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2007-05-28

Screen Size and Physical Location

The screen configuration settings in Zelda: Twilight Princess are enough information for the game to determine the approximate screen size and physical location of the screen edges.

Potential uses of this data includes determining if the player really is pointing at the screen (as opposed to off to the side) as well as increasing the precision of the pointer. In fact, the method described below might be exactly what the game does now.

One of the game's settings have a screen showing a black background with a centered orange column that you can change the width of. It asks you to change the width of the column until it's approximately the width of the sensor bar.

The game system assumes:
  • the sensor bar is pointing the same direction as the screen,
  • the screen is pointing at a level angle, and
  • the sensor bar is directly above or below the screen.
The game system knows:
  • the screen resolution,
  • the screen ratio,
  • the physical width of an official Wii sensor bar, and
  • whether the sensor bar is above or below the screen.
It can now calculate the ratio in pixels of your sensor bar to the screen width. Since it knows the physical width of the sensor bar it can also calculate the physical width of the screen. Since it knows the screen ratio it can calculate the physical height of the screen as well. Finally, knowing the position (above or below) of the sensor bar allows it to roughly judge the physical location in 3D space of the screen relative to the sensor bar.

Since the game now knows the physical size and location of the screen, it can "stretch" your input resolution down to fit what it knows as the edges of the screen. When the Wii remote is pointing at the screen, this results in much better aiming precision.

This has limited applications, as the Wii remote currently only knows what angle up or down it's pointing. With this alone, the system can't tell the difference between pointing down and to the left at a point on the screen or simply pointing down at that same point. If it did, it could potentially calculate the approximate position of the Wii remote in 3D space, but only when it's pointing at the screen. This settings screen in Zelda: Twilight Princess could also get more vertical precision by asking the player how far approximately (in cm) above or below the edge of the screen the sensor bar is.

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