obj->handler()
Game objects carry behavior as data: a struct field that holds a function's address. Calling it is one load plus one new instruction. Here's runThink, which invokes an actor's think callback:
typedef struct {
s32 id; // offset 0
void (*think)(void); // offset 4
} Actor;
void runThink(Actor *a) {
a->think();
}
0: addiu sp, sp, -24 # ── frame setup
4: sw ra, 20(sp) # save the return address
8: lw t9, 4(a0) # load the function POINTER field
c: jalr t9 # call whatever address t9 holds
10: nop # (delay slot)
14: lw ra, 20(sp) # ── frame teardown
18: addiu sp, sp, 24 #
1c: jr ra
20: nop
The heart is two lines. lw t9, 4(a0) reads the field at offset 4 — not a value to compute with, but an address to jump to. Then jalr t9 — jump-and-link register — calls it: jump to the address in t9, leaving the return address in ra, exactly what jal name does when the destination is known at compile time. IDO always stages an indirect call through t9; treat lw t9 + jalr t9 as one unit meaning "call the function stored here."
And notice what the call cost: four lines of scaffolding. The moment a function calls anything, its own ra gets overwritten by the call — so it must park ra on the stack first (addiu sp/sw ra) and restore it after (lw ra/addiu sp). That's a stack frame, and the next tier is all about them. For now, read the four lines as one fixed sandwich around any call and don't let them distract you.
In the target, a Sprite's callback gets invoked — check the lw t9 offset against the layout below to see which field that is.
Your task
Write func_800dacfc to reproduce the target assembly.