Update motion trails sample page to reflect soon-to-be-added sample

Author: rdb

more-resources/samples/index.rst

@@ -100,7 +100,8 @@ Alternatively, you can download the samples separately from the download page.
 
 .. rubric:: :ref:`motion-trails`
 
-* Difficulty: Advanced
+* Difficulty: Intermediate (or Advanced)
+* Creating a trail behind a moving object.
 * Captures contents of screen and reuses it later.
 
 .. rubric:: :ref:`music-box`

more-resources/samples/motion-trails.rst

@@ -9,14 +9,27 @@ If you're a Linux user, you'll find the sample programs in /usr/share/panda3d.
 
 .. rubric:: Screenshots
 
-.. image:: screenshot-sample-programs-motion-trails.jpg
+.. image:: screenshot-sample-programs-motion-trails-fireball.png
+   :width: 49%
+
+.. image:: screenshot-sample-programs-motion-trails-framebuffer-feedback.png
+   :width: 49%
 
 .. rubric:: Explanation
 
-This tutorial shows how to create motion trails in panda. The basic process is
-this: after rendering the scene, you copy the scene into a texture. You apply
-that texture to a full-screen quad. You integrate that quad into the rendering
-of the next frame. That creates a feedback loop.
+These sample programs shows two different ways to create motion trails in panda.
+The first one is a geometry-based method, which uses the
+:py:class:`~direct.motiontrail.MotionTrail.MotionTrail` class (which is a
+wrapper around the C++ class :class:`.CMotionTrail`) in order to extrude a
+cross-section of geometry along the path that an object takes. This method can
+be used to achieve a wide range of effects, and is usually applied applied to
+individual objects.
+
+The second one is entirely different, and based around reusing the contents of
+the framebuffer in the following frame. The basic process is this: after
+rendering the scene, you copy the scene into a texture. You apply that texture
+to a full-screen quad. You integrate that quad into the rendering of the next
+frame. That creates a feedback loop.
 
 The basic steps are: create a texture that will hold the contents of the main
 window. Tell the main window to copy is output into this texture using