Drawing bitmaps on a display using arrays.

Hi Bill and all the other members.

I am currently in the process of making a gear shift knob for my car that has the shift pattern lit up on a tiny round display on top of it, and is also dynamic in the fact that it displays which gear the transmission is currently in. This is not my idea, I only came across it while scanning YouTube videos one day. Here's the link to the video that describes it all:

The fellow that did the work did a fantastic job, and has shared his code as well which makes it even better. Now since my car is not a BMW but a VW, I have changed the graphic in the center of the knob, however I would also like to have the center picture swapped out on a timed delay to show the outside temperature via a DHT22 (since my car has no outside thermometer) I planned on having it rotate between car graphic, temperature in Celsius, temperature in Fahrenheit, then loop again. 

The issue I am having a hard time understanding is drawing a bitmap on the screen without using an external library. The round screen does not have a display that is compatible with AdaFruit's graphics drivers or any that I could find so it has to be done using a bitmap array. When I use his code exactly the way he wrote it, and I make the graphic the exact same size he made it, I can get it to work, but when I want to make a change to the size I just can't get it to work. Unfortunately there is surprisingly little content on YouTube or anywhere else that explains in detail how this actually works. I'm not a coding expert but when it's explained as well as Bill does it I can follow along easily and pick it up. 

So after all that, that's my content suggestion. If you did a video Bill, explaining the in's and out's of drawing a bitmap from an array with all the coding broken down so we can see how it's actually done that would be fantastic! I think it would also fill a gap in the content world as to how its done as well. The few videos I watched just seem to gloss over that portion of the code without a full explanation of each part. 

Thanks in advance for your consideration.