From: Lars Ingebrigtsen <larsi@gnus.org>
Date: Thu, 25 Aug 2022 14:38:14 +0000 (+0200)
Subject: Document how :map and :scale interacts in image maps
X-Git-Tag: emacs-29.0.90~1893^2~39
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=ec4f976e8e1c072d6d6e05d77009e79da9efe885;p=emacs.git

Document how :map and :scale interacts in image maps

* doc/lispref/display.texi (Image Descriptors): Mention problems
with scaling (bug#50487).
---

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index d336cda6743..fde7274d591 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -5886,6 +5886,14 @@ When you click the mouse when the mouse pointer is over a hot-spot, an
 event is composed by combining the @var{id} of the hot-spot with the
 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
 @var{id} is @code{area4}.
+
+Note that the map's coordinates should reflect the displayed image
+after all transforms have been done (rotation, scaling and so on), and
+also note that Emacs (by default) performs auto-scaling of images, so
+to make things match up, you should either specify @code{:scale 1.0}
+when creating the image, or use the result of
+@code{image-compute-scaling-factor} to compute the elements of the
+map.
 @end table
 
 @defun image-mask-p spec &optional frame