From 8a18d7f1ba7a5271751b7f33b012ee24eac10234 Mon Sep 17 00:00:00 2001
From: kwolekr <kwolekr@minetest.net>
Date: Tue, 29 Mar 2016 11:31:52 -0400
Subject: [PATCH] Mapgen: Spread both night and day light banks in spreadLight

---
 src/mapgen.cpp | 55 ++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 42 insertions(+), 13 deletions(-)

diff --git a/src/mapgen.cpp b/src/mapgen.cpp
index 36d19bfa7..29af83517 100644
--- a/src/mapgen.cpp
+++ b/src/mapgen.cpp
@@ -242,18 +242,38 @@ void Mapgen::setLighting(u8 light, v3s16 nmin, v3s16 nmax)
 
 void Mapgen::lightSpread(VoxelArea &a, v3s16 p, u8 light)
 {
-	if (light <= 1 || !a.contains(p))
+	if (light <= 1)
 		return;
 
 	u32 vi = vm->m_area.index(p);
-	MapNode &nn = vm->m_data[vi];
-
-	light--;
-	// should probably compare masked, but doesn't seem to make a difference
-	if (light <= nn.param1 || !ndef->get(nn).light_propagates)
+	if (!a.contains(vi))
 		return;
 
-	nn.param1 = light;
+	MapNode &n = vm->m_data[vi];
+
+	// Decay light in each of the banks separately
+	u8 light_day = light & 0x0F;
+	if (light_day > 0)
+		light_day -= 0x01;
+
+	u8 light_night = light & 0xF0;
+	if (light_night > 0)
+		light_night -= 0x10;
+
+	// Bail out only if we have no more light from either bank to propogate, or
+	// we hit a solid block that light cannot pass through.
+	if ((light_day  <= (n.param1 & 0x0F) &&
+		light_night <= (n.param1 & 0xF0)) ||
+		!ndef->get(n).light_propagates)
+		return;
+
+	// Since this recursive function only terminates when there is no light from
+	// either bank left, we need to take the max of both banks into account for
+	// the case where spreading has stopped for one light bank but not the other.
+	light = MYMAX(light_day, n.param1 & 0x0F) |
+			MYMAX(light_night, n.param1 & 0xF0);
+
+	n.param1 = light;
 
 	lightSpread(a, p + v3s16(0, 0, 1), light);
 	lightSpread(a, p + v3s16(0, 1, 0), light);
@@ -284,6 +304,9 @@ void Mapgen::propagateSunlight(v3s16 nmin, v3s16 nmax, bool propagate_shadow)
 	bool block_is_underground = (water_level >= nmax.Y);
 	v3s16 em = vm->m_area.getExtent();
 
+	// NOTE: Direct access to the low 4 bits of param1 is okay here because,
+	// by definition, sunlight will never be in the night lightbank.
+
 	for (int z = a.MinEdge.Z; z <= a.MaxEdge.Z; z++) {
 		for (int x = a.MinEdge.X; x <= a.MaxEdge.X; x++) {
 			// see if we can get a light value from the overtop
@@ -320,15 +343,21 @@ void Mapgen::spreadLight(v3s16 nmin, v3s16 nmax)
 			u32 i = vm->m_area.index(a.MinEdge.X, y, z);
 			for (int x = a.MinEdge.X; x <= a.MaxEdge.X; x++, i++) {
 				MapNode &n = vm->m_data[i];
-				if (n.getContent() == CONTENT_IGNORE ||
-					!ndef->get(n).light_propagates)
+				if (n.getContent() == CONTENT_IGNORE)
 					continue;
 
-				u8 light_produced = ndef->get(n).light_source & 0x0F;
-				if (light_produced)
-					n.param1 = light_produced;
+				const ContentFeatures &cf = ndef->get(n);
+				if (!cf.light_propagates)
+					continue;
 
-				u8 light = n.param1 & 0x0F;
+				// TODO(hmmmmm): Abstract away direct param1 accesses with a
+				// wrapper, but something lighter than MapNode::get/setLight
+
+				u8 light_produced = cf.light_source;
+				if (light_produced)
+					n.param1 = light_produced | (light_produced << 4);
+
+				u8 light = n.param1;
 				if (light) {
 					lightSpread(a, v3s16(x,     y,     z + 1), light);
 					lightSpread(a, v3s16(x,     y + 1, z    ), light);