Color Combiner and Combined Color called for the first cycle

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Narann
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Color Combiner and Combined Color called for the first cycle

Post by Narann » Sat Aug 02, 2014 4:22 pm

Hi all!

Any of you know any informations about how the Color Combiner is supposed to react when the first cycle (of two) is supposed to use a "Combined output color (or alpha) from cycle 1". I mean, how the hardware react? What does it draw on screen? It seems a lot of games store a Color Combiner mux with "combined color" used in first cycle and I don't understand how it's supposed to work).

Any informations (or help where I could find information) is appreciate.

Thanks in advance all! :)

Edit: I wonder if angrylion note is not the beginning of an answer.
Ah, forgot to mention a combiner input called "combined color". In one-cycle mode and the 1st cycle of two-cycle mode it refers to the previous pixel.

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MarathonMan
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Re: Color Combiner and Combined Color called for the first c

Post by MarathonMan » Tue Sep 02, 2014 6:09 pm

Forgive me if I'm stating the obvious, but nothing is 'drawn' in the either cycle as far as the CC goes. The RDP, just like the RSP and VR4300, is a pipelined processor where computation flows from one phase to the next.

The stage(s?) or cycle(s?) which you were to are muxing color values somehow.

I don't enough enough about the RDP yet to state much more than that.

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Narann
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Re: Color Combiner and Combined Color called for the first c

Post by Narann » Tue Sep 02, 2014 6:43 pm

I'm not sure to understand but thanks for the answer! :mrgreen:

I don't have a Low Level understanding of the hardware and my question was HLE related (feel free to remove it if it's not suitable here).

As you maybe know. Official SDK provide multiple ways to control the RDP. One of them is to set the RDP in 1 Cycle or 2 Cycles mode. In 2 Cycles modes, the RDP will write the Framebuffer twice with two different pipeline configurations (you send a DWORD containing two WORD, each of them contain the pipeline configuration for each cycle).

This "pipeline configurations" can involve a lot of inputs (colors, floats, texture, etc...) and define how they combine using the RDP pipeline (A-B)*C+D. One of them is "Combined Color". Most of the time, this "Combined Color" is used in one of the four entries of the second cycle. This make sense: The first cycle write the buffer, then the second cycle use the "Combined Colors" as input for the second cycle to compute advanced effects.

But I noticed LLE RSP emulators tend to ask for a "Combined Color" for the first cycle. This is as the framebuffer is not supposed to contain anything at this moment.

angrylion almost answer to this question stating RDP just use what "Combined Color" is supposed to be (aka "What is in the Framebuffer").

I'm not an hardware engineer but I wonder if there is not a way to control the sync of the RDP and some devs try to use this for some effects to do some 3 cyles + 1 cycle rendering, having a complex effect rendering (3 cyles) and a simple effect (the last cycle).

If this is out of the scope of CEN64, feel free to remove the post. :)

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MarathonMan
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Re: Color Combiner and Combined Color called for the first c

Post by MarathonMan » Tue Sep 02, 2014 7:37 pm

Narann wrote:If this is out of the scope of CEN64, feel free to remove the post. :)
The forums here don't have to pertain only to CEN64. In fact, I'd go so far to say that I encourage discussion, especially when it pertains to the hardware or console in general. :P

Unfortunately my understanding of the RDP is well below what you've described so I can't help you much I don't think. :lol:

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