Re-use use_logo for multiple logos/multiple rules templates

[rsimonmd]

Disclaimer: This is my first ever pull request so please feel free to dunk me for all the things I have certainly missed and the etiquette I am not following: I am very eager to learn! Also, I love your package so much 😄

Hello,

I work for a french public health/government organisation and we have a very strict ppt template to follow. I am allowed to pursue the use of html slides but only if I use the official template (example here, although you shouldn't look it will make your eyes bleed).

Up until today and diving into the use_logo() function from your package, I was stuck on a simple problem: our template has different background images/logos depending on the slide ... And if I made CSS rules for slide classes using background-image property, then I couldn't use background-image when I needed it for presentation purposes (at least my users wouldn't understand why the logos suddenly disapeared).

I tried your package but using the function twice resulted in the last call erasing the first so I went ahead and slightly changed some arguments to allow for the naming of the added image and thus adding as many divs as needed !

PS: if you took a look at the example ppt format (again, I advise against it for your eyes safety), the images that I need to change are vertical colored bars. I figured I also could use a variation of what you did there (before use_logo existed I guess?) to add spans with a colored background but I don't know if thats a better way of doing things in HTML ...

Have a great day

Raphaël

[gadenbuie]

Hi @rsimonmd, thanks for the PR! The idea of having multiple logos has certainly come up before and your approach seems like a good place to start. I took a look at your official template (with sunglasses on to protect my eyes [ouch!]), but it would be helpful if you could share a small example that demonstrates how the updated version works. You could copy/paste an example Rmd source into a code block in a comment in this PR, rather than having to commit the file to the PR branch.

[rsimonmd]

Of course ! Here it is :

---
title: "A clever title"
subtitle: "Demoing xaringanExtra's expanded use_logo()"
author: "Raphael Simon"
institute: "Myself"
date: "`r Sys.Date()`"
output:
  xaringan::moon_reader:
    lib_dir: libs
    seal: false
    nature:
      ratio: 16:10
      highlightStyle: github
      highlightLines: true
      countIncrementalSlides: false
---
class: middle center someclass

```{r setup, echo = FALSE, warning=FALSE}
library(xaringanExtra)

use_logo(
  image_url = "logo1", 
  width = "150px",
  height = "150px",
  position = css_position(top = "1em", left = "1em"),
  logo_class = "my-xaringan-logo1",
  exclude_class = c("hide_logo", "someotherclass")
)

use_logo(
  image_url = "logo2", 
  width = "150px",
  height = "150px",
  position = css_position(top = "1em", right = "1em"),
  logo_class = "my-xaringan-logo2",
  exclude_class = c("hide_logo", "someclass")
)

A slide

With only the left-side logo

---

class: middle center someotherclass

A slide

With only the right-side logo

---

class: middle center

Or both !

Notice how they both appear on the title slide as well!
You can change that by excluding "title-slide" from use_logo(exclude_class = c(...)) as well

I hope that answers your query, thanks for allowing me to contribute 😄 

EDIT : added some punctuation so that this Rmd actually knits withotu errors