diff --git a/chunk.py b/chunk.py
index 99019b6..56e58ef 100644
--- a/chunk.py
+++ b/chunk.py
@@ -503,6 +503,7 @@ def generate_facemasks():
 facemasks = generate_facemasks()
 black_color = Image.new("RGB", (24,24), (0,0,0))
 red_color = Image.new("RGB", (24,24), (229,36,38))
+white_color = Image.new("RGB", (24,24), (255,255,255))
 
 # Render 128 different color images for color coded depth blending in cave mode
 def generate_depthcolors():
diff --git a/config.js b/config.js
index 9296853..f52c170 100644
--- a/config.js
+++ b/config.js
@@ -44,7 +44,8 @@ var mapTypeData=[
   {'label': 'Unlit', 'path': 'tiles'},
 //  {'label': 'Day',   'path': 'lighting/tiles'},
 //  {'label': 'Night', 'path': 'night/tiles'},
-//  {'label': 'Spawn', 'path': 'spawn/tiles', 'base': 'http://example.cdn.amazon.com/'}
+//  {'label': 'Spawn', 'path': 'spawn/tiles', 'base': 'http://example.cdn.amazon.com/'},
+//  {'label': 'Overlay', 'path': 'overlay/tiles', 'overlay': true}
 ];
  */
 
diff --git a/googlemap.py b/googlemap.py
index 840d2ac..9ae846a 100644
--- a/googlemap.py
+++ b/googlemap.py
@@ -95,8 +95,12 @@ class MapGen(object):
                 "{imgformat}", str(imgformat))
         
         # create generated map type data, from given quadtrees
+        # FIXME hook this into render_modes in setup.py, somehow
+        overlay_types = ['overlay']
         maptypedata = map(lambda q: {'label' : q.rendermode.capitalize(),
-                                     'path' : q.tiledir}, self.quadtrees)
+                                     'path' : q.tiledir,
+                                     'overlay' : q.rendermode in overlay_types},
+                          self.quadtrees)
         config = config.replace("{maptypedata}", json.dumps(maptypedata))
         
         with open(os.path.join(self.destdir, "config.js"), 'w') as output:
diff --git a/overviewer.py b/overviewer.py
index b2aa275..7082d0c 100755
--- a/overviewer.py
+++ b/overviewer.py
@@ -64,7 +64,8 @@ def main():
     parser.add_option("-z", "--zoom", dest="zoom", help="Sets the zoom level manually instead of calculating it. This can be useful if you have outlier chunks that make your world too big. This value will make the highest zoom level contain (2**ZOOM)^2 tiles", action="store", type="int", configFileOnly=True)
     parser.add_option("-d", "--delete", dest="delete", help="Clear all caches. Next time you render your world, it will have to start completely over again. This is probably not a good idea for large worlds. Use this if you change texture packs and want to re-render everything.", action="store_true", commandLineOnly=True)
     parser.add_option("--chunklist", dest="chunklist", help="A file containing, on each line, a path to a chunkfile to update. Instead of scanning the world directory for chunks, it will just use this list. Normal caching rules still apply.")
-    parser.add_option("--rendermodes", dest="rendermode", help="Specifies the render type: normal (default), lighting, night, or spawn.", type="choice", choices=["normal", "lighting", "night", "spawn"], required=True, default="normal", listify=True)
+    # TODO hook this up to render_modes in setup.py
+    parser.add_option("--rendermodes", dest="rendermode", help="Specifies the render type: normal (default), lighting, night, or spawn.", type="choice", choices=["normal", "lighting", "night", "spawn", "overlay"], required=True, default="normal", listify=True)
     parser.add_option("--imgformat", dest="imgformat", help="The image output format to use. Currently supported: png(default), jpg. NOTE: png will always be used as the intermediate image format.", configFileOnly=True )
     parser.add_option("--optimize-img", dest="optimizeimg", help="If using png, perform image file size optimizations on the output. Specify 1 for pngcrush, 2 for pngcrush+optipng+advdef. This may double (or more) render times, but will produce up to 30% smaller images. NOTE: requires corresponding programs in $PATH or %PATH%", configFileOnly=True)
     parser.add_option("--web-assets-hook", dest="web_assets_hook", help="If provided, run this function after the web assets have been copied, but before actual tile rendering begins. It should accept a QuadtreeGen object as its only argument.", action="store", metavar="SCRIPT", type="function", configFileOnly=True)
diff --git a/setup.py b/setup.py
index 34f646b..27bb755 100644
--- a/setup.py
+++ b/setup.py
@@ -49,9 +49,13 @@ try:
 except AttributeError:
     numpy_include = numpy.get_numpy_include()
 
+# used to figure out what files to compile
+# TODO and, potentially, to check which are available
+render_modes = ['normal', 'lighting', 'night', 'spawn', 'overlay']
+
+c_overviewer_files = ['src/main.c', 'src/composite.c', 'src/iterate.c', 'src/endian.c', 'src/rendermodes.c']
+c_overviewer_files += map(lambda mode: 'src/rendermode-%s.c' % (mode,), render_modes)
 
-c_overviewer_files = ['src/main.c', 'src/composite.c', 'src/iterate.c', 'src/endian.c']
-c_overviewer_files += ['src/rendermodes.c', 'src/rendermode-normal.c', 'src/rendermode-lighting.c', 'src/rendermode-night.c', 'src/rendermode-spawn.c']
 setup_kwargs['ext_modules'].append(Extension('c_overviewer', c_overviewer_files, include_dirs=['.', numpy_include], extra_link_args=[]))
 # tell build_ext to build the extension in-place
 # (NOT in build/)
diff --git a/src/composite.c b/src/composite.c
index 4a03d23..432ece8 100644
--- a/src/composite.c
+++ b/src/composite.c
@@ -273,7 +273,8 @@ alpha_over_wrap(PyObject *self, PyObject *args)
  * also, it multiplies instead of doing an over operation
  */
 PyObject *
-tint_with_mask(PyObject *dest, unsigned char sr, unsigned char sg, unsigned char sb,
+tint_with_mask(PyObject *dest, unsigned char sr, unsigned char sg,
+               unsigned char sb, unsigned char sa,
                PyObject *mask, int dx, int dy, int xsize, int ysize) {
     /* libImaging handles */
     Imaging imDest, imMask;
@@ -332,9 +333,11 @@ tint_with_mask(PyObject *dest, unsigned char sr, unsigned char sg, unsigned char
                 out++;
                 *out = MULDIV255(*out, sb, tmp1);
                 out++;
+                *out = MULDIV255(*out, sa, tmp1);
+                out++;
             } else if (*inmask == 0) {
                 /* do nothing -- source is fully transparent */
-                out += 3;
+                out += 4;
             } else {
                 /* general case */
                 
@@ -345,9 +348,10 @@ tint_with_mask(PyObject *dest, unsigned char sr, unsigned char sg, unsigned char
                 out++;
                 *out = MULDIV255(*out, (255 - *inmask) + MULDIV255(sb, *inmask, tmp1), tmp2);
                 out++;
+                *out = MULDIV255(*out, (255 - *inmask) + MULDIV255(sa, *inmask, tmp1), tmp2);
+                out++;
             }
 
-            out++;
             inmask += mask_stride;
         }
     }
diff --git a/src/overviewer.h b/src/overviewer.h
index 3475fdf..4045313 100644
--- a/src/overviewer.h
+++ b/src/overviewer.h
@@ -44,7 +44,8 @@ PyObject *alpha_over(PyObject *dest, PyObject *src, PyObject *mask,
 PyObject *alpha_over_full(PyObject *dest, PyObject *src, PyObject *mask, float overall_alpha,
                           int dx, int dy, int xsize, int ysize);
 PyObject *alpha_over_wrap(PyObject *self, PyObject *args);
-PyObject *tint_with_mask(PyObject *dest, unsigned char sr, unsigned char sg, unsigned char sb,
+PyObject *tint_with_mask(PyObject *dest, unsigned char sr, unsigned char sg,
+                         unsigned char sb, unsigned char sa,
                          PyObject *mask, int dx, int dy, int xsize, int ysize);
 
 /* in iterate.c */
@@ -79,7 +80,7 @@ PyObject *chunk_render(PyObject *self, PyObject *args);
 #include "rendermodes.h"
 
 /* in endian.c */
-void init_endian();
+void init_endian(void);
 unsigned short big_endian_ushort(unsigned short in);
 unsigned int big_endian_uint(unsigned int in);
 
diff --git a/src/rendermode-normal.c b/src/rendermode-normal.c
index d7a1367..f0cdb96 100644
--- a/src/rendermode-normal.c
+++ b/src/rendermode-normal.c
@@ -158,7 +158,7 @@ rendermode_normal_draw(void *data, RenderState *state, PyObject *src, PyObject *
             b = PyInt_AsLong(PyTuple_GET_ITEM(color, 2));
             Py_DECREF(color);
 
-            tint_with_mask(state->img, r, g, b, facemask, state->imgx, state->imgy, 0, 0);
+            tint_with_mask(state->img, r, g, b, 255, facemask, state->imgx, state->imgy, 0, 0);
         }
     }
 }
diff --git a/src/rendermode-overlay.c b/src/rendermode-overlay.c
new file mode 100644
index 0000000..32cb03a
--- /dev/null
+++ b/src/rendermode-overlay.c
@@ -0,0 +1,75 @@
+/* 
+ * 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 "overviewer.h"
+
+static int
+rendermode_overlay_start(void *data, RenderState *state) {
+    PyObject *facemasks_py;
+    RenderModeOverlay *self = (RenderModeOverlay *)data;
+    
+    facemasks_py = PyObject_GetAttrString(state->chunk, "facemasks");
+    /* borrowed reference, needs to be incref'd if we keep it */
+    self->facemask_top = PyTuple_GetItem(facemasks_py, 0);
+    Py_INCREF(self->facemask_top);
+    Py_DECREF(facemasks_py);
+    
+    self->white_color = PyObject_GetAttrString(state->chunk, "white_color");
+    
+    return 0;
+}
+
+static void
+rendermode_overlay_finish(void *data, RenderState *state) {
+    RenderModeOverlay *self = (RenderModeOverlay *)data;
+    
+    Py_XDECREF(self->facemask_top);
+    Py_XDECREF(self->white_color);
+}
+
+static int
+rendermode_overlay_occluded(void *data, RenderState *state) {
+    int x = state->x, y = state->y, z = state->z;
+    
+    if ( (x != 0) && (y != 15) && (z != 127) &&
+         !is_transparent(getArrayByte3D(state->blocks, x-1, y, z)) &&
+         !is_transparent(getArrayByte3D(state->blocks, x, y, z+1)) &&
+         !is_transparent(getArrayByte3D(state->blocks, x, y+1, z))) {
+        return 1;
+    }
+
+    return 0;
+}
+
+static void
+rendermode_overlay_draw(void *data, RenderState *state, PyObject *src, PyObject *mask) {
+    RenderModeOverlay *self = (RenderModeOverlay *)data;
+    
+    /* clear the draw space -- set alpha to 0 within mask */
+    tint_with_mask(state->img, 255, 255, 255, 0, mask, state->imgx, state->imgy, 0, 0);
+    
+    /* do the overlay */
+    alpha_over_full(state->img, self->white_color, self->facemask_top, 0.5, state->imgx, state->imgy, 0, 0);
+}
+
+RenderModeInterface rendermode_overlay = {
+    sizeof(RenderModeOverlay),
+    rendermode_overlay_start,
+    rendermode_overlay_finish,
+    rendermode_overlay_occluded,
+    rendermode_overlay_draw,
+};
diff --git a/src/rendermodes.c b/src/rendermodes.c
index f4fbe89..46cc432 100644
--- a/src/rendermodes.c
+++ b/src/rendermodes.c
@@ -31,6 +31,10 @@ RenderModeInterface *get_render_mode(RenderState *state) {
         iface = &rendermode_night;
     } else if (strcmp(rendermode, "spawn") == 0) {
         iface = &rendermode_spawn;
+    } else if (strcmp(rendermode, "overlay") == 0) {
+        /* TODO temporarily use overlay directly, but later on
+           you want to use overlay-derived modes */
+        iface = &rendermode_overlay;
     }
     
     Py_DECREF(rendermode_py);
diff --git a/src/rendermodes.h b/src/rendermodes.h
index d26091d..87c7cb1 100644
--- a/src/rendermodes.h
+++ b/src/rendermodes.h
@@ -71,6 +71,13 @@ typedef struct {
 } RenderModeNormal;
 extern RenderModeInterface rendermode_normal;
 
+/* OVERLAY */
+typedef struct {
+    /* top facemask and white color image, for drawing overlays */
+    PyObject *facemask_top, *white_color;
+} RenderModeOverlay;
+extern RenderModeInterface rendermode_overlay;
+
 /* LIGHTING */
 typedef struct {
     /* inherits from normal render mode */
diff --git a/web_assets/functions.js b/web_assets/functions.js
index 174a43a..9b7ac12 100644
--- a/web_assets/functions.js
+++ b/web_assets/functions.js
@@ -14,6 +14,61 @@ function prepareSignMarker(marker, item) {
 
 }
 
+function createDropDown(title, items) {
+    var control = document.createElement("DIV");
+    control.id = "customControl"; // let's let a style sheet do most of the styling here
+
+    var controlBorder = document.createElement("DIV");
+    controlBorder.id="top";
+    control.appendChild(controlBorder);
+
+    var controlText = document.createElement("DIV");
+
+    controlBorder.appendChild(controlText);
+
+    controlText.innerHTML = title;
+    
+    var dropdownDiv = document.createElement("DIV");
+
+
+    $(controlText).click(function() {
+            $(dropdownDiv).toggle();
+
+            });
+
+
+    dropdownDiv.id="dropDown";
+    control.appendChild(dropdownDiv);
+    dropdownDiv.innerHTML="";
+
+    map.controls[google.maps.ControlPosition.TOP_RIGHT].push(control);
+
+    for (idx in items) {
+        var item = items[idx];
+        //console.log(item);
+        label = item.label;
+        action = item.action;
+        var d = document.createElement("div");
+        var n = document.createElement("input");
+        n.type="checkbox";
+
+        $(n).data("label",label);
+        jQuery(n).click(function(e) {
+                            var t = $(e.target);
+                            action(idx, label, e.target.checked);
+                        });
+
+        if (item.checked) {
+            n.checked = true;
+            action(idx, label, item.checked);
+        }
+        dropdownDiv.appendChild(d);
+        d.appendChild(n)
+        var textNode = document.createElement("text");
+        textNode.innerHTML = label + "<br/>";
+        d.appendChild(textNode);
+    }
+}
 
 function drawMapControls() {
 
@@ -42,69 +97,43 @@ function drawMapControls() {
 
 
     if (signGroups.length > 0) {
-    // signpost display control
-    //
-
-    var signControl = document.createElement("DIV");
-    signControl.id = "signControl"; // let's let a style sheet do most of the styling here
-
-    var controlBorder = document.createElement("DIV");
-    controlBorder.id="top";
-    signControl.appendChild(controlBorder);
-
-    var controlText = document.createElement("DIV");
-
-    controlBorder.appendChild(controlText);
-
-    controlText.innerHTML = "Signposts";
-    
-    var dropdownDiv = document.createElement("DIV");
-
-
-    $(controlText).click(function() {
-            $(dropdownDiv).toggle();
-
-            });
-
-
-    dropdownDiv.id="dropDown";
-    signControl.appendChild(dropdownDiv);
-    dropdownDiv.innerHTML="";
-
-    map.controls[google.maps.ControlPosition.TOP_RIGHT].push(signControl);
-
-
-
-    var hasSignGroup = false;
-    for (idx in signGroups) {
-        var item = signGroups[idx];
-        //console.log(item);
-        label = item.label;
-        hasSignGroup = true;
-        var d = document.createElement("div");
-        var n = document.createElement("input");
-        n.type="checkbox";
-
-        $(n).data("label",label);
-        jQuery(n).click(function(e) {
-                var t = $(e.target);
-                jQuery.each(markerCollection[t.data("label")], function(i,elem) {elem.setVisible(e.target.checked);});
-                });
-
-
-        if (item.checked) {
-            n.checked = true;
-            jQuery.each(markerCollection[label], function(i,elem) {elem.setVisible(n.checked);});
+        // signpost display control
+        
+        var items = [];
+        for (idx in signGroups) {
+            var item = signGroups[idx];
+            items.push({"label": item.label, "checked": item.checked,
+                        "action": function(n, l, checked) {
+                            jQuery.each(markerCollection[l], function(i,elem) {elem.setVisible(checked);});
+                        }});
         }
-        dropdownDiv.appendChild(d);
-        d.appendChild(n)
-        var textNode = document.createElement("text");
-        textNode.innerHTML = label + "<br/>";
-        d.appendChild(textNode);
-
+        createDropDown("Signposts", items);
     }
-
-
+    
+    if (overlayMapTypes.length > 0) {
+        // overlay maps control
+        
+        var items = [];
+        for (idx in overlayMapTypes) {
+            var overlay = overlayMapTypes[idx];
+            items.push({"label": overlay.name, "checked": false,
+                        "action": function(i, l, checked) {
+                            if (checked) {
+                                map.overlayMapTypes.push(overlay);
+                            } else {
+                                var idx_to_delete = -1;
+                                map.overlayMapTypes.forEach(function(e, j) {
+                                                                if (e == overlay) {
+                                                                    idx_to_delete = j;
+                                                                }
+                                                            });
+                                if (idx_to_delete >= 0) {
+                                    map.overlayMapTypes.removeAt(idx_to_delete);
+                                }
+                            }
+                        }});
+        }
+        createDropDown("Overlays", items);
     }
 }
 
@@ -303,7 +332,7 @@ function initialize() {
     for (idx in MCMapType) {
       map.mapTypes.set('mcmap' + MCMapType[idx].name, MCMapType[idx]);
     }
-
+    
     // We can now set the map to use the 'coordinate' map type
     map.setMapTypeId(mapTypeIdDefault);
 
@@ -412,6 +441,7 @@ var MCMapOptions = new Array;
 var MCMapType = new Array;
 var mapTypeIdDefault = null;
 var mapTypeIds = [];
+var overlayMapTypes = [];
 for (idx in mapTypeData) {
   var view = mapTypeData[idx];
 
@@ -427,10 +457,15 @@ for (idx in mapTypeData) {
   MCMapType[view.label].name = view.label;
   MCMapType[view.label].alt = "Minecraft " + view.label + " Map";
   MCMapType[view.label].projection = new MCMapProjection();
-  if (mapTypeIdDefault == null) {
-    mapTypeIdDefault = 'mcmap' + view.label;
+  
+  if (view.overlay) {
+    overlayMapTypes.push(MCMapType[view.label]);
+  } else {
+    if (mapTypeIdDefault == null) {
+      mapTypeIdDefault = 'mcmap' + view.label;
+    }
+    mapTypeIds.push('mcmap' + view.label);
   }
-  mapTypeIds.push('mcmap' + view.label);
 }
   
   function CoordMapType() {
diff --git a/web_assets/style.css b/web_assets/style.css
index e6029dc..32389bf 100644
--- a/web_assets/style.css
+++ b/web_assets/style.css
@@ -17,13 +17,13 @@ body { height: 100%; margin: 0px; padding: 0px ; background-color: #000; }
     font-family: monospace;
 }
 
-#signControl {
+#customControl {
     padding: 5px;
     height: 15px;
     font-family: Arial, sans-serif;
 }
 
-#signControl > div#top {
+#customControl > div#top {
     background-color: #fff;
     border: 2px solid #000;
     text-align: center;
@@ -33,7 +33,7 @@ body { height: 100%; margin: 0px; padding: 0px ; background-color: #000; }
     cursor: pointer;
 }
 
-#signControl > div#dropDown {
+#customControl > div#dropDown {
     border: 1px solid #000;
     font-size: 12px;
     background-color: #fff;