Smooth lighting: Fix light leaking through edge-connected corners

For solid nodes, the lighting at a corner becomes face-dependent, which
means that only the four nodes in face-direction contribute to the
lighting (getSmoothLightSolid).
For special nodes, which use the lighting values at the eight corners of
a node, the lighting is not face-dependent, but certain nodes of the
eight surrounding nodes of a corner (here indices 4, 5, 6 and 7) can be
obstructed.

Ambient occlusion now also occurs for solid nodes, if two, three or four
of the four nodes in face-direction are solid.

3 files changed, 110 insertions, 42 deletions

diff --git a/src/content_mapblock.cpp b/src/content_mapblock.cpp
index 577fbc5f8..4e32e27ca 100644
--- a/src/content_mapblock.cpp
+++ b/src/content_mapblock.cpp
@@ -276,7 +276,7 @@ void MapblockMeshGenerator::drawCuboid(const aabb3f &box,
 void MapblockMeshGenerator::getSmoothLightFrame()
 {
 	for (int k = 0; k < 8; ++k) {
-		u16 light = getSmoothLight(blockpos_nodes + p, light_dirs[k], data);
+		u16 light = getSmoothLightTransparent(blockpos_nodes + p, light_dirs[k], data);
 		frame.lightsA[k] = light & 0xff;
 		frame.lightsB[k] = light >> 8;
 	}
diff --git a/src/mapblock_mesh.cpp b/src/mapblock_mesh.cpp
index dc37c0c5f..7708fb438 100644
--- a/src/mapblock_mesh.cpp
+++ b/src/mapblock_mesh.cpp
@@ -28,6 +28,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "content_mapblock.h"
 #include "util/directiontables.h"
 #include "client/renderingengine.h"
+#include <array>
 
 /*
 	MeshMakeData
@@ -68,7 +69,7 @@ void MeshMakeData::fill(MapBlock *block)
 
 	fillBlockData(v3s16(0,0,0), block->getData());
 
-	// Get map for reading neigbhor blocks
+	// Get map for reading neighbor blocks
 	Map *map = block->getParent();
 
 	for (const v3s16 &dir : g_26dirs) {
@@ -194,19 +195,9 @@ u16 getFaceLight(MapNode n, MapNode n2, v3s16 face_dir, INodeDefManager *ndef)
 	Calculate smooth lighting at the XYZ- corner of p.
 	Both light banks
 */
-static u16 getSmoothLightCombined(const v3s16 &p, MeshMakeData *data)
+static u16 getSmoothLightCombined(const v3s16 &p,
+	const std::array<v3s16,8> &dirs, MeshMakeData *data, bool node_solid)
 {
-	static const v3s16 dirs8[8] = {
-		v3s16(0,0,0),
-		v3s16(0,0,1),
-		v3s16(0,1,0),
-		v3s16(0,1,1),
-		v3s16(1,0,0),
-		v3s16(1,1,0),
-		v3s16(1,0,1),
-		v3s16(1,1,1),
-	};
-
 	INodeDefManager *ndef = data->m_client->ndef();
 
 	u16 ambient_occlusion = 0;
@@ -215,32 +206,58 @@ static u16 getSmoothLightCombined(const v3s16 &p, MeshMakeData *data)
 	u16 light_day = 0;
 	u16 light_night = 0;
 
-	for (const v3s16 &dir : dirs8) {
-		MapNode n = data->m_vmanip.getNodeNoExNoEmerge(p - dir);
-
-		// if it's CONTENT_IGNORE we can't do any light calculations
-		if (n.getContent() == CONTENT_IGNORE)
-			continue;
-
+	auto add_node = [&] (int i) -> const ContentFeatures& {
+		MapNode n = data->m_vmanip.getNodeNoExNoEmerge(p + dirs[i]);
 		const ContentFeatures &f = ndef->get(n);
 		if (f.light_source > light_source_max)
 			light_source_max = f.light_source;
 		// Check f.solidness because fast-style leaves look better this way
 		if (f.param_type == CPT_LIGHT && f.solidness != 2) {
 			light_day += decode_light(n.getLightNoChecks(LIGHTBANK_DAY, &f));
-			light_night += decode_light(
-				n.getLightNoChecks(LIGHTBANK_NIGHT, &f));
+			light_night += decode_light(n.getLightNoChecks(LIGHTBANK_NIGHT, &f));
 			light_count++;
 		} else {
 			ambient_occlusion++;
 		}
-	}
+		return f;
+	};
 
-	if(light_count == 0)
-		return 0xffff;
+	if (node_solid) {
+		ambient_occlusion = 3;
+		bool corner_obstructed = true;
+		for (int i = 0; i < 2; ++i) {
+			if (add_node(i).light_propagates)
+				corner_obstructed = false;
+		}
+		add_node(2);
+		add_node(3);
+		if (corner_obstructed)
+			ambient_occlusion++;
+		else
+			add_node(4);
+	} else {
+		std::array<bool, 4> obstructed = {{ 1, 1, 1, 1 }};
+		add_node(0);
+		bool opaque1 = !add_node(1).light_propagates;
+		bool opaque2 = !add_node(2).light_propagates;
+		bool opaque3 = !add_node(3).light_propagates;
+		obstructed[0] = opaque1 && opaque2;
+		obstructed[1] = opaque1 && opaque3;
+		obstructed[2] = opaque2 && opaque3;
+		for (int k = 0; k < 4; ++k) {
+			if (obstructed[k])
+				ambient_occlusion++;
+			else if (add_node(k + 4).light_propagates)
+				obstructed[3] = false;
+		}
+	}
 
-	light_day /= light_count;
-	light_night /= light_count;
+	if (light_count == 0) {
+		light_day = light_night = 0;
+	} else {
+		light_day /= light_count;
+		light_night /= light_count;
+	}
 
 	// Boost brightness around light sources
 	bool skip_ambient_occlusion_day = false;
@@ -283,20 +300,70 @@ static u16 getSmoothLightCombined(const v3s16 &p, MeshMakeData *data)
 /*
 	Calculate smooth lighting at the given corner of p.
 	Both light banks.
+	Node at p is solid, and thus the lighting is face-dependent.
 */
-u16 getSmoothLight(v3s16 p, v3s16 corner, MeshMakeData *data)
+u16 getSmoothLightSolid(const v3s16 &p, const v3s16 &face_dir, const v3s16 &corner, MeshMakeData *data)
 {
-	if (corner.X == 1)
-		++p.X;
-	// else corner.X == -1
-	if (corner.Y == 1)
-		++p.Y;
-	// else corner.Y == -1
-	if (corner.Z == 1)
-		++p.Z;
-	// else corner.Z == -1
-
-	return getSmoothLightCombined(p, data);
+	v3s16 neighbor_offset1, neighbor_offset2;
+
+	/*
+	 * face_dir, neighbor_offset1 and neighbor_offset2 define an
+	 * orthonormal basis which is used to define the offsets of the 8
+	 * surrounding nodes and to differentiate the "distance" (by going only
+	 * along directly neighboring nodes) relative to the node at p.
+	 * Apart from the node at p, only the 4 nodes which contain face_dir
+	 * can contribute light.
+	 */
+	if (face_dir.X != 0) {
+		neighbor_offset1 = v3s16(0, corner.Y, 0);
+		neighbor_offset2 = v3s16(0, 0, corner.Z);
+	} else if (face_dir.Y != 0) {
+		neighbor_offset1 = v3s16(0, 0, corner.Z);
+		neighbor_offset2 = v3s16(corner.X, 0, 0);
+	} else if (face_dir.Z != 0) {
+		neighbor_offset1 = v3s16(corner.X,0,0);
+		neighbor_offset2 = v3s16(0,corner.Y,0);
+	}
+
+	const std::array<v3s16,8> dirs = {{
+		// Always shine light
+		neighbor_offset1 + face_dir,
+		neighbor_offset2 + face_dir,
+		v3s16(0,0,0),
+		face_dir,
+
+		// Can be obstructed
+		neighbor_offset1 + neighbor_offset2 + face_dir,
+
+		// Do not shine light, only for ambient occlusion
+		neighbor_offset1,
+		neighbor_offset2,
+		neighbor_offset1 + neighbor_offset2
+	}};
+	return getSmoothLightCombined(p, dirs, data, true);
+}
+
+/*
+	Calculate smooth lighting at the given corner of p.
+	Both light banks.
+	Node at p is not solid, and the lighting is not face-dependent.
+*/
+u16 getSmoothLightTransparent(const v3s16 &p, const v3s16 &corner, MeshMakeData *data)
+{
+	const std::array<v3s16,8> dirs = {{
+		// Always shine light
+		v3s16(0,0,0),
+		v3s16(corner.X,0,0),
+		v3s16(0,corner.Y,0),
+		v3s16(0,0,corner.Z),
+
+		// Can be obstructed
+		v3s16(corner.X,corner.Y,0),
+		v3s16(corner.X,0,corner.Z),
+		v3s16(0,corner.Y,corner.Z),
+		v3s16(corner.X,corner.Y,corner.Z)
+	}};
+	return getSmoothLightCombined(p, dirs, data, false);
 }
 
 void get_sunlight_color(video::SColorf *sunlight, u32 daynight_ratio){
@@ -816,7 +883,7 @@ static void getTileInfo(
 
 		v3s16 light_p = blockpos_nodes + p_corrected;
 		for (u16 i = 0; i < 4; i++)
-			lights[i] = getSmoothLight(light_p, vertex_dirs[i], data);
+			lights[i] = getSmoothLightSolid(light_p, face_dir_corrected, vertex_dirs[i], data);
 	}
 }
 
diff --git a/src/mapblock_mesh.h b/src/mapblock_mesh.h
index b4bfedb84..13cee537c 100644
--- a/src/mapblock_mesh.h
+++ b/src/mapblock_mesh.h
@@ -232,7 +232,8 @@ video::SColor encode_light(u16 light, u8 emissive_light);
 // Compute light at node
 u16 getInteriorLight(MapNode n, s32 increment, INodeDefManager *ndef);
 u16 getFaceLight(MapNode n, MapNode n2, v3s16 face_dir, INodeDefManager *ndef);
-u16 getSmoothLight(v3s16 p, v3s16 corner, MeshMakeData *data);
+u16 getSmoothLightSolid(const v3s16 &p, const v3s16 &face_dir, const v3s16 &corner, MeshMakeData *data);
+u16 getSmoothLightTransparent(const v3s16 &p, const v3s16 &corner, MeshMakeData *data);
 
 /*!
  * Returns the sunlight's color from the current