Interview with Don Ursem taken from James Hague's great site.
"Tank Trap was actually first released for the Ohio Scientific C2P in 1977 by SPD Software - yes, a tape packaged in the de rigueur plastic bag - then converted and released on the Exidy Sorcerer cassette in 1978 (Quality Software) and last on the Atari computers in 1981 as both cassette and diskette with color and sound. It used assembler code for sprite movement because, at that time, nobody outside Atari had any docs and no clue how the built-in player-missile sprites could be programmatically accessed, so I wrote my own version, which code is within the game stored as a big long string of opcodes that were poked into memory at game launch and then used as needed. But it did support smooth movement, overlays and collision detection for arbitrary sized bitmap objects."
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