; --------------------------------

; "Castle Master 2: The Crypt" by Incentive Software Ltd., 1990

; Disassembled by Santiago Ontañón in 2023

;

; Disclaimer: All the comments, label and constant names in this disassembly are my best interpretation of what the

;   code actually does. Fully annotating a disassembly like this one requires a large amount of work (this one took

;   me over a month, dedicating 2-3 hours every day). Therefore, it might contain errors or misunderstandings.

;   Please report if you find something that is incorrect. When I am very unsure of what some code does, I added

;   a note, but I might have missed many.

; 

; Notes and curiosities from the codebase:

; - There are two identical functions:

;   - La9de_hl_eq_h_times_64

;   - Lcb6d_hl_eq_h_times_64

; - There are two implemented versions of the same multiplication operation "(de,hl) = de * hl":

;   - La15e_de_times_hl_signed

;   - L8ab4_de_times_hl_signed

;   - Interestingly: the first is redundant, since the second is smaller and faster. However, it is the

;     first that is the most commonly used in the code!!!

; - There is self-modifying code

; - The 3d rendering engine is quite advanced for the year it was written:

;   - It contains all basic elements of later 3d engines

;   - It only considers 2 rotation angles (pitch and yaw), but it would be trivial to add a third, if it

;       wasn't because of the skybox (which would have to rotate if we added "roll").

;   - It contains skybox rendering code for outdoor areas (and even a "lightning" animation over the skybox!)

;   - It supports textured shapes

;   - Objects can be lines, triangles, quads or pentagons

;   - It implements many levels of culling (quick rendering cube, rendering frustum/pyramid)

;   - It implements polygon clipping for those that are only partly within the screen

;   - Different stages of rendering are "cached" in memory, so that we do not need to repeat them. For example,

;     when entering a menu, and going back to the game, all the 3d -> 2d projection does not need to be redone,

;     as positions have not changed. So, this is skipped. Similarly, when player does not move, rotation matrices

;     are not recalculated.

;   - All in all, even if the individual functions are not very optimized (things can be done significantly faster),

;     the overall structure is very nice (and some of the low-level functions are indeed quite optimized, such as

;     the one that renders textured horizontal lines).

; - All the computations are done with fixed point arithmetic. Even line and polygon drawing uses this fixed-point

;   calculations, rather than the more optimized Bresenham routines. This makes the code simpler, even if

;   slower than it could be.

; - Sorting of objects for rendering is quite curious, as it happens in coordinates *before* they are projected to

;   camera coordinates (just distance from player in each separate axis). I am sure this causes many issues in corner

;   cases. 

; - I think the code has a couple of bugs, I marked them with "BUG?" tags. Of course, I am not 100% sure, but I

;   think they are bugs.

; 

; Potential optimization of the code:

; - The code seems more functional than optimized. The lowest level drawing routines seem to be optimized well, but most

;   of the math routines are not. So, there is a lot of opportunity to make the engine faster.

; - I have added "OPTIMIZATION" tags in places where small things could be optimized. I only added those that

;   an automatic optimizer (in this case MDL: https://github.com/santiontanon/mdlz80optimizer) would not already

;   detect automatically. Basically, these are notes for an potential optimized version. Only small things are noted

;   large architectural changes (like moving from fixed-point arithmetic line-drawing to Bresenham-style, are not

;   annotated in the code).

;

; Related work:

; - See Phantasma, a reimplementation of the Freescape engine: https://github.com/TomHarte/Phantasma

; - See the information on the Freescape reimplementation in SCUMMVM: https://wiki.scummvm.org/index.php?title=Freescape

;

; --------------------------------

; BIOS Functions and constants:

; - Information obtained from "The Spectrum Machine Code Reference Guide" book.

; Saves a collection of bytes to tape

; Input:

; - ix: address to save

; - de: byte count

L04c6_BIOS_CASSETTE_SAVE_NO_BREAK_TEST: equ #04c6

; Saves a collection of bytes to tape

; Input:

; - ix: address where to load

; - de: byte count

L0562_BIOS_READ_FROM_TAPE_SKIP_TESTS: equ #0562

ULA_PORT: equ #fe  ; Writing to this port ignores the high 8bits.

                   ; The 8 bit value written is used as follows:

                   ; - bits 0, 1, 2: border color

                   ; - bit 3: MIC (tape output)

                   ; - bit 4: speaker output

; --------------------------------

; Video memory constants:

; - Information obtained from: http://www.breakintoprogram.co.uk/hardware/computers/zx-spectrum/screen-memory-layout

L4000_VIDEOMEM_PATTERNS: equ #4000

L5800_VIDEOMEM_ATTRIBUTES: equ #5800

SCREEN_WIDTH: equ 24

SCREEN_HEIGHT: equ 14

SCREEN_WIDTH_IN_PIXELS: equ SCREEN_WIDTH * 8  ; 192  ; mdl: SCREEN_WIDTH_IN_PIXELS = 192 (#00c0)

SCREEN_HEIGHT_IN_PIXELS: equ SCREEN_HEIGHT * 8  ; 112  ; mdl: SCREEN_HEIGHT_IN_PIXELS = 112 (#0070)

; --------------------------------

; Game constants:

CONTROL_MODE_KEYBOARD: equ 0

CONTROL_MODE_SINCLAIR_JOYSTICK: equ 1

CONTROL_MODE_KEMPSTON_JOYSTICK: equ 2

CONTROL_MODE_CURSOR_JOYSTICK: equ 3

MAX_COORDINATE: equ 127 * 64  ; mdl: MAX_COORDINATE = 8128 (#1fc0)

MAX_PRESSED_KEYS: equ 5

FILENAME_BUFFER_SIZE: equ 12

SPIRIT_METER_MAX: equ 64

MAX_STRENGTH: equ 24

GAME_OVER_REASON_OVERPOWERED: equ 1

GAME_OVER_REASON_YOU_COLLAPSE: equ 2

GAME_OVER_REASON_CRUSHED: equ 3

GAME_OVER_REASON_FATAL_FALL: equ 4

GAME_OVER_REASON_ESCAPED: equ 5

; Sound FX:

SFX_MENU_SELECT: equ 3  ; Also used for when player collides with an object

SFX_THROW_ROCK_OR_LAND: equ 5

SFX_FALLING: equ 6

SFX_GAME_START: equ 7

SFX_LIGHTNING: equ 8

SFX_GATE_CLOSE: equ 9

SFX_PICK_UP_ITEM: equ 10

SFX_OPEN_CHEST: equ 11

SFX_CLIMB_DROP: equ 12

SFX_OPEN_ESCAPED: equ 13

; There are other SFX defined, but only used in the game scripts:

; 1  ; sounds like if you die / get hit / error

; 2  ; sounds like game over

; 4  ; short high -> higher pitch beep

; 14  ; low-pitch repeated sound, not sure what

; 15  ; tiny short SFX

INPUT_FORWARD: equ 3

INPUT_BACKWARD: equ 4

INPUT_TURN_LEFT: equ 5

INPUT_TURN_RIGHT: equ 6

INPUT_LOOK_UP: equ 7

INPUT_LOOK_DOWN: equ 8

INPUT_CRAWL: equ 9

INPUT_WALK: equ 10

INPUT_RUN: equ 11

INPUT_FACE_FORWARD: equ 12

INPUT_U_TURN: equ 13

INPUT_MOVEMENT_POINTER_ON_OFF: equ 21

INPUT_THROW_ROCK: equ 22

INPUT_MOVE_POINTER_RIGHT: equ 23

INPUT_MOVE_POINTER_LEFT: equ 24

INPUT_MOVE_POINTER_DOWN: equ 25

INPUT_MOVE_POINTER_UP: equ 26

INPUT_ACTION: equ 27

INPUT_SWITCH_BETWEEN_MOVEMENT_AND_POINTER: equ 30

INPUT_INFO_MENU: equ 41

; How many degrees is a full circle:

FULL_ROTATION_DEGREES: equ 72

; Datablock structures:

AREA_HEADER_SIZE: equ 8

; Area struct:

AREA_FLAGS: equ 0

AREA_N_OBJECTS: equ 1

AREA_ID: equ 2

AREA_RULES_OFFSET: equ 3  ; 2 bytes

AREA_SCALE: equ 5

AREA_ATTRIBUTE: equ 6

AREA_NAME: equ 7

; Object struct:

OBJECT_TYPE_AND_FLAGS: equ 0

OBJECT_X: equ 1

OBJECT_Y: equ 2

OBJECT_Z: equ 3

OBJECT_SIZE_X: equ 4

OBJECT_SIZE_Y: equ 5

OBJECT_SIZE_Z: equ 6

OBJECT_ID: equ 7

OBJECT_SIZE: equ 8

OBJECT_ADDITIONAL_DATA: equ 9

; Object types:

OBJECT_TYPE_ENTRANCE: equ 0

OBJECT_TYPE_CUBE: equ 1

OBJECT_TYPE_SPIRIT: equ 2

OBJECT_TYPE_RECTANGLE: equ 3

; - Object types in between 4 and 9 are different solids, like pyramids,

; hourglasses, wedges, etc. that are synthesized on the fly.

; - I believe the object ID here just indicates their orientation (one of

; the 6 possible cardinal directions in 3d), and their additional data

; is used to determine their exact shape (via some checks in at the bedinning of

; function "L97bb_project_other_solids").

OBJECT_TYPE_LINE: equ 10

OBJECT_TYPE_TRIANGLE: equ 11

OBJECT_TYPE_QUAD: equ 12

OBJECT_TYPE_PENTAGON: equ 13

OBJECT_TYPE_HEXAGON: equ 14

; Rule types:

RULE_TYPE_ADD_TO_SCORE: equ 1

RULE_TYPE_TOGGLE_OBJECT_VISIBILITY: equ 3

RULE_TYPE_MAKE_OBJECT_VISIBILE: equ 4

RULE_TYPE_MAKE_OBJECT_INVISIBILE: equ 5

RULE_TYPE_TOGGLE_OBJECT_FROM_AREA_VISIBILITY: equ 6

RULE_TYPE_MAKE_OBJECT_FROM_AREA_VISIBILE: equ 7

RULE_TYPE_MAKE_OBJECT_FROM_AREA_INVISIBILE: equ 8

RULE_TYPE_INCREMENT_VARIABLE: equ 9

RULE_TYPE_DECREMENT_VARIABLE: equ 10

RULE_TYPE_END_RULE_IF_VARIABLE_DIFFERENT: equ 11

RULE_TYPE_SET_BOOLEAN_TRUE: equ 12

RULE_TYPE_SET_BOOLEAN_FALSE: equ 13

RULE_TYPE_END_RULE_IF_BOOLEAN_DIFFERENT: equ 14

RULE_TYPE_PLAY_SFX: equ 15

RULE_TYPE_DESTROY_OBJECT: equ 16

RULE_TYPE_DESTROY_OBJECT_FROM_AREA: equ 17

RULE_TYPE_TELEPORT: equ 18

RULE_TYPE_STRENGTH_UPDATE: equ 19

RULE_TYPE_SET_VARIABLE: equ 20

RULE_TYPE_REDRAW: equ 26

RULE_TYPE_PAUSE: equ 27

RULE_TYPE_REQUEST_SFX_NEXT_FRAME: equ 28

RULE_TYPE_TOGGLE_BOOLEAN: equ 29

RULE_TYPE_END_RULE_IF_OBJECT_INVISIBLE: equ 30

RULE_TYPE_END_RULE_IF_OBJECT_VISIBLE: equ 31

RULE_TYPE_END_RULE_IF_OBJECT_FROM_AREA_INVISIBLE: equ 32

RULE_TYPE_END_RULE_IF_OBJECT_FROM_AREA_VISIBLE: equ 33

RULE_TYPE_SHOW_MESSAGE: equ 34

RULE_TYPE_RENDER_EFFECT: equ 35

RULE_TYPE_FLIP_SKIP_RULE: equ 44

RULE_TYPE_UNSET_SKIP_RULE: equ 45

RULE_TYPE_END_RULE_IF_VARIABLE_LARGER: equ 46

RULE_TYPE_END_RULE_IF_VARIABLE_LOWER: equ 47

RULE_TYPE_SELECT_OBJECT: equ 48

; --------------------------------

; RAM Variables before the game data:

L5cbc_render_buffer: equ #5cbc  ; 2712 bytes ((SCREEN_HEIGHT * 8 + 1) * SCREEN_WIDTH)

; Variables that overlap with the render buffer, these are used when projecting

; the 3d vertices into 2d, so, they are discarded and not needed when using the 

; render buffer.

L5e4c_pitch_rotation_matrix: equ #5e4c

L5e55_rotation_matrix: equ #5e55

L5e5e_at_least_one_vertex_outside_rendering_frustum: equ #5e5e

L5e5f_add_to_projected_objects_flag: equ #5e5f  ; If this is 1, the current object being projected from 3d to 2d, will be added to the list of objects to draw.

L5e60_projection_pre_work_type: equ #5e60  ; Indicates whether we need to do additional computations before projecting each face.

L5e61_object_currently_being_processed_type: equ #5e61

L5e62_player_collision_with_object_flags: equ #5e62

L5e63_3d_vertex_coordinates_relative_to_player: equ #5e63

L5e75_48_bit_accumulator: equ #5e75

L5e7b_48bitmul_tmp1: equ #5e7b

L5e7d_48bitmul_tmp2: equ #5e7d

L5e9f_3d_vertex_coordinates_after_rotation_matrix: equ #5e9f  ; 16 bit representation.

L5edc_vertex_rendering_frustum_checks: equ #5edc  ; 5 bits per vertex, indicating if they passed or not each of the 5 culling tests for the rendering frustum.

L5ee8_already_projected_vertex_coordinates: equ #5ee8

L5f24_shape_edges_ptr: equ #5f24  ; Pointer to the array with the order of edges to use for projection.

L5f26_alternative_shape_edges_ptr: equ #5f26  ; Alternative edges pointer (for when object is seen from below, this is only needed for flat shapes).

L5f28_cull_face_when_no_projected_vertices: equ #5f28

L5f29_extra_solid_dimensions: equ #5f29  ; stores 4 additional dimensions used temporarily to synthesize solids like pyramids, hourglasses, etc. on the fly. (4 16bit numbers).

L5f31_sorting_comparison_result: equ #5f31  ; result of comparing the coordinates of two objects to see if they should be flipped for rendering.

L5f32_sorting_any_change: equ #5f32

L5f33_sorting_boundingbox_ptr1: equ #5f33

L5f35_sorting_boundingbox_ptr2: equ #5f35

L5f37_sorting_bbox1_c1: equ #5f37  ; These four variables hold the values of the min/max coordinates for the current axis of the two bounding boxes being compared for sorting.

L5f39_sorting_bbox2_c1: equ #5f39

L5f3b_sorting_bbox1_c2: equ #5f3b

L5f3d_sorting_bbox2_c2: equ #5f3d

L5f3f_n_objects_covering_the_whole_screen_left: equ #5f3f

L5f40_16_bit_tmp_matrix: equ #5f40  ; Used internally to save the results of matrix multiplication.

L5f52_16_bit_tmp_matrix_ptr: equ #5f52  ; Used to keep track of the elements in the matrix above.

L5fa2_3d_object_bounding_boxes_relative_to_player: equ #5fa2  ; in 16 bit precision: x1, x2, y1, y2, z1, z2

L6664_row_pointers: equ #6664  ; Pointers to each row of pixels in the buffer.

L6754_end_of_render_buffer: equ #6754

; This contains the current room objects, already projected to 2d coordinates:

; - Each entry has 2 pointers:

;   - One pointer to the "L67f4_projected_vertex_data" (with the projected vertices)

;   - One pointer to the "L5fa2_3d_object_bounding_boxes_relative_to_player"

L6754_current_room_object_projected_data: equ #6754

; For each projected object, the data is organized as follows:

; - 1 byte: object ID

; - 1 byte: number of primitives/faces:

;   - If the most significant bit is set, it means this object covers the whole screen.

; - face data:

;   - 1 byte (texture / # vertices),

;   - and then 2 bytes per vertex screen x, screen y (screen y is reversed, 0 = bottom).

L67f4_projected_vertex_data: equ #67f4

    org #6a00

; --------------------------------

; Program start

L6a00_start:

c3 2f 6a 

    jp L6a2f_game_init

; --------------------------------

; Set up the interrupt routine to "Lbe66_interrupt_routine".

L6a03_setup_interrupts:

f3 

    di

e5 

    push hl

d5 

    push de

c5 

    push bc

f5 

    push af

af 

        xor a

32 7c 74 

        ld (L747c_within_interrupt_flag), a

21 00 fe 

        ld hl, Lfe00_interrupt_vector_table

7c 

        ld a, h

ed 47 

        ld i, a

54 

        ld d, h

5d 

        ld e, l

1c 

        inc e

36 fd 

        ld (hl), #fd

01 00 01 

        ld bc, 256

ed b0 

        ldir

3e c3 

        ld a, #c3  ; jp opcode

21 66 be 

        ld hl, Lbe66_interrupt_routine

32 fd fd 

        ld (Lfdfd_interrupt_jp), a

22 fe fd 

        ld (Lfdfe_interrupt_pointer), hl

ed 5e 

        im 2

f1 

    pop af

c1 

    pop bc

d1 

    pop de

e1 

    pop hl

fb 

    ei

c9 

    ret

; --------------------------------

; Initializes the game the very first time.

L6a2f_game_init:

31 f8 ff 

    ld sp, #fff8  ; initialize the stack

f3 

    di

af 

    xor a  ; Set control mode to keyboard

32 83 76 

    ld (L7683_control_mode), a

fd 22 7d 74 

    ld (L747d), iy  ; Note: This instruction is very strange, as at this point "iy" is undefined.

cd c9 a4 

    call La4c9_init_game_state

cd 03 6a 

    call L6a03_setup_interrupts

c3 7e 6a 

    jp L6a7e_main_application_loop

; --------------------------------

; Unused?

    db #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00

    db #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00

    db #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00

    db #00, #00, #00, #00, #00, #00, #00, #00, #00, #00

; --------------------------------

; Main application loop: calls title screen, starts game, restarts title screen, etc.

; I think this is a game loop

L6a7e_main_application_loop:

21 fd ff 

    ld hl, #fffd

22 6c 74 

    ld (L746c_game_flags), hl

3e 02 

    ld a, 2

32 77 74 

    ld (L7477_render_buffer_effect), a  ; Request gate opening effect

cd 2e c7 

    call Lc72e_title_screen_loop

cd aa 83 

    call L83aa_redraw_whole_screen

af 

    xor a

32 79 74 

    ld (L7479_current_game_state), a

c3 99 6a 

    jp L6a99

L6a96_game_loop:

cd aa 83 

    call L83aa_redraw_whole_screen

L6a99:

cd ec 9d 

    call L9dec_game_tick

cd 05 a0 

    call La005_check_rules

2a 6c 74 

    ld hl, (L746c_game_flags)

cb 4d 

    bit 1, l  ; check the "game over" flag

ca 96 6a 

    jp z, L6a96_game_loop

cd c9 a4 

    call La4c9_init_game_state

c3 7e 6a 

    jp L6a7e_main_application_loop

; --------------------------------

; Game state variables:

; Saving game saves data starting from here:

L6aad_savegame_data_start:

L6aad_player_current_x:

    dw #00a0

L6aaf_player_current_y:

    dw #09e0

L6ab1_player_current_z:

    dw #1b60

L6ab3_current_speed_in_this_room:

    dw #11d0

L6ab5_current_speed:  ; This is a value form the Ld0c8_speed_when_crawling array, depending on L6b0b_selected_movement_mode.

    db #f0

L6ab6_player_pitch_angle:  ; from 18 to -18 (54)

    db #00

L6ab7_player_yaw_angle:  ; from 0 - 71

    db #1a

L6ab8_player_crawling:  ; 2 when standing up, 1 when crawling.

    db 2

L6ab9_player_height:  ; player height * room scale

    db #26

L6aba_max_falling_height_without_damage:  ; 2 * room scale

    db #26

L6abb_max_climbable_height:

    db #13

L6abc_current_room_scale:

    db #13

L6abd_cull_by_rendering_volume_flag:

    db #00

L6abe_use_eye_player_coordinate:  ; When this is 0, we will use "feet" coordinates for collision checks, when 1, we will use "eye" coordinates.

    db #00

L6abf_current_area_name_string:

    db 0, "   THE CRYPT   "

L6acf_current_area_id:

    db #02

L6ad0_current_area_n_objects:

    db #18

L6ad1_current_area_objects:

    dw #d6ca

    db #00, #00  ; unused?

L6ad5_current_area_rules:

    dw #d8ce

L6ad7_current_border_color:

    db #14, #00

L6ad9_current_attribute_color:

    db #16, #0b

L6adb_desired_border_color:

    db #14, #00

L6add_desired_attribute_color:

    db #47, #0b

L6adf_game_boolean_variables:

    ; One bit corresponding to each variable. 

    ; The first few correspond to collected keys.

    db #00, #00, #00, #00

L6ae3_visited_areas:  ; one bit per area (keeps track of which areas the player has already visited).

    db #00, #00, #00, #00, #00, #00, #00, #00

L6aeb_score:  ; 3 bytes

    db #00, #00, #00

L6aee_game_variables:  ; These can be accessed by the game scripts.

    db #00, #00, #00, #00, #00, #00, #00, #00

    db #00, #00, #00, #00, #00, #00, #00, #00

    db #00, #00, #00, #00, #00, #00, #00, #00

    db #00, #00, #00

L6b09_number_of_spirits_destroyed:

    db 0

L6b0a_current_strength:

    db 16

L6b0b_selected_movement_mode:  ; 0: crawl, 1: walk, 2: run

    db 2

L6b0c_num_collected_keys:

    db 0

L6b0d_new_key_taken:

    db 0  ; Contains the ID of a key just picked up, before being added to the inventory.

L6b0e_lightning_time_seconds_countdown:

    db #14

L6b0f_collected_keys:

    ; Different from "L6adf_game_boolean_variables", this array has the keys in

    ; the order the player picked them, directly as a list of IDs.

    db #00, #00, #00, #00, #00, #00, #00, #00, #00, #00

L6b19_current_area_flags:

    db #00

L6b1a_pointer_x:

    db 0

L6b1b_pointer_y:

    db 0

L6b1c_movement_or_pointer:

    db 0  ; 0: movement, otherwise: pointer

L6b1d_time_interrupts:

    db #01

L6b1e_time_unit5:  ; Changes once per second, counting from 10 to 1

    db #00

L6b1f_current_spirit_meter:  ; Increments in 1 each time Lbe65_time_unit3 wraps around (each 120 seconds).

    db #20

L6b20_display_movement_pointer_flag:  ; Whether to draw a small cross in the center of the screen when in movement mode.

    db #ff

L6b21_time_unit6_previous:  ; to keep track of when L6b22_time_unit6 changes.

    db #00

L6b22_time_unit6:  ; Increments by one each time L6b1e_time_unit5 cycles.

    db #00

L6b23_set_bit7_byte_3_flag_at_start:  ; If this is != 0, when starting a game, bit 7 of the 3rd byte of the boolean variables is set to 1 (not sure of the effect of this).

    db #00

L6b24_savegame_data_end:

    db #00, #00, #07, #00  ; Unused?

L6b28_player_radius:

    dw #000a

L6b2a_spirit_in_room:  ; 0: no spirit, 1: spirit

    db 0

L6b2b_desired_eye_compass_frame:

    db #00

; If an object definition has more bytes than this, it means there are rule effects associated with it:

L6b2c_expected_object_size_by_type:

    db #09, #0c, #0e, #0a, #10, #10, #10, #10, #10, #10, #10, #13, #16, #19, #1c, #00

L6b3c_rule_size_by_type:  ; Assuming there are only 49 rule types (maximum type if 48).

    db #01, #04, #02, #02, #02, #02, #03, #03, #03, #02, #02, #03, #02, #02, #03, #02

    db #02, #03, #03, #02, #03, #00, #00, #00, #00, #02, #01, #02, #02, #02, #02, #02

    db #03, #03, #02, #02, #00, #00, #00, #00, #00, #02, #01, #00, #01, #01, #03, #03

    db #02

; Edges for cubes:

L6b6d_cube_edges:

    db #0c

    db #00, #01, #01, #02, #02, #03, #03, #00

    db #04, #05, #05, #06, #06, #07, #07, #04

    db #00, #04, #01, #05, #02, #06, #03, #07

; byte 0: number of faces

; Each face then:

; - byte: texture

; - byte: number of vertices/edges

; - bytes 2+: edge indexes from where to get the vertices

; - the msb in the index indicates if we need to flip the vertexes in the edge in question.

L6b86_face_definition_for_cubes:

    db #06

    db #00, #04, #83, #0b, #07, #88

    db #00, #04, #05, #8a, #81, #09

    db #00, #04, #08, #04, #89, #80

    db #00, #04, #0a, #06, #8b, #82

    db #00, #04, #00, #01, #02, #03

    db #00, #04, #84, #87, #86, #85

; Edges for pyramids:

L6bab_pyramid_edges:

    db #08

    db #00, #01, #01, #02, #02, #03, #03, #00

    db #00, #04, #01, #04, #02, #04, #03, #04

L6bbc_face_definition_for_pyramids:

    db #05

    db #00, #03, #83, #07, #84

    db #00, #03, #82, #06, #87

    db #00, #03, #81, #05, #86

    db #00, #03, #80, #04, #85

    db #00, #04, #00, #01, #02, #03

L6bd7_wedge_edges:

    db #09

    db #00, #01, #01, #02, #02, #03

    db #03, #00, #00, #04, #01, #04

    db #02, #05, #03, #05, #04, #05

L6bea_face_definition_for_wedges:

    db #05

    db #00, #04, #83, #07, #88, #84

    db #00, #03, #82, #06, #87

    db #00, #04, #81, #05, #08, #86

    db #00, #03, #80, #04, #85

    db #00, #04, #00, #01, #02, #03

L6c07_triangle_houglass_edges:

    db #09

    db #00, #01, #01, #02, #02, #03

    db #03, #00, #00, #04, #01, #05

    db #02, #05, #03, #04, #04, #05

L6c1a_face_definition_for_triangle_hourglasses:

    db #05

    db #00, #03, #83, #07, #84

    db #00, #04, #82, #06, #88, #87

    db #00, #03, #81, #05, #86

    db #00, #04, #80, #04, #08, #85

    db #00, #04, #00, #01, #02, #03

L6c37_hourglass_edges:

    db #0c

    db #00, #01, #01, #02, #02, #03, #03, #00

    db #04, #07, #07, #05, #05, #06, #06, #04

    db #00, #04, #01, #06, #02, #05, #03, #07

L6c50_face_definition_for_hourglasses:

    db #06

    db #00, #04, #83, #0b, #84, #88

    db #00, #04, #82, #0a, #85, #8b

    db #00, #04, #81, #09, #86, #8a

    db #00, #04, #80, #08, #87, #89

    db #00, #04, #00, #01, #02, #03

    db #00, #04, #04, #05, #06, #07

; Edge definition for different shapes (lines, triangles, rectangles and pentagons),

; - the first byte is the # of edges

; - after that, each pair of bytes defines an edge.

L6c75_line_edges:

    db #02, #00, #01, #01, #00

; Edges for triangles:

L6c7a_triangle_edges_top:

    db #03, #00, #01, #01, #02, #02, #00

L6c81_triangle_edges_bottom:

    db #03, #00, #02, #02, #01, #01, #00

; Edges for rectangles:

L6c88_rectangle_edges_top:

    db #04, #00, #01, #01, #02, #02, #03, #03, #00

L6c91_rectangle_edges_bottom:

    db #04, #00, #03, #03, #02, #02, #01, #01, #00

; Edges for pentagons:

L6c9a_pentagon_edges_top:

    db #05, #00, #01, #01, #02, #02, #03, #03, #04, #04, #00

L6ca5_pentagon_edges_bottom:

    db #05, #00, #04, #04, #03, #03, #02, #02, #01, #01, #00

L6cb0_face_definition_for_flat_objects:

    db #01

    db #00, #06, #00, #01, #02, #03, #04, #05

; --------------------------------

L6cb9_game_text:

    db 0, " PRESS ANY KEY "

L6cc9_text_overpowered:

    db 0, "  OVERPOWERED  "

    db 1, " YOU COLLAPSE  "

    db 0, "    CRUSHED    "

    db 1, "  FATAL FALL   "

    db 0, "   ESCAPE !!   "

    db 0, "   THE CRYPT   "

L6d29_text_out_of_reach:

    db 1, " OUT OF REACH  "

L6d39_text_no_effect:

    db 0, "   NO EFFECT   "

    db 1, "   NO ENTRY    "

    db 0, "  WAY BLOCKED  "

L6d69_text_not_enough_room:

    db 0, "NOT ENOUGH ROOM"

L6d79_text_too_weak:

    db 1, "   TOO WEAK    "

L6d89_text_crawl:

    db 1, "CRAWL SELECTED "

L6d99_text_walk:

    db 0, " WALK SELECTED "

L6da9_text_run:

    db 1, " RUN SELECTED  "

    db 1, " AAAAAARRRGH!  "

    db 0, " KEY COLLECTED "

    db 0, " NO KEYS FOUND "

    db 1, "NEED RIGHT KEY "

    db 0, "  IT IS EMPTY  "

    db 1, "  DOOR TO...   "

    db 0, "IN CASE OF FIRE"

    db 0, "CHOMP CHOMP AHH"

    db 1, "   OOOOFFF!    "

    db 1, "TREASURE FOUND "

    db 1, "THE DOOR OPENS "

    db 0, "THE DOOR CLOSES"

    db 0, "   PADLOCKED   "

    db 0, "IT'S VERY HEAVY"

    db 0, "    SMASH !    "

    db 0, "SHOWS LEVEL NO."

    db 0, "   PADLOCKED   "

    db 0, "HMM, NEED A BIT"

    db 1, "MORE SPRING IN "

    db 1, "YOUR STEP HERE "

    db 0, " THE LID OPENS "

    db 1, "THE LID CLOSES "

    db 1, "GLUG GLUG GLUG "

    db 0, "RETRY THE CHEST"

    db 1, "REVITALISATION "

L6f49_area_names:

    db 1, "  WILDERNESS   "

    db 0, "   THE CRYPT   "

    db 1, "CRYPT CORRIDOR "

    db 0, " THE MOUSETRAP "

    db 0, " LAST TREASURE "

    db 1, "   TANTALUS    "

    db 0, "    BELENUS    "

    db 0, "    POTHOLE    "

    db 0, "   THE STEPS   "

    db 1, " LOOKOUT POST  "

    db 1, "   KERBEROS    "

    db 0, "   CRYPT KEY   "

    db 0, "   GATEHOUSE   "

    db 0, "  BELENUS KEY  "

    db 1, "SPIRITS' ABODE "

    db 1, "    RAVINE     "

    db 1, "  LIFT SHAFT   "

    db 0, "  LEVEL 2 KEY  "

    db 0, "LIFT ENTRANCE 6"

    db 1, "    TUNNEL     "

    db 0, "  LEVEL 3 KEY  "

    db 1, "   THE TUBE    "

    db 0, "LIFT ENTRANCE 5"

    db 0, "     EPONA     "

    db 0, "  LEVEL 4 KEY  "

    db 0, "LIFT ENTRANCE 4"

    db 0, "  NANTOSUELTA  "

    db 0, "  STALACTITES  "

    db 0, "    NO ROOM    "

    db 0, "  THE TRAPEZE  "

    db 1, "TREASURE CHEST "

    db 0, "LIFT ENTRANCE 3"

    db 1, "  THE SWITCH   "

    db 1, "  THE PILLAR   "

    db 1, " GROUND FLOOR  "

    db 1, " THE RAT TRAP  "

    db 0, "    YIN KEY    "

    db 1, "     LIFT      "

    db 0, "  TRAPEZE KEY  "

    db 1, "   YANG KEY    "

; --------------------------------

L71c9_text_status_array:

    db 0, "FEEBLE    "

    db 0, "WEAK      "

    db 0, "HEALTHY   "

    db 0, "STRONG    "

    db 0, "MIGHTY    "

    db 0, "HERCULEAN "

; --------------------------------

; Used to store the filename the user inputs in the load/save menu.

L720b_text_input_buffer:

    db 0, "             "

    db 19  ; Unused?

L721a_text_asterisks:

    db 0, "*********************"

    db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

    db #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #00, #30, #72, #30, #72, #30

    db #72, #30, #72, #30, #72, #30, #72, #30, #72, #30, #72, #30, #72, #30, #72

; --------------------------------

L725c_videomem_row_pointers:

    dw #4084, #4184, #4284, #4384, #4484, #4584, #4684, #4784

    dw #40a4, #41a4, #42a4, #43a4, #44a4, #45a4, #46a4, #47a4

    dw #40c4, #41c4, #42c4, #43c4, #44c4, #45c4, #46c4, #47c4

    dw #40e4, #41e4, #42e4, #43e4, #44e4, #45e4, #46e4, #47e4

    dw #4804, #4904, #4a04, #4b04, #4c04, #4d04, #4e04, #4f04

    dw #4824, #4924, #4a24, #4b24, #4c24, #4d24, #4e24, #4f24

    dw #4844, #4944, #4a44, #4b44, #4c44, #4d44, #4e44, #4f44

    dw #4864, #4964, #4a64, #4b64, #4c64, #4d64, #4e64, #4f64

    dw #4884, #4984, #4a84, #4b84, #4c84, #4d84, #4e84, #4f84

    dw #48a4, #49a4, #4aa4, #4ba4, #4ca4, #4da4, #4ea4, #4fa4

    dw #48c4, #49c4, #4ac4, #4bc4, #4cc4, #4dc4, #4ec4, #4fc4

    dw #48e4, #49e4, #4ae4, #4be4, #4ce4, #4de4, #4ee4, #4fe4

    dw #5004, #5104, #5204, #5304, #5404, #5504, #5604, #5704

    dw #5024, #5124, #5224, #5324, #5424, #5524, #5624, #5724

; --------------------------------

; Unused?

L733c:

    db #30, #72, #30, #72, #30, #72, #30, #72, #30, #72

    db #30, #72, #30, #72, #30, #72, #30, #72, #30, #72