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Inserting an Axel Sprite in Super Street Fighter II MD

SEGA Mega Drive & Genesis Classics

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There are a lot of steps involved when inserting a sprite. The order in which I do the steps is very inconsistent, so you may want to do these steps in the order that feels the most comfortable to you.

The programs I use are:

-Notepad, to keep notes of the sprites and other data.
-A Hex Editor called Hex Workshop. Other Hex Editors such as XVI32 and HxD can also work.
That last Hex Editor's name makes me think of an anime called High School DxD.
-Paint.NET. I prefer using an old version of it from 2012.
-GraphicsGale, for indexed images
-A reference tool that I wrote in Game Maker 7, called Street Fighter II MD Tile Arranger.
It displays the tile maps in the format that the Mega Drive Street Fighter II games use.
-Tile Layer Pro, to insert the art into the ROM.

Sprites can range from roughly 25 minutes, to an hour, depending on how many tiles the sprite uses, and the complexity of their tile layouts.

What I like to do, is change the sprite tiles of the character I want to replace, into numbered tiles that are indexed to fit my replacement character's palette.

I take notes of the sprites' art pointers and tile maps. I like to make a PDN file that consists of the remaining sprites that have yet to be inserted, and another PDN that's a spritesheet of the sprites inserted, with their sprite index numbers printed over them. This way, I have a visual reference of which sprite index is which sprite.

One way to find a fighter sprite's art pointer, is to take the ROM Address loaded at FF805A (for Player 1), and advance forward in the ROM by the Hex Value that the pointer leads to, 2 times.

Alternatively, you can breakpoint RAM Address FFA1AC, assuming you're in the Object Test, while the axis mark and everything else but the text and character is hidden. Then go 8 ROM Addresses backwards.

One of the first steps you want to do, is to update the address where the art pointer is going to load art into the VRAM. In the case of sprites that use multiple art pointers, you might also want to change the relative VRAM address that the art pointer loads the art tiles into.

The Art Pointer's Format goes like this:

TTTTAAAAAAAAVVVV

TT Number of tiles to load
AA Art Address, half of actual location in the ROM
VV Relative VRAM Address, double of the intended location

The character's sprite is internally facing left.

Before you insert the art, you want to define the sprite's tile layout.

The Sprite Tile Map's Format goes like this:

NNNN XXXXYYYYTTCC

N = Number of Tile Maps Sprite uses

X = X Position
Y = Y Position
T = Starting Tile Number
C = Tile Assembly Value

Map Shape Values
00 08x08
01 08x16
02 08x24
03 08x32
04 16x08
05 16x16
06 16x24
07 16x32
08 24x08
09 24x16
0A 24x24
0B 24x32
0C 32x08
0D 32x16
0E 32x24
0F 32x32

+0x00 Neutral
+0x10 Horizontally Mirrored
+0x20 Vertically Mirrored
+0x30 Horizontally and Vertically Mirrored
+0x40 (same as +0x00?)
+0x50 (same as +0x20?)
+0x60 (same as +0x30?)
+0x70 (same as +0x40?)
+0x80 to use 1st Palette Line, like with Dictator's Psycho Punches
+0x90 1st Palette Line, Horizontally Mirrored
+0xA0 1st Palette Line, Vertically Mirrored
+0xB0 1st Palette Line, Horizontally and Vertically Mirrored
+0xC0 (same as +0x80?)
+0xD0 (same as +0x90?)
+0xE0 (same as +0xA0?)
+0xF0 (same as +0xB0?)

(Basically, 1st digit of Map Size Value)

Don't need to worry about position when mirroring a Tile Map

00:00 Part 1 Changing art into numbered tiles, determinig sprite's tile space
02:16 Part 2 Determining the sprite's tile layout
06:34 Part 3 Laying out the numbered tiles, using my tile arranger to make a mockup
13:19 Part 4 Revealing the sprite map values and taking notes of them
14:11 Part 5 Copying sprite map notes into the ROM
15:05 Part 6 Testing tile layout in-game
16:09 Part 7 Inserting the art, proof of concept
24:01 Part 8 Spritesheet for reference

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