Following Derek Fountain’s suggestion, I have prepared a video presentation on my previous SP1 Scrolling articles. Some SP1 background and detailed explanations on how the examples work are included; they are also shown running:

I have reconfigured all tests to use a 16x24-cell scrolling zone, which is a more realistic size for a scrolling game on the ZX. The results are proportionally similar to the previous ones, but with bigger differences between the baseline measurements and the optimized ones in Test 3 and Test 4.

In this section I have compiled the performance characteristics for all the previous tests. For this, I have needed to normalize the code so that comparison between measurements are meaninful.

I have decided not to explore the mentioned Test 5 case (partial column scroll), since again we will have the degenerated case of having to scroll most of the column most of the time, and also the scrolling is not the most time-consuming operation which is being executed.

It can be found in the src/sp1-partial-inv-2 directory. Based on Test 3, but changing the algorithm which keeps track of the cells to invalidate. Conceptually, this method keeps track of the position of each and every tile which is seen on screen, and periodically adjusts the cells that it invalidates in lockstep with the scrolling routine.