From de621d5d4b0b75441e034f15f766145ede2bace8 Mon Sep 17 00:00:00 2001
From: Paramat <paramat@users.noreply.github.com>
Date: Sun, 24 Jun 2018 17:14:18 +0100
Subject: Decoration API: Add lightweight ability to have complete coverage
 (#7456)

When the noise value or fill_ratio >= 10.0 complete coverage is enabled.
This disables random placement to avoid redundant multiple placements
at one position. Instead, 1 decoration per surface node is placed by
looping across each division.

'10' was chosen as this is the fill_ratio that previously created
very near complete coverage. The complete coverage feature therefore
integrates smoothly when noise is used for variable decoration density.

'fill_ratio = 10' should be used by modders who want a decoration
placed on every surface node. Compared to before such a decoration
placement will be 10 times faster.
---
 doc/lua_api.txt              |  4 ++++
 src/mapgen/mg_decoration.cpp | 38 +++++++++++++++++++++++++++++---------
 2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index db340e415..743cca47d 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -5769,6 +5769,8 @@ Definition tables
         fill_ratio = 0.02,
     --  ^ The value determines 'decorations per surface node'.
     --  ^ Used only if noise_params is not specified.
+    --  ^ If >= 10.0 complete coverage is enabled and decoration placement uses
+    --  ^ a different and much faster method.
         noise_params = {
             offset = 0,
             scale = 0.45,
@@ -5783,6 +5785,8 @@ Definition tables
     --  ^ distribution.
     --  ^ A noise value is calculated for each square division and determines
     --  ^ 'decorations per surface node' within each division.
+    --  ^ If the noise value >= 10.0 complete coverage is enabled and decoration
+    --  ^ placement uses a different and much faster method.
         biomes = {"Oceanside", "Hills", "Plains"},
     --  ^ List of biomes in which this decoration occurs. Occurs in all biomes
     --  ^ if this is omitted, and ignored if the Mapgen being used does not
diff --git a/src/mapgen/mg_decoration.cpp b/src/mapgen/mg_decoration.cpp
index 6daa8216e..28dde0209 100644
--- a/src/mapgen/mg_decoration.cpp
+++ b/src/mapgen/mg_decoration.cpp
@@ -155,23 +155,43 @@ size_t Decoration::placeDeco(Mapgen *mg, u32 blockseed, v3s16 nmin, v3s16 nmax)
 			nmin.Z + sidelen + sidelen * z0 - 1
 		);
 
+		bool cover = false;
 		// Amount of decorations
 		float nval = (flags & DECO_USE_NOISE) ?
 			NoisePerlin2D(&np, p2d_center.X, p2d_center.Y, mapseed) :
 			fill_ratio;
 		u32 deco_count = 0;
-		float deco_count_f = (float)area * nval;
-		if (deco_count_f >= 1.f) {
-			deco_count = deco_count_f;
-		} else if (deco_count_f > 0.f) {
-			// For low density decorations calculate a chance for 1 decoration
-			if (ps.range(1000) <= deco_count_f * 1000.f)
-				deco_count = 1;
+
+		if (nval >= 10.0f) {
+			// Complete coverage. Disable random placement to avoid
+			// redundant multiple placements at one position.
+			cover = true;
+			deco_count = area;
+		} else {
+			float deco_count_f = (float)area * nval;
+			if (deco_count_f >= 1.0f) {
+				deco_count = deco_count_f;
+			} else if (deco_count_f > 0.0f) {
+				// For very low density calculate a chance for 1 decoration
+				if (ps.range(1000) <= deco_count_f * 1000.0f)
+					deco_count = 1;
+			}
 		}
 
+		s16 x = p2d_min.X - 1;
+		s16 z = p2d_min.Y;
+
 		for (u32 i = 0; i < deco_count; i++) {
-			s16 x = ps.range(p2d_min.X, p2d_max.X);
-			s16 z = ps.range(p2d_min.Y, p2d_max.Y);
+			if (!cover) {
+				x = ps.range(p2d_min.X, p2d_max.X);
+				z = ps.range(p2d_min.Y, p2d_max.Y);
+			} else {
+				x++;
+				if (x == p2d_max.X + 1) {
+					z++;
+					x = p2d_min.X;
+				}
+			}
 			int mapindex = carea_size * (z - nmin.Z) + (x - nmin.X);
 
 			if ((flags & DECO_ALL_FLOORS) ||
-- 
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