A few Q's about the Saturn and emulation
Is the saturn's hardware 2d processor really needed for good 2d games? ie. Capcom arcade ports, snk, 2d sidescrollers..
No, but it helps. Especially if there are any raster effects, which are animation effects that are designed around traditional scanline-oriented 2D hardware manipulation; a lot of old-school screen warping/waving and perspective effects are achieved with this, and there's no cheap way to achieve the same effect on framebuffer-oriented hardware. It can be done of course, but you'll take a performance hit compared to just being able to shift scroll registers around.
Should the psx also be able to do the same 2d like the saturn for those ports if it had the ram?
Generally speaking, yes.
How does the saturn bend quads? Create smaller quads? Or actually hardware accelerated curves? How does it affect performance?
I'm not sure what you mean here. Can you give a more concrete example? As far as I understand VDP1 operation, it really just draws a quad line-by-line, with the orientation of the "lines" being appropirately transformed for the supplied coordinates. The biggest VDP1 performance issues are in per-pixel operations like semitransparency (which does exist, but can only be used with RGB modes, and only if the rendering order is correct, and takes something like 6 times as long to draw, which is why you see a lot of games using the crappy "mesh" pseudotransparency) and shading, which are mostly unrelated to geometry (i.e. it's a fill rate limitation). Saturn does not have hardware-accelerated curves in the sense of modern 3D hardware (and neither do PSX or N64).
4. Does Nights Into Dreams use non-coplaner quads? If so, how does the current saturn emulators draw them correctly/incorrectly?
Saturn's VDP1, like most "3D" processors of its time, doesn't actually deal with a Z axis, so the question of non-coplanar geometry is a software one.
What I'm wondering, if the saturn could have done better by removing it's 2d vpu and having just one more powerful 3d vpu instead.
Well, that raises other questions:
- What makes a rendering unit "more powerful"? The obvious choice and industry consensus seems to be higher fill rate, which is dependent on the clock speed of the processor, the bandwidth of the video memory, and the number of pixels that can be rendered in parallel by the hardware. For a given production process, it doesn't make much sense to assume that arbitrary clock speed targets can be selected, and faster/wider memory and more pixel pipelines cost more money, which brings us to the next question:
- Was the split-VDP architecture so expensive that merely eliminating VDP2's background generation portions (the display generation parts would have had to stick around as part of our hypothetical super-chip, since rendering isn't very useful unless you can see the result) would have made up the cost difference? I doubt this would be the case. For one thing, it's generally cheaper to fabricate two smaller chips than one larger one on a given manufacturing process, because yield suffers as die size increases. Then you'd also be looking at a need for wider and/or faster memory to feed the improved processor, so I'm a little skeptical that such a tradeoff could have been feasibly made.
Unless, of course, the question you were asking was "Would Saturn have done better if Sega's engineers weren't constrained by reality?", to which the answer is an emphatic "Hell yes!" :cheers