Not that surprising, given the CPU in the NES is a second sourced near-6502 (Ricoh 2A03) though running a bit faster apparently. But there's nothing in there that's hard to do on a C64 (and in fact before this there was The Great Giana Sisters, released in '87, that was so similar - including a near identical first level - that Nintendo threatened to sue and it was taken out of the stores; but of course "everyone" had copies soon enough anyway)

EDIT: Here's a video of the C64 version of Giana Sisters: https://www.youtube.com/watch?v=8teXm6723-g&t=1309s

I think the NES's PPU is a lot more powerful in some ways than the C64 VIC-II chip. The NES's PPU supports multiple background layers, priority, pixel collision detection and has up to 64 sprites on screen at once - albeit with some limitations on how many are on each scanline. The VIC-II can only do 8 sprites at a time without scanline raster tricks (and if we count those the NES can do more than 64 too)

IIRC the NES PPU only supports one background layer. You can just change the scroll position mid-frame to give it the illusion of multiple background layers.

See here for some clever examples of this technique. Everything that's overlapping is done with sprites:

https://youtu.be/ZGyFQ9aRp_U?t=579

You're right, I was thinking of the SNES which had multiple background layers.

It's not near-6502 it's an exact 6502. Die-shots show the exact same transistor layout; even the decimal section is there but disabled.

There are differences in terms of some IO pins. But yes, the changes are minimal.

Oh wow, nostalgia! Giana Sisters was absolutely fantastic. I played it to death. My NES owning friends were kinda grumpy about how good it was.

I'd like to give a shoutout to machinae supremacy https://www.youtube.com/watch?v=XKkmyMKbPKE

Chris Hülsbeck https://www.youtube.com/watch?v=XKkmyMKbPKE

and all the guys at https://www.slayradio.org

for keeping the scene alive!

This is more like off/store brand soda than anything. While not Dr Pepper, it's like Mr Pibb or Dr Thunder, still tastes good, but it's not quite the same.

You take that back, Mr Pibb is clearly the best. It doesn't put on airs like some other sodas.

Real Mr Pibb was awesome, although wasn't available in my region growing up.

When they moved over to Pibb Extra, that stuff was just nasty.

It's based on the reverse-engineered source code of the NES original, though.

I'd bet Mr Pibb and Dr Thunder are based on the reverse-engineered ingredients analysis of Dr Pepper.

Well, the version of Tapper I used to play on the C64 used root beer rather than so it works.

Except for the slow-downs.

Nice touch: the clock has an extra pixel on it when it’s running slow.

How did you even spot that?

In the readme:

> Since the NES-processor is clocked (roughly 70%) faster than a stock C64 there can be slowdowns during gameplay. A pixel indicates this on the time-watch graphics in the status bar.

I find the music/audio artefacts give it away.

Even the colors look almost right - I wonder how that can be...

There's a technique called "IFLI" that leverages the analog characteristics of 60/50fps CRTs - it's basically switching between two colors each alternating frame to "mix" two colors.

However the colors look like C64 colors. The Goombas and skin of the turtles are pink. Except possibly the Mario sprite.