added slime overlay, colors chunks green if slimes can spawn

overviewer_core/src/primitives/overlay-slime.c

@@ -0,0 +1,126 @@
+/*
+ * This file is part of the Minecraft Overviewer.
+ *
+ * Minecraft Overviewer is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Minecraft Overviewer is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with the Overviewer.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "overlay.h"
+#include <math.h>
+
+typedef struct {
+    /* inherits from overlay */
+    RenderPrimitiveOverlay parent;
+    long seed;
+} RenderPrimitiveSlime;
+
+/*
+ * random_* are a re-implementation of java's Random() class
+ * since Minecraft's slime algorithm depends on it
+ * http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Random.html
+ */
+
+static void random_set_seed(long *seed, long new_seed) {
+    *seed = (new_seed ^ 0x5deece66dL) & ((1L << 48) - 1);
+}
+
+static int random_next(long *seed, int bits) {
+    *seed = (*seed * 0x5deece66dL + 0xbL) & ((1L << 48) - 1);
+    return (int)(*seed >> (48 - bits));
+}
+
+static int random_next_int(long *seed, int n) {
+    int bits, val;
+    
+    if (n <= 0) {
+        /* invalid */
+        return 0;
+    }
+    
+    if ((n & -n) == n) {
+        /* n is a power of two */
+        return (int)((n * (long)random_next(seed, 31)) >> 31);
+    }
+    
+    do {
+        bits = random_next(seed, 31);
+        val = bits % n;
+    } while (bits - val + (n - 1) < 0);
+    return val;
+}
+
+static int is_slime(long map_seed, long chunkx, long chunkz) {
+    /* lots of magic numbers, but they're all correct! I swear! */
+    long seed;
+    random_set_seed(&seed, map_seed + (chunkx * chunkx * 0x4c1906L) + (chunkx * 0x5ac0dbL) + (chunkz * chunkz * 0x4307a7L) + (chunkz * 0x5f24fL) ^ 0x3ad8025fL);
+    return (random_next_int(&seed, 10) == 0);
+}
+
+static void get_color(void *data, RenderState *state,
+                      unsigned char *r, unsigned char *g, unsigned char *b, unsigned char *a) {
+    RenderPrimitiveSlime *self = (RenderPrimitiveSlime *)data;
+        
+    /* set a nice, pretty green color */
+    *r = 40;
+    *g = 230;
+    *b = 40;
+    
+    /* default to no overlay, until told otherwise */
+    *a = 0;
+    
+    if (is_slime(self->seed, state->chunkx, state->chunkz)) {
+        /* slimes can spawn! */
+        *a = 240;
+    }
+}
+
+static int
+overlay_slime_start(void *data, RenderState *state, PyObject *support) {
+    RenderPrimitiveSlime *self;
+    PyObject *pyseed;
+
+    /* first, chain up */
+    int ret = primitive_overlay.start(data, state, support);
+    if (ret != 0)
+        return ret;
+    
+    /* now do custom initializations */
+    self = (RenderPrimitiveSlime *)data;
+    self->parent.get_color = get_color;
+    
+    pyseed = PyObject_GetAttrString(state->world, "seed");
+    if (!pyseed)
+        return 1;
+    self->seed = PyInt_AsLong(pyseed);
+    Py_DECREF(pyseed);
+    if (PyErr_Occurred())
+        return 1;
+    
+    return 0;
+}
+
+static void
+overlay_slime_finish(void *data, RenderState *state) {
+    /* chain up */
+    primitive_overlay.finish(data, state);
+}
+
+RenderPrimitiveInterface primitive_overlay_slime = {
+    "overlay-slime",
+    sizeof(RenderPrimitiveSlime),
+    overlay_slime_start,
+    overlay_slime_finish,
+    NULL,
+    NULL,
+    overlay_draw,
+};