Just what is "analog sprite scaling" ?

[Jorpho]

There's probably a better board out there for asking this question, but maybe someone here knows:

Part of the reason that Buck Rogers was a relative latecomer to MAME was that it had "analog sprite scaling circuitry", and that was a difficult thing to emulate.

It occurs to me I have no idea as to what this actually means, and I'm kind of curious about the details. How exactly could you use analog circuitry to scale a sprite? It doesn't quite make sense.

[kedawa]

There are all sorts of weird raster tricks that older hardware uses, but I've never heard of analog sprite scaling.

[Mayhem]

Possible supposition... usually back then you had to draw all the individual frames of animation, so there was a need to store images of all the ship sizes from small to large. Maybe the circuitry automatically calculated and created the correct sprite size for the ship on the fly instead?

[APE992]

If its analog it can't be digitally emulated, only simulated.

[Drath]

Just my idea, not 100% on this:

The "analog" in that phrase is kind of a misnomer. It just means it uses the screen resolution (analog) to scale the sprites rather than through hardware. This would be hard in terms of emulation because the game/chip detects the analog screen resolution to scale the sprites which isn't there through emulation.

[APE992]

Perhaps. I did some googling and found this:

- 0.108u2: Removed machine\turbo.c. Further turbo driver cleanup. Still in WIP. [Aaron Giles]: Derived sprite scaling from PROMs and R/C values (still not 100%). Rewrote most of the video/sprite handling.

Seems Giles was reverse engineering the data on hand to do so. Obviously if the machine relied on an analog value to determine how to scale the sprites they'd have to simulate it at best. A few games on MAME rely entirely on samples store as WAV files to have actual sound due to their hardware being impossible to emulate (analog generated audio) or incomplete knowledge of the hardware not allowing them to even start work. I believe one of the Star Wars games was (maybe still is) like this.