pokeemerald/docs/bugs_and_glitches.md

Bugs and Glitches

These are known bugs and glitches in the original Pokémon Emerald game: code that clearly does not work as intended, or that only works in limited circumstances but has the possibility to fail or crash. Defining the BUGFIX preprocessor variable will fix some of these automatically.

Fixes are written in the diff format. If you've used Git before, this should look familiar:

 this is some code
-delete red - lines
+add green + lines

Contents

• RNG does not get seeded
• Scrolling through items in the bag causes the image to flicker

RNG does not get seeded

Fix: Add the following function to src/main.c:

+static void SeedRngWithRtc(void)
+{
+	u32 seed = RtcGetMinuteCount();
+	seed = (seed >> 16) ^ (seed & 0xFFFF);
+	SeedRng(seed);
+}

And edit AgbMain:

	...
	RtcInit();
	CheckForFlashMemory();
	InitMainCallbacks();
	InitMapMusic();
+	SeedRngWithRtc();
	ClearDma3Requests();
	...

This restores the code of Ruby/Sapphire.

Alternate Fix: Edit the following function in src/title_screen.c:

void CB2_InitTitleScreen(void)
{
	switch (gMain.state)
	{
	default:
	case 0:
		SetVBlankCallback(NULL);
+		StartTimer1();
		SetGpuReg(REG_OFFSET_BLDCNT, 0);
		SetGpuReg(REG_OFFSET_BLDALPHA, 0);
		SetGpuReg(REG_OFFSET_BLDY, 0);
		...

This matches what FRLG does and obtains the seed differently than RS, independently of the RTC.

Scrolling through items in the bag causes the image to flicker

Fix: Add the following function to src/item_menu_icons.c:

+void HideBagItemIconSprite(u8 id)
+{
+	u8 *spriteId = &gBagMenu->spriteId[10];
+	if (spriteId[id] != 0xFF)
+	{
+		gSprites[spriteId[id]].invisible = TRUE;
+	}
+}

and its corresponding declaration in include/item_menu_icons.h:

+void HideBagItemIconSprite(u8 id);

Then edit BagMenu_MoveCursorCallback in src/item_menu.c:

	...
{
-	RemoveBagItemIconSprite(1 ^ gBagMenu->unk81B_1);
+	HideBagItemIconSprite(gBagMenu->unk81B_1 ^ 1);
+	RemoveBagItemIconSprite(gBagMenu->unk81B_1);
	if (a != -2)
	...

Pokémon that have an affine transform as part of their entry animation glitch when going in and out of Poké Balls without a screen transition in between

Fix: Edit sub_817F77C in src/pokemon_animation.c:

    ...
-#ifdef BUGFIX
    else
    {
        // FIX: Reset these back to normal after they were changed so Poké Ball catch/release
        // animations without a screen transition in between don't break
        sprite->affineAnimPaused = FALSE;
        sprite->affineAnims = gUnknown_082FF694;
    }
-#endif // BUGFIX
}