Documentation: Improve multihead documentation slightly.

git-svn-id: file:///beryl/trunk@4025 d7aaf104-2d23-0410-ae22-9d23157bf5a3

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diff --git a/Documentation/Multihead b/Documentation/Multihead
index 2d41b8f..cc3f85f 100644
--- a/Documentation/Multihead
+++ b/Documentation/Multihead
@@ -1,5 +1,21 @@
 WARNING: Incomplete and possibly incorrect information follows.
 
+Multihead and beryl
+===================
+0. Scope of this document
+1. Two fundamentally diffrent ways of doing multihead
+2. What beryl needs from X
+3. Code-related concerns.
+
+
+0. Scope of this document
+=========================
+This document is meant mainly for developers or advanced users. It does not
+cover configuration of X for specific video cards or situations. It is meant
+to explain how Beryl deals with multihead, not how you set up X.
+
+1. Two fundamentally diffrent ways of doing multihead
+=====================================================
 Multihead is when more than one monitor, projector, tv, etc (head) is 
 hooked up to the same computer. 
 
@@ -21,6 +37,27 @@ several video cards than it is to provide a single xinerama screen.
 Another rather neat result is that you get one cube per head which can
 rotate independently of each other. 
 
+2. What beryl needs from X
+==========================
+Beryl supports both xinerama-hinted multihead, and multiscreen. However, that 
+does not mean it will work.
+
+With nVidia, you should have no real problems. Just set up TwinView and you
+should be good to go. nVidia users can also use multiscreen, though it is not
+as polished driver-wise as TwinView.
+
+FIXME: Better input from Intel/ATI users.
+
+ATI users might run into problems, as the open source drivers does not provide
+DRI on both screens in multihead. 
+
+Beryl needs a working AIGLX, Xgl or nVidia rendering path for all screens
+to work. Beryl also needs composite working on all screens. Check for these
+in the X log if you are having trouble starting beryl on multiscreen. 
+
+3. Code-related concerns.
+=========================
+
 There isn't much to think about for most programmers when it comes to
 multiscreen. Just make sure you don't mix the CompDisplay and CompScreen
 data. Also, never use d->screens without cycling through it. On normal