How does a G-Con work?

[Sharky.]

This has always boggled me.

The TV doesn't know you're pointing a lightgun at it, so how does the gun work?

 

[wfooshee]

The software controlling the light gun is also painting the picture on the TV. It knows where the scanning beam is at any given time, and its field of view is only a fraction of the set's screen, and it sees the scan flicker that we humans don't notice. When the light gun sees the scan get suddenly bright, the software knows exactly where that is in the picture, what scan line and how far across the screen.

You're right, the TV doesn't know, but the {game,cad-program,console} does.

 

[Wolfe]

I personally think that infrared sensors are better solution. Sega's arcade shooters use infrared sensors surrounding the screen, and the Nintendo Wii, as many people know, has a Sensor bar with two infrared points in it.

The advantage infrared holds over the CRT-based light gun is that it can easily track a gun's position at all times, even when you aren't pulling the trigger. This is why Sega's arcade shooters sometimes feature minigames or gameplay gimmicks (such as a rocket launcher locking onto a target or snipping the wires on a bomb using an on-screen wire clipper icon), and why the Wii is able to utilize a cursor for its menus and such.

 

[Sharky.]

So a G-Con sends information about the pixel it sees to the PlayStation, which then determines which part of the picture it is?

 

[wfooshee]

It sends nothing about the pixel, it just sends a pulse whenever it sees the small area of screen that's visible to it get brighter. That means the scan line just went by, and the Playstation knows where the scan line is.

Not an exact analogy, but kind of like if you had all your neighbors turn their lights on and back off at random times while you watched. You'd know when a light got brighter, and you'd know exactly where that light is. From that you know which neighbor turned on his light.

All the light gun knows is that the point on the screen it's looking at got brighter suddenly. The console knows what part of the screen was being drawn, so it can locate that point.

 

[Sharky.]

Ah, cool. I understand now. 👍

 

[OUABlackBird]

Ah, cool. I understand now. 👍

...I'm still a little lost.
Is there any more detailed info on this subject, for example what hardware does the gun use, or are there any "do-it-yourself" videos that anyone knows of? I really want to make one of these bad boys! XD

I found this but I don't think it's quite the same :3
http://makezine.com/projects/make-43/infrared-shooting-arcade/

 

[BobK]

...I'm still a little lost.
Is there any more detailed info on this subject, for example what hardware does the gun use, or are there any "do-it-yourself" videos that anyone knows of? I really want to make one of these bad boys! XD

I found this but I don't think it's quite the same :3
http://makezine.com/projects/make-43/infrared-shooting-arcade/

The "gun" is simply a photosensor. The software driving the display causes a bright dot to appear on the screen in, say, the upper left corner for a period of time too brief for the human eye to register but long enough for the gun's sensor to register. If the gun sees the dot, it sends a pulse back to the controller. If the controller sees a pulse, it knows the gun is pointed at the dot and if no pulse then the gun is not pointed at the dot. It then causes another dot to appear at another location and looks for a pulse from the gun. This is repeated until the whole screen has been scanned. The cycle repeats fast enough that it appears to be continuous.

 

[Wolfe]

The dot is actually the beam of the electron guns inside a CRT display as they draw the image on the screen; the scan line, as wfooshee said. The photosensor activates when you pull the trigger on the gun controller, and waits for the scan line to pass by. When the scan line passes in front of the photosensor, the gun controller sends a signal to the console (or arcade cabinet). The video hardware in the console/cabinet can then identify where the gun controller is being aimed by timing how long it took for the scan line to reach the spot where the photosensor is pointed, starting from the beginning of the current video frame.

That type of gun only works with CRT displays, and won't work on modern flatscreen displays, which is why modern gun controllers operate with infrared emitters. Now the guns have infrared cameras, which track the orientation and position of infrared dots to determine where and at what angle the gun is being aimed. The infrared type isn't as accurate as the CRT type and may require calibration, but the continuous tracking allows for an aiming reticule or a player-controlled camera that can be moved by using the gun like a mouse pointer.