Level: Difference between revisions
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Piranhaplant (talk | contribs) Created page with "The number of regular levels is located at $9F:8000. This count includes level 0 and the credit level, but not any of the bonus levels. The level data pointers are located at $9F:8002. In a regular ROM, these are 16-bit pointers relative to bank $9F. In a Necrofy built ROM, these are 24-bit pointers padded to 4 bytes each. == Level data structure == === Header === {| class="wikitable" |- ! Offset !! Length !! Type !! Description |- | 0x00 || 4 || pointer24 ||..." |
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{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 4 ||
|-
| 0x04 || 4 ||
|-
| 0x08 || 4 ||
|-
| 0x0C || 4 ||
|-
| 0x10 || 4 ||
|-
| 0x14 || 4 ||
|-
| 0x18 || 4 ||
|-
| 0x1C || 2 || pointer16 || Pointer to the [[#Respawning monster data|respawning monster data]]
|-
| 0x1E || 2 || pointer16 || Pointer to the
|-
| 0x20 || 2 || pointer16 || Pointer to the [[#Item pickup data|item pickup data]]
|-
| 0x22 || 2 || uint16 || Level background width
Line 49:
| 0x34 || 2 || uint16 || Extra sounds ID
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| 0x36 || 2 || pointer16 || Pointer to the first [[#Level title page data|level title page data]]
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| 0x38 || 2 || pointer16 || Pointer to the second level title page data
|-
| 0x3A || 2 || optional pointer16 || Pointer to the [[#Bonus data|bonus data]]
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| 0x3C || 2 || pointer16 || Necrofy ROMs only. Pointer to the [[secret item]] bonus subroutine
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=== Boss monster data ===
{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 4 || pointer32 || [[Boss monster]] entity pointer
|-
| 0x04 || 4 || byte[4] || Properties
|}
This data is repeated for each boss monster. The list is terminated with four consecutive zero bytes.
The format of "Properties" depends on the type of boss monster. For [[UFO]], [[giant baby]], [[snakeoid]], [[giant spider]], and [[giant head]], it is:
{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 2 || int16 || X position
|-
| 0x02 || 2 || int16 || Y position
|}
For [[palette fade]] and [[tile animator]], it is:
{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 4 || pointer32 || Pointer to additional data
|}
For the format of the additional data, see the page for the given boss monster.
=== Respawning monster data ===
{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 1 || byte || Respawn delay
|-
| 0x01 || 2 || int16 || X position
|-
| 0x03 || 2 || int16 || Y position
|-
| 0x05 || 1 || byte || Respawn area size
|-
| 0x06 || 4 || pointer32 || [[Respawning monster]] entity pointer
|}
This data is repeated for each respawning monster. The list is terminated with two consecutive zero bytes.
=== Victim/one-shot monster data ===
{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 2 || int16 || X position
|-
| 0x02 || 2 || int16 || Y position
|-
| 0x04 || 2 || byte[2] || Extra data
|-
| 0x06 || 2 || uint16 bcd || Victim number
|-
| 0x08 || 4 || pointer32 || Entity pointer
|}
This data is repeated for each [[victim]] and [[one-shot monster]]. The list is terminated with two consecutive zero bytes.
Typically the victims are all listed first, in order from 1 to 10, then all of one-shot monsters, but this is not required. "Extra data" provides 2 bytes of arbitrary data that can be used by the entity for any purpose. In the original game, this is only used by the [[developer credit]]. Victim number is 0 for one-shot monsters.
=== Item pickup data ===
{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 2 || int16 || X position
|-
| 0x02 || 2 || int16 || Y position
|-
| 0x04 || 1 || byte || [[Item pickup]] ID
|}
This data is repeated for each item pickup. The list is terminated with two consecutive zero bytes.
=== Bonus data ===
{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 2 || uint16 || [[Bonus]] ID
|}
This data is repeated for each bonus. The list is terminated with two consecutive zero bytes.
=== Level title page data ===
{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 1 || byte || X position (in 8x8 tiles)
|-
| 0x01 || 1 || byte || Y position (in 8x8 tiles)
|-
| 0x02 || 1 || byte || Palette
|-
| 0x03 || 1 || byte || Page
|-
| 0x04 || X || byte[X] || Characters
|-
| X+4 || 1 || byte || Continue
|}
This is repeated until the continue value is zero. This value is set to 0xFF otherwise.
Page is set to 0x01 on the first title page, and 0x00 on the second title page. Palette is generally set to a multiple of two since level title palettes use two palette rows each.
=== Level background data ===
{| class="wikitable"
|-
! Offset !! Length !! [[Data types|Type]] !! Description
|-
| 0x00 || 2 || uint16 || Tile ID
|}
This is repeated for each 64x64 tile in the background, up to "width * height" of the level. Tiles are listed in row-major order.
== Necrofy enhancements ==
Necrofy changes the level pointers from 16-bit to 24-bit (padded to 4 bytes each). This allows an arbitrary amount of level data to be stored in the ROM. 16-bit pointers within the level data itself are made relative to the bank in which the level data is located.
Necrofy also adds two additional values to the level header: the secret item bonus subroutine and the the secret level number. These are replacements of the tables at [[$82:D1EE]] and [[$82:D17E]] respectively. This was done to support more than 55 levels in a ROM without having to expand these tables.
[[Category:Necrofy enhancements]]
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