princess engine specs

Mapper:
selectable between these, with initialization and bankswitching adjusting:
UNROM/UOROM with PRG RAM circuit
SNROM/SUROM
TNROM
mapper 28

General:
12.4 fixed point in coordinates, so that the big byte goes up in increments of metatiles
horizontal scrolling only (up to 8px/frame)
sprite HUD instead of needing sprite zero or an interrupt
NMI has slots for updating metatiles in the nametable and a slot for updating 4 CHR tiles

Sound:
same engine as RHDE

Graphics:
list of PPU resources containing CHR compressed with pb53 and palette information
levels specify a list of PPU resources needed and they are uploaded when the level is loaded
levels choose four .5KB sprite graphics banks; sprites detect which one contains the needed tiles

CHR RAM $0xxx:
0x: |\ Common tiles, always loaded
1x: | \
2x: | /
3x: |/
4x: |\ Tiles like ground and platforms that vary by theme
5x: | \
6x: | /
7x: |/
8x: |\ Background tiles, VWF, more foreground tiles, etc
9x: | \
ax: |  \
bx: |   \
cx: |   /
dx: |  /
ex: | /
fx: |/

CHR RAM $1xxx:
0x: |\ Player tiles
1x: | \
2x: | /
3x: |/
4x: |\ Common
5x: | \
6x: | /
7x: |/
8x: |\ Slot 1
9x: |/
ax: |\ Slot 2
bx: |/
cx: |\ Slot 3
dx: |/
ex: |\ Slot 4
fx: |/

Levels:
256x16 map of 8-bit metatile IDs (4096 bytes)
level is split up into 16x16 screens that can be linked to each other vertically, and scroll stops can be inserted inbetween screen horizontally
two low-resolution bitmaps of the level for destroyed/collected metatiles
stored in ROM as a series of rectangles which is then processed to add edges and corners
backgrounds can be added after the level is decompressed
data can be stored per-column that specifies destinations for doors, contents of ? blocks, etc

Sprites:
only 128 maximum sprites, but sprites have 3 bits for variants when spawning them in the level
each sprite can opt-in for common sprite behaviors instead of explicitly calling routines in their handlers

Metatiles:
256 maximum metatiles
palettes can be assigned freely per-metatile
metatiles can be solid on top, solid on all sides or not solid
metatiles can specify a "type" out of 32 (water, ladder, etc)
metatile interaction only uses the type if possible