Rework the image property getter/setters

* doc/lispref/display.texi (Defining Images): Document the
renamed `image-get/set-property' functions.

* lisp/image.el (image--set-property): Rename from
image-set-property.
(image-property): Declare a setf form.
(image-property): Rename from `image-get-property'.

1 files changed, 9 insertions, 5 deletions

diff --git a/lisp/image.el b/lisp/image.el
index 3522c5bc75c..96afa98bb3e 100644
--- a/lisp/image.el
+++ b/lisp/image.el
@@ -435,10 +435,9 @@ Image file names that are not absolute are searched for in the
                        (image-compute-scaling-factor image-scaling-factor)))
 	    props)))
 
-(defun image-set-property (image property value)
+(defun image--set-property (image property value)
   "Set PROPERTY in IMAGE to VALUE.
-If VALUE is nil, PROPERTY is removed from IMAGE.  IMAGE is
-returned."
+Internal use only."
   (if (null value)
       (while (cdr image)
         ;; IMAGE starts with the symbol `image', and the rest is a
@@ -451,8 +450,13 @@ returned."
     (plist-put (cdr image) property value))
   image)
 
-(defun image-get-property (image property)
-  "Return the value of PROPERTY in IMAGE."
+(defun image-property (image property)
+  "Return the value of PROPERTY in IMAGE.
+Properties can be set with
+
+  (setf (image-property IMAGE PROPERTY) VALUE)
+If VALUE is nil, PROPERTY is removed from IMAGE."
+  (declare (gv-setter image--set-property))
   (plist-get (cdr image) property))
 
 (defun image-compute-scaling-factor (scaling)