From 16c31d61b44e7ece18e0d2039449d2ae4a0710e0 Mon Sep 17 00:00:00 2001
From: Ariel A <24759293+aarant@users.noreply.github.com>
Date: Sat, 25 Jan 2025 20:58:22 -0500
Subject: [PATCH] fix: removed fadescreenswapbuffers palette dependence, via
 hardware fade

---
 asm/macros/event.inc        |  9 +++++----
 src/event_object_movement.c |  2 ++
 src/field_weather.c         |  6 +++++-
 src/scrcmd.c                | 17 +++++++++--------
 4 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/asm/macros/event.inc b/asm/macros/event.inc
index 7125e71643..06396af8d2 100644
--- a/asm/macros/event.inc
+++ b/asm/macros/event.inc
@@ -1674,13 +1674,14 @@
 	.4byte \text
 	.endm
 
-	@ Equivalent to fadescreen but copies gPlttBufferUnfaded to gPaletteDecompressionBuffer on the fade out
-	@ and the reverse on the fade in, in effect saving gPlttBufferUnfaded to restore it.
-  @ If nowait set, does not wait for the fade to complete
+	@ Equivalent to fadescreen but uses a hardware fade and darken/lighten blend modes,
+	@ to avoid modifying palettes at all.
+	@ Useful for fade-out/fade-in without leaving the overworld or entering a new scene.
+	@ If nowait set, doesn't wait for the fade to complete
 	.macro fadescreenswapbuffers mode:req, nowait=0
 	.byte 0xdc
 	.byte \mode
-  .byte \nowait
+	.byte \nowait
 	.endm
 
 	@ Buffers the specified trainer's class name to the given string var.
diff --git a/src/event_object_movement.c b/src/event_object_movement.c
index f7f0f3e2df..18ca30bb96 100644
--- a/src/event_object_movement.c
+++ b/src/event_object_movement.c
@@ -2397,6 +2397,8 @@ void UpdateLightSprite(struct Sprite *sprite) {
         return;
     }
 
+    // Note to self: Don't set window registers during hardware fade!
+
     switch (sprite->data[5]) { // lightType
     case 0:
         if (gPaletteFade.active) { // if palette fade is active, don't flicker since the timer won't be updated
diff --git a/src/field_weather.c b/src/field_weather.c
index 2bcaa2f857..199cff15e1 100644
--- a/src/field_weather.c
+++ b/src/field_weather.c
@@ -818,6 +818,7 @@ void FadeScreen(u8 mode, s8 delay)
 // fades screen using BLDY
 // Note: This enables blending in all windows;
 // These bits may need to be disabled later
+// (i.e if blending lighting effects using WINOBJ)
 u16 FadeScreenHardware(u8 mode, s8 delay) {
     u16 bldCnt = GetGpuReg(REG_OFFSET_BLDCNT) & BLDCNT_TGT2_ALL;
     bldCnt |= BLDCNT_TGT1_ALL;
@@ -1008,7 +1009,10 @@ void Weather_SetBlendCoeffs(u8 eva, u8 evb)
     gWeatherPtr->currBlendEVB = evb;
     gWeatherPtr->targetBlendEVA = eva;
     gWeatherPtr->targetBlendEVB = evb;
-    SetGpuReg(REG_OFFSET_BLDALPHA, BLDALPHA_BLEND(eva, evb));
+
+    // don't update BLDALPHA if a hardware fade is on-screen
+    if ((GetGpuReg(REG_OFFSET_BLDCNT) & BLDCNT_EFFECT_EFF_MASK) < BLDCNT_EFFECT_LIGHTEN)
+        SetGpuReg(REG_OFFSET_BLDALPHA, BLDALPHA_BLEND(eva, evb));
 }
 
 void Weather_SetTargetBlendCoeffs(u8 eva, u8 evb, int delay)
diff --git a/src/scrcmd.c b/src/scrcmd.c
index a51e81aa91..edca8dbbbe 100644
--- a/src/scrcmd.c
+++ b/src/scrcmd.c
@@ -23,6 +23,7 @@
 #include "field_tasks.h"
 #include "field_weather.h"
 #include "fieldmap.h"
+#include "gpu_regs.h"
 #include "item.h"
 #include "lilycove_lady.h"
 #include "main.h"
@@ -661,19 +662,19 @@ bool8 ScrCmd_fadescreenswapbuffers(struct ScriptContext *ctx)
 
     switch (mode)
     {
-    case FADE_TO_BLACK:
-    case FADE_TO_WHITE:
-    default:
-        CpuCopy32(gPlttBufferUnfaded, gPaletteDecompressionBuffer, PLTT_SIZE);
-        FadeScreen(mode, 0);
-        break;
     case FADE_FROM_BLACK:
     case FADE_FROM_WHITE:
-        CpuCopy32(gPaletteDecompressionBuffer, gPlttBufferUnfaded, PLTT_SIZE);
-        FadeScreen(mode, 0);
+        // Restore last weather blend before fading in,
+        // since BLDALPHA was modified by fade-out
+        SetGpuReg(
+            REG_OFFSET_BLDALPHA,
+            BLDALPHA_BLEND(gWeatherPtr->currBlendEVA, gWeatherPtr->currBlendEVB)
+        );
         break;
     }
 
+    FadeScreenHardware(mode, 0);
+
     if (nowait)
         return FALSE;
     SetupNativeScript(ctx, IsPaletteNotActive);