New functions for getting and setting image properties

* doc/lispref/display.texi (Defining Images): Document
image-get/set-property.

* lisp/image.el (image-set-property): New function.
(image-get-property): Ditto.

1 files changed, 20 insertions, 0 deletions

diff --git a/lisp/image.el b/lisp/image.el
index 855dffad293..3522c5bc75c 100644
--- a/lisp/image.el
+++ b/lisp/image.el
@@ -435,6 +435,26 @@ 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)
+  "Set PROPERTY in IMAGE to VALUE.
+If VALUE is nil, PROPERTY is removed from IMAGE.  IMAGE is
+returned."
+  (if (null value)
+      (while (cdr image)
+        ;; IMAGE starts with the symbol `image', and the rest is a
+        ;; plist.  Decouple plist entries where the key matches
+        ;; the property.
+        (if (eq (cadr image) property)
+            (setcdr image (cddr image))
+          (setq image (cddr image))))
+    ;; Just enter the new value.
+    (plist-put (cdr image) property value))
+  image)
+
+(defun image-get-property (image property)
+  "Return the value of PROPERTY in IMAGE."
+  (plist-get (cdr image) property))
+
 (defun image-compute-scaling-factor (scaling)
   (cond
    ((numberp image-scaling-factor)