Hit Detection
The Super Scope makes use of the scanning process used in cathode ray tube monitors, as CRTs were the only affordable TV monitors until the late 1990s. In short, the screen is drawn by a scanning electron beam that travels horizontally across each line of the screen from top to bottom. A fast photodiode will see any particular area of the screen illuminated only briefly as that point is scanned, while the human eye will see a consistent image due to persistence of vision.
The Super Scope takes advantage of this in a fairly simple manner: it simply outputs a '0' signal when it sees the television raster scan and a '1' signal when it does not. Inside the console this signal is delivered to the PPU, which notes which screen pixel it is outputting at the moment the signal transitions from 1 to 0. At the end of the frame, the game software can retrieve this stored position to determine where on the screen the gun was aimed. Most licensed Super Scope games include a calibration mode to account for both electrical delays and maladjustment of the gunsight.
The Super Scope ignores red light, as do many guns of this type, because red phosphors have a much slower rate of decay than green or blue phosphors. Since the Super Scope depends on the short persistence and scan pattern of CRT pixels, it will not function with modern displays (such as plasma screens or LCDs) that continuously light each pixel.
Read more about this topic: Super Scope
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