Subject: Re: [stella] stick/paddle combos From: Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx (Eckhard Stolberg) Date: Tue, 30 Sep 1997 16:52:12 +0200 |
> I was wondering how difficult it is to implement paddles since >Glenn in an earlier message said they're sometimes difficult to get things >working with. However there's a number of Paddle games which implement >all four pots (or there's a number of 4 player paddle games with really, >really, really good programmers behind them) Paddles are just potentiometers. To read their position you have to discharge them and then increase a counter until the paddle port signals that the pot has recharged again. Since this takes some time, you usually discharge the pot at the beginning of a TV frame and then read the port and increase the counter in every scanline. Or if you can live with lower resolution, read the port every couple of scanlines. Reading all four ports in a scanline takes a lot of processing power, that you need to update the graphics registers for that line. So reading paddles and displaying good graphics is quite a challenge. > How much of a challenge are the Driving controllers? Technically >they're just joysticks with the left & right contacts ripped out. But >turning it one direction involves more than a simple "up up up up up..." Bob Colbert uses driving controlers in Stell-A-Scetch. You can check his source code, if you are interested in his routine for reading DCs. In the DC the up and down pins get moved around in a way that they connect to open or closed circuits, so that they can produce all four possible constellations. So, e.g. turning left would produce a sequence of 00 01 10 11 and turning right would be 11 10 01 00, or something similar. To read a DC you would have to read the joystick port and check if the current up/down status is before or after the last checked one in this sequence. > And, how about the light gun? Thing I'm leading up to is creating >a "Lucky & Wild" rip. Think Night Driver, but this time you get to shoot >those cars. >=^) Enduro, but you get to shoot those cars. Pole Position, >but... you get the idea. (Or use the model of Gran Prix if perspective >causes a problem.) I don't have a lightgun, but I think it is the same as a paddle with a photo sensor instead of a potentiometer. You would read it the same way and it would take longer to recharge depending on how much light reaches the sensor. Since the amount of light, that reaches the sensor, depends on the room your TV is in, you can only distinguish between black background and bright objects. If you have more than one object on the screen, you would need to turn them off one per frame and check if the value changes. This also help against lightbulp cheating. :-) Ciao, Eckhard Stolberg -- Archives updated once/day at http://www.biglist.com/lists/stella/archives/ Unsubscribing and other info at http://www.biglist.com/lists/stella/stella.html
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