up vote 1 down vote favorite

Some early consoles like the NES and the Sega Master had a horizontal screen resolution of 256.

That sounds good for an 8-bit machine, until you consider that a sprite sometimes needs a slightly negative position in order to be partly off the left side of the screen. (Consider e.g. the bad guys in Super Mario Bros, who move onto the screen from the right, and if you and they miss each other, end up moving off the screen to the left.) The upshot is that you need to track an extra bit for sprite positions. Not a huge problem, but it's got to be annoying being so close to being able to track positions in one byte, and just missing the mark.

It would seem that by reducing the resolution to 248, you could represent positions in one byte, without making any discernible change in the quality of the display. Why didn't they do this?

share|improve this question
up vote 4 down vote accepted

The NES did not use an extra bit for sprite positions. A sprite's X-position was the position of its left edge, which means that sprites cannot be placed partially off the left side of the screen:

enter image description here

However, the NES did actually provide the feature you're suggesting, in a way: bits 1 and 2 of the PPUMASK register can be used to keep the leftmost 8 pixels of the screen blank. This not only allows sprites on the left side to be hidden, but also helps to reduce the mirroring glitches on the sides of the screen in some games.

As an example, here's a screenshot of Super Mario Bros. 3:

enter image description here

It's especially obvious in areas where the background color configured in the PPU palette is different from what we humans would consider the background color:

enter image description here

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.