[Discussion] 60FPS patches for PSP games that run at 30FPS

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(01-05-2016 12:51 AM)Kabuto_Kun Wrote:  "Technical" info:
According to some user from a different forum, the dither effect on PSP "It is done to save VRAM so that more textures can be loaded and helps to keep higher fram rate. It is same trick as used in PS1 games thats why you can see it on those games."
Another user says: "Blame it on the PSP's limited memory bandwidth, which forced a lot of games to run in 16-bit color or less."

Also, READ HERE about 16/32 bit color from PPSSPP devs.

...

So, what we REALLY need to do is force the games to run with 32 bit color on a REAL PSP, identifying the code that set this. If you read the link from PPSSPP devs, you can see that Kingdom hearts has an option to choose 16 or 32 bit color and this could be a way to understand what function does this, and port it to other games. I have Kingdom Hearts and this is what I will try now.

Well, forcing games to run at 32-bit color on a real PSP may be a feat, unfortunately.

The PSP had 2MB of VRAM, or in other words 2048KB.

A 16-bit color buffer requires 272KB. But a 32-bit one requires 544KB. Additionally, you essentially must double buffer on the PSP, meaning you need two of those buffers. So it's actually 555KB vs 1088KB.

Even more, most games will require a depth buffer to render properly at all. That costs another 272KB.

So you can see that with 32-bit color, you're quickly left with only 2048MB (VRAM) - 272KB (depth) - 1088KB (colors) = 688KB of remaining VRAM.

But you say, "it fits, doesn't it? Is that a problem?" But this VRAM has to be used for other things:

* Textures
* CLUTs
* Other buffers (to create bloom effects, or shadows, etc.)

So many games may have chosen 32-bit color simply due to free space, not even because of bandwidth. You basically double your remaining VRAM by using 16-bit colors, allowing you to do a lot more other effects. So it may have become a decision of more vibrant colors or better shadows, for example.

That being said, it's theoretically possible to relocate textures and CLUTs to regular RAM. There may be a performance penalty, but it might be livable. However, this would definitely mean non-trivial changes to the game's code. So that's why I say it might be an undertaking.

In PPSSPP, we represent the color buffers on your modern device, that might even have > 1GB of VRAM. So 32 bit color, or even double the resolution, is not really a problem to fit in there. We don't have to be limited by the VRAM the PSP had.

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