allow for varied image filetypes in shortcode and partial

layouts/partials/image.html

@@ -4,12 +4,15 @@ Renders an image with the given class, alt, and sizes.
 @context {image} the image resource.
 @context {sizes} each size to include in the srcset.
 @context {classes} classes for the image.
+@context {ext} extension of output image.
 */}}
 
   {{- $alt := .alt }}
   {{- $img := .image }}
   {{- $sizes := .sizes }}
   {{- $classes := .classes }}
+  {{- $ext := .ext }}
+
 
   {{- $srcsetParts := slice }}
   {{- $sizesParts := slice }}
@@ -18,7 +21,7 @@ Renders an image with the given class, alt, and sizes.
 {{- if .image }}
   {{/* Loop through widths to resize images and build attributes */}}
   {{- range $index, $width := $sizes }}
-    {{- $resizeSpec := printf "%dx webp q90" $width }}
+    {{- $resizeSpec := printf "%dx %s q90" $width $ext }}
     {{- $resized := ($img.Resize $resizeSpec) }}
 
     {{- $srcsetParts = $srcsetParts | append (printf "%s %dw" $resized.RelPermalink $width) }}
@@ -33,7 +36,7 @@ Renders an image with the given class, alt, and sizes.
   {{- end }}
 
   {{- $smallestWidth := index $sizes 0 }}
-  {{- $smallestResizeSpec := printf "%dx webp q90" $smallestWidth }}
+  {{- $smallestResizeSpec := printf "%dx %s q90" $smallestWidth $ext }}
   {{- $smallest := ($img.Resize $smallestResizeSpec) }}
   {{- $src := $smallest.RelPermalink }}
 <img class="{{ delimit $classes " " }}"

layouts/shortcodes/image.html

@@ -4,4 +4,5 @@
    "image" $image
    "alt" (.Get "alt")
    "sizes" (slice 320 480 600)
-   "classes" (slice "fill-wh")) }}
+   "classes" (slice "fill-wh"))
+   "ext" (.Get "ext" | default "webp" ) }}