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Yeah. You have a point. My proposed changes only really bring the Saturn's 3D graphics into roughly the same technical capabilities as the Playstation. They d

by phire 3y ago

Yeah. You have a point. My proposed changes only really bring the Saturn's 3D graphics into roughly the same technical capabilities as the Playstation. They don't do anything to help with the performance issues or the higher manufacturing costs. Or the string of bad moves from SEGA management that alienated everyone. But an alternative history with these minor changes might have been enough to stop developers complaining about the Saturns non-standard 3D graphics and keep a healthy market of cross-platform games. It might have also prevented commenters on the internet from making overally broad claims about the Saturn's lack of 3D capabilities. --------------- Fixing the performance limitations and BoM cost issues would have required a larger redesign. I'm thinking something along the lines of eliminating most specialised 2D capabilities (especially all of VDP2). Unify what's left to a single chip and simplify the five blocks of video memory down to a single block on a 32bit wide bus. This would significantly increase the bandwidth to the framebuffer, compared to VDP1's framebuffer which uses a 16bit bus, while decreasing part count and overall cost. The increased performance of this new 3D focused VDP should hopefully be powerful enough to emulate the lost VDP2 background functionality as large 3D quads.

mmaniac 3y ago
The design you're describing sounds a lot more like the Playstation. I find most of these hypotheticals about "fixing" the Saturn work out that way :) Playstation indeed had unified video memory on a 32 bit bus, but the bus is only saturated when drawing 2D elements or untextured polygons[1]. Sprite-heavy 2D games like DoDonPachi already run better on Playstation than Saturn due to the faster framebuffer, while games like Spyro the Dragon, Crash Bandicoot and Final Fantasy 7 demonstrate the effective strategic use of untextured polygons. [1] https://psx.arthus.net/sdk/Psy-Q/DOCS/CONF/SCEA/adv_gpu.pdf https://psx.arthus.net/sdk/Psy-Q/DOCS/CONF/SCEA/adv_gpu.pdf , slide 17.
- phire 3y ago
  Yeah. It essentially ends up as the Playstation GPU, but with quads and forwards texturing. It's basically inevitable. Any proposal for fixing the Saturn that slaps on a "optimise for BoM" requirement will be pushed towards unified video memory. And the only contemporary example of such a GPU was the playstation. Not to mention, the design of the playstation GPU appears to be pretty close to optimal for it's era and price point. And if you were to also switch your hypothetical Saturn design to triangles and inverse texturing, the resulting design looks even more like the Playstation GPU. > but the bus is only saturated when drawing 2D elements or untextured polygons The Playstation's bus will also be saturated when loading the texture cache, or when scanning out the previous frame (only on the later SGRAM versions of the GPU). Even with textured triangles framebuffer writes are limited to 16bit bandwidth, less time is wasted on those other tasks which periodically interrupt rasterisation. Though, now that I think about it, inverse texturing probably gives the playstation a massive performance advantage over and forwards texturing. Inverse texturing allows triangles to be rasterized in strict left-to-right then top-to-bottom order, which is also the order that the framebuffer is laid out in memory. This order will minimise the amount of time spent waiting for the next DRAM row to be prefeched. The order of framebuffer writes with forwards texturing is somewhat chaotic and probably wastes a bunch more time closing and opening DRAM rows.
  - mmaniac 3y ago
    The memory access pattern of inverse texturing is just as chaotic when it comes to reading texels, which is why the Playstation's texture cache plays an important role in its performance characteristics. Saturn doesn't have a texture cache, since texel reads should be nice and sequential. But then it pays a penalty when writing to the framebuffer.
    - phire 3y ago
      I guess since forwards rendering doesn't need a proper texture cache, you could used the savings to implement a write combining buffer. But I'm only saying that because I know write combining is a thing, and I'm not sure a hardware engineer in 1993 would have gone down that path.

by phire 3y ago

mmaniac 3y ago

The design you're describing sounds a lot more like the Playstation. I find most of these hypotheticals about "fixing" the Saturn work out that way :) Playstation indeed had unified video memory on a 32 bit bus, but the bus is only saturated when drawing 2D elements or untextured polygons[1]. Sprite-heavy 2D games like DoDonPachi already run better on Playstation than Saturn due to the faster framebuffer, while games like Spyro the Dragon, Crash Bandicoot and Final Fantasy 7 demonstrate the effective strategic use of untextured polygons. [1] https://psx.arthus.net/sdk/Psy-Q/DOCS/CONF/SCEA/adv_gpu.pdf https://psx.arthus.net/sdk/Psy-Q/DOCS/CONF/SCEA/adv_gpu.pdf , slide 17.

phire 3y ago
Yeah. It essentially ends up as the Playstation GPU, but with quads and forwards texturing. It's basically inevitable. Any proposal for fixing the Saturn that slaps on a "optimise for BoM" requirement will be pushed towards unified video memory. And the only contemporary example of such a GPU was the playstation. Not to mention, the design of the playstation GPU appears to be pretty close to optimal for it's era and price point. And if you were to also switch your hypothetical Saturn design to triangles and inverse texturing, the resulting design looks even more like the Playstation GPU. > but the bus is only saturated when drawing 2D elements or untextured polygons The Playstation's bus will also be saturated when loading the texture cache, or when scanning out the previous frame (only on the later SGRAM versions of the GPU). Even with textured triangles framebuffer writes are limited to 16bit bandwidth, less time is wasted on those other tasks which periodically interrupt rasterisation. Though, now that I think about it, inverse texturing probably gives the playstation a massive performance advantage over and forwards texturing. Inverse texturing allows triangles to be rasterized in strict left-to-right then top-to-bottom order, which is also the order that the framebuffer is laid out in memory. This order will minimise the amount of time spent waiting for the next DRAM row to be prefeched. The order of framebuffer writes with forwards texturing is somewhat chaotic and probably wastes a bunch more time closing and opening DRAM rows.
- mmaniac 3y ago
  The memory access pattern of inverse texturing is just as chaotic when it comes to reading texels, which is why the Playstation's texture cache plays an important role in its performance characteristics. Saturn doesn't have a texture cache, since texel reads should be nice and sequential. But then it pays a penalty when writing to the framebuffer.
  - phire 3y ago
    I guess since forwards rendering doesn't need a proper texture cache, you could used the savings to implement a write combining buffer. But I'm only saying that because I know write combining is a thing, and I'm not sure a hardware engineer in 1993 would have gone down that path.