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Latency is one dimension. Another one is peripheral compatibility. Devices such as light pens and light guns are incompatible with LCDs. These peripherals depen

Latency is one dimension. Another one is peripheral compatibility. Devices such as light pens and light guns are incompatible with LCDs. These peripherals depend on the timing information encoded by the raster scan of CRTs. This means classic light gun games such as Duck Hunt for the NES are impossible to play without a CRT.

Dylan16807 4y ago
Doesn't duck hunt use an entire frame of black then white? You don't need raster scan emulation for that, just very low latency. Edit: Apparently there is a 15kHz filter inside the light gun. So it's not really about beam accuracy or brightness, it's about pulsing at the right frequency.
- chongli 4y ago
  LCDs aren't capable of pulsing at 15kHz. The twisting/untwisting of the liquid crystals is an electromechanical process and very slow (compared to a racing electron beam). Even though the fastest gaming LCD monitors claim a 360Hz refresh rate, they cannot get anywhere near this 2.8ms latency (implied) when going from black to white (0 to 100% brightness). Of course, the monitor manufacturers go to great lengths to avoid talking about it, so the whole industry is flooded with a bunch of marketing material to distract from the issue.
  - Dylan16807 4y ago
    > LCDs aren't capable of pulsing at 15kHz. Yeah, I know. But you don't need the LCD to pulse, you need the backlight to pulse. An LCD might still have issues switching fast enough, but an HDR OLED tuned to 15kHz PWM might be able to handle it. If it was designed with minimum latency in mind of course. Most screens buffer a full frame and that won't work. But playing duck hunt doesn't require timing the actual beam as it sweeps across the screen. You just need to be displaying rows with a buffer that's no more than a few rows high, and have the rows flicker. Also many third party controllers don't care that much about the flicker.
    - chongli 4y ago
      Oh, with OLED you could probably design it to mimic the raster scan of a CRT perfectly, cascading the row and column signals along at 15kHz. The issue is, who is going to build that? I don't think Duck Hunt is too high on the priority list for OLED panel makers. The really sad thing is that some day all of the CRTs will be dead and all of the expertise to build them too. The tooling and factories are already gone, so it's unlikely new CRTs will ever be built, unless some Ben Krasnow-esque super-hobbyist gets really passionate about it.
      - Dylan16807 4y ago
        > Oh, with OLED you could probably design it to mimic the raster scan of a CRT perfectly, cascading the row and column signals along at 15kHz. You could but it wouldn't have the same brightness as it sweeps so I don't know if that's good enough to trick a light gun by itself. But I still think you shouldn't discount LCD. If you can get an LCD to switch a good fraction of the way in half a millisecond, and use the right backlight, you could make duck hunt work. > The issue is, who is going to build that? I don't think Duck Hunt is too high on the priority list for OLED panel makers. To trick the frequency filter might be too much effort, but the latency of having each row come along instantly might get some effort into it. Marketing loves low latency.
        chongli 4y ago
        The low latency claimed by LCD marketers concerns narrow grey-to-grey transitions. Black to white remains as slow as ever. The other issue is all of the other causes of latency along pipeline. The NES emits an composite video signal directly from its video chip, the PPU. This composite signal travels along a coax cable into the back of the TV where it’s split by the analogue circuitry into signals driving the luminance and colour, synchronized to the horizontal and vertical retrace. The whole process happens in less time than it takes to convert that signal into digital before it could even be sent to an LCD. That is, before our LCD display even receives a frame it’s already on the screen of the CRT. The NES is explicitly designed around the NTSC timing structure, with the rendering in the PPU happening “just in time” to be sent to the CRT. There is no place in the NES to buffer a frame.
avhon1 4y ago
Current consumer LCDs, sure, but there's no realson a high-refresh-rate LCD couldn't emulate the flying spot of a CRT, and thus be compatible with light pens / guns.
- chongli 4y ago
  The horizontal scan rate of a CRT TV is 15,625 Hz. Good luck getting an LCD to refresh that quickly.
  - rbanffy 4y ago
    In order for that to work, it’d need to be able to switch individual pixels in sequence, one at a time. The display panel would need to be designed for this - current panels aren’t, but as long as a screen position could switch to 100% in about 250ns, a sensor could tell precisely which pixel it’s looking at.
    - chongli 4y ago
      Liquid crystals cannot switch from 0 to 100% in less than 10ms, never mind 250ns. They’re electromechanical devices that need to physically twist/untwist to affect the polarization of light. Contrast that with a CRT which uses a 25kV acceleration voltage to drive an electron beam up to 30% the speed of light (takes about 3.3 nanoseconds to travel 1 foot from the back of the CRT to the screen), which then strikes a phosphor that glows due to its valence electrons falling from excited states (which takes a few nanoseconds).

Dylan16807 4y ago

Doesn't duck hunt use an entire frame of black then white? You don't need raster scan emulation for that, just very low latency. Edit: Apparently there is a 15kHz filter inside the light gun. So it's not really about beam accuracy or brightness, it's about pulsing at the right frequency.

chongli 4y ago
LCDs aren't capable of pulsing at 15kHz. The twisting/untwisting of the liquid crystals is an electromechanical process and very slow (compared to a racing electron beam). Even though the fastest gaming LCD monitors claim a 360Hz refresh rate, they cannot get anywhere near this 2.8ms latency (implied) when going from black to white (0 to 100% brightness). Of course, the monitor manufacturers go to great lengths to avoid talking about it, so the whole industry is flooded with a bunch of marketing material to distract from the issue.
- Dylan16807 4y ago
  > LCDs aren't capable of pulsing at 15kHz. Yeah, I know. But you don't need the LCD to pulse, you need the backlight to pulse. An LCD might still have issues switching fast enough, but an HDR OLED tuned to 15kHz PWM might be able to handle it. If it was designed with minimum latency in mind of course. Most screens buffer a full frame and that won't work. But playing duck hunt doesn't require timing the actual beam as it sweeps across the screen. You just need to be displaying rows with a buffer that's no more than a few rows high, and have the rows flicker. Also many third party controllers don't care that much about the flicker.
  - chongli 4y ago
    Oh, with OLED you could probably design it to mimic the raster scan of a CRT perfectly, cascading the row and column signals along at 15kHz. The issue is, who is going to build that? I don't think Duck Hunt is too high on the priority list for OLED panel makers. The really sad thing is that some day all of the CRTs will be dead and all of the expertise to build them too. The tooling and factories are already gone, so it's unlikely new CRTs will ever be built, unless some Ben Krasnow-esque super-hobbyist gets really passionate about it.
    - Dylan16807 4y ago
      > Oh, with OLED you could probably design it to mimic the raster scan of a CRT perfectly, cascading the row and column signals along at 15kHz. You could but it wouldn't have the same brightness as it sweeps so I don't know if that's good enough to trick a light gun by itself. But I still think you shouldn't discount LCD. If you can get an LCD to switch a good fraction of the way in half a millisecond, and use the right backlight, you could make duck hunt work. > The issue is, who is going to build that? I don't think Duck Hunt is too high on the priority list for OLED panel makers. To trick the frequency filter might be too much effort, but the latency of having each row come along instantly might get some effort into it. Marketing loves low latency.
      - chongli 4y ago
        The low latency claimed by LCD marketers concerns narrow grey-to-grey transitions. Black to white remains as slow as ever. The other issue is all of the other causes of latency along pipeline. The NES emits an composite video signal directly from its video chip, the PPU. This composite signal travels along a coax cable into the back of the TV where it’s split by the analogue circuitry into signals driving the luminance and colour, synchronized to the horizontal and vertical retrace. The whole process happens in less time than it takes to convert that signal into digital before it could even be sent to an LCD. That is, before our LCD display even receives a frame it’s already on the screen of the CRT. The NES is explicitly designed around the NTSC timing structure, with the rendering in the PPU happening “just in time” to be sent to the CRT. There is no place in the NES to buffer a frame.

avhon1 4y ago

Current consumer LCDs, sure, but there's no realson a high-refresh-rate LCD couldn't emulate the flying spot of a CRT, and thus be compatible with light pens / guns.

chongli 4y ago
The horizontal scan rate of a CRT TV is 15,625 Hz. Good luck getting an LCD to refresh that quickly.
- rbanffy 4y ago
  In order for that to work, it’d need to be able to switch individual pixels in sequence, one at a time. The display panel would need to be designed for this - current panels aren’t, but as long as a screen position could switch to 100% in about 250ns, a sensor could tell precisely which pixel it’s looking at.
  - chongli 4y ago
    Liquid crystals cannot switch from 0 to 100% in less than 10ms, never mind 250ns. They’re electromechanical devices that need to physically twist/untwist to affect the polarization of light. Contrast that with a CRT which uses a 25kV acceleration voltage to drive an electron beam up to 30% the speed of light (takes about 3.3 nanoseconds to travel 1 foot from the back of the CRT to the screen), which then strikes a phosphor that glows due to its valence electrons falling from excited states (which takes a few nanoseconds).