FWIW, I did manage to do this. I added a line 155 to the MMM-BackgroundSlideshow.js:
image.src = encodeURI(this.imageList[this.imageIndex]);
this.sendNotification("IMAGEFILEPATH", image.src); //my stuff
Then I created a small module that displayed the notification.
Module.register("MMM-ShowMessage", {
defaults: {},
getDom: function() {
var element = document.createElement("div");
element.className = this.config.size;
element.id = "IMGPATHFILE";
return element;
},
notificationReceived: function(notification, payload, sender) {
switch(notification) {
case "IMAGEFILEPATH":
var elem = document.getElementById("IMGPATHFILE")
var subpayload = payload.substring(53)
elem.innerHTML = subpayload
break
}
},
});
In my config.js I just added:
{
module: "MMM-ShowMessage",
position: "bottom_left",
config: {
size: "small"
}
},
Now each time the image changes a notification is sent and picked up by the show message module which displays it on screen. I trim the path because the beginning was consistent among all the pictures.