Author here. Yes, it is integral. I chose this approach to first show how to draw it from back to front, because the code is easier to understand this way.

I think it's worth noting that you can tilt with this method, but not roll.

Great for a helicopter game, Less so for general flight sim.

That was a large part of how games were designed back in the day. Start with what you have the ability to do, find the game that matches what you can do.

Notice the demo video from Comanche also shows roll.

Edit: To support roll, the renderer essentially rendered the voxel terrain into a frame buffer and then applied camera transformations that gave the appearance of a fully rotating viewpoint. The terrain itself was not being raycast through a true 3D voxel volume.

Reverse painters algorithm is still painters algorithm. You trade off the cost of a full screen clear before the frame, in return for eliminating overdraw

You could avoid a full screen clear by using the y-buffer to draw in sky segments after rendering terrain.

You still need to have some sort of mask to tell you which pixels have not yet been written this frame

that's what the y-buffer is that the article mentions in the front-to-back rendering section.

it tracks how tall each columns write is so you can use it to only write the diff between it and the voxel behind it, skipping writing anything at all if the voxel behind is shorter than the current height.

So once you're done rendering front-to-back, you've got a y-buffer of highest-writes you can slap your blue sky across from highest-to-screentop on each line, avoiding the need to clear by write the sky to the full screen before starting the render.

yes, I guess you can get away with only clearing the y buffer, rather than the whole screen