fairland: Compute resources by interpolating tables

The functions mapping elevation to resources are piecewise linear.
Replace them by linear interpolation on data points defined in tables.
Tables are easier to tweak for deities than code.

The data points are a bit awkward because the functions they replace
are.  The next commit will tweak them to address that.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>

diff --git a/src/util/fairland.c b/src/util/fairland.c
index 44824bd6b9d49503ea886cfd4531e3138aa37b9c..405021e964146498543c0e6fff89807c3fec2095 100644 (file)
--- a/src/util/fairland.c
+++ b/src/util/fairland.c
@@ -109,8 +109,8 @@
  * 5. Set resources
  *
  * Sector resources are simple functions of elevation.  You can alter
- * macros OIL_MAX, IRON_MIN, GOLD_MIN, FERT_MAX, and URAN_MIN to
- * customize them.
+ * iron_conf[], gold_conf[], fert_conf[], oil_conf[], and uran_conf[]
+ * to customize them.
  */
 
 #include <config.h>
@@ -129,31 +129,69 @@
 #include "version.h"
 #include "xy.h"
 
-/* The following five numbers refer to elevation under which (in the case of
-   fertility or oil) or over which (in the case of iron, gold, and uranium)
-   sectors with that elevation will contain that resource.  Elevation ranges
-   from 0 to 100 */
-
-/* raise FERT_MAX for more fertility */
-#define FERT_MAX   56
-
-/* raise OIL_MAX for more oil */
-#define OIL_MAX           33
-
-/* lower IRON_MIN for more iron */
-#define IRON_MIN   22
-
-/* lower GOLD_MIN for more gold */
-#define GOLD_MIN   36
-
-/* lower URAN_MIN for more uranium */
-#define URAN_MIN   56
-
 /* do not change these defines */
 #define LANDMIN                1       /* plate altitude for normal land */
 #define PLATMIN                36      /* plate altitude for plateau */
 #define HIGHMIN                98      /* plate altitude for mountains */
 
+/*
+ * Resource configuration
+
+ * Resources are determined by elevation.  The map from elevation to
+ * resource is defined as a linear interpolation of resource data
+ * points (elev, res) defined in the tables below.  Elevations range
+ * from -127 to 127, and resource values from 0 to 100.
+ */
+
+struct resource_point {
+    int elev;
+    double res;
+};
+
+struct resource_point iron_conf[] = {
+    { -127, 0 },
+    { 21, 0 },
+    { 84, 120.0 * 63 / 76 },
+    { 85, 100 },
+    { HIGHMIN - 1, 100 },
+    { HIGHMIN , 0 },
+    { 127, 0 } };
+
+struct resource_point gold_conf[] = {
+    { -127, 0 },
+    { 35, 0 },
+    { HIGHMIN - 1, 80 },
+    { HIGHMIN, 80 },
+    { 127, 85 } };
+
+struct resource_point fert_conf[] = {
+    { -127, 100 },
+    { -59, 100 },
+    { LANDMIN - 1, 41 },
+    { LANDMIN, 100 },
+    { 10, 100 },
+    { 11, 120.0 * 45 / 55 },
+    { 56, 0 },
+    { 127, 0 } };
+
+struct resource_point oil_conf[] = {
+    { -127, 100 },
+    { -49, 100 },
+    { LANDMIN - 1, 2 },
+    { LANDMIN, 100 },
+    { 6, 100 },
+    { 7, 120.0 * 27 / 33 },
+    { 34, 0 },
+    { 127, 0 } };
+
+struct resource_point uran_conf[] = {
+    { -127, 0 },
+    { 55, 0 },
+    { 90, 100 },
+    { 97, 100 },
+    { 98, 0 },
+    { 127, 0 } };
+
 static void qprint(const char * const fmt, ...)
     ATTRIBUTE((format (printf, 1, 2)));
 
@@ -1361,77 +1399,36 @@ elev_to_sct_type(int elevation)
   ADD THE RESOURCES
 ****************************************************************************/
 
+/*
+ * Map elevation @elev to a resource value according to @conf.
+ * This is a linear interpolation on the data points in @conf.
+ */
 static int
-set_fert(int e)
-{
-    int fert = 0;
-    if (e < LANDMIN)
-       fert = LANDMIN - e + 40;
-    else if (e < FERT_MAX)
-       fert = (120 * (FERT_MAX - e)) / (FERT_MAX - LANDMIN);
-    if (fert > 100)
-       fert = 100;
-    return fert;
-}
-
-static int
-set_oil(int e)
-{
-    int oil = 0;
-    if (e < LANDMIN)
-       oil = (LANDMIN - e) * 2;
-    else if (e <= OIL_MAX)
-       oil = (120 * (OIL_MAX - e + 1)) / (OIL_MAX - LANDMIN + 1);
-    if (oil > 100)
-       oil = 100;
-    return oil;
-}
-
-static int
-set_iron(int e)
-{
-    int iron = 0;
-    if (e >= IRON_MIN && e < HIGHMIN)
-       iron = (120 * (e - IRON_MIN + 1)) / (HIGHMIN - IRON_MIN);
-    if (iron > 100)
-       iron = 100;
-    return iron;
-}
-
-static int
-set_gold(int e)
-{
-    int gold = 0;
-    if (e >= GOLD_MIN) {
-       if (e < HIGHMIN)
-           gold = (80 * (e - GOLD_MIN + 1)) / (HIGHMIN - GOLD_MIN);
-       else
-           gold = 80 + 5 * (e - HIGHMIN) / (127 - HIGHMIN);
-    }
-    if (gold > 100)
-       gold = 100;
-    return gold;
-}
-
-static int
-set_uran(int e)
+elev_to_resource(int elev, struct resource_point conf[])
 {
-    int uran = 0;
-    if (e >= URAN_MIN && e < HIGHMIN)
-       uran = (120 * (e - URAN_MIN + 1)) / (HIGHMIN - URAN_MIN);
-    if (uran > 100)
-       uran = 100;
-    return uran;
+    int i, elev1, elev2, delev;
+    double res1, res2, dres;
+
+    for (i = 1; elev > conf[i].elev; i++) ;
+    assert(conf[i - 1].elev <= elev);
+
+    elev1 = conf[i - 1].elev;
+    elev2 = conf[i].elev;
+    delev = elev2 - elev1;
+    res1 = conf[i - 1].res;
+    res2 = conf[i].res;
+    dres = res2 - res1;
+    return (int)(res1 + ((elev - elev1) * dres) / delev);
 }
 
 static void
 add_resources(struct sctstr *sct)
 {
-    sct->sct_fertil = set_fert(sct->sct_elev);
-    sct->sct_oil = set_oil(sct->sct_elev);
-    sct->sct_min = set_iron(sct->sct_elev);
-    sct->sct_gmin = set_gold(sct->sct_elev);
-    sct->sct_uran = set_uran(sct->sct_elev);
+    sct->sct_min = elev_to_resource(sct->sct_elev, iron_conf);
+    sct->sct_gmin = elev_to_resource(sct->sct_elev, gold_conf);
+    sct->sct_fertil = elev_to_resource(sct->sct_elev, fert_conf);
+    sct->sct_oil = elev_to_resource(sct->sct_elev, oil_conf);
+    sct->sct_uran = elev_to_resource(sct->sct_elev, uran_conf);
 }
 
 /****************************************************************************