Clean up based on feedback

docs/guides/stonesense-art-guide.rst

@@ -5,12 +5,6 @@ Stonesense art creation guide
 
 Understanding sprites
 ---------------------
-Understanding how Stonesense deals with sprites is central to anyone who wishes to modify the content.
-The scheme is not very complicated, and this guide will give a short introduction to how they work.
-The way sprites are loaded is fairly generalized. With the exception of floors, which we will discuss later,
-all sprites are 32x32 pixels big and come in groups known as Sprite Sheets. All sprites are loaded and
-rendered in 32-bit full-color PNGs.
-
 
 .. image:: ../images/stonesense-sprite-sample.png
     :align: left
@@ -19,28 +13,35 @@ Here's an example of a typical Stonesense sprite.
 
 Note that, in order not to conflict with neighboring sprites, a sprite must actually be within a smaller
 area than its 32x32 block.
-A template for the area used by most sprites is:
+A template for the area used by sprites is:
 
 .. image:: ../images/stonesense-sprite-template.png
     :align: left
 
 The solid area is the floor space taken up by a sprite, while the dotted box indicates the volume above this
 area corresponding to one z-level.
 
+Understanding how Stonesense deals with sprites is central to anyone who wishes to modify the content.
+The scheme is not very complicated, and this guide will give a short introduction to how they work.
+The way sprites are loaded is fairly generalized. With the exception of floors, which we will discuss later,
+all sprites are 32x32 pixels big and come in groups known as Sprite Sheets. All sprites are loaded and
+rendered in 32-bit full-color PNGs. The image files should have a transparent background but pure magenta
+(RGB: 255,0,255) is also treated as transparent. 
+
 Sprite sheets
 -------------
-There can be an arbitrary number of sprite sheets configured for Stonesense, yet some are always present as
-they contain default sprites (see further down). Most of the content XML files allow users to specify sprite
-sheets, and this is done by adding a file attribute to the content nodes. By convention sprite sheets should
-be placed in their appropriate folder, with creature sprite sheets in the creatures folder etc.
+There can be an arbitrary number of sprite sheets configured for Stonesense, though there are 3 sheets that are
+always present as they contain default sprites (see further down). Most of the content XML files allow users to
+specify sprite sheets, and this is done by adding a file attribute to the content nodes. By convention sprite
+sheets should be placed in their appropriate folder, with creature sprite sheets in the creatures folder etc.
 
 Sprite index
 ------------
 Sprite Index (sometimes referred to as Sheet Index) is a concept for referring to a specific sprite on a sheet.
 The index starts with the upper left sprite which has index zero. It then increments to the right. Stonesense
-is hardcoded to 20 sprites wide sheets, this means that the last sprite to the right in the first row has Sprite
-Index 19. The first sprite on the second row has index 20. This boundary is hardcoded and changing the size of
-the sheet will not affect it.
+is hardcoded to 20 sprites wide sheets, this means that anything past 20 "sprite slots" is ignored, though less
+than 20 slots is fine. The first sprite on the second row has index 20, the next row is 40, and so on. This
+boundary is hardcoded and changing the size of the sheet will not affect it.
 
 This image shows how sprites are indexed. Note: Grid added for readability.