more shortcode tweaks for valid RSS

layouts/shortcodes/image.rss.html

@@ -1 +0,0 @@
-image.html

layouts/shortcodes/image.rss.html

@@ -0,0 +1,35 @@
+{{- /* Automatic resizing for HiDPI/retina images */ -}}
+
+{{- $original := .Page.Resources.GetMatch (.Get "src") -}}
+{{- .Scratch.Set "image" $original -}}
+
+{{- $maxWidth := 910 -}}
+{{- $setWidth := 0 -}}
+
+{{- if .Get "width" -}}
+  {{- $setWidth = (int (.Get "width")) -}}
+  {{- $retinaWidth := (mul $setWidth 2) -}}
+
+  {{- if gt $original.Width $retinaWidth -}}
+    {{- $finalWidth := (printf "%dx" $retinaWidth) -}}
+    {{- .Scratch.Set "image" ($original.Resize $finalWidth) -}}
+  {{- end -}}
+{{- else -}}
+  {{- $setWidth = $maxWidth -}}
+  {{- if gt $original.Width 1820 -}}
+    {{- .Scratch.Set "image" ($original.Resize "1820x") -}}
+  {{- end -}}
+{{- end -}}
+
+{{- $image := .Scratch.Get "image" -}}
+
+{{- $origRatio := (div (float $image.Height) $image.Width) -}}
+{{- $displayWidth := $setWidth -}}
+{{- $displayHeight := (math.Ceil (mul $origRatio $setWidth)) -}}
+
+<p style="text-align: center;">
+<img src="{{ $image.Permalink }}" width="{{ $displayWidth }}" height="{{ $displayHeight }}"
+     {{- with .Get "alt" }} alt="{{ . }}"{{ end }}
+     {{- with .Get "caption" }} title="{{ . }}"{{ end }}>
+{{ with .Get "caption" }}<br>{{ . }}{{ end -}}
+</p>