This is the disassembled and slightly modernized version of the intro Storm Coming Up by the Amiga scene group Storm, released in November 1989.
The intro does not have credits and only lists some member names of Storm, but it can be assumed the coding was done by "Chris" who is mentioned as the coder in other Storm productions.
The disassembly was done using ReSource V6.06 on an emulated Amiga. The graphics were extracted from the executable file using Maptapper and HxD for Windows. Further editing and testing was done using Visual Studio Code with the Amiga Assembly extension.
I found the intro always fascinating because of its perfect rotating checkerboard. The effect is done in two ways:
- The vertical coloring is exclusively done with the Copper coprocessor. Colors are set at calculated Y-positions and switch between white and gray.
- The horizontal coloring is done with lines drawn from top to bottom with the Blitter line functions and then filling them in with the Blitter, creating wide stripes.
To make calculations and drawing easier, the stripes are drawn on bitplane 1 and a board mask is drawn on bitplane 2. The part of the screen not covered by the mask is shown as black by setting the color registers appropriately.
Both bitplanes are shown here as examples:
Because the Blitter is not almighty fast, the intro uses triple-buffering (three screen buffers) for the checkerboard and while one screen is shown, another is being drawn and while it is filled with the Blitter, the third is being cleared using the CPU.
The disassembly was not done to the last bit and I might have misunderstood certain functions of the code, so bear with me. The intro assembles in VS Code and works in the supplied form.
The following changes were done to the code:
- Added the modern startup.i code by StingRay.
- Removed restoring the system display that is now handled by startup.i.
- Removed waiting for the floppy drives to shut down which
was done by looking at the motor status in undocumented
system variables which is not compatible to newer OS ROMs.
See the commented function
WaitDisksOffin the code. - Modified the existing SoundTracker music playback routine to wait using raster lines instead of a CPU wait that is too quick on faster processors.
The music called "kawai-k1" or "transformer" was created by Starbuck in SoundTracker and taken from another intro by scene group Spreadpoint. No credit was given. (Boo!)
Here's a screenshot of the intro running (click for YouTube video):
The STORM logo by itself:
And the font graphics used for the scroll text with the drop shadow colored in:
MnemoTroN / Spreadpoint, Jan 2024