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Nexus 7 (2012 version) not powerful enough?
03-03-2015, 12:59 AM
Post: #4
RE: Nexus 7 (2012 version) not powerful enough?
I'm actually surprised if you can't get little or no stutter at 1x PSP in that game.

It is possible to set specific settings for each game, although doing that is not really my preference. There's a button in the pause menu for it. This allows not changing settings each time you play a different game.

To be more specific, whenever you pan the screen (it's not actually moving that causes it, it's the screen panning), the game writes brand new stencil values to its stencil buffer, on the PSP (it is actually just the same values as before but panned as you move - unfortunately, even knowing this doesn't really help us.)

PSP games can do this; they can write directly to the stencil buffer and it's fast. Modern GPUs, however, allow no such thing. Instead, the stencil buffer can be interacted with in certain, very fixed ways.

This means we end up having to upload to the stencil buffer 8 separate times. Each pass makes the stencil buffer progressively more accurate, until the 8th when it's finally accurate enough to use. What's more, because we are setting only *some* stencil values (the ones the game uploaded), we most likely trigger the GPU's "slow path". GPUs don't like the word "some".

We've actually already optimized this some. It was really bad before at > 1x PSP, so we figured out a trick: when you use 2x PSP or higher, we create a temporary buffer at 1x, and upload the stencil values there (since the game is only uploading 1x anyway.) Then, we tell the GPU to scale that up to 1x and copy it to the actual stencil buffer (we only do this when the GPU supports that, and Tegra 3 does actually support that afaik.)

Nevertheless, it still does a lot more work than just doing 1x. This is why 1x PSP will still be faster.

There may be other tricks we can use, so "never" is a strong word to use. Maybe that tablet will be able to run Star Ocean better in PPSSPP 2.0.1. But right now, we haven't come up with any better ideas.

-[Unknown]
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RE: Nexus 7 (2012 version) not powerful enough? - [Unknown] - 03-03-2015 12:59 AM

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