Multitexturing

Graphic based area of development (Graphics Processing Unit), including the Geometry Transform Engine (GTE), TIM, STR (MDEC), etc.
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Misscelan
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Multitexturing

Post by Misscelan » July 7th, 2017, 7:21 am

Hi,

I watched today a video of Gran Turismo and the environment mapping they use on the cars, go me thinking.

It seems there is a base diffuse texture and then some semitransparent one on top simulating the sky reflections.
How do you think they achieved this? Did they render first the car (only diffuse) and then render the car mesh again this time using the semitransparent? Or, is there a way of passing 2 textures to a poly during the same pass?

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LameGuy64
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Re: Multitexturing

Post by LameGuy64 » July 7th, 2017, 9:17 am

PlayStation graphics programmer here, the GPU cannot render multiple textures on a single polygon primitive at once. However, you can overlap a polygon over another one to achieve a multi-texturing effect. I've used this technique on one of my projects to achieve cel-shaded rendering with a shading technique similar to that used on Gamecube games (such as Wind Waker).
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Misscelan
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Re: Multitexturing

Post by Misscelan » July 7th, 2017, 6:01 pm

Thanks, that's what I thought.

But then you think in this case (GT1), to render the environment mapping:
Image


they rendered all the car models twice? It seems to me like a bit of an overkill.

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LameGuy64
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Re: Multitexturing

Post by LameGuy64 » July 9th, 2017, 1:33 am

Environment maps are usually prerendered as a texture and is usually enough to make it look believable and then the same polygon overlay technique I mentioned was used to give objects a shiny, reflective look.

It is not necessarily rendering the model twice but more like rendering 2 polygons per polygon of the model with the other applying the shiny effect. It does not require twice the number of GTE operations to achieve it efficiently.
Please don't forget to include my name if you share my work around. Credit where it is due.

Dev. Console: SCPH-7000 with SCPH-7501 ROM, MM3, PAL color fix, Direct AV ports, DB-9 port for Serial I/O, and a Xplorer FX with Caetla 0.35.

DTL-H2000 PC: Dell Optiplex GX110, Windows 98SE & Windows XP, Pentium III 933MHz, 384MB SDRAM, ATI Radeon 7000 VE 64MB, Soundblaster Audigy, 40GB Seagate HDD, Hitachi Lite-on CD-RW Drive, ZIP 250 and 3.5" Floppy.

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