Embedded Files
I've been spending some time using Ghidra to disassemble the game program. Ghidra is an open source software reverse engineering suite written the NSA. It's an incredibly powerful tool, once you get the hang of it.
Making good progress, have figured out many of the data structures and core game loop design. Using the knowledge gained to build a level viewer and eventual editor
Contact me if you're interested in joining the effort.
Careful analysis of the code has revealed the following:
The message "you have hit a black hole" is the software's way of recovering from a general mathbox failure.
There's a hidden debug mode that displays various hardware timing values onscreen, likely used to tune performance by better synchronizing the 6809 / mathbox / video processor
There are two unused game levels left over in the ROM. One of them has a "valley", sort of an inverted vesion of the "mountain" seen on level 1.
There is a software flag which doesn't allow a land bridge to be built after the robot jumps -- although unused in the final game, the feature would have been used on some levels to make it harder to get to certain areas, limiting the options for travel
Another flag exists to force the levels to render in vector wireframe mode -- sort of a darker "nighttime" mode
The big "beach balls" on level 5 are destructible! However they require 30 shots to kill, which is impossible given the firing speed of the robot. If you manage to kill one it awards 1,000 points!
Bird behaviors:
The birds in the game were programmed to fly in zig-zag patterns.
There was also a mode where they would circle the robot from above, like a vulture. If they hit a column they could be destroyed, likely the robot could "lure" them into columns to get them off his tail.
The code tries to detect when players are "mining" the birds for points, and reacts by makes it less likely for birds to spawn near the robot.
The balls that the birds dropped were able to bounce
There are provisions for "surprises" for the robot to find on the game playfield. If the robot hit a special tile certain things would happen like:
Award a bonus life for the player
Kill player on contact
"Get all red squares at once" to quickly end the level
Super-zapper / smart-bomb feature to kill all enemies at once
Auto bridge building (perhaps to unlock an otherwise impossible to get to area on the level)
The unused "hand" in seen in Doodle City was part of a "blimp" feature that activates when the robot touches a special "surprise" tile. Upon activation the hand would rise up and float over to the eye, where it would cover it for about 15 seconds.
Many unused sound effects never made it into the final game, including a 2001 "Thus Spoke Zarathustra" theme that would have played when the robot enters the bonus pyramid.
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