https://www.eurogamer.net/articles/digitalfoundry-2017-gran-turismo-sport-is-hdrs-killer-app
"GT Sport offers a remarkable level of detail in every facet of the presentation. The move to PlayStation 4 means that materials, textures and lighting are all amped up beyond what was previously possible. In making the leap to physically-based rendering, the game features more realistic surfaces and objects throughout its environments and across the lineup of cars. Textures are much sharper and more realistic as a result even up-close. The game retains a sense of scale that no other sim racer can quite match - the way its environments stretch out into the distance create the illusion of a large world."
I really don't think it's as simple as flipping a switch. Even the premium vehicle models from last gen had to be reworked to be able to function correctly with PBR IIRC, which is something that is
current gen. I got in a big discussion with someone about this years back but I can't remember for the life of me who it was.
Let's break that down...
"GT Sport offers a remarkable level of detail in every facet of the presentation. The move to PlayStation 4 means that materials, textures and lighting are all amped up beyond what was previously possible"
Easy enough - more horsepower, particularly GPU.
"In making the leap to physically-based rendering, the game features more realistic surfaces and objects throughout its environments and across the lineup of cars. Textures are much sharper and more realistic as a result even up-close."
I can only guess that 'textures are much sharper and more realistic as a result' means as a result of having more GPU grunt on tap with the PS4. PBR doesn't inherently sharpen textures. It does help surfaces look more realistic though - they respond more accurately to light at more angles and more conditions. HDR also helps a lot with this.
"The game retains a sense of scale that no other sim racer can quite match - the way its environments stretch out into the distance create the illusion of a large world."
Again, more to do with GPU grunt.
As for having to rework everything in a huge ordeal, not really.
Meshes don't actually need to be changed. PBR is about conserving (light) energy. Mesh quality has little to do with that.
The vast majority of textures should be in the 0-1 range. Metallic, Smoothness/Roughness, emission masks, etc, etc, etc. You could save them in HDR, but you get very diminishing returns in terms of precision - just more numbers after the decimal point. Smoothness should use the same texture as before, maybe exported at a higher res from (even higher res) source files. Base color for car paint, you'd never save as a texture. Likewise any special color values used for colorshift paints. So, adjusting the textures to PBR isn't THAT hard.
Shaders? Sure. They were likely using 'physically informed' shaders previously for things like car paint, glass. But the change isn't actually that drastic. And once you set that one shader, all you do is then go and make sure it's still fine for each paint color. Things like carbonfiber, grass, rubber all get written once and they should be fairly well bulletproof after that.
To be clear a 3D model of any level of detail is "compatible" with ray tracing, that's not the issue. Quake 2 RTX still uses the same 3D models from the original release.
You can import a PS1 era model from GT1 into a ray traced lighting engine, but obviously it would not be worth it because the poly count just isn't there to achieve the desired level of realism.
It was obviously a design decision to drop standard cars, and thank god for that. To me it is still ridiculous they even did that in the first place. THey had no place in GT5, let alone GT7.
Actually, ray-tracing responds really really well to low-poly / low-detail stuff.
The big gains - softer realtime bounced light and nice reflections on everything - don't actually require super-hi-poly models.
Sure there's gains to be had by having good super-detailed models and well-made textures. But there's nothing really DXR specific that helps with models. You just make better models, that tessellate better, and are more accurate. Which is what anyone would tend to do anyway.
GT7 has been in development as long as GTS, maybe longer. 2013 it was first talked about being in development, and at that stage we don't know how long for.
It should be noted that GTSport is also known as GT7 Sport. This is in internal names, and lasted long enough to make it into various code references (and elsewhere). So when they were talking about a 'GT7' in 2013 it kinda muddles the history a bit.
Though, having two things named GT7 will tend to do that....
