update

Author: neveler

_plugins/link.rb

@@ -110,15 +110,18 @@ def relative_url(input)
   webp_list = []
   site.each_site_file do |file|
     Link::HtmlExtension.file[file.relative_path] = file
-    if ENV["JEKYLL_ENV"] == "production" && ENV["WEBP"] == "enabled"
-      require "webp-ffi"
-      if file.is_a?(Jekyll::StaticFile) && %w[.png .jpg .jpeg .tif .tiff].include?(file.extname.downcase)
-        webp_url = "#{file.url}.webp"
-        destination = File.join(site.dest, webp_url)
-        FileUtils.mkdir_p(File.dirname(destination))
-        WebP.encode(file.path, destination)
-        webp_list.push(Link::WebpFile.new(site, site.dest, File.dirname(webp_url), File.basename(webp_url)))
-        Link::HtmlExtension.webp[file.url] = webp_url
+    require "webp-ffi" if ENV["JEKYLL_ENV"] == "production" && ENV["WEBP"] == "enabled"
+    if file.is_a?(Jekyll::StaticFile) && %w[.png .jpg .jpeg .tif .tiff].include?(file.extname.downcase)
+      url = "#{file.url}.webp"
+      source = "#{file.path}.webp"
+      destination = File.join(site.dest, url)
+      if File.exist?(source) || ENV["JEKYLL_ENV"] == "production" && ENV["WEBP"] == "enabled"
+        unless File.exist?(source)
+          FileUtils.mkdir_p(File.dirname(destination))
+          WebP.encode(file.path, destination)
+        end
+        webp_list.push(Link::WebpFile.new(site, site.dest, File.dirname(url), File.basename(url)))
+        Link::HtmlExtension.webp[file.url] = url
       end
     end
   end