Document the representation of DX and DY in pinch events

* doc/lispref/commands.texi (Misc Events): Document
the precise meaning of DX and DY in pinch events.

diff --git a/doc/lispref/commands.texi b/doc/lispref/commands.texi
index dd36bace18e5a32afe48cbe489099d17d7e56c3a..bfb1f5a9474eb4523010af080567067efd8f20ae 100644 (file)
--- a/doc/lispref/commands.texi
+++ b/doc/lispref/commands.texi
@@ -2107,6 +2107,9 @@ the user placing two fingers on the touchpad, and ends with the user
 removing those fingers.  @var{dx}, @var{dy}, and @var{angle} will be
 @code{0.0} in the first event sent after a sequence begins.
 
+@var{dx} and @var{dy} are represented in imaginary units, in which
+@code{1.0} is the width and height of the touchpad respectively.
+
 @cindex @code{drag-n-drop} event
 @item (drag-n-drop @var{position} @var{files})
 This kind of event is generated when a group of files is