added sealevel option to HeightFading primitive

docs/config.rst

@@ -619,6 +619,13 @@ Nether
 HeightFading
     Draws a colored overlay on the blocks that fades them out according to their
     height.
+    
+    **Options**
+    
+    sealevel
+        sealevel of the word you're rendering. Note that the default,
+        128, is usually *incorrect* for most worlds. You should
+        probably set this to 64. Default: 128
 
 Depth
     Only renders blocks between the specified min and max heights.

overviewer_core/rendermodes.py

@@ -52,6 +52,10 @@ class Nether(RenderPrimitive):
 
 class HeightFading(RenderPrimitive):
     name = "height-fading"
+    options = {
+        # 128 is *WRONG*, it should be 64. but we're grandfathered in for now
+        "sealevel": ("target sea level", 128),
+    }
     
     black_color = Image.new("RGB", (24,24), (0,0,0))
     white_color = Image.new("RGB", (24,24), (255,255,255))

overviewer_core/src/overviewer.h

@@ -26,7 +26,7 @@
 
 // increment this value if you've made a change to the c extesion
 // and want to force users to rebuild
-#define OVERVIEWER_EXTENSION_VERSION 34
+#define OVERVIEWER_EXTENSION_VERSION 35
 
 /* Python PIL, and numpy headers */
 #include <Python.h>

overviewer_core/src/primitives/height-fading.c

@@ -20,12 +20,16 @@
 typedef struct {
     PyObject *black_color;
     PyObject *white_color;
+    unsigned int sealevel;
 } PrimitiveHeightFading;
 
 static int
 height_fading_start(void *data, RenderState *state, PyObject *support) {
     PrimitiveHeightFading *self = (PrimitiveHeightFading *)data;
     
+    if (!render_mode_parse_option(support, "sealevel", "I", &(self->sealevel)))
+        return 1;
+    
     self->black_color = PyObject_GetAttrString(support, "black_color");
     self->white_color = PyObject_GetAttrString(support, "white_color");
     
@@ -50,7 +54,7 @@ height_fading_draw(void *data, RenderState *state, PyObject *src, PyObject *mask
     PyObject *height_color = self->white_color;
 
     /* current formula requires y to be between 0 and 127, so scale it */
-    y = (y * 128) / (16 * SECTIONS_PER_CHUNK);
+    y = (y * 128) / (2 * self->sealevel);
     
     /* negative alpha => darkness, positive => light */
     alpha = (1.0 / (1 + expf((70 - y) / 11.0))) * 0.6 - 0.55;