Access custom web parts fields in custom layout (for aforementioned web part)

ED: Totally missinterpreted your question

for future reference

Here is a little provider method I wrote for this use case

    public static class ImageProvider
    {
        public static string GetImageUrl(string permanentUrl, int width, int height)
        {
            var querylessUrl = URLHelper.RemoveQuery(permanentUrl);
            var query = URLHelper.GetQuery(permanentUrl);
            var queryCollection = HttpUtility.ParseQueryString(query);

            queryCollection["width"] = width.ToString();
            queryCollection["height"] = height.ToString();

            return URLHelper.AppendQuery(querylessUrl, queryCollection.ToString());
        } 
    } 

Make sure, you have the use of permanent image URLs activates for your Media Library.

By using this method, you'll get the Image URL, which you can add into your aspx then. Inside your cs class, you should work with something like this:

public string Background = ImageProvider.GetImageUrl(this.GetStringValue("BackgroundImage", string.Empty), 400, 250));

You can then simply access the url with the default apsx <%# Background %>

Edit: When you have permanent URLs enabled, it should be enough, to just use public string Background = this.GetStringValue("BackgroundImage", string.Empty);

Trevor, not sure where you are with configuration right now. This is how I will do.

I am taking example of Editable Image Webpart based Widget

1. Create a Widget using my custom webpart.
2. Go to widget properties. Select the field that I would like to editor to update without changing code. In my case it was "Default Image"
3. See on the right side that this field is checked. Display field in the editing form
4. The column name was "Default Image". Now in my html code I can access this field as {%DefaultImage%}. That's it.

Image Attached.

Thank you gentlemen! As I suspected, this isn't doable without some code meddling, which for this particular instance I would prefer to avoid. At the end of the day we will only be using this on three to five different pages, and as such it is easy enough to just duplicate the regular Editable Text with the before/after parts prefilled and just have the content editor copy paste the background path.

Your responses gave me a much better understanding of the inner workings of the system and when I come across something that merits actually creating a proper custom widget/part, I will be sure to refer to this thread!

Thanks again!