Jumping Jack for WP7 – GameDev Fun Facts

Last night was time for another XNA Pizza Night event at Microsoft Portugal (Tagus Park). Once again ZPX presented a “new” game. “New” between quotes because the original game is from 1983 and it was older than 90-95% of the people in the audience. The game is none other than Jumping Jack for ZX Spectrum.

I played this game for the first time almost 27 years ago when I had just made 5. In fact, this was the first game I ever played on a computer and it’s probably because of it I’m here making games.

I want to dedicate this game to the memory of Nuno Sabino, my brother. It was him who received the ZX Spectrum 48k as a Christmas present and it was him who got this great game and so many others that influenced me and made me want to program and make games since then. Thanks for everything bro.

jumping_jack_wp7

Let’s get into the development fun facts:

  • It took me about two weeks working after my daily job to get this working for the demo. This would take less time if I worked on it regularly everyday, I would say 1 week. I don’t know how much time it took Albert Ball to program the original version but my guess is that it took him a little longer. He had  to program it in Z80 assembly and didn’t have help from tools we have available today, specially for debugging, it must have been a challenge at that time.
  • Although we had the Spectrum 48k, the original version of the game ran on the Spectrum 16k, i.e., it ran in less than 16k of memory. The actual version for WP7 takes about 10-16 MB, more than 1000 times larger than the original version. I didn’t and won’t make an effort at this time to make the game as smaller as the original version and I probably couldn’t do it for the WP7 but I think I could do it for the PC version if I had some time. Maybe someday, who knows.
  • The game took around 23 seconds to display a splash screen and 55 seconds to load the game making that 1 minute and 18 seconds total to be able to play it. The WP7 version takes about takes 3 seconds to load (and that’s because it displays the splash screen for 3 seconds otherwise the splash screen would pop in and out too quickly.)
  • At this moment this version has about 2000 lines of code. Once again I don’t know the exact number of lines for the original version but I think it will probably be more than 2k lines of Z80.
  • I started by using Farseer Physics but during development I realized that doing the “physics” by hand would be easier than tweaking Farseer Physics. In this demo I’m still using Farseer doing raycasts to see if the player can jump or falls and the debug to draw the lines “Fixtures”. I will probably end up removing Farseer completely in the final version.
  • The graphics and sounds are exact replicas of the original game. I took screenshots from the game playing on a Spectrum emulator and edited them to adjust the transparencies. I was going to record the sounds from the emulator but Zalo had already done that and I used the sounds from his 3d version.
  • The last thing I want to talk about comes from a Spectrum limitation in the graphics display. Spectrum machines had a 256×192 resolution and 15 available colors (3-bit palette that makes 8 colors and another additional bit that says if a color is bright or dark but since one of those colors was black, that didn’t have the bright version making the 15 colors.) The way the information was drawn on the screen was in blocks of 8×8 pixels known as attribute blocks. Only two colors could be used in each of these blocks and if a program tried to display 3 colors in any attribute block one of the colors would change to match one of the other colors, this was known as attribute clash. In Jumping Jack this problem was evident in various situations, one of them was when Jack crashed against a line/wall as seen in the following image:

jumping_jack_wp7_headcrash

Jack was rendered in red due to this limitation and I decided to keep it rendered in red as I thought it was funnier and made sense to show the shocking moment.

And that’s it, Jumping Jack for Windows Phone 7 will be released eventually (soon I hope), maybe by other name.

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