50Hz sync in WinUAE

[gary]

Originally Posted by Toni Wilen

Amiga (and basically all 8-bit and 16-bit home computers) used "progressive" PAL mode where odd and even frames start at same position. (this is also the reason for "scanline" effect)

Regular PAL TV signal was always interlaced and 25fps.

So thats how they achieved a steady "non-interlaced" display on a TV. I've wondered how that did that.

25Hz isn't smooth. (perhaps it was interlaced?)

I agree, but I didn't mean 25Hz. I'll use the word picture as 'frame' can mean multiple things here. The anim player (and smooth scrolling games like Turrican) would show 25 pictures each second while the hardware would be using the progressive PAL mode you mentioned above. That would mean a single animation picture in video memory is processed by the video hardware for both an even and odd frame making 25 * 2 = 50 frames per second = 50Hz for the display.

Or to put it another way, the software only has to 'draw' the complete screen 25 times per second to get smooth scrolling. Thats probably the correct way to put it regarding Turrican.

[alexh]

AFAIK Turrican is 1 VBL i.e. it updates the complete screen 50 times per second.

I'm not sure why a 2 VBL scroller would not look smooth? As long as the number of pixels moved was constant? I guess it would limit the maximum speed of scrolling objects?

[Toni Wilen]

Originally Posted by alexh

I'm not sure why a 2 VBL scroller would not look smooth? As long as the number of pixels moved was constant? I guess it would limit the maximum speed of scrolling objects?

1pixel/frame scrolling is always smooth, even at 1fps..

But for faster scrolling (more than 1 pixel / frame) you really need 50fps screen update or it will look ugly.

Simply compare for example Turrican II's scrolling to any Bitmap Brothers game for example

To Tony Wilen

Can there be a future update so that we have perfect scrolling especially in games like saint dragon etc

[Retro-Nerd]

Originally Posted by Toni Wilen

1pixel/frame scrolling is always smooth, even at 1fps..

But for faster scrolling (more than 1 pixel / frame) you really need 50fps screen update or it will look ugly.

Simply compare for example Turrican II's scrolling to any Bitmap Brothers game for example

Thanks, so this is finally the answer i was waiting for. This explains the blurred scrolling backgrounds in Ruff'n Tumble, Fire and Ice or Wolchild too. Right? And is it the same in PC emulation with Hz doubling 100/120Hz for PAL/NTSC?

Edit: Not exact the same what i've meant. Just tried Gods on my real Amiga. This game has a jerky scrolling AND motion blur. But games like Ruff'n Tumble or Wolfchild scrolls really smooth, but they have also the motion blur or ghosting.

[Photon]

Originally Posted by alexh

It only moves every second frame, but the frames stay on the screen for only half the time.

If there is no visual difference on the screen (i.e. brightness) between frames then there is no difference between a 100Hz display updated every second frame and a 50Hz screen!

I cannot see any comparison with fast camera panning..??


Empirically I would agree, I just do not know why.

The reason is easy to explain. If your TV updates at 25Hz, 25fps scrolling will be as smooth as it gets (tho even more flickery than 50 Hz). But it doesn't. The beam draws 50 pictures per second on PAL, and any screen contents that isn't updated at 50 fps will be redrawn twice (or stay onscreen for more than 1 frame anyway). This results in a staggering picture sequence, which above 18fps or so appears as ghosting, since the human eye retains a bit of the previous image.

But it's not like it needs to be explained, all it takes is to a) play a game on a display that syncs to 50 Hz exactly, and b) play it on another with any other frequency. Then it's easy to decide which gives the best experience Retro-Nerd touched on this.

[Retro-Nerd]

Thanks Photon, now i've got it.

[alexh]

Originally Posted by Photon

The beam draws 50 pictures per second on PAL

Yes.

Originally Posted by Photon

and if any screen contents that isn't updated at 50 fps will be redrawn twice (or stay onscreen for more than 1 frame anyway).

Yes.

Originally Posted by Photon

This results in a staggering picture sequence

I do not understand what you mean by a "staggering picture sequence".

If a moving object is always redrawn twice then how does that differ from a display at half the rate?

[chiark]

The "Never. No" comment was tongue in cheek, or sarcasm. Without tricking the human eye, animation wouldn't work... But that's beside the point.

If you're TV is purely displaying the input and not doing any processing, I still don't understand why there'd be a difference between 2 frames@100Hz and 1 frame@50Hz.

I thought that 100Hz TVs tried to "interpolate" a 50Hz alternating field PAL image into a full 100Hz frame by actually doing something to the signal to attempt to smooth it? I know that horizontal scrolling titles on terrestrial TV tended to look useless on my 100Hz sony CRT for this reason.

But if that smoothing/interpolation processing can be turned off, is there any difference?

[Photon]

Yeah, if you have some motion blur processing thingy in your TV, it could complicate matters as it's made for the "TV as movie output" and not "TV as computer display".

Staggering. Let's say there's a limping Frankenstein monster walking by you IRL. You stand there, blinking incredulously 50 times per second. You wonder why the monster, limping as he does, stands perfectly still every odd blink and takes a step (other leg staying in the same place) every even blink.

Yet, as you see both the motion and non-motion bombardments of photons on your retina, you see that he limps.

You get scared, so you go upstairs and have a Smoke. Somebody speaks and you go into a dream. Ahh. Life at 25 blinks. You glance out the window and see the monster again. Now he seems to glide graciously down the road, one leg forever dragging. It's a beautiful world alright..!

[alexh]

Interesting if somewhat cryptic response.

You are basically saying what I said in an earlier post, there must be a change in intensity between screen refreshes which is noticeable. If not then there would be absolutely no difference between an 1x-Hz and a 2x-Hz refresh rate if the source material is moving at 1x-Hz

[chiark]

Aha: the penny drops! A change in intensity would indeed happen, and I get what you mean now. So the eye sees two "bright" frames instead of 1 frame that fades...

Actually, this could also explain the blurring (and sorry if you were making this point, I'm feeling slow ) - if the phosphors output light for x milliseconds whether they're being refreshed at 100Hz or 50Hz, I can see why you *would* get ghosting on a 100Hz tv.

But surely they use different phosphors that do not "luminesce" (or glow, I guess) for so long in a 100Hz tv.

Thanks, at least I can see what the debate is about now.

I bump this topic just to let you know that i switched to linux, and e-uae via sdl+directfb now really rocks ad 100hz (ad hoc modeline), really smooth, not a jerky frame, perfect vsync.
Byebye winuae

[Rabbit80]

My 50Hz TV won't accept 50Hz through VGA input In Vista I get tearing on vertical scrolling (and no - Vsync still doesn't fix it)

Solution: Use 50Hz through HDMI on XP

[Supamax]

Originally Posted by kokoko3k

I bump this topic just to let you know that i switched to linux, and e-uae via sdl+directfb now really rocks ad 100hz (ad hoc modeline), really smooth, not a jerky frame, perfect vsync.
Byebye winuae

Another good solution is using the old Xbox (modified, so it can run homebrew). On it, WinUAE runs @ 50Hz interlaced and it's smooth, also because the OS is *much* more light than Windows. An Xbox could merely be considered like a 733 MHz Celeron PC, but in reality it's more powerful and smooth than that, because:
a) all commercial games and homebrews rely on the same, exactly-specified hardware (while in the PC world there are hundreds of components combinations)
b) same for the OS. It's highly optimized for the Xbox architecture