3D rendering

3D Rendering engine

The Nintendo DS dispose of hardware that can perform 3D rendering in addition to its dedicated 2D system. EoS mostly use the 2D system, but occasionally make use of the 3D engine for some effects. Those are:

• The dialogue box border and background
• Rendering of the quick status at the top of the bottom screen during a dungeon
• The various weather effect
• Boss transition wipe
• A few other effect during cutscenes

The 3D engine is capable of rendering in 2D, simply by rendering rectangle in front of the virtual camera, which is what EoS always does. The way this game work is by first buffering the elements to render to a buffer and then a function will submit those to render (probably during VBlank), which will then take effect on the next frame.

The DS 3D hardware can only render on the main screen, which in EoS is the bottom screen. Some game (but not EoS) render on both screen by switching the main screen every frame, dividing by two the frame rate from 60 to 30 FPS.

Memory management

The bank D is dedicated to storing the textures used for the 3D render, and bank F is used to store the palettes. Bank D is 128KiB large, and bank F is 16KiB large. The game seems to mostly allocate texture on a multiple of 1KiB, and palette on a multiple of 0x100 bytes, thought it is possible to perform allocation not aligned on those arbitrary values (but it still (maybe, untested) need to be 4-bytes aligned).

The game store its 3D data in WTE files. It contain the texture and the palette, but not where the file will be stored in the RAM, which is specified in the game’s code. Here is table of the (known) allocation the game make. It is probably exhaustive.

ProcessWTE is the function used to load them (function address is for EU ROM, but palette and texture allocation have no reason to be different).

file location	dungeon or overworld	description	call to ProcessWTE	texture offset	texture size (bytes)	palette offset	note
1025 in dungeon pack	dungeon		overlay_29::022eda20	0x400	0xc00	0x1d00
1007 to 1011 in dungeon pack	dungeon	Numbers and "Miss" text. Used to display damage taken and misses.	overlay_29::02336200	0x0	0x400	0x0	which one is loaded depend on language
1031 or 1003 in dungeon pack	dungeon	1031: Mist/Steam texture. Visual-only effect paired with some tilesets. 1003: Poison mist texture used only during Sky Peak boss fight.	overlay_29::023394e4 or overlay_29::023395f8	0xB000	0x2000	0x1400	unknown how which one is chosen
1005 in dungeon pack	dungeon	Sandstorm texture used during its weather condition.	overlay_29::023394e4	0xD000	0x2000	0x1500
1001 in dungeon pack	dungeon	Fog texture used during its weather condition.	overlay_29::023394e4	0xF000	0x2000	0x1600
some between 1012 to 1020 in dungeon pack	dungeon	Level/HP display text and HP bar.	overlay_29::0233614c	0x1000	0x400	0x200	which one is loaded depend on language
c_wipe.wte or w_wipe2.wte		Horizontal bar of differing colors, used by Team Charm's special wipe effect in SE4.	0x0206afb0		0x8000	0x0
w_heart.wte		Multiple hearts symbol, filled and shaded. More Team Charm.	0x0206b000		0x2000	0x100
circle.wte		Heart symbol, not filled. More Team Charm.	0x0206b050		0x2000	0x200
s13p01t1.wte	overworld	boss wipe graphic	overlay_11::02316d4c	0x8000	0x8000	0x100
d04p31t1.wte	overworld	big wave of the waterfall cave diamond	overlay_11::02314b9c	0x0	0x4800	0x0
v15p03t1.wte	overworld	Some crystal cave crystals	overlay_11::02314d20	0x0	0x8000	0x0
p03p01t1.wte	overworld	Fog texture for Groudon Statue cutscene.	overlay_11::02314eec overlay_11::022f33d8	0x0	0x6000	0x0
frameX.wte (where X is between 0 to 4)	both	dialog box frame	0x020274e4	0x1F000	0x800	0x1F00
t01p01t1.wte	overworld	Treasure Town cloud shadows.	overlay_11::022f3368 (loading weather 1)	0x0	0x4000	0x0
t01p01t2.wte	overworld	More Treasure Town cloud shadows.	overlay_11::022f3394 (loading weather 1)	0x4000	0x4000	0x100
d73p41t1.wte	overworld	Poison mist. Only used on top of Sky Peak on first visit.	overlay_11::022f341c (loading weather 3)	0x0	0x6000	0x0

Based on those allocations, it seems that VRAM from 0x11000 to 0x1EFFF (included) are free to be used both in overworld and dungeon. For the palette, it seems everything from 0x300 to 0x13FF (included) are unused.

Loading texture

Once you have your texture in the WTE format saved in the rom, you need to call a function to load WTE (LoadWteFromRom) and then copy stuff to the appropriate texture RAM with ProcessWTEWrapper (this will create a task to process the copy, once access to texture-RAM is safe), and then call DelayWTEFree (to make sure the original texture is freed once copy to texture-RAM is finished).