smooth scrolling.is it possible?

[kirk]

can anyone suggest why games that scroll silky smooth on my amiga,jerk a little bit in winuae.ive tried various settings(sometimes running at 60fps smooths a few games out,but also increases the game speed/music etc).my cpu is 3ghz.
is it because pc monitors/tfts refresh at 60fps,and if so how to get my monitor to refresh at 50?.
cheers.

[keropi]

make the refresh rate 100Hz. that will fix this.
edit: now I see u have a TFT monitor. I don't think u can change that....

[Toni Wilen]

Unfortunate PC hardware limitation. You need either 50Hz or 100Hz to get smooth scrolling. (or 56Hz/60Hz but everything speeds up as you have already noticed)

Some TFTs will sync down to 50Hz (which is nice because you won't get any flicker like with CRTs)

[amiga]

@kirk:

attach your PC to a PAL TV.

[Toni Wilen]

Originally Posted by amiga

@kirk:

attach your PC to a PAL TV.

Real Amiga is better solution in this case

[P-J]

Hey guys.

I've been interested in this thread. Is the benefit of using a TV the ability to get the vertical refresh at 50hz, and does this really help with smooth scrolling?

If so I'll have to get myself an S-Video to SCART adapter

On a somewhat unrelated note... If you have a SCART switchbox and two inputs from two PCs with nVidia cards it, do you know if they will both be able to recognise that they are connected to a TV even if only one of them is 'switched' at any one time?

I know the last part is off-topic but anyone with experience could help

[Sune Salminen]

Originally Posted by P-J

If you have a SCART switchbox and two inputs from two PCs with nVidia cards it, do you know if they will both be able to recognise that they are connected to a TV even if only one of them is 'switched' at any one time?

I'm not sure, but if not, the driver control panel has an option to force TV detection.

[alexh]

I know this would probably be a lot of work for Toni, but would it be possible to detect the Windows / Monitor frame rate and then interpolate between Amiga frames?

Such a technique would keep scrolling smooth but increase the memory overhead of the buffering (as you now need sub-pixel accuracy) and obviously hit the cpu power required to interpolate.

I would imagine 75Hz would be possible? 1.5x frame rate?

[rare_j]

That would be cool. My monitor will only do 60, 75, or 85Hz.

[Toni Wilen]

Originally Posted by alexh

I know this would probably be a lot of work for Toni, but would it be possible to detect the Windows / Monitor frame rate and then interpolate between Amiga frames?

Such a technique would keep scrolling smooth but increase the memory overhead of the buffering (as you now need sub-pixel accuracy) and obviously hit the cpu power required to interpolate.

I would imagine 75Hz would be possible? 1.5x frame rate?

Please explain how this can make scrolling smooth. Interpolation would in my opinion make it even worse.

[alexh]

Bear with me and I will explain what I think causes jerky scrolling. I may very likely be wrong.

When the refresh rate of the PC is a match to (or whole multiple of) the Amiga refresh rate, the moving images spend an equal amount of time on each pixel of the screen. (Assuming that the original Amiga scroller was smooth). This equal amount of time on each pixel (together with how many pixels you move the graphics by per frame) is what gives scrollers their smoothness.

Are we agreed so far?

If you increase the PC refresh rate to 75Hz and increase ALL emulation timings by the same amount (I dont think this is currently possible with WinUAE?) the scrolling will still stay smooth, moving images will still spend an equal amount of time on each pixel of the screen, BUT the emulator speed is increased which will result in sound playback issues (it will sound faster / higher pitch).

If you wanted to increase the refresh rate to say 75Hz but keep the emulation timings at 50Hz you (in my mind) "hold" 50% of frames. That is you display 50% for 1x frames and 50% for 2x frames?

It is this repeating of frames (or rather "variable frame time") which I thought was responsible for the "jerky scrolling".

In order to get around this jerky scrolling I was suggesting an alternative to displaying frames for variable lengths of time. Instead create interpolated frames which (at 75Hz) would be half way between the current and next and displaying that instead. You would have 75 different frames per second and that (in my mind) will eliminate the jerky scrolling.

Do you not think so?

I admit that compensating for "ANY" refresh rate my prove a nightmare, but I think for the "easy" example of 75Hz it should work.

It is possible that I have made a basic "faux pas" and you are going to throw this right back at me.

[rsn8887]

Here's my little remark:

100 Hz is _second_ best to 50 Hz (which sadly most monitors/gfx cards don't support). At 100 Hz however, you will _still_ see more jerkiness than at 50 Hz. While scrolling is smooth, you will see the last frame a bit like a shadow(check with e.g. poing on WB, you will see the ball twice at certain speeds instead of once like in 50 Hz). This is because each frame is displayed twice instead of once. Even though it happens at a high frequency, somehow the eye will pick this up and register this little bit of jerkiness when directly compared to 50 Hz.

This was also a problem on the first 100 Hz TVs that came out. It manifested itself on the scrolly text, e.g. on the weather channel. It made some of the text unreadable at certain scroll-speeds. The companies that produced those TVs added some weird complicated digital processing to get rid of the effect on 100 Hz TVs, if I remember the story right....

But apart from that, 100 Hz is definitely the way to go. The little program called "refreshlock" might help you fiddeling with refresh rates, especially on other emulators like winvice, that don't have auch a nice manifold of options that WinUAE has.

[P-J]

Originally Posted by Toni Wilen

Real Amiga is better solution in this case

Akira may be absent, but his spirit lives on

[Toni Wilen]

Originally Posted by alexh

In order to get around this jerky scrolling I was suggesting an alternative to displaying frames for variable lengths of time. Instead create interpolated frames which (at 75Hz) would be half way between the current and next and displaying that instead. You would have 75 different frames per second and that (in my mind) will eliminate the jerky scrolling.

Perhaps but what about parts that don't scroll or animate (scrore/time) or move to different direction (enemies, player) Try to interpolate that without making it look terrible

[alexh]

Originally Posted by Toni Wilen

Perhaps but what about parts that don't scroll or animate (scrore/time) or move to different direction (enemies, player) Try to interpolate that without making it look terrible

Hmmm, I see where you are going... I'll have a think about it.

As an experiment would in be possible in WinUAE to sync ALL aspects of the emulation to the vsync? Increase the speed of the emulation, all timings etc. to the refresh rate. Most flat panels will do 56Hz, would an 11% speed increase be an acceptable compromise for the benefits of smooth scrolling?

Side-Line:

I never owned an NTSC Amiga, but what happens with Euro-Demos and games on a 60Hz NTSC Amiga? Do they have poor-scrolling / glitches?

[Toni Wilen]

Originally Posted by alexh

As an experiment would in be possible in WinUAE to sync ALL aspects of the emulation to the vsync? Increase the speed of the emulation, all timings etc. to the refresh rate. Most flat panels will do 56Hz, would an 11% speed increase be an acceptable compromise for the benefits of smooth scrolling?

WinUAE has always done it this way. (since vsync was implemented, and also fps adj. does the same)

[spiff]

Originally Posted by Toni Wilen

Perhaps but what about parts that don't scroll or animate (scrore/time) or move to different direction (enemies, player) Try to interpolate that without making it look terrible

OK, apart from all the not so small problems of implemententation in UAE

But won't this be about the same thing as interpolation of NTSC (NTSC telecine)? 3progressive/2 blended frames. It will look just fine on things that don't scroll.. and will blend on scrolling objects but should be relatively OK unless you pause on a blended picture or vertical res is interlaced.

[Toni Wilen]

I still can't see it working (and if it can work, why it isn't it implemented in any existing emulator?)

[alexh]

Originally Posted by Toni Wilen

WinUAE has always done it this way. (since vsync was implemented, and also fps adj. does the same)

I will have to experiment. I tried it last night and it sort of works (I see the increase in speed etc.) but the results (i.e. smooth scrolling) were not quite what I expected.

Perhaps my graphics card (Geforce 2 MX 400) & driver doesn't accurately report VSYNC interrupts to WinUAE?

if it can work, why it isn't it implemented in any existing emulator?

Memory / CPU overhead? Most emulators I know of were started a long time ago. When these things were at a premium.

I am going to have a think about it and try and work out all the "gotchas". I'll also run it by Lord of Emulators, David "Sparcade" Spicer, if anyone will know it will be him.

[DamienD]

Originally Posted by alexh

I'll also run it by Lord of Emulators, David "Sparcade" Spicer, if anyone will know it will be him.

Sorry, bit off topic...

I remember David Spicer... Hmmm, don't think he still works on Sparcade anymore though? This was one of the first arcade emulators I tried