Structures

Aside from few highly optimized paired-single algorithms, Mario Kart Wii and the first-party Wii EAD libraries were written in C and C++ and compiled to PowerPC Assembly. This article presents several highly-used structures and classes reconstructed to C and C++ structures.

Primitive Sizes

The following table presents the size of primitive elements as they are in Mario Kart Wii. This is the equivalent of sizeof(...).

Sizeof Primitives

Shorthand	Type	Size in bytes.
s32, u32	(unsigned) int, long int	4
s16, u16	(unsigned) short int	2
u8, s8	(unsigned) char	1
-	bool	1
-	enum	4
u64, s64	(unsigned) long long int	8
f32	float	4
f64	double	8

Alignment

All members are aligned to multiples of their size. For example, an int is four bytes and therefore must be aligned to a multiple of four bytes. Consider the following:

struct Example {
 short FieldA;
 int   FieldB;
};

FieldA will be placed at +00 and end at +02. However, FieldB will not end at +02 as it is not a multiple of four. The compiler will instead place two bytes of implicit padding between FieldA and FieldB. Structures presented in this article will omit implicit padding.

Structures

Multithreading

Thread

The Thread class defines an implementation of a thread that game threads must inherit. Wrapping an OSThread, Thread is the successor to JSYSTEM's JKRThread.

Thread virtual table data structure

Offset	Return Type	Description
0x08	-	Virtual destructor.
0x0C	int	Function to run the thread.
0x10	void	Called on entering the thread.
0x14	void	Called on exiting the thread.
0x3C		End of this structure

Thread data structure

Offset	Type	Description
0x00	-	Virtual Table
0x04	Heap*	Heap to use for thread-specific allocations. It's used immediately in the constructor to allocate the stack and optionally OSThread on heap.
0x08	OSThread*	The OS thread this object wraps.
0x0C	OSMessageQueue	The message queue of this thread.
0x2C	OSMessage*	The message buffer.
0x30	u32	The number of messages in the buffer.
0x34	void*	The base (beginning) of the stack.
0x38	u32	Size of the stack.
0x3C	Heap*	When not NULL, it will override the heap used for allocations. (Note: Does not escape the global heap restriction if enabled.)
0x3C		End of this structure

System

RKSystem

The following structures describe the Mario Kart Wii specific system class. The system class in actuality has a complex class hierarchy, however for readability, has been condensed into one structure. The incredibly specific descriptions of members are based on decompilation of the game, not speculation.

The system instance is located in BSS at PAL 802A4080. Two main pointers to this class are located at PAL 80386F60 (parent main class instance pointer used only by system classes) and PAL 80385FC8 (RK SystemManager System instance pointer used by game code). The SystemManager getter for the System is at PAL 80008E84.

RKSystem virtual table data structure

Offset	Return Type	Description
0x08	Video*	Returns a pointer to the video wrapper.
0x0C	Heap*	Returns a pointer to the system heap.
0x10	Display*	Returns a pointer to the display wrapper.
0x14	XfbManager*	Returns a pointer to the external framebuffer manager.
0x18	PerformanceView*	Returns a pointer to the debug bar. Mario Kart Wii's debug bar inherits Thread before PerformanceView, so sizeof(Thread) is added when returning.
0x1C	SceneManager*	Returns a pointer to the system scene manager.
0x20	AudioManager*	Returns a pointer to the system audio manager.
0x24	void	Called before every frame. Nullsub.
0x28	void	Called at the end of every frame. Nullsub.
0x2C	void	Called in initialization functions. Nullsub.
0x30	void	Initializes the system memory.
0x34	void	The main game loop!
0x38	void	Initializes the system.
0x3C		End of this structure

RKSystem data structure

Offset	Type	Description
0x00	-	Virtual Table
0x04	void*	Lower boundary of MEM1 arena.
0x08	void*	Upper boundary of MEM1 arena (start of FST).
0x0C	void*	Lower boundary of MEM2 arena.
0x10	void*	Upper boundary of MEM2 arena.
0x14	u32	Memory size, as set in the boot info.
0x18	Heap*	Pointer to the MEM1 root expanded heap. Encompasses all of the MEM1 arena. Name pointer set to "EGGRootMEM1".
0x1C	Heap*	Pointer to the MEM2 root expanded heap. Encompasses all of the MEM2 arena. Name pointer set to "EGGRootMEM2".
0x20	Heap*	Pointer to the Debug root expanded heap. Size is either 0x3B50000 when enabled or 0 when empty. Only created if Mem2ArenaSize >= 0x4000000, as debug units have an additional 64MB of MEM2 memory (ending at 7FFFFFF; retail ends at 3FFFFFF). Several stripped debug tasks use this. Name pointer set to "EGGRootDebug".
0x24	Heap*	Pointer to the System expanded heap. The system heap is a child of the root MEM1 heap. Name pointer set to "EGGSystem".
0x28	Thread*	Pointer to the thread that initialized the system.
0x2C	void*	Set to the cached base (0x80000000).
0x30	void*	Set to the MEM1 arena low.
0x34	u32	Determines the size of the system heap to create.
0x38	u32	Determines the GXFifo buffer size.
0x3C	GXRenderModeObj*	Render mode used when configuring the video wrapper.
0x40	ExpandedAudioManager*	The system audio manager.
0x44	Video*	The system video wrapper.
0x48	XfbManager*	The system external framebuffer manager. Holds two XFBs.
0x4C	AsyncDisplay*	The system asynchronous display wrapper.
0x50	ProcessMeter*	The system debug bar.
0x54	SceneManager*	The system scene manager.
0x58	void*	KPAD working memory.
0x5C	u32	Unknown.
0x60	Heap*	Heap to use when linking StaticR.rel.
0x64	ExpHeap*	Another system heap. Overrided system heap getter returns this heap in the RK system rather than the heap returned by the debug main class system heap getter.
0x68	u8[4]	Misc
0x70	void*	Unknown
0x3C		End of this structure