Case in point: The Atari 2600 had no screen buffer. You drew lines on the screen in real time, as the electron gun was firing. As the gun moves, so does your code, immediately rendering whatever is being drawn by the gun. This means everything had to be calculated at the exact moment the electron gun is where you want the tank to be drawn. It all took place through the TIA chip designed by Joe DeCuir and others at Atari.
Additionally, drawing the background of the screen was even more difficult, as the Atari 2600 could only address half the screen: you had to mirror whatever background was on one side, onto the other side of the screen, mirrored vertically.
But wait, it gets even more complicated! That one side of the screen was composed of 20 columns of possible addressing, making for 40 columns total across the screen. The 20 columns you could address on the left side of the screen were numbered, and I am not making this up, as follows:
1 2 3 4 5 6 7 8 8 7 6 5 4 3 2 1 1 2 3 4
That means you addressed the first part of the screen in ascending, left to right. Then, you had to draw right to left in reverse order (though numerically, it was still ascending), then you had 4 more bits to address, left to right.
Absolutely nuts. You can actually see the graphics if you look at the assembly of a 2600 game because the graphics were literally dot, no dot. The graphics were stacks of one's and zero's. Check out these Distella maps. They're in the NY MOMA, and the MADE. http://benfry.com/distellamap/