master ec4f976e8e 1/2: Document how :map and :scale interacts in image maps

[Lars Ingebrigtsen]

branch: master
commit ec4f976e8e1c072d6d6e05d77009e79da9efe885
Author: Lars Ingebrigtsen <larsi@gnus.org>
Commit: Lars Ingebrigtsen <larsi@gnus.org>

    Document how :map and :scale interacts in image maps
    
    * doc/lispref/display.texi (Image Descriptors): Mention problems
    with scaling (bug#50487).
---
 doc/lispref/display.texi | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index d336cda674..fde7274d59 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