1.1 --- a/mapcode.oph	Sat Aug 20 23:22:01 2011 +0200
     1.2 +++ b/mapcode.oph	Sun Aug 21 01:24:55 2011 +0200
     1.3 @@ -1032,246 +1032,233 @@
     1.4  emerge_explode_chars_low: .byte $00,$40,$80,$c0,$00,$40,$80,$c0
     1.5  emerge_explode_chars_high: .byte $41,$41,$41,$41,$42,$42,$42,$42
     1.6  
     1.7 -plot_characters:
     1.8 +unplot_character:       ; $74,$75=character address
     1.9  
    1.10 -    lda #$00
    1.11 -    sta $74
    1.12 -    lda #$33
    1.13 -    sta $75
    1.14 +    lda $82
    1.15 +    sta $78
    1.16 +    lda $83
    1.17 +    sta $79
    1.18 +    jsr plot_character_sprite
    1.19 +    lda $78
    1.20 +    sta $82
    1.21 +    rts
    1.22  
    1.23 -    plot_characters_loop:
    1.24 +plot_character:         ; $74,$75=character address
    1.25  
    1.26 -        ldy #0
    1.27 -        lda ($74),y
    1.28 -        cmp #0
    1.29 -        bne plot_characters_read_character
    1.30 -        jmp plot_characters_next
    1.31 +    lda $84
    1.32 +    sta $78
    1.33 +    lda $85
    1.34 +    sta $79
    1.35 +    jsr plot_character_sprite
    1.36 +    lda $78
    1.37 +    sta $84
    1.38 +    rts
    1.39  
    1.40 -        plot_characters_read_character:
    1.41 -        clc
    1.42 +plot_character_sprite:  ; $74,$75=character address
    1.43 +                        ; $78,$79=plot buffer address
    1.44  
    1.45 -        sta $77         ; temporarily store the object type
    1.46 +    ldy #0
    1.47 +    lda ($74),y
    1.48 +    cmp #0
    1.49 +    bne plot_characters_read_character
    1.50 +    jmp plot_characters_next
    1.51  
    1.52 -        ; Use lookup tables to load the offsets into the sprite.
    1.53 +    plot_characters_read_character:
    1.54 +    clc
    1.55  
    1.56 -        ; Direction
    1.57 -        iny
    1.58 -        lda ($74),y
    1.59 -        sta $80         ; temporarily store the direction
    1.60 +    sta $77         ; temporarily store the object type
    1.61  
    1.62 -        ; y
    1.63 -        iny
    1.64 -        lda ($74),y
    1.65 -        tax
    1.66 -        lda screen_rows_low,x
    1.67 -        sta $72
    1.68 -        lda screen_rows_high,x
    1.69 -        sta $73
    1.70 -        clc
    1.71 +    ; Use lookup tables to load the offsets into the sprite.
    1.72  
    1.73 -        ; dy
    1.74 -        iny
    1.75 -        lda ($74),y
    1.76 -        sta $76
    1.77 -        tax
    1.78 -        lda screen_subrows_low,x
    1.79 -        adc $72
    1.80 -        sta $72
    1.81 -        lda screen_subrows_high,x
    1.82 -        adc $73
    1.83 -        sta $73
    1.84 -        clc
    1.85 +    ; Direction
    1.86 +    iny
    1.87 +    lda ($74),y
    1.88 +    sta $80         ; temporarily store the direction
    1.89  
    1.90 -        ; x
    1.91 -        iny
    1.92 -        lda ($74),y
    1.93 -        tax
    1.94 -        lda screen_columns_low,x
    1.95 -        adc $72
    1.96 -        sta $72
    1.97 -        lda screen_columns_high,x
    1.98 -        adc $73
    1.99 -        sta $73
   1.100 -        clc
   1.101 +    ; y
   1.102 +    iny
   1.103 +    lda ($74),y
   1.104 +    tax
   1.105 +    lda screen_rows_low,x
   1.106 +    sta $72
   1.107 +    lda screen_rows_high,x
   1.108 +    sta $73
   1.109 +    clc
   1.110  
   1.111 -        ; dx
   1.112 -        iny
   1.113 -        lda ($74),y
   1.114 -        tax
   1.115 -        lda screen_subcolumns_low,x
   1.116 -        adc $72
   1.117 -        sta $72
   1.118 -        clc
   1.119 +    ; dy
   1.120 +    iny
   1.121 +    lda ($74),y
   1.122 +    sta $76
   1.123 +    tax
   1.124 +    lda screen_subrows_low,x
   1.125 +    adc $72
   1.126 +    sta $72
   1.127 +    lda screen_subrows_high,x
   1.128 +    adc $73
   1.129 +    sta $73
   1.130 +    clc
   1.131  
   1.132 -        lda $77
   1.133 -        cmp #1
   1.134 -        bne plot_characters_loop_not_player
   1.135 -        
   1.136 -        ; Plot 8x24 sprites (player)
   1.137 +    ; x
   1.138 +    iny
   1.139 +    lda ($74),y
   1.140 +    tax
   1.141 +    lda screen_columns_low,x
   1.142 +    adc $72
   1.143 +    sta $72
   1.144 +    lda screen_columns_high,x
   1.145 +    adc $73
   1.146 +    sta $73
   1.147 +    clc
   1.148  
   1.149 -        ldx $80
   1.150 -        lda player_direction_chars_low,x
   1.151 -        sta $70
   1.152 -        lda player_direction_chars_high,x
   1.153 -        sta $71
   1.154 +    ; dx
   1.155 +    iny
   1.156 +    lda ($74),y
   1.157 +    tax
   1.158 +    lda screen_subcolumns_low,x
   1.159 +    adc $72
   1.160 +    sta $72
   1.161 +    clc
   1.162  
   1.163 -        ; Use the dy value to determine which plotting routine to use.
   1.164 +    lda $77
   1.165 +    cmp #1
   1.166 +    bne plot_characters_loop_not_player
   1.167  
   1.168 -        ldy #0
   1.169 -        lda $76
   1.170 -        and #1
   1.171 -        bne plot_characters_plot_8x24_1
   1.172 +    ; Plot 8x24 sprites (player)
   1.173  
   1.174 -        lda #<plot8x24_y0
   1.175 -        sta ($84),y
   1.176 -        iny
   1.177 -        lda #>plot8x24_y0
   1.178 -        sta ($84),y
   1.179 -        jmp plot_characters_stored
   1.180 +    ldx $80
   1.181 +    lda player_direction_chars_low,x
   1.182 +    sta $70
   1.183 +    lda player_direction_chars_high,x
   1.184 +    sta $71
   1.185  
   1.186 -        plot_characters_plot_8x24_1:
   1.187 -        clc
   1.188 -        lda #<plot8x24_y1
   1.189 -        sta ($84),y
   1.190 -        iny
   1.191 -        lda #>plot8x24_y1
   1.192 -        sta ($84),y
   1.193 -        jmp plot_characters_stored
   1.194 +    ; Use the dy value to determine which plotting routine to use.
   1.195  
   1.196 +    ldy #0
   1.197 +    lda $76
   1.198 +    and #1
   1.199 +    bne plot_characters_plot_8x24_1
   1.200  
   1.201 -        plot_characters_loop_not_player:
   1.202 -        cmp #2
   1.203 -        bne plot_characters_loop_not_projectile
   1.204 +    lda #1
   1.205 +    sta ($78),y
   1.206 +    jmp plot_characters_stored
   1.207  
   1.208 -        ; Plot 8x8 sprites (projectiles)
   1.209 +    plot_characters_plot_8x24_1:
   1.210 +    clc
   1.211 +    lda #2
   1.212 +    sta ($78),y
   1.213 +    jmp plot_characters_stored
   1.214  
   1.215 -        ; Use the dy value to determine which plotting routine to use.
   1.216  
   1.217 -        ldy #0
   1.218 -        lda $76
   1.219 -        and #1
   1.220 -        bne plot_characters_plot_8x8_1
   1.221 +    plot_characters_loop_not_player:
   1.222 +    cmp #2
   1.223 +    bne plot_characters_loop_not_projectile
   1.224  
   1.225 -        lda #<plot8x8_y0
   1.226 -        sta ($84),y
   1.227 -        iny
   1.228 -        lda #>plot8x8_y0
   1.229 -        sta ($84),y
   1.230 -        jmp plot_characters_stored
   1.231 +    ; Plot 8x8 sprites (projectiles)
   1.232  
   1.233 -        plot_characters_plot_8x8_1:
   1.234 -        clc
   1.235 -        lda #<plot8x8_y1
   1.236 -        sta ($84),y
   1.237 -        iny
   1.238 -        lda #>plot8x8_y1
   1.239 -        sta ($84),y
   1.240 -        jmp plot_characters_stored
   1.241 +    ; Use the dy value to determine which plotting routine to use.
   1.242  
   1.243 +    ldy #0
   1.244 +    lda $76
   1.245 +    and #1
   1.246 +    bne plot_characters_plot_8x8_1
   1.247  
   1.248 -        plot_characters_loop_not_projectile:
   1.249 -        cmp #3
   1.250 -        bne plot_characters_loop_not_explosion
   1.251 +    lda #3
   1.252 +    sta ($78),y
   1.253 +    jmp plot_characters_stored
   1.254  
   1.255 -        ; Plot 16x16 sprites (emerging, explosions)
   1.256 +    plot_characters_plot_8x8_1:
   1.257 +    clc
   1.258 +    lda #4
   1.259 +    sta ($78),y
   1.260 +    jmp plot_characters_stored
   1.261  
   1.262 -        ; Select the sprites to use.
   1.263  
   1.264 -        lda $80         ; remove the least significant bit, used to delay
   1.265 -        lsr             ; the animation
   1.266 -        and #7          ; only keep the bits required to find the correct sprite
   1.267 -        tax
   1.268 -        lda emerge_explode_chars_low,x
   1.269 -        sta $70
   1.270 -        lda emerge_explode_chars_high,x
   1.271 -        sta $71
   1.272 +    plot_characters_loop_not_projectile:
   1.273 +    cmp #3
   1.274 +    bne plot_characters_loop_not_explosion
   1.275  
   1.276 -        jmp plot_characters_16x16
   1.277 +    ; Plot 16x16 sprites (emerging, explosions)
   1.278  
   1.279 -        plot_characters_loop_not_explosion:
   1.280 -        cmp #4
   1.281 -        bmi plot_characters_loop_not_enemy
   1.282 +    ; Select the sprites to use.
   1.283  
   1.284 -        ; Plot 16x16 sprites (enemies)
   1.285 +    lda $80         ; remove the least significant bit, used to delay
   1.286 +    lsr             ; the animation
   1.287 +    and #7          ; only keep the bits required to find the correct sprite
   1.288 +    tax
   1.289 +    lda emerge_explode_chars_low,x
   1.290 +    sta $70
   1.291 +    lda emerge_explode_chars_high,x
   1.292 +    sta $71
   1.293  
   1.294 -        ; Select the set of sprites to use.
   1.295 +    jmp plot_characters_16x16
   1.296  
   1.297 -        and #$38
   1.298 -        lsr
   1.299 -        lsr     ; bits 3,4,5 >> 2 -> bits 1,2,3
   1.300 -        clc
   1.301 -        sta $71 ; 0x00, 0x02, 0x04, 0x06, 0x08
   1.302 +    plot_characters_loop_not_explosion:
   1.303 +    cmp #4
   1.304 +    bmi plot_characters_loop_not_enemy
   1.305  
   1.306 -        ldx $80
   1.307 -        lda enemy_direction_chars_low,x
   1.308 -        sta $70
   1.309 -        lda enemy_direction_chars_high,x
   1.310 -        adc $71
   1.311 -        sta $71
   1.312 +    ; Plot 16x16 sprites (enemies)
   1.313  
   1.314 -        plot_characters_16x16:
   1.315 +    ; Select the set of sprites to use.
   1.316  
   1.317 -        ; Use the dy value to determine which plotting routine to use.
   1.318 +    and #$38
   1.319 +    lsr
   1.320 +    lsr     ; bits 3,4,5 >> 2 -> bits 1,2,3
   1.321 +    clc
   1.322 +    sta $71 ; 0x00, 0x02, 0x04, 0x06, 0x08
   1.323  
   1.324 -        ldy #0
   1.325 -        lda $76
   1.326 -        and #1
   1.327 -        bne plot_characters_plot_16x16_1
   1.328 +    ldx $80
   1.329 +    lda enemy_direction_chars_low,x
   1.330 +    sta $70
   1.331 +    lda enemy_direction_chars_high,x
   1.332 +    adc $71
   1.333 +    sta $71
   1.334  
   1.335 -        lda #<plot16x16_y0
   1.336 -        sta ($84),y
   1.337 -        iny
   1.338 -        lda #>plot16x16_y0
   1.339 -        sta ($84),y
   1.340 -        jmp plot_characters_stored
   1.341 +    plot_characters_16x16:
   1.342  
   1.343 -        plot_characters_plot_16x16_1:
   1.344 -        clc
   1.345 -        lda #<plot16x16_y1
   1.346 -        sta ($84),y
   1.347 -        iny
   1.348 -        lda #>plot16x16_y1
   1.349 -        sta ($84),y
   1.350 +    ; Use the dy value to determine which plotting routine to use.
   1.351  
   1.352 +    ldy #0
   1.353 +    lda $76
   1.354 +    and #1
   1.355 +    bne plot_characters_plot_16x16_1
   1.356  
   1.357 -        plot_characters_stored:
   1.358 +    lda #5
   1.359 +    sta ($78),y
   1.360 +    jmp plot_characters_stored
   1.361  
   1.362 -        iny
   1.363 -        lda $70
   1.364 -        sta ($84),y
   1.365 -        iny
   1.366 -        lda $71
   1.367 -        sta ($84),y
   1.368 -        iny
   1.369 -        lda $72
   1.370 -        sta ($84),y
   1.371 -        iny
   1.372 -        lda $73
   1.373 -        sta ($84),y
   1.374 +    plot_characters_plot_16x16_1:
   1.375 +    clc
   1.376 +    lda #6
   1.377 +    sta ($78),y
   1.378  
   1.379 -        clc
   1.380 -        lda $84
   1.381 -        adc #12
   1.382 -        sta $84
   1.383  
   1.384 -        plot_characters_loop_not_enemy:
   1.385 +    plot_characters_stored:
   1.386  
   1.387 -        plot_characters_next:
   1.388 -        clc
   1.389 +    iny
   1.390 +    lda $70
   1.391 +    sta ($78),y
   1.392 +    iny
   1.393 +    lda $71
   1.394 +    sta ($78),y
   1.395 +    iny
   1.396 +    lda $72
   1.397 +    sta ($78),y
   1.398 +    iny
   1.399 +    lda $73
   1.400 +    sta ($78),y
   1.401  
   1.402 -        ; Examine the next character.
   1.403 -        lda $74
   1.404 -        adc #6
   1.405 +    clc
   1.406 +    lda $78
   1.407 +    adc #12
   1.408 +    sta $78
   1.409  
   1.410 -        cmp #$24
   1.411 -        bpl plot_characters_exit
   1.412 -        sta $74
   1.413 -        jmp plot_characters_loop
   1.414 +    plot_characters_loop_not_enemy:
   1.415  
   1.416 -    plot_characters_exit:
   1.417 -    lda #255
   1.418 +    plot_characters_next:
   1.419 +
   1.420 +    lda #255    ; terminate this stream of entries in the plot buffer
   1.421      ldy #0
   1.422 -    sta ($84),y
   1.423 +    sta ($78),y
   1.424      clc
   1.425      rts
   1.426  
   1.427 @@ -1280,15 +1267,26 @@
   1.428      sta $84
   1.429      lda #$47
   1.430      sta $85
   1.431 +
   1.432 +    lda #255    ; terminate the plot list
   1.433 +    ldy #0
   1.434 +    sta ($84),y
   1.435      rts
   1.436  
   1.437  reset_unplot_buffer:
   1.438      lda #$00    ; reset the index into the plot buffer
   1.439 -    sta $84
   1.440 +    sta $82
   1.441      lda #$47
   1.442 -    sta $85
   1.443 +    sta $83
   1.444 +
   1.445 +    lda #255    ; terminate the unplot list
   1.446 +    ldy #0
   1.447 +    sta ($82),y
   1.448      rts
   1.449  
   1.450 +plot_buffer_types_low:  .byte <plot_buffer_loop_next, <plot8x24_y0, <plot8x24_y1, <plot8x8_y0, <plot8x8_y1, <plot16x16_y0, <plot16x16_y1
   1.451 +plot_buffer_types_high: .byte >plot_buffer_loop_next, >plot8x24_y0, >plot8x24_y1, >plot8x8_y0, >plot8x8_y1, >plot16x16_y0, >plot16x16_y1
   1.452 +
   1.453  plot_buffer:
   1.454  
   1.455      lda #$00
   1.456 @@ -1307,10 +1305,10 @@
   1.457          beq plot_buffer_loop_skip
   1.458  
   1.459          clc
   1.460 +        tax
   1.461 +        lda plot_buffer_types_low,x
   1.462          sta $86
   1.463 -        
   1.464 -        iny
   1.465 -        lda ($84),y
   1.466 +        lda plot_buffer_types_high,x
   1.467          sta $87
   1.468  
   1.469          iny
   1.470 @@ -1366,6 +1364,8 @@
   1.471      and #1
   1.472      eor #1      ; toggle animation flag
   1.473      sta $3301   ; left (directional bits are 0)
   1.474 +
   1.475 +    jsr plot_character
   1.476      rts
   1.477  
   1.478  animate_player_right:
   1.479 @@ -1377,6 +1377,8 @@
   1.480      eor #1      ; toggle animation flag
   1.481      ora #2      ; right
   1.482      sta $3301
   1.483 +
   1.484 +    jsr plot_character
   1.485      rts
   1.486  
   1.487  animate_player_up:
   1.488 @@ -1388,6 +1390,8 @@
   1.489      eor #1      ; toggle animation flag
   1.490      ora #4      ; up
   1.491      sta $3301
   1.492 +
   1.493 +    jsr plot_character
   1.494      rts
   1.495  
   1.496  animate_player_down:
   1.497 @@ -1399,10 +1403,17 @@
   1.498      eor #1      ; toggle animation flag
   1.499      ora #6      ; down
   1.500      sta $3301
   1.501 +
   1.502 +    jsr plot_character
   1.503      rts
   1.504  
   1.505  move_player:
   1.506  
   1.507 +    lda #$00    ; set up the address of the player character
   1.508 +    sta $74
   1.509 +    lda #$33
   1.510 +    sta $75
   1.511 +
   1.512      ; Handle the left key.
   1.513  
   1.514      ldx #158            ; (Z)
   1.515 @@ -1414,6 +1425,7 @@
   1.516      cmp #0
   1.517      beq move_player_left_check_x
   1.518  
   1.519 +    jsr unplot_character        ; unplot the player character
   1.520      dec $3305
   1.521      clc
   1.522      jmp animate_player_left ; optimise away the rts
   1.523 @@ -1453,6 +1465,9 @@
   1.524  
   1.525      move_player_allow_left:
   1.526      tya
   1.527 +    sta $81                 ; temporary
   1.528 +    jsr unplot_character    ; unplot the player character
   1.529 +    lda $81
   1.530      sta $3304               ; store the new room x offset
   1.531      lda #3
   1.532      sta $3305               ; dx = 3
   1.533 @@ -1467,14 +1482,17 @@
   1.534      clc
   1.535  
   1.536      ; Set the player's position on the right of the screen.
   1.537 +    
   1.538 +    ; No need to unplot.
   1.539  
   1.540      lda #9      ; x = 9
   1.541      sta $3304
   1.542      lda #2      ; dx = 2
   1.543      sta $3305
   1.544  
   1.545 +    jsr animate_player_left
   1.546      sec                     ; indicate to the calling routine that the player
   1.547 -    jmp animate_player_left ; has left the room (optimising away the rts)
   1.548 +    rts                     ; has left the room
   1.549  
   1.550      move_player_not_left_key:
   1.551  
   1.552 @@ -1491,6 +1509,7 @@
   1.553      cmp #3
   1.554      beq move_player_right_tile
   1.555  
   1.556 +    jsr unplot_character        ; unplot the player character
   1.557      inc $3305
   1.558      clc
   1.559      jmp animate_player_right    ; optimise away the rts
   1.560 @@ -1530,12 +1549,14 @@
   1.561  
   1.562      move_player_allow_right:
   1.563  
   1.564 +    jsr unplot_character        ; unplot the player character
   1.565      inc $3305                   ; update dx
   1.566      clc
   1.567      jmp animate_player_right    ; optimise away the rts
   1.568  
   1.569      move_player_right_tile:
   1.570  
   1.571 +    jsr unplot_character    ; unplot the player character
   1.572      inc $3304               ; store the new room x offset
   1.573      lda #0
   1.574      sta $3305               ; dx = 0
   1.575 @@ -1551,14 +1572,16 @@
   1.576  
   1.577      ; Set the player's position on the left of the screen.
   1.578  
   1.579 +    ; No need to unplot.
   1.580 +
   1.581      lda #0      ; x = 0
   1.582      sta $3304
   1.583      lda #0      ; dx = 0
   1.584      sta $3305
   1.585  
   1.586 +    jsr animate_player_right    
   1.587      sec                         ; indicate to the calling routine that the
   1.588 -    jmp animate_player_right    ; player has left the room (optimising away the
   1.589 -                                ; rts)
   1.590 +    rts                         ; player has left the room
   1.591  
   1.592      move_player_not_right_key:
   1.593  
   1.594 @@ -1573,6 +1596,7 @@
   1.595      cmp #0
   1.596      beq move_player_up_check_y
   1.597  
   1.598 +    jsr unplot_character        ; unplot the player character
   1.599      dec $3303
   1.600      clc
   1.601      jmp animate_player_up       ; optimise away the rts
   1.602 @@ -1610,6 +1634,9 @@
   1.603  
   1.604      move_player_allow_up:
   1.605      txa
   1.606 +    sta $81                 ; temporary
   1.607 +    jsr unplot_character    ; unplot the player character
   1.608 +    lda $81
   1.609      sta $3302               ; store the new room y offset
   1.610      lda #5
   1.611      sta $3303               ; dy = 5
   1.612 @@ -1625,13 +1652,16 @@
   1.613  
   1.614      ; Set the player's position on the bottom of the screen.
   1.615  
   1.616 +    ; No need to unplot.
   1.617 +
   1.618      lda #9      ; y = 9
   1.619      sta $3302
   1.620      lda #0      ; dy = 0
   1.621      sta $3303
   1.622  
   1.623 +    jsr animate_player_up
   1.624      sec                     ; indicate to the calling routine that the player
   1.625 -    jmp animate_player_up   ; has left the room (optimising away the rts)
   1.626 +    rts                     ; has left the room
   1.627  
   1.628      move_player_not_up_key:
   1.629  
   1.630 @@ -1648,6 +1678,7 @@
   1.631      cmp #5
   1.632      beq move_player_down_tile
   1.633  
   1.634 +    jsr unplot_character        ; unplot the player character
   1.635      inc $3303                   ; 0 < dy < 5
   1.636      clc
   1.637      jmp animate_player_down    ; optimise away the rts
   1.638 @@ -1685,12 +1716,14 @@
   1.639  
   1.640      move_player_allow_down:
   1.641  
   1.642 +    jsr unplot_character        ; unplot the player character
   1.643      inc $3303                   ; update dy
   1.644      clc
   1.645      jmp animate_player_down     ; optimise away the rts
   1.646  
   1.647      move_player_down_tile:
   1.648  
   1.649 +    jsr unplot_character        ; unplot the player character
   1.650      inc $3302                   ; store the new room y offset
   1.651      lda #0
   1.652      sta $3303                   ; dy = 0
   1.653 @@ -1706,14 +1739,16 @@
   1.654  
   1.655      ; Set the player's position on the top of the screen.
   1.656  
   1.657 +    ; No need to unplot.
   1.658 +
   1.659      lda #0      ; y = 0
   1.660      sta $3302
   1.661      lda #0      ; dy = 0
   1.662      sta $3303
   1.663  
   1.664 +    jsr animate_player_down
   1.665      sec                         ; indicate to the calling routine that the
   1.666 -    jmp animate_player_down     ; player has left the room (optimising away the
   1.667 -                                ; rts)
   1.668 +    rts                         ; player has left the room
   1.669  
   1.670      move_player_not_down_key:
   1.671      clc
   1.672 @@ -1740,11 +1775,115 @@
   1.673      clc
   1.674      rts
   1.675  
   1.676 +emerge_character:           ; $74,$75=character address
   1.677 +
   1.678 +    lda #63
   1.679 +    sta $33ff
   1.680 +
   1.681 +    jsr emerge_position     ; obtain a y position
   1.682 +    tax
   1.683 +    jsr emerge_position     ; obtain an x position
   1.684 +    sta $80                 ; temporary
   1.685 +    tay
   1.686 +
   1.687 +    lda room_row_offsets_low,x
   1.688 +    sta $70
   1.689 +    lda #$57
   1.690 +    sta $71
   1.691 +    lda ($70),y             ; load the tile
   1.692 +
   1.693 +    cmp #0
   1.694 +    bne emerge_character_exit
   1.695 +
   1.696 +    ; There is a space in the room, so add an emerging enemy.
   1.697 +
   1.698 +    ldy #0
   1.699 +    lda #3
   1.700 +    sta ($74),y
   1.701 +
   1.702 +    jsr emerge_type         ; obtain an enemy type
   1.703 +    iny
   1.704 +    sta ($74),y
   1.705 +
   1.706 +    txa
   1.707 +    iny
   1.708 +    sta ($74),y             ; store the y position
   1.709 +    lda #1
   1.710 +    iny
   1.711 +    sta ($74),y             ; store the dy offset
   1.712 +
   1.713 +    lda $80
   1.714 +    iny
   1.715 +    sta ($74),y             ; store the x position
   1.716 +    lda #0
   1.717 +    iny
   1.718 +    sta ($74),y             ; store the dx offset
   1.719 +
   1.720 +    jsr plot_character
   1.721 +
   1.722 +    emerge_character_exit:
   1.723 +    clc
   1.724 +    rts
   1.725 +
   1.726 +emerge_explode:             ; $74,$75=character address
   1.727 +
   1.728 +    jsr unplot_character
   1.729 +
   1.730 +    ldy #1
   1.731 +    lda ($74),y     ; direction/animation
   1.732 +    tax
   1.733 +    adc #1          ; update the counter
   1.734 +    and #7          ; mask off everything else
   1.735 +    sta $80         ; store the masked counter value
   1.736 +    bne move_characters_explosion_not_finished
   1.737 +
   1.738 +    txa
   1.739 +    and #8
   1.740 +    bne move_characters_remove_character
   1.741 +
   1.742 +    ; For emerges, convert into an enemy.
   1.743 +    txa
   1.744 +    and #$70        ; only keep bits 4,5,6
   1.745 +    lsr             ; bits 4,5,6 -> 3,4,5
   1.746 +    ora #4          ; make this an enemy
   1.747 +
   1.748 +    ldy #0
   1.749 +    sta ($74),y     ; update the type
   1.750 +    iny
   1.751 +    lda #0          ; prepare the direction and animation offset
   1.752 +    sta ($74),y
   1.753 +
   1.754 +    jsr plot_character
   1.755 +    jmp emerge_explode_exit
   1.756 +
   1.757 +    move_characters_remove_character:
   1.758 +
   1.759 +    ; For finished explosions, just write 0 into the character array.
   1.760 +    lda #0
   1.761 +    ldy #0
   1.762 +    sta ($74),y
   1.763 +    jmp emerge_explode_exit
   1.764 +
   1.765 +    move_characters_explosion_not_finished:
   1.766 +    txa
   1.767 +    and #$f8
   1.768 +    ora $80
   1.769 +
   1.770 +    ldy #1
   1.771 +    sta ($74),y
   1.772 +
   1.773 +    jsr plot_character
   1.774 +
   1.775 +    emerge_explode_exit:
   1.776 +    clc
   1.777 +    rts
   1.778 +
   1.779 +
   1.780  move_characters:
   1.781  
   1.782      dec $33ff
   1.783  
   1.784 -    lda #$0c
   1.785 +    lda #$0c            ; set the character address
   1.786      sta $74
   1.787      lda #$33
   1.788      sta $75
   1.789 @@ -1761,48 +1900,7 @@
   1.790          cmp #0
   1.791          bne move_characters_next
   1.792  
   1.793 -        lda #63
   1.794 -        sta $33ff
   1.795 -
   1.796 -        jsr emerge_position     ; obtain a y position
   1.797 -        tax
   1.798 -        jsr emerge_position     ; obtain an x position
   1.799 -        sta $80                 ; temporary
   1.800 -        tay
   1.801 -
   1.802 -        lda room_row_offsets_low,x
   1.803 -        sta $70
   1.804 -        lda #$57
   1.805 -        sta $71
   1.806 -        lda ($70),y             ; load the tile
   1.807 -
   1.808 -        cmp #0
   1.809 -        bne move_characters_next
   1.810 -
   1.811 -        ; There is a space in the room, so add an emerging enemy.
   1.812 -
   1.813 -        ldy #0
   1.814 -        lda #3
   1.815 -        sta ($74),y
   1.816 -
   1.817 -        jsr emerge_type         ; obtain an enemy type
   1.818 -        iny
   1.819 -        sta ($74),y
   1.820 -
   1.821 -        txa
   1.822 -        iny
   1.823 -        sta ($74),y             ; store the y position
   1.824 -        lda #1
   1.825 -        iny
   1.826 -        sta ($74),y             ; store the dy offset
   1.827 -
   1.828 -        lda $80
   1.829 -        iny
   1.830 -        sta ($74),y             ; store the x position
   1.831 -        lda #0
   1.832 -        iny
   1.833 -        sta ($74),y             ; store the dx offset
   1.834 -
   1.835 +        jsr emerge_character
   1.836          jmp move_characters_next
   1.837  
   1.838          move_characters_read_character:
   1.839 @@ -1811,45 +1909,7 @@
   1.840          cmp #3
   1.841          bne move_characters_next
   1.842  
   1.843 -        iny
   1.844 -        lda ($74),y     ; direction/animation
   1.845 -        tax
   1.846 -        adc #1
   1.847 -        and #7
   1.848 -        sta $80
   1.849 -        bne move_characters_explosion_not_finished
   1.850 -
   1.851 -        dey
   1.852 -
   1.853 -        txa
   1.854 -        and #8
   1.855 -        bne move_characters_remove_character
   1.856 -
   1.857 -        ; For emerges, convert into an enemy.
   1.858 -        txa
   1.859 -        and #$70        ; only keep bits 4,5,6
   1.860 -        lsr             ; bits 4,5,6 -> 3,4,5
   1.861 -        ora #4          ; make this an enemy
   1.862 -
   1.863 -        sta ($74),y     ; update the type
   1.864 -        iny
   1.865 -        lda #0          ; prepare the direction and animation offset
   1.866 -
   1.867 -        jmp move_characters_update_character
   1.868 -
   1.869 -        move_characters_remove_character:
   1.870 -        
   1.871 -        ; For explosions, just write 0 into the character array.
   1.872 -        lda #0
   1.873 -        jmp move_characters_update_character
   1.874 -
   1.875 -        move_characters_explosion_not_finished:
   1.876 -        txa
   1.877 -        and #$f8
   1.878 -        ora $80
   1.879 -
   1.880 -        move_characters_update_character:
   1.881 -        sta ($74),y
   1.882 +        jsr emerge_explode
   1.883  
   1.884          move_characters_next:
   1.885          clc
   1.886 @@ -1867,19 +1927,19 @@
   1.887      clc
   1.888      rts
   1.889  
   1.890 -clear_characters:
   1.891 +remove_characters:
   1.892  
   1.893      ; Clear the character table.
   1.894  
   1.895      ldx #6
   1.896 -    clear_character_loop:
   1.897 +    remove_characters_loop:
   1.898          lda #0
   1.899          sta $3300,x
   1.900          txa
   1.901          adc #6
   1.902          tax
   1.903          cpx #$24
   1.904 -        bmi clear_character_loop
   1.905 +        bmi remove_characters_loop
   1.906  
   1.907      rts
   1.908  
   1.909 @@ -2005,84 +2065,6 @@
   1.910      sta $3304
   1.911      lda #0      ; dx=0
   1.912      sta $3305
   1.913 -
   1.914 -;    lda #$3     ; explode/emerge
   1.915 -;    sta $330c
   1.916 -;    lda #0      ; emerge (first frame)
   1.917 -;    sta $330d
   1.918 -;    lda #3      ; y=3
   1.919 -;    sta $330e
   1.920 -;    lda #1      ; dy=1
   1.921 -;    sta $330f
   1.922 -;    lda #3      ; x=3
   1.923 -;    sta $3310
   1.924 -;    lda #0      ; dx=0
   1.925 -;    sta $3311
   1.926 -;
   1.927 -;    lda #$4     ; enemy (0)
   1.928 -;    sta $330c
   1.929 -;    lda #0      ; left up (first frame)
   1.930 -;    sta $330d
   1.931 -;    lda #3      ; y=3
   1.932 -;    sta $330e
   1.933 -;    lda #1      ; dy=1
   1.934 -;    sta $330f
   1.935 -;    lda #3      ; x=3
   1.936 -;    sta $3310
   1.937 -;    lda #0      ; dx=0
   1.938 -;    sta $3311
   1.939 -;
   1.940 -;    lda #$c     ; enemy (1)
   1.941 -;    sta $3312
   1.942 -;    lda #4      ; left down (first frame)
   1.943 -;    sta $3313
   1.944 -;    lda #3      ; y=3
   1.945 -;    sta $3314
   1.946 -;    lda #0      ; dy=0
   1.947 -;    sta $3315
   1.948 -;    lda #7      ; x=7
   1.949 -;    sta $3316
   1.950 -;    lda #0      ; dx=0
   1.951 -;    sta $3317
   1.952 -;
   1.953 -;    lda #$14    ; enemy (2)
   1.954 -;    sta $3318
   1.955 -;    lda #2      ; right up (first frame)
   1.956 -;    sta $3319
   1.957 -;    lda #7      ; y=7
   1.958 -;    sta $331a
   1.959 -;    lda #0      ; dy=0
   1.960 -;    sta $331b
   1.961 -;    lda #3      ; x=3
   1.962 -;    sta $331c
   1.963 -;    lda #0      ; dx=0
   1.964 -;    sta $331d
   1.965 -;
   1.966 -;    lda #$1c    ; enemy (3)
   1.967 -;    sta $331e
   1.968 -;    lda #2      ; right up (first frame)
   1.969 -;    sta $331f
   1.970 -;    lda #7      ; y=7
   1.971 -;    sta $3320
   1.972 -;    lda #0      ; dy=0
   1.973 -;    sta $3321
   1.974 -;    lda #3      ; x=3
   1.975 -;    sta $3322
   1.976 -;    lda #0      ; dx=0
   1.977 -;    sta $3323
   1.978 -;
   1.979 -;    lda #$24    ; enemy (4)
   1.980 -;    sta $3324
   1.981 -;    lda #6      ; right down (first frame)
   1.982 -;    sta $3325
   1.983 -;    lda #7      ; y=7
   1.984 -;    sta $3326
   1.985 -;    lda #0      ; dy=0
   1.986 -;    sta $3327
   1.987 -;    lda #7      ; x=7
   1.988 -;    sta $3328
   1.989 -;    lda #0      ; dx=0
   1.990 -;    sta $3329
   1.991      rts
   1.992  
   1.993  main:
   1.994 @@ -2106,34 +2088,29 @@
   1.995              lda $33f3
   1.996              sta $79
   1.997              jsr plot_room
   1.998 -            jsr clear_characters
   1.999 +            jsr remove_characters
  1.1000  
  1.1001              jsr reset_unplot_buffer
  1.1002 -            lda #255    ; terminate the unplot list by default because the
  1.1003 -            ldy #0      ; initial plotting of the buffer only plots characters
  1.1004 -            sta ($84),y
  1.1005              jsr reset_plot_buffer
  1.1006 -            jsr plot_characters
  1.1007 +
  1.1008 +            lda #$00        ; plot the player
  1.1009 +            sta $74
  1.1010 +            lda #$33
  1.1011 +            sta $75
  1.1012 +            jsr plot_character
  1.1013 +
  1.1014              jsr plot_buffer
  1.1015  
  1.1016              lda #63
  1.1017              sta $33ff
  1.1018  
  1.1019              room_loop:
  1.1020 -                lda #$00    ; reset the index into the plot buffer
  1.1021 -                sta $84
  1.1022 -                lda #$47
  1.1023 -                sta $85
  1.1024 -
  1.1025                  jsr reset_unplot_buffer
  1.1026 -                jsr plot_characters ; unplot
  1.1027 +                jsr reset_plot_buffer
  1.1028                  jsr move_characters
  1.1029                  jsr move_player
  1.1030                  bcs after_room_loop
  1.1031  
  1.1032 -                jsr reset_plot_buffer
  1.1033 -                jsr plot_characters ; plot
  1.1034 -
  1.1035                  lda #19
  1.1036                  jsr $fff4
  1.1037                  jsr plot_buffer