From e11d050423d13abe773d38716c69628e582b38fd Mon Sep 17 00:00:00 2001
From: Ariel Antonitis <arant@mit.edu>
Date: Tue, 6 Apr 2021 01:02:37 -0400
Subject: [PATCH] Added weighted palette average.

---
 include/palette.h |  1 +
 src/overworld.c   | 13 +++++++++++--
 src/palette.c     | 29 +++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/include/palette.h b/include/palette.h
index 0be99d3c64..406f56b84a 100644
--- a/include/palette.h
+++ b/include/palette.h
@@ -76,6 +76,7 @@ void BeginHardwarePaletteFade(u8, u8, u8, u8, u8);
 void BlendPalettes(u32 selectedPalettes, u8 coeff, u16 color);
 void BlendPalettesUnfaded(u32, u8, u16);
 void BlendPalettesGradually(u32 selectedPalettes, s8 delay, u8 coeff, u8 coeffTarget, u16 color, u8 priority, u8 id);
+void AveragePalettes(u16 *palette0, u16* palette1, u16* dest, u16 weight);
 void TimeBlendPalette(u16 palOffset, u16 numEntries, u8 coeff, u16 blendColor);
 void TintPalette_RGB_Copy(u16 palOffset, u16 numEntries, u8 coeff, u16 blendColor);
 void TimeBlendPalettes(u32 palettes, u8 coeff, u16 color);
diff --git a/src/overworld.c b/src/overworld.c
index 6e7542109f..cd1a1df966 100644
--- a/src/overworld.c
+++ b/src/overworld.c
@@ -1496,7 +1496,8 @@ static bool8 FadePalettesWithTime(void) {
 void UpdatePalettesWithTime(u32 palettes) {
   // Only blend if not transitioning between times and the map type allows
   if (gTimeOfDayState == 0 && MapHasNaturalLight(gMapHeader.mapType)) {
-    u8 i;
+    u8 i, j;
+    u16 tempPaletteBuffer[16];
     for (i = 0; i < 16; i++) {
       if (GetSpritePaletteTagByPaletteNum(i) & 0x8000) // Don't blend special sprite palette tags
         palettes &= ~(1 << (i + 16));
@@ -1505,7 +1506,15 @@ void UpdatePalettesWithTime(u32 palettes) {
     gTimeOfDay = min(TIME_OF_DAY_MAX, gTimeOfDay);
     if (!palettes)
       return;
-    TimeBlendPalettes(palettes, sTimeOfDayBlendVars[gTimeOfDay].coeff, sTimeOfDayBlendVars[gTimeOfDay].blendColor);
+    for (i = 0; palettes; i++) {
+      if (palettes & 1) {
+        TimeBlendPalette(i*16, 16, sTimeOfDayBlendVars[gTimeOfDay].coeff, sTimeOfDayBlendVars[gTimeOfDay].blendColor);
+        CpuFastCopy(&gPlttBufferFaded[i*16], tempPaletteBuffer, 32);
+        TimeBlendPalette(i*16, 16, sTimeOfDayBlendVars[TIME_OF_DAY_TWILIGHT].coeff, sTimeOfDayBlendVars[TIME_OF_DAY_TWILIGHT].blendColor);
+        AveragePalettes(tempPaletteBuffer, &gPlttBufferFaded[i*16], &gPlttBufferFaded[i*16], 256);
+      }
+      palettes >>= 1;
+    }
   }
 }
 
diff --git a/src/palette.c b/src/palette.c
index 34cf0286da..a285a48257 100644
--- a/src/palette.c
+++ b/src/palette.c
@@ -978,6 +978,35 @@ void BlendPalettes(u32 selectedPalettes, u8 coeff, u16 color)
     }
 }
 
+// Computes a weighted average of two palettes, as (p0*weight + (256-weight)*p1)/256
+void AveragePalettes(u16 *palette0, u16* palette1, u16* dest, u16 weight) {
+  u8 i;
+  u32 tempColor;
+  u16 r0, g0, b0, r1, g1, b1, r, g, b;
+  u16 color0, color1, destColor;
+  *dest++ = *palette0++; // Copy palette0's transparency color as is
+  palette1++;
+  for (i = 1; i < 16; i++) { // Skip transparent color
+    color0 = *palette0++;
+    color1 = *palette1++;
+    r0 = color0 & 0x1F;
+    g0 = (color0 >> 5) & 0x1F;
+    b0 = (color0 >> 10) & 0x1F;
+    r1 = color1 & 0x1F;
+    g1 = (color1 >> 5) & 0x1F;
+    b1 = (color1 >> 10) & 0x1F;
+    r = (weight*r0 + (256-weight)*r1) >> 8;
+    g = (weight*g0 + (256-weight)*g1) >> 8;
+    b = (weight*b0 + (256-weight)*b1) >> 8;
+    r = r > 31 ? 31 : r;
+    g = g > 31 ? 31 : g;
+    b = b > 31 ? 31 : b;
+    destColor = (color0 | color1) & 0x8000;
+    destColor += r + (g << 5) + (b << 10);
+    *dest++ = destColor;
+  }
+}
+
 #define DEFAULT_LIGHT_COLOR 0x3f9f
 
 // Like BlendPalette, but ignores blendColor if the transparency high bit is set