bug#13887: 24.3; doc-view will render blurry images when image-magick is available

[Tassilo Horn <tsdh@gnu.org>]

E Sabof <esabof@gmail.com> writes:

> The first time (doc-view-insert-image) is called, the doc-view buffer
> isn't selected, and (doc-view-current-overlay) returns the t overlay.
>
> The "fake" overlay gets "resurrected" when (doc-view-insert-image)
> calls (move-overlay) on it.

Thanks Evgeni, I think that brought me on track.  Could you please
test-drive this patch (which also contains the centering stuff) and
check if the issue is fixed by it?  It seems it is for me, but I only
did some very brief testing.

--8<---------------cut here---------------start------------->8---
=== modified file 'lisp/doc-view.el'
--- lisp/doc-view.el    2013-02-28 04:02:36 +0000
+++ lisp/doc-view.el    2013-03-14 07:21:18 +0000
@@ -1250,17 +1250,33 @@
   (when doc-view-pending-cache-flush
     (clear-image-cache)
     (setq doc-view-pending-cache-flush nil))
-  (let ((ol (doc-view-current-overlay))
-        (image (if (and file (file-readable-p file))
+  (let ((ol (doc-view-current-overlay)))
+    ;; ol might be a deleted (see `doc-view-new-window-function'), in
+    ;; which case we don't want to modify it.
+    (when (overlay-buffer ol)
+      (let* ((image (if (and file (file-readable-p file))
                   (if (not (and doc-view-scale-internally
                                  (fboundp 'imagemagick-types)))
                       (apply 'create-image file doc-view--image-type nil args)
                     (unless (member :width args)
                       (setq args `(,@args :width ,doc-view-image-width)))
                     (apply 'create-image file 'imagemagick nil args))))
-        (slice (doc-view-current-slice)))
+            (slice (doc-view-current-slice))
+            (img-width (and image (car (image-size image))))
+            (displayed-img-width (if (and image slice)
+                                     (* (/ (float (nth 2 slice))
+                                           (car (image-size image 'pixels)))
+                                        img-width)
+                                   img-width))
+            (window-width (window-width (selected-window))))
     (setf (doc-view-current-image) image)
     (move-overlay ol (point-min) (point-max))
+       ;; In case the window is wider than the image, center the image
+       ;; horizontally.
+       (overlay-put ol 'before-string
+                    (when (and image (> window-width displayed-img-width))
+                      (propertize " " 'display
+                                  `(space :align-to (+ center (-0.5 . ,displayed-img-width))))))
     (overlay-put ol 'display
                  (cond
                   (image
@@ -1287,7 +1303,7 @@
               (vscroll (image-mode-window-get 'vscroll win)))
           ;; Reset scroll settings, in case they were changed.
           (if hscroll (set-window-hscroll win hscroll))
-          (if vscroll (set-window-vscroll win vscroll)))))))
+             (if vscroll (set-window-vscroll win vscroll)))))))))
 
 (defun doc-view-sort (a b)
   "Return non-nil if A should be sorted before B.
--8<---------------cut here---------------end--------------->8---

Bye,
Tassilo