Add workaround to render svg>image case

It's very common to have `<svg ...><image href="..."></svg>` for cover
pages. However, not all uses of the `<svg>` tag use `<image>` inside,
for example some EPUB documents use it for vector logos instead.

The given workaround checks whether the SVG node can be safely
replaced with an equivalent image and otherwise falls back to regular
SVG rendering.

1 files changed, 29 insertions, 0 deletions

diff --git a/nov.el b/nov.el
index 946564b..3fe78b6 100644
--- a/nov.el
+++ b/nov.el
@@ -515,6 +515,8 @@ Each alist item consists of the identifier and full path."
   (mapcar 'nov-urldecode (list (url-filename url) (url-target url))))
 
 ;; adapted from `shr-rescale-image'
+;; TODO: adjust to latest shr code (which added zooming support)
+;; TODO: support width/height as supplied in img/image/svg attributes
 (defun nov-insert-image (path alt)
   "Insert an image for PATH at point, falling back to ALT.
 This function honors `shr-max-image-proportion' if possible."
@@ -556,6 +558,31 @@ internal ones."
       (setq url (expand-file-name (nov-urldecode url)))
       (nov-insert-image url alt))))
 
+(defun nov--render-image (dom &optional url)
+  (let ((img-tag (dom-node 'img
+                           (dom-attributes dom)
+                           (dom-children dom))))
+    (nov-render-img img-tag url)))
+
+(defun nov-render-svg (dom)
+  "Custom <svg> rendering function for DOM.
+If the SVG element only contains <image> tags with an internal
+URL, insert each image with `nov-insert-image'. Otherwise, fall
+back to regular <img> rendering via `nov-render-img' (for
+external URLs) or regular SVG rendering via `shr-tag-svg'."
+  (when (and (image-type-available-p 'svg)
+	     (not shr-inhibit-images))
+    (let ((children (dom-children dom)))
+      (if (seq-every-p (lambda (child) (eq (dom-tag child) 'image)) children)
+          (dolist (image-tag children)
+            (let ((url (or (dom-attr image-tag 'href)
+                           (dom-attr image-tag 'xlink:href))))
+              (if (nov-external-url-p url)
+                  (nov--render-image dom)
+                (nov-insert-image
+                 (expand-file-name (nov-urldecode url)) ""))))
+        (shr-tag-svg dom)))))
+
 (defun nov-render-title (dom)
   "Custom <title> rendering function for DOM.
 Sets `header-line-format' according to `nov-header-line-format'."
@@ -578,6 +605,8 @@ Sets `header-line-format' according to `nov-header-line-format'."
 (defvar nov-shr-rendering-functions
   '(;; default function uses url-retrieve and fails on local images
     (img . nov-render-img)
+    ;; likewise, but for SVG tags containing local images
+    (svg . nov-render-svg)
     ;; titles are rendered *inside* the document by default
     (title . nov-render-title))
   "Alist of rendering functions used with `shr-render-region'.")