Video mode color depth for snes emulation

vanfanel · Post by **vanfanel** » Mon Mar 23, 2009 9:26 am

Hello there

I take the deepest video mode needed for faithfull snes video emulation is 16 bits, but I see most emulators (SnesGT) have 32 bit modes.

Should be 16 bit modes any faster? In WinUAE here's a notable speed improvement in 16 bit modes when running on ddraw.
Or do 16 bit modes involve some image conversion making those modes slower than 32 bit modes on nowadays cards?

Thanks!

AamirM · Post by **AamirM** » Mon Mar 23, 2009 11:45 am

Displaying 16-bit on 32-bit does require conversion so yes it will be a little slower than 32-bit.

But some emulators can render (like mine) directly in 32-bit which doesn't involve any conversion.

I just did some quick benchmarking. I was running Sonic 3D in Regen 0.95. Note that the FPS I got are only valid for my system:

Render 16-bit in 16-bit mode: 424 FPS
Render 32-bit in 32-bit Mode: 448 FPS
Render 16-bit in 32-bit mode (using DDraw's 16 bit surface creation): 398 FPS

I have an onboard Intel card (yeah I know it sucks yada yada).

Of course someone else may get completely different results.

Squall_Leonhart · Post by **Squall_Leonhart** » Mon Mar 23, 2009 11:53 am

You'll actually find on modern video cards, its rendering at 16bit that is slower then 32bit.

Apparently its because most 16bit modes are sampled back to 32bit in the graphics hardware or something??

I.S.T. · Post by **I.S.T.** » Mon Mar 23, 2009 12:09 pm

See this link to basically get the answer why that happens: http://forum.beyond3d.com/showthread.php?t=46378

vanfanel · Post by **vanfanel** » Mon Mar 23, 2009 12:58 pm

AamirM: I also have an intel onboard card (GMA950) and it seems faster on 32 bit modes, too.
What do you mean by 32 bits on 32 bits? Do you mean 32 bits desktop and a 32 bits mode selected on the emulator?

Thanks!

franpa · Post by **franpa** » Mon Mar 23, 2009 1:19 pm

he means the emulator renders the graphics in 32bits then your video card displays in 32bit. It never converts 16bit -> 32bit.

vanfanel · Post by **vanfanel** » Mon Mar 23, 2009 2:29 pm

thanks for the obvious answer, franpa. I knew that. I wanted to know what he meant configuration-wise.
What's 32bits on 32 bits? an emulator configured with a 32bpp resolution that switches to that 32bpp resolution , I understand.
But if I configure, let's say, SnesGT with 640x480@16bpp or 32bpp it will switch to that resolution without color conversion involvment whatever I do... How could I have 16bpp on 32bpp for example? Thanks

Squall_Leonhart · Post by **Squall_Leonhart** » Mon Mar 23, 2009 4:31 pm

depends on your hardware.

if its newer then a G80, its 32bpp no matter what you do since its internally resampled to 32bpp regardless of desktop/window depth setting.

vanfanel · Post by **vanfanel** » Mon Mar 23, 2009 4:42 pm

well, the GMA950 seems to be newer but less advanced. What's the case then? anybody knows what's faster for GMA950?

Squall_Leonhart · Post by **Squall_Leonhart** » Mon Mar 23, 2009 5:07 pm

Rocketfuel would burn heaps faster.... err i mean lol.

16bpp, the 950 is Dx9 tech, and only supports emulated TnL

byuu · Post by **byuu** » Mon Mar 23, 2009 5:23 pm

vanfanel wrote:I take the deepest video mode needed for faithfull snes video emulation is 16 bits, but I see most emulators (SnesGT) have 32 bit modes.

Yes and no. The SNES itself is 15-bit, so technically yes. But in practice a few issues come up.

First, TV to PC monitor gamma is very different. To adjust that with only 16-bits is not really enough precision, and you'll end up crushing especially the lower-band colors together. The extra precision also helps with other adjustments: brightness, contrast, etc.

Second, I've seen some shitty video cards / drivers that upconvert improperly. At 16bpp the color white is 11111 111111 11111. Yet on these cards, that gets converted to 11111000 11111100 11111000, or RGB 248, 252, 248. So what should be bright white ends up slightly gray with a green tint. You can tell by running 32-bit mode with a 16-bit mode emulator, and use a white background for your desktop. Again, only some drivers do this. Otherwise the difference is very minor, especially for red and blue.

Lastly, sometimes it's faster to render at 32bpp, sometimes at 16bpp. Depends on the card and drivers. But either way, the bottleneck is PPU emulation, which takes at least 10x as long as blitting either 16bpp or 32bpp @ 256x224 to your monitor. It's not really worth worrying about the overhead involved.

Squall_Leonhart · Post by **Squall_Leonhart** » Mon Mar 23, 2009 5:46 pm

As it is,... coupled with a decent cpu, the 950 should be capable of fullspeed snes emulation with atleast 2xSaI.

byuu · Post by **byuu** » Mon Mar 23, 2009 6:07 pm

An S3 ViRGE is capable of full-speed emulation. The bottleneck for emulation and video filters (sans pixel shaders) is entirely on the CPU-side, and there's no point in discussing what CPU power should be required for that.

Squall_Leonhart · Post by **Squall_Leonhart** » Mon Mar 23, 2009 6:39 pm

a video card does become a limiting factor when scale filters are used at higher resolutions. on an old 2000+ with an mx440, Hq2x was impossible at 1280x1024, but with a 6600GT suddenly it works fine.

funkyass · Post by **funkyass** » Mon Mar 23, 2009 7:17 pm

are both AGP cards?

Post by **grinvader** » Mon Mar 23, 2009 7:28 pm

I could run zsnes in hq4x 1024x768@60FPS fine on Century, my previous comp; (p3 450 + mx440); same old w98se install i transferred over to this one.

Squall_Leonhart · Post by **Squall_Leonhart** » Mon Mar 23, 2009 7:42 pm

funkyass wrote:are both AGP cards?

Yeah they were, I'm sure its a XP thing though.

i have an app which tests Dxdraw performance, and it was faster on windows 98, then it was on XP.

grinvader wrote:I could run zsnes in hq4x 1024x768@60FPS fine on Century, my previous comp; (p3 450 + mx440); same old w98se install i transferred over to this one.

Yeah, like i said, it was probably the fact XP is generally slower with DirectDraw then windows 98 is.

snkcube · Post by **snkcube** » Mon Mar 23, 2009 7:44 pm

funkyass wrote:are both AGP cards?

I'm pretty sure the MX440 was only AGP.

Squall_Leonhart · Post by **Squall_Leonhart** » Mon Mar 23, 2009 7:45 pm

It came in PCI as well.

snkcube · Post by **snkcube** » Mon Mar 23, 2009 10:28 pm

Squall_Leonhart wrote:It came in PCI as well.

I totally forgot about those old PCI slots.

I.S.T. · Post by **I.S.T.** » Mon Mar 23, 2009 10:53 pm

Squall_Leonhart wrote:depends on your hardware.

if its newer then a G80, its 32bpp no matter what you do since its internally resampled to 32bpp regardless of desktop/window depth setting.

Actually, I think it's been that way since the GeForce 7 generation and the Radeon 1K generation.

Squall_Leonhart · Post by **Squall_Leonhart** » Sun Mar 29, 2009 10:06 am

Hmm, no... I'm fairly sure its G80+ since the 7 series isn't effected by the Dithering bug in Thief.

franpa · Post by **franpa** » Sun Mar 29, 2009 10:09 am

I.S.T. wrote:See this link to basically get the answer why that happens: http://forum.beyond3d.com/showthread.php?t=46378

If you read what you posted (the link) you would have seen that the g80 and newer cards only render in 32bit.

vanfanel · Post by **vanfanel** » Mon Mar 30, 2009 9:02 am

ok, I may sound stupid, but GMA950 is not comparable to those Nvidia cards. It has a i915-based design afaik and the Intel chipsets release timeline isn't related to Nvidia timeline.
It's a DirectX 9 card, ok, so what does that mean?
Should it be faster in 16 bits mode?

I.S.T. · Post by **I.S.T.** » Mon Mar 30, 2009 9:39 am

Possibly. After a while 32 bit color stops being a performance bottleneck. Cutting back to 16 bit won't help in those cases. It also wouldn't help if something else was cutting into performance, such as the CPU, amount of RAM(Either system or video), the chip being too slow anyway, etc.

ZSNES board

Video mode color depth for snes emulation

Video mode color depth for snes emulation

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