Add a makeWebpVariant option

[khalwat]

The .webp support is awesome, but it would be super-duper awesome of there was a boolean flag in the config:

makeWebpVariant = false,

...and I could pass it in as an option in the settings array I pass into Imager when doing my existing transforms. If set, it would do the regular transform, and -also- make a .webp version of the transform, suffixed with .webp

e.g.:

{% set transformedImages = craft.imager.transformImage('woof.jpg', [
    { width: 1200, ratio: 2/1, jpegQuality: 75, webpQuality: 75 },
    { width: 1024, ratio: 2/1, jpegQuality: 75, webpQuality: 75 },
    { width: 768, ratio: 4/3, jpegQuality: 60, webpQuality: 60 },
    ],{ format: 'jpg', makeWebpVariant: true, allowUpscale: false, mode: 'crop', position: image.focusPctX ~ '% ' ~ image.focusPctY ~ '%', interlace: true }) %}

In this case it would churn out:

/imager/woof_AS2412ADSS.jpg
/imager/woof_AS2412ADSS.jpg.webp

The reason for this is the recipes for serving up .webp files automatically depend on the file being named the normal image filename with .webp tacked on the end:

Nginx: https://github.com/uhop/grunt-tight-sprite/wiki/Recipe:-serve-WebP-with-nginx-conditionally

Apache: https://gist.github.com/seeekr/2415528

This is really the "right" way to do .webp right now, imo, due to the spotty browser support, and if it's as simple as turning on a flag to have Imager make a variant of what it's transforming already—with the correct .webp suffix appended—it'd be fantastic.

[aelvan]

Can we agree that this is not the best way to support webp images? :)