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Comment by ChicagoBoy11 | Hacker News Reader

WRT to the light guns, I never quite really understood why you couldn't somehow simulate this with LCDs. Isn't the refresh rate on LCDs higher? So couldn't you work around that somehow? Obviously the answer is prob. not since no one (that I know of) has done it, but I was genuinely curious of what precisely the technical limitation is.

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The way light guns work, they rely on the fact that a white frame is not displayed all at once but "drawn" by the CRT ray - if you flash a single white frame, one location will flash white slightly later than other, and you can infer the location from the timing.

LCDs, well, change all the frame at once. The issue isn't with the frame rate but at what happens when the device is drawing a single frame change.

But following the same logic as GP, if you have a higher refresh rate, can't you just split the frame into several frames where you simulate that refresh scan as an animation?

Not in practice. To completely simulate the CRT refresh, you'd need to flash each pixel separately along the electron gun path. If your LCD has 1,000,000 pixels, you'd need 1,000,000 times faster refresh rate to do that.

>LCDs, well, change all the frame at once.

Is this true? It doesn't seem like it is, if it were then we'd not experience tearing in games, etc.

Tearing is a property of the output from the GPU. The data takes time to send, and the GPU can be directed to send different data halfway through the process (or the memory it's in the process of sending can be modified, etc.). The display just shows what it's sent... it shows it as it receives it (CRT), or it buffers it up and draws it later (LCD), but if there's a tear, you'll see it just the same.

There may be intermediate buffering, but the panel is still updated in a scanning fashion.

Screen tearing is, iirc from the gpu buffer only partially overwritten with the next frame when it's sent to the screen.

Tearing is, IIRC, a product of only part of the next frame being rendered when the refresh happens.

Obviously not, there is no memory inside the glass, and bandwidth is limited. LCD screens still scan in.

The difference is LCD keeps picture until told otherwise, whole picture is emitting light. CRT has limited phosphor persistence, there is only one point/pixel being lit at any given time.

https://www.youtube.com/watch?v=nCHgmCxGEzY

The latency on LCDs is much much higher, often as much as several frames. This could be removed but only at the cost of disabling all manufacturer's image post-processing including upscaling.

I have a "100Hz" CRT television that won't support light guns because the manufacturers decided they'd put this kind of image-"improving" technology in.

There are actually two techniques for light gun operation, one of which is "racing the beam" (unreliable in the presence of high retention phosphor) and the other of which is to draw a single frame of white squares for targets. https://en.wikipedia.org/wiki/NES_Zapper#Technical_details

I remember buying a Playstation2 light-gun as the console was already in its "sunset period" and when i got home i found out it wouldn't work on my TV. My TV was a late CRT model before flat screen LCD took-over and this particular CRT had 100Hz refresh rate.

LCDs cannot simulate this because their latency is too high. By the time the pattern is on the screen the lightgun has already recorded a miss.

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