The Vintage Computers Society: Biojet gameplay

Another one new release for the Amiga.

This time paranoicb tests on his Vampire600 a new game called Biojet.

Its a game made by Roy Schneider. This game was released on Aminet today.

Written in ASM 68k this game offers parallax scrolling fast paced 50hz gameplay and a really

nice music and graphics. On the video below you will see some gameplay footage.

Overview:

In 1997 a game released was called 'Cybergene' for the MS-DOS platform.

The graphics for that project had been drawn on several AMIGA's. The Author always

wanted to use the graphics again for an AMIGA platformer. Well the result

is a bit different and it is 22 years late - but finally...

Technical Info:

The game is entirely written in 68K assembly, taking advantage of horizontal

sprite multiplexing, using a heavy copperlist, in order to make the scrolling

background image. To generate that 'stone' background image, sprite stripes

are used, 16 pixels wide and 192 pixels high. Sprite 4 is placed at x=0,y=0

and sprite 5 is placed x=16,y=0. The sprite priority register is set, so that

sprites appear beyond the playfield bitmap data. When the raster beam reaches

the sprite 5 on the first line, the sprite control register for sprite 4 is

changed x-wise by 32 pixels, making the chipset repeating the pixel line of

sprite 4 right to sprite 5. Then when the raster beam has reached that

'multiplexed' line, the control register for sprite 5 is changed, so that this

sprite is repeated right to the already repeated sprite 4. This is now repeated

until the scanline ends.

To put it into a nutshell, the copper is 'running' ahead of the beam, twisting

the sprite registers. On the end of each scanline the sprite positions are

turned back to normal and the procedure is now repeated for the next and next

scanline, until we reach the bottom line of the playfield. The slow scrolling

effect is made simply by changing the sprite images for the two sprites. The

foreground graphics is a standard 4-plane playfield giving 16 colors using a 352

pixel wide screen with a modulo of 4, ending up with 320 logical pixels per

scanline. For scrolling purposes 16 pixels are hidden on the left, by setting up

the window accordingly. So we end up with 304 visible pixels per scanline. The

game character is build up from two 16-color sprites made from four 4-color

sprites 0/1/2/3.

Sprite 6-7 stay unused. The bottom drop graphics is 5 planes, filling up the

screen to scan line 245. So on NTSC machines some of the credits might not be

visible, but that does not effect the game play.

Requirements:

- Any AMIGA with 68k CPU.

- 512 KB Chip and 512 KB (Slow)Fast or more.

- OCS/ECS/AGA chipset, PAL/NTSC supported.

- Kickstart 1.2 or higher

The game runs under Kickstart 1.2, 1.3, 2.0, 3.0 and

3.1 on OCS, ECS and AGA computers.

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