Talk:Sketchpad

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Hello! was it actually possible to draw with the sketchpad using the light pen? The display was a vector graphics display, where you can only point to positions that are actually hit by the e-beam. (background positions cannot be determined?)

Yes, there are various techniques for finding the pen when it isn't pointing to an existing dot or vector. The approach used for free-hand drawing if the pen location was "recently known" and is not likely to have moved far is to draw a cluster of points or vectors around the last known location, in an increasing area until the pen is found. If the pen location is completely unknown, filling the screen with "white noise" dots will find it quickly. Both techniques were used on the DEC PDP-1 with Type 30 point-plot display, so they were probably used on TX-2 as well. --Brouhaha 00:14, 7 February 2007 (UTC)

thank you!