From 3154cebb004da61e64ece4735803fa21485775d1 Mon Sep 17 00:00:00 2001
From: Carlo Sciolla <carlo.sciolla@gmail.com>
Date: Fri, 3 May 2019 17:15:30 +0200
Subject: [PATCH] Avoid messing up with buffers
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This is yet another attempt at fixing #66, using a different approach than #93
By using `display-buffer` the preview buffer should stay wherever the user put it last
without jumping around and without stealing focus from the source buffer.

As an additional bonus, a temporary buffer is used to enable some sort of double
buffering and avoid the flicker of seeing the preview buffer disappear
---
 plantuml-mode.el | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/plantuml-mode.el b/plantuml-mode.el
index 2cf2cf6..c81a204 100644
--- a/plantuml-mode.el
+++ b/plantuml-mode.el
@@ -262,33 +262,35 @@ to choose where to display it:
 - 4  (when prefixing the command with C-u) -> new window
 - 16 (when prefixing the command with C-u C-u) -> new frame.
 - else -> new buffer"
-  (let ((b (get-buffer plantuml-preview-buffer)))
-    (when b
-      (kill-buffer b)))
-
   (let* ((imagep (and (display-images-p)
                       (plantuml-is-image-output-p)))
          (process-connection-type nil)
-         (buf (get-buffer-create plantuml-preview-buffer))
+         (preview-buf (get-buffer-create plantuml-preview-buffer))
          (coding-system-for-read (and imagep 'binary))
-         (coding-system-for-write (and imagep 'binary)))
-
-    (let ((ps (plantuml-start-process buf)))
+         (coding-system-for-write (and imagep 'binary))
+         (temp-buffer (make-temp-name "__plantuml__")))
+    (let ((ps (plantuml-start-process temp-buffer)))
       (process-send-string ps string)
       (process-send-eof ps)
       (set-process-sentinel ps
                             (lambda (_ps event)
                               (unless (equal event "finished\n")
                                 (error "PLANTUML Preview failed: %s" event))
-                              (cond
-                               ((= prefix 16)
-                                (switch-to-buffer-other-frame plantuml-preview-buffer))
-                               ((= prefix 4)
-                                (switch-to-buffer-other-window plantuml-preview-buffer))
-                               (t (switch-to-buffer plantuml-preview-buffer)))
-                              (when imagep
-                                (image-mode)
-                                (set-buffer-multibyte t)))))))
+                              (with-current-buffer preview-buf
+                                (let ((inhibit-read-only t))
+                                  (fundamental-mode) ; prevent weird loops
+                                  (erase-buffer)
+                                  (replace-buffer-contents temp-buffer))
+                                (when imagep
+                                  (image-mode)))
+                              (save-excursion
+                                (cond
+                                 ((= prefix 16)
+                                  (switch-to-buffer-other-frame plantuml-preview-buffer))
+                                 ((= prefix 4)
+                                  (switch-to-buffer-other-window plantuml-preview-buffer))
+                                 (t (display-buffer plantuml-preview-buffer))))
+                              (kill-buffer temp-buffer))))))
 
 (defun plantuml-preview-buffer (prefix)
   "Preview diagram from the PlantUML sources in the current buffer.