SCI32: Stop optimising palette merges

While this optimisation helped to reduce unnecessary palette
updates in KQ7, it broke Phant1, which relies on changes to index
255 in the source palette causing palette invalidation.

Refs Trac#9788.

1 files changed, 6 insertions, 5 deletions

diff --git a/engines/sci/graphics/palette32.cpp b/engines/sci/graphics/palette32.cpp
index d7f6710e12..fded8f00b0 100644
--- a/engines/sci/graphics/palette32.cpp
+++ b/engines/sci/graphics/palette32.cpp
@@ -566,11 +566,12 @@ Palette GfxPalette32::getPaletteFromResource(const GuiResourceId resourceId) con
 }
 
 void GfxPalette32::mergePalette(Palette &to, const Palette &from) {
-	// The last color is always white in SCI, so it is not copied. (Some
-	// palettes, particularly in KQ7, try to set the last color, which causes
-	// unnecessary palette updates since the last color is forced by SSCI to a
-	// specific value)
-	for (int i = 0; i < ARRAYSIZE(to.colors) - 1; ++i) {
+	// All colors MUST be copied, even index 255, despite the fact that games
+	// cannot actually change index 255 (it is forced to white when generating
+	// the hardware palette in updateHardware). While this causes some
+	// additional unnecessary source palette invalidations, not doing it breaks
+	// some badly programmed rooms, like room 6400 in Phant1 (see Trac#9788)
+	for (int i = 0; i < ARRAYSIZE(to.colors); ++i) {
 		if (from.colors[i].used) {
 			to.colors[i] = from.colors[i];
 		}