Linear Gradient Image With SVG Option

[mhemesath]

I think adding an SVG format option would be great for the linear gradient image. There would be no need for node-canvas and the image can be configured to scale content if size isn't provided, or made to fit a specific dimension without impacting size.

This should be relatively simple. We could use Jade to create some SVG templates, render them with the options, and then run the Stylus.url method on the output.

[notslang]

close - dupe of #33