Partytrap was released at Light and Phenomena easterparty in 1992 held in Alingsas, Sweden. Coding in this demo was done by Gremlin, Sam and Tnt. The demo finished second in the demo competition.
The demo starts with an introduction to this first ever palindromical demo on C-64, if you don't understand just read the name of the demo backwards. The introduction features only a simple text flasher on top of 3-dimesional starfield. Starfield is based on stars containing three freedom degrees and moving in a box. In case you are having hard time figuring out what it looks like you can watch below to see an imitation of the routine if your browser has java support. The original routine and the java version was programmed by Gremlin. The introduction music was composed by Page of Death Sector (at that time).
The original routine uses a fast projection table methods combined with a fast plotter designed specifically for this routine. Screen clearance uses unrolled loops and plot drawing is accomplished with zeropage loop - a loop which projects two stars on a step. Of course the drawing and projecting a single plot has to be optimized carefully in respect to both memory and opcode cycles. In case you didn't know the branch operations on C-64 can branch at most to 128 bytes apart of the branching point. In this routine a single star handling takes 63 bytes and the braching command 2 bytes which means that if the drawing of one star would take one more byte then the looping speed would fall dramatically.
The second part features two logos saying 'Beyond' and 'Force'. The other is on the upper part of the screen and the other on the lower part of the screen. The routine in this part is that both logos are flexing horizontally and there is a backgroung pattern behind them (like a parallax effect with lower level staying still). Additionally there's a dycp (different y char positioning) text with 16x8 pixels font in the middle of the screen. The routine moves naturally in every frame. Both routines were coded by Sam and the logos are also drawn by Sam.
The third part, which was programmed by TNT, shows another star routine. Accidentally this is the latest real "serious" work published by TNT of Beyond Force on C-64. However his loader's have been used after that in our demos and he did code a flexer for our meeting demo released in february 1997. Well the star routine is really a lot different from the one in the introduction. In essence, the stars are departing from the centre on an arc of a circle and moving out of the screen. The interesting point is that the centre of the circle is moving and it creates with some parametres an illusion of a star tunnel that is changing all the time. The music in this part was composed by Mixer of Origo.
The fourth part includes a dot scroller with 892 dots plotted in every frame. There are a few different curves that are changing after a small period of scroll text. The first one is a 3d-style of scroller moving from upper right corner and from far away and moving towards the lower left corner and coming closer. The second one is like a sinusoidal circlescroller on xz-plane projected with perspective. The dots themselves are not moving, the only thing that is checked is that whether to draw them or not. The whole screen is used for the scroll area. The coding itself is not that complicated. The main job is to calculate new code to handle new curves as all the code lies as an unrolled loop in memory and there is only room for code for one curve at a time. The font in the scroll and coding was done by Gremlin. The logo lying in the lower border which is actually constructed from a font was drawn by someone in Actual Trading Generation. Great music in this part was composed by Zardax of Origo Dreamline.
The part after dot scroller features a metamorphoses routine. There eight pictures morphosizing on screen. The pictures are on two rows and they lie in the upper part of the screen. Each of the have their own set of three colours so all the pictures are in bitmap. There's no real clue in the coding section the frames of the morphoses are precalculated and only animated with changing speeds and a bit occasionally. The part's purpose is really only to look good. There is also a big scroller in the lower part of the screen. The coding in this part was done by Gremlin. Music was composed by Moz(ic)art.
The last part of the demo includes a star ball rotating around all three axises. The starball includes a bit under 400 dots and they lie on surface of the ball. There's no hidden dots, the ball is transparent and when the dots are on the back they are colored a bit darker. Every fourth dot is precalculated and the other are mirrored from them. This makes it possible to have this many precalculated curves for the dots. The plotting itself is specially made for this routine. It is designed so that it draws 4 dots at once so the mirroring process is integrated into the drawing process. The part also features a 8x8 pixels font scroller and a logo drawn by Max of Beyond Force. Coding is done by Gremlin.