Updated layers (markdown)

layers.md

@@ -1,6 +1,6 @@
 The game uses **layers** to order the rendering of graphics. Layers are updated and drawn in order, starting from the lowest layer to the highest. That means the top (last drawn) layer is drawn over everything else.
 
-The editor maps the 9 regular layers to the number keys 1-9 (the top row; the numbad keys are used for tile effects), the 6 parallax layers to the bottom row starting from _B_, _N_, _M_, and the 3 keys following to the right (_Comma_, _Period_, _Slash_), and the dark layer (_J_).
+The editor maps the 9 regular layers to the number keys 1-9 (the top row; the numbad keys are used for tile effects), the 6 parallax layers to the bottom row starting from _B_, _N_, _M_ + the 3 keys following to the right (_Comma_, _Period_, _Slash_), and the dark layer (_J_).
 
 Internally, the game uses a lot more layers, but only some are available in the editor. The rest can be accessed via scripting.
 
@@ -55,6 +55,20 @@ Having a wide-screen resolution also helps. 4:3 or 5:4 resolutions are not a pro
 
 # The Dark Layer (_J_)
 
-The dark layer is special. It's used in conjunction with sun form to darken the screen and to enable lighting up areas.
+The dark layer is special. It's used in conjunction with e.g. sun form to darken the screen and to enable lighting up areas.
 For easier use the editor draws it like a normal layer, but in-game it will look differently:
 Tiles placed on the dark layer are then used to modulate the color of the layers underneath it.
+You can press _Alt_+_J_ to toggle the dark layer; it stays disabled until you re-enable it.
+
+![Dark layer](http://fg.wzff.de/pub/aquaria/wikidata/darklayer.jpg)
+
+Rules of thumb:
+
+* White graphics on the dark layer remove darkness
+* Black graphics on the dark layer add darkness
+* Colored graphics add sort of a "tint" and can be used to modulate color.
+
+As on every layer, the order of things drawn on the dark layer is important: If you have a black graphic covering a large area and a small white graphic is drawn _afterwards_ (ie. is on top) then you will have a small hole (visible area) in a sea of blackness.
+
+If the black graphic was drawn first it would be drawn over the white one and thus everything would be black. Therefore don't forget to move things that are meant to add some sort of light to the front, and things that add darkness to the back. The same applies for adding things on the dark layer via scripting.
+