8004 42 db %01000010 015 8005 99 db %10011001 016 8006 85 db %10000101 017 8007 85 db %10000101 018 8008 81 db %10000001 019 8009 42 db %01000010 020 800A 3C db %00111100 021 800B 022 800B SCREENSTART = $4000 023 800B 024 800B 025 800B getposition: 026 800B 027 800B 3A 04 FF ld a,($FF04) 028 800E 47 ld b,a 029 800F 3A 05 FF ld a,($FF05) 030 8012 4F ld c,a 031 8013 032 8013 ;set up e which will hold y5,y4,y3,x4,x3,x2,x1,x0 033 8013 3E 00 ld a,$0 ; set a to 0 034 8015 80 add b ; add on the x colomb co-ordinate from 4x-x0 035 8016 1F rra 036 8017 1F rra 037 8018 1F rra 038 8019 E6 1F and %00011111 039 801B 5F ld e,a ; e contains 0,0,0,x4,x3,x2,x1,x0 040 801C ;now we need y5,y4, y3 041 801C 79 ld a,c ; load c which holds the y corordianes into a 042 801D E6 38 and %00111000 ; a now contains 0,0,y5,y4,y3,0,0,0 043 801F 17 rla ; move this to the left twice 044 8020 17 rla ; a now contains y5,y4,y3,0,0,0,0,0 045 8021 83 add e ; add it to e - a is now y5,y4,y3,x4,x2,x1,x0 046 8022 5F ld e,a ; put it into e to complete e part of address 047 8023 048 8023 ;now we need d to hold 0,1,0,y7,y6,y2,y1,y0 in that order 049 8023 ;c holds the y co-ordinate y7,y6,y5,y4,y3,y2,y1,y0 050 8023 79 ld a,c ; load c into a 051 8024 E6 07 and %00000111 ; a holds 0,0,0,0,0,y2,y1,y0 052 8026 57 ld d,a ; d now holds 0,0,0,0,0,y2,y1,y0 053 8027 79 ld a,c 054 8028 E6 C0 and %11000000; a holds y7,y6,0,0,0,0,0,0 055 802A 1F rra ; move to the right three times 056 802B 1F rra; 057 802C 1F rra ; a holds 0,0,0,y7,y6,0,0,0 058 802D 82 add d ; a holds 0,0,0,y7,y6,y2,y1,y0 059 802E C6 40 add %01000000 ; a holds 0,1,0,y7,y6,y2,y1,y0 060 8030 57 ld d,a; load result into d 061 8031 C9 ret 062 8032 063 8032 start: 064 8032 3E 01 ld a,$1 065 8034 32 15 FF ld ($FF15),a ;direction x 1 +ve, 0 -ve 066 8037 3E 01 ld a,$1 067 8039 32 16 FF ld ($FF16),a ;direction y 1 +ve, 0 -ve 068 803C 3E 64 ld a,100 069 803E 32 10 FF ld ($FF10),a 070 8041 3E 15 ld a,21 071 8043 32 11 FF ld($FF11),a 072 8046 073 8046 074 8046 move: 075 8046 21 03 80 ld hl,bitmap 076 8049 3A 10 FF ld a,($FF10) 077 804C 32 04 FF ld ($FF04),a ; store XPos at FF04 078 804F 3A 11 FF ld a,($FF11) 079 8052 32 05 FF ld($FF05),a ; store YPos at FF05 080 8055 081 8055 3E 08 ld a,$8 082 8057 32 00 FF ld ($FF00),a ;counter for loop 083 805A 3E 00 ld a,$0 084 805C 32 01 FF ld($FF01),a ; off set for sprite 085 805F 086 805F loop: 087 805F 088 805F 089 805F CD 0B 80 call getposition ; takes bc (x,y) and returns values for de (graphics address) 090 8062 091 8062 ;set off set 092 8062 093 8062 3A 04 FF ld a,($FF04) ; load x co-ord into a 094 8065 E6 07 and %00000111;the 3 least sig figures 095 8067 3C inc a; 096 8068 32 01 FF ld ($FF01),a; load this value into the off set memory address 097 806B ;call createsprites to create two diffrent sprites from the one sprite based on the x coordinate 098 806B 099 806B ;create byte one and store it at $FF02 100 806B 101 806B 7E ld a,(hl) 102 806C 32 02 FF ld ($FF02),a 103 806F 3E 00 ld a,$0 104 8071 32 03 FF ld ($FF03),a 105 8074 3A 01 FF ld a,($FF01) 106 8077 3D dec a 107 8078 CA 98 80 jp z, shifted 108 807B 47 ld b,a 109 807C 3A 02 FF ld a,($FF02) 110 807F shiftfirstbyte: 111 807F 1F rra 112 8080 CB BF res 7,a 113 8082 10 FB djnz shiftfirstbyte 114 8084 32 02 FF ld ($FF02),a 115 8087 116 8087 3A 01 FF ld a,($FF01) 117 808A 118 808A 47 ld b,a 119 808B 3E 09 ld a,9 120 808D 90 sub b 121 808E 47 ld b,a 122 808F 7E ld a,(hl) 123 8090 shiftsecondbyte: 124 8090 07 rlca 125 8091 CB 87 res 0,a 126 8093 10 FB djnz shiftsecondbyte 127 8095 32 03 FF ld ($FF03),a 128 8098 129 8098 shifted: 130 8098 131 8098 3A 02 FF ld a,($FF02) ; load first sprite byte into a 132 809B 12 ld (de),a ; place a (sprite byte) into address from get position -de. 133 809C 13 inc de 134 809D 3A 03 FF ld a,($FF03) 135 80A0 12 ld(de),a ; place second (sprite byte) 136 80A1 137 80A1 ;get a sprite shift based on the x co-ordinate three least significant bits. 138 80A1 ;create a shifted sprite by 139 80A1 140 80A1 23 inc hl ; point to the next sprie byte 141 80A2 3A 05 FF ld a,($FF05); increase the y position for the next line of the sprite 142 80A5 3C inc a ; increase the y position for the next line of the sprite 143 80A6 32 05 FF ld ($FF05),a; increase the y position for the next line of the sprite 144 80A9 3A 00 FF ld a,($FF00); use memory location $FF00 to hold the counter 145 80AC 3D dec a ;decrement the counter 146 80AD 32 00 FF ld ($FF00),a ; put the counter poistion back 147 80B0 20 AD jr nz,loop 148 80B2 149 80B2 ;delay start 150 80B2 3E 0A ld a,DELAYVALUE 151 80B4 32 06 FF ld($FF06),a 152 80B7 32 07 FF ld($FF07),a 153 80BA delay: 154 80BA 3A 07 FF ld a,($FF07) 155 80BD 3D dec a 156 80BE 32 07 FF ld($FF07),a 157 80C1 20 F7 jr nz,delay 158 80C3 3E 0A ld a,DELAYVALUE 159 80C5 3A 06 FF ld a,($FF06) 160 80C8 3D dec a 161 80C9 32 06 FF ld ($FF06),a 162 80CC 20 EC jr nz,delay 163 80CE 164 80CE ;delete sprite 165 80CE 3E 08 ld a,$8;counter 166 80D0 32 00 FF ld ($FF00),a ;counter for loop 167 80D3 3A 10 FF ld a,($FF10) ;x pos 168 80D6 32 04 FF ld ($FF04),a 169 80D9 3A 11 FF ld a,($FF11) ; y pos 170 80DC 32 05 FF ld ($FF05),a 171 80DF deleteloop: 172 80DF CD 0B 80 call getposition 173 80E2 3E 00 ld a,$0 174 80E4 12 ld (de),a ; place blank 175 80E5 13 inc de 176 80E6 3E 00 ld a,$0 177 80E8 12 ld(de),a ; place blank 178 80E9 179 80E9 3A 05 FF ld a,($FF05); increase the y position for the next line of the sprite 180 80EC 3C inc a ; increase the y position for the next line of the sprite 181 80ED 32 05 FF ld ($FF05),a; increase the y position for the next line of the sprite 182 80F0 183 80F0 3A 00 FF ld a,($FF00); use memory location $FF00 to hold the counter 184 80F3 3D dec a ;decrement the counter 185 80F4 32 00 FF ld ($FF00),a ; put the counter poistion back 186 80F7 20 E6 jr nz,deleteloop 187 80F9 188 80F9 ;increase x pos 189 80F9 ; ld a,($FF10) 190 80F9 ; cp 240 191 80F9 ; jr nc,skip 192 80F9 ; inc a 193 80F9 ;skip: 194 80F9 ; ld($FF10),a 195 80F9 ;inc y pos 196 80F9 ; ld a,($FF11) 197 80F9 ; inc a 198 80F9 ; ld ($FF11),a 199 80F9 200 80F9 testxdirection: 201 80F9 3A 15 FF ld a,($FF15) ; the x direction 202 80FC FE 00 cp $0 203 80FE 20 13 jr nz, goright 204 8100 3A 10 FF ld a,($FF10) 205 8103 3D dec a 206 8104 32 10 FF ld ($FF10),a 207 8107 FE 0A cp 10 208 8109 30 18 jr nc, testydirection 209 810B 3E 01 ld a,1 210 810D 32 15 FF ld($FF15),a 211 8110 C3 23 81 jp testydirection 212 8113 213 8113 goright: 214 8113 3A 10 FF ld a,($FF10) 215 8116 3C inc a 216 8117 32 10 FF ld ($FF10),a 217 811A FE DC cp 220 218 811C 38 05 jr c, testydirection 219 811E 3E 00 ld a,0 220 8120 32 15 FF ld($FF15),a 221 8123 222 8123 223 8123 testydirection: 224 8123 225 8123 3A 16 FF ld a,($FF16) ; the y direction 226 8126 FE 00 cp $0 227 8128 20 13 jr nz, godown 228 812A 3A 11 FF ld a,($FF11) 229 812D 3D dec a 230 812E 32 11 FF ld ($FF11),a 231 8131 FE 0A cp 10 232 8133 30 18 jr nc, finishedSettingDirection 233 8135 3E 01 ld a,1 234 8137 32 16 FF ld($FF16),a 235 813A C3 4D 81 jp finishedSettingDirection 236 813D 237 813D godown: 238 813D 3A 11 FF ld a,($FF11) 239 8140 3C inc a 240 8141 32 11 FF ld ($FF11),a 241 8144 FE 96 cp 150 242 8146 38 05 jr c, finishedSettingDirection 243 8148 3E 00 ld a,0 244 814A 32 16 FF ld($FF16),a 245 814D 246 814D 247 814D 248 814D 249 814D 250 814D 251 814D finishedSettingDirection: 252 814D 253 814D C3 46 80 jp move 254 8150 255 8150 256 8150 257 8150 C9 ret 258 8151 259 8151 260 8151 ;Depoyment snapshot 261 8151 SAVESNA "graphics2.sna",start