bug#69992: Minor improvement to image map transformation logic

[Joseph Turner via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Hello,

This patch is slight simplification/optimization.

Joseph


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From 96a30a0450384eaeda21f234911f947952c4dcde Mon Sep 17 00:00:00 2001
From: Joseph Turner <joseph@breatheoutbreathe.in>
Date: Sat, 23 Mar 2024 13:29:17 -0700
Subject: [PATCH] copy-tree just image map, not entire image.

* lisp/image.el (image--compute-original-map):
---
 lisp/image.el | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/lisp/image.el b/lisp/image.el
index 55340ea03dc..d7496485aca 100644
--- a/lisp/image.el
+++ b/lisp/image.el
@@ -1455,24 +1455,23 @@ image--compute-original-map
 If IMAGE lacks :map property, return nil.
 When :rotation is not a multiple of 90, return copy of :map."
   (when (image-property image :map)
-    (let* ((image-copy (copy-tree image t))
-           (map (image-property image-copy :map))
-           (scale (or (image-property image-copy :scale) 1))
-           (rotation (or (image-property image-copy :rotation) 0))
-           (flip (image-property image-copy :flip))
-           (size (image-size image-copy t)))
+    (let* ((original-map (copy-tree (image-property image :map) t))
+           (scale (or (image-property image :scale) 1))
+           (rotation (or (image-property image :rotation) 0))
+           (flip (image-property image :flip))
+           (size (image-size image t)))
       (when (and ; Handle only 90-degree rotations
              (zerop (mod rotation 1))
              (zerop (% (truncate rotation) 90)))
         ;; In rendered images, rotation is always applied before flip.
-        ;; To undo the transformation, flip before rotating.
-        ;; SIZE fits MAP before it is transformed back to ORIGINAL-MAP.
-        ;; Therefore, scale MAP after flip and rotate operations, since
-        ;; both need MAP to fit SIZE.
-        (image--flip-map map flip size)
-        (image--rotate-map map (- rotation) size)
-        (image--scale-map map (/ 1.0 scale)))
-      map)))
+        ;; To undo the transformation, flip before rotating.  SIZE fits
+        ;; ORIGINAL-MAP before transformations are applied.  Therefore,
+        ;; scale ORIGINAL-MAP after flip and rotate operations, since
+        ;; both need ORIGINAL-MAP to fit SIZE.
+        (image--flip-map original-map flip size)
+        (image--rotate-map original-map (- rotation) size)
+        (image--scale-map original-map (/ 1.0 scale)))
+      original-map)))
 
 (defun image--scale-map (map scale)
   "Scale MAP according to SCALE.
-- 
2.41.0