commit 357c8453be32c5e6261c6a5a8946907ae024fd86
Author: kwolekr <kwolekr@minetest.net>
Date:   Wed Mar 27 15:08:34 2013 -0400

    Vary ore density by height

diff --git a/src/mapgen.cpp b/src/mapgen.cpp
index b5deaae..20e8a89 100644
--- a/src/mapgen.cpp
+++ b/src/mapgen.cpp
@@ -86,6 +86,20 @@ void Ore::resolveNodeNames(INodeDefManager *ndef) {
 }


+s16 Ore::getScarcity(s16 y) {
+   s16 smin  = clust_scarcity_min;
+   s16 smax  = clust_scarcity_max;
+   s16 sramp = clust_scarcity_ramp;
+
+   if (y <= sramp)
+       return smin;
+
+   float factor = (float)(sramp - y) / (float)(sramp - height_max);
+   s16 scarcity = smin + factor * (smax - smin);
+   return scarcity;
+}
+
+
 void OreScatter::generate(Mapgen *mg, u32 blockseed, v3s16 nmin, v3s16 nmax) {
    if (nmin.Y > height_max || nmax.Y < height_min)
        return;
@@ -106,8 +120,8 @@ void OreScatter::generate(Mapgen *mg, u32 blockseed, v3s16 nmin, v3s16 nmax) {
                 (nmax.Z - nmin.Z + 1);
    int csize     = clust_size;
    int orechance = (csize * csize * csize) / clust_num_ores;
-   int nclusters = volume / clust_scarcity;
-
+   int nclusters = volume / getScarcity(nmin.Y);
+
    for (int i = 0; i != nclusters; i++) {
        int x0 = pr.range(nmin.X, nmax.X - csize + 1);
        int y0 = pr.range(ymin,   ymax   - csize + 1);
diff --git a/src/mapgen.h b/src/mapgen.h
index a900985..31aef8c 100644
--- a/src/mapgen.h
+++ b/src/mapgen.h
@@ -110,7 +110,9 @@ class Ore {

    content_t ore;
    content_t wherein;  // the node to be replaced
-   s16 clust_scarcity; //
+   s16 clust_scarcity_min;
+   s16 clust_scarcity_ramp;
+   s16 clust_scarcity_max;
    s16 clust_num_ores; // how many ore nodes are in a chunk
    s16 clust_size;     // how large (in nodes) a chunk of ore is
    s16 height_min;
@@ -127,6 +129,7 @@ class Ore {
    }

    void resolveNodeNames(INodeDefManager *ndef);
+   s16 getScarcity(s16 y);
    virtual void generate(Mapgen *mg, u32 blockseed, v3s16 nmin, v3s16 nmax) = 0;
 };

diff --git a/src/scriptapi.cpp b/src/scriptapi.cpp
index 80abffa..5f213d8 100644
--- a/src/scriptapi.cpp
+++ b/src/scriptapi.cpp
@@ -712,7 +712,9 @@ static int l_register_ore(lua_State *L)

    ore->ore_name       = getstringfield_default(L, index, "ore", "");
    ore->wherein_name   = getstringfield_default(L, index, "wherein", "");
-   ore->clust_scarcity = getintfield_default(L, index, "clust_scarcity", 1);
+   ore->clust_scarcity_min  = getintfield_default(L, index, "clust_scarcity_min", 100);
+   ore->clust_scarcity_ramp = getintfield_default(L, index, "clust_scarcity_ramp", 0);
+   ore->clust_scarcity_max  = getintfield_default(L, index, "clust_scarcity_max", 100);
    ore->clust_num_ores = getintfield_default(L, index, "clust_num_ores", 1);
    ore->clust_size     = getintfield_default(L, index, "clust_size", 0);
    ore->height_min     = getintfield_default(L, index, "height_min", 0);
@@ -725,7 +727,7 @@ static int l_register_ore(lua_State *L)

    ore->noise = NULL;

-   if (ore->clust_scarcity <= 0 || ore->clust_num_ores <= 0) {
+   if (ore->clust_num_ores <= 0) {
        errorstream << "register_ore: clust_scarcity and clust_num_ores"
            "must be greater than 0";
        delete ore;