4 ms·

Since most retro games ran around 60fps, so about 17ms, That’s an oversimplification. Many retro game consoles don’t use a frame buffer. Instead they render th

by chongli 6mo ago

Since most retro games ran around 60fps, so about 17ms, That’s an oversimplification. Many retro game consoles don’t use a frame buffer. Instead they render the game state to the screen on the fly, one scanline at a time, and they’re able to process input mid-screen because they read the controller input many times faster than 60Hz (on the order of 2kHz). In practice, this means input lag is way below even 1ms. Lightgun games, for example, rely on very precise timing of the control input vs the CRT raster and simply do not work without a CRT.

mrob 6mo ago
>Lightgun games, for example, rely on very precise timing of the control input vs the CRT raster and simply do not work without a CRT. Perhaps the most famous light gun game of all time (Duck Hunt on the NES), does not rely on especially precise timing. It draws one white rectangle per frame over each duck when you pull the trigger and checks if the Zapper can see it. LCD latency will probably still break this, but it's not like the later Super Scope for the SNES that actually does track the precise raster position. I expect it would be possible to patch the timing in software to make it work for a specific model of LCD. But even if you did this, the Zapper also includes a bandpass filter at the CRT horizontal retrace rate (about 15kHz) to better reject other light sources, so you'd need to mod it to bypass that, or mod the LCD to strobe the backlight at the right frequency.
- chongli 6mo ago
  It draws one white rectangle per frame over each duck when you pull the trigger and checks if the Zapper can see it Almost, but not quite. First it blanks the entire screen to solid black and uses that to calibrate the black level of the gun, then it draws a white rectangle over one duck on one frame, then a white rectangle over the other duck on the next frame. The NES could use this information to determine where the gun was pointing by firing an interrupt at the exact moment when the zapper’s photodiode reached a threshold brightness level above black, and then only register a hit if that occurred while the game was drawing the white rectangle. I think in reality the game didn’t care that much about the timing, only that a rising edge occurred after the fully black frame but before the return to a normal colour frame. Either way, an LCD doesn’t work because it can’t transition full black to full white within a one frame window. It sometimes works in the 2 duck mode, but it usually records a hit on the wrong duck. In any case, it requires black to white latency less than 16ms
tombert 6mo ago
I'm not disputing that CRTs have lower input lag than LCDs or OLED. I was disputing the specific 50ms of lag claim that the parent post made; modern LCDs aren't that bad, and OLEDs are getting to a point that it's getting close to undetectable to human eyes. Even with horizontal interrupts that could be done between scanlines, there's still a limit to how fast we can actually perceive it (and frankly I'd be skeptical of anyone that claims that the 8ms of input lag that an OLED is actually affecting your gameplay). For light gun games, yeah, that timing might matter, but I'm not convinced it matters anywhere else.
- chongli 6mo ago
  LCDs have a further issue that CRTs do not have: transition time. When an LCD pixel is displaying black and it is driven to white, the voltage change across the driving transistor happens a lot faster than the change in brightness of the pixel (caused by the mechanical twisting of the crystal). This has opened the space for a lot of display marketers to play games with latency numbers. Often they will quote numbers for transitions between 2 similar grey levels rather than between full black and full white, which takes a lot longer. CRTs don't have this issue at all. The phosphor lights up extremely quickly to maximum brightness, even from fully black. It's a bit slower for the phosphor to "cool back down" to black, but it's much faster than an LCD unless you're using a specific high-persistence phosphor. Typical consumer CRT monitors had a persistence in the low microseconds, except the IBM 5151 monochrome monitor which was much longer to give a stable, flicker-free image for heavy office work.

by chongli 6mo ago

mrob 6mo ago

>Lightgun games, for example, rely on very precise timing of the control input vs the CRT raster and simply do not work without a CRT. Perhaps the most famous light gun game of all time (Duck Hunt on the NES), does not rely on especially precise timing. It draws one white rectangle per frame over each duck when you pull the trigger and checks if the Zapper can see it. LCD latency will probably still break this, but it's not like the later Super Scope for the SNES that actually does track the precise raster position. I expect it would be possible to patch the timing in software to make it work for a specific model of LCD. But even if you did this, the Zapper also includes a bandpass filter at the CRT horizontal retrace rate (about 15kHz) to better reject other light sources, so you'd need to mod it to bypass that, or mod the LCD to strobe the backlight at the right frequency.

chongli 6mo ago
It draws one white rectangle per frame over each duck when you pull the trigger and checks if the Zapper can see it Almost, but not quite. First it blanks the entire screen to solid black and uses that to calibrate the black level of the gun, then it draws a white rectangle over one duck on one frame, then a white rectangle over the other duck on the next frame. The NES could use this information to determine where the gun was pointing by firing an interrupt at the exact moment when the zapper’s photodiode reached a threshold brightness level above black, and then only register a hit if that occurred while the game was drawing the white rectangle. I think in reality the game didn’t care that much about the timing, only that a rising edge occurred after the fully black frame but before the return to a normal colour frame. Either way, an LCD doesn’t work because it can’t transition full black to full white within a one frame window. It sometimes works in the 2 duck mode, but it usually records a hit on the wrong duck. In any case, it requires black to white latency less than 16ms

tombert 6mo ago

I'm not disputing that CRTs have lower input lag than LCDs or OLED. I was disputing the specific 50ms of lag claim that the parent post made; modern LCDs aren't that bad, and OLEDs are getting to a point that it's getting close to undetectable to human eyes. Even with horizontal interrupts that could be done between scanlines, there's still a limit to how fast we can actually perceive it (and frankly I'd be skeptical of anyone that claims that the 8ms of input lag that an OLED is actually affecting your gameplay). For light gun games, yeah, that timing might matter, but I'm not convinced it matters anywhere else.

chongli 6mo ago
LCDs have a further issue that CRTs do not have: transition time. When an LCD pixel is displaying black and it is driven to white, the voltage change across the driving transistor happens a lot faster than the change in brightness of the pixel (caused by the mechanical twisting of the crystal). This has opened the space for a lot of display marketers to play games with latency numbers. Often they will quote numbers for transitions between 2 similar grey levels rather than between full black and full white, which takes a lot longer. CRTs don't have this issue at all. The phosphor lights up extremely quickly to maximum brightness, even from fully black. It's a bit slower for the phosphor to "cool back down" to black, but it's much faster than an LCD unless you're using a specific high-persistence phosphor. Typical consumer CRT monitors had a persistence in the low microseconds, except the IBM 5151 monochrome monitor which was much longer to give a stable, flicker-free image for heavy office work.