On Royal Caribbean all bar sales will include a 15% tip automatically added on the receipt. They also have a line on them for 'extra' gratuities should you feel so inclined to do so. You can write down an extra tip amount to be charged on top of the automatic one. Otherwise just sign the receipt and you are done, and the bar staff gets tipped.
Tips for the dining and housekeeping staff still default to cash in envelopes handed out on the last evening. However you can fill out a form to have them charged to your account, and that is essentially handled like the auto-tipping you had on your first cruise except you have to initiate it. Now, if you have selected My Time Dining then you have already signed up for pre-paid gratuities for the dining and housekeeping staff, and these are part of your cruise price. They require pre-paid tips for MTD.