94 lines
4.0 KiB
Sed
94 lines
4.0 KiB
Sed
# Render next frame of falling balls with rockets and stuff
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#
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# Copyright (C) 2018 Mike Gerwitz
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# A remarkably interactive environment can be created using only regular
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# expressions and treating the input frame as a character matrix. By
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# encoding all rules and state into the characters themselves, we can create
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# a dynamic world using only a series of deterministic finite automata
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# (DFAs).
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#
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# The core concept here is that, if we load the entire frame into the
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# pattern space so that we can match on newlines, and we know the width of
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# the frame (every line must be 40 characters), then we can easily match on
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# the lines above and below by matching 40 characters, +/- some number.
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#
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# There is one caveat here that I haven't bothered addressing: if some
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# movable object is caught up in the pattern of another object (e.g. is on
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# the same line), then it will not be processed until the following
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# frame. This could be mitigated by looping using `t', but it's not quite
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# that simple: can you think of what's needed?
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#
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# This script only renders one frame. To use it for an animation, run it
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# in a loop, or use the provided helper script `animate'.
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##
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# Accumulate all text (including newlines) into pattern space so that
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# regular expressions can span lines.
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:a; N; $!ba
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# A ball is represented by `o' and is moved left or right depending on
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# what object is underneath it (`<' for left and `>' for right), provided
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# that there is space to move into.
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s#o \(.\{40\}>\)# o\1#g
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s# o\(.\{41\}<\)#o \1#g
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# Angled walls are represented by `\' and `/' and cause movement at an
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# angle, again provided that space is available.
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s#o\(.\{41\}\\\) # \1o#g
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s#o\(.\{40\}\) /# \1o/#g
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# Plungers look like `=|' or `|=' when retracted and will push to the
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# right or left (respectively) when a ball appears next to it. Expanded
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# plungers will retract if no ball is next to it. The effect is that one
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# frame will push the ball and then it will retract the next frame.
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s#=~|#=| #g; s#=|o #=~|o#g
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s#|~=# |=#g; s# o|=#o|~=#g
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# A rocket (`^') will explode if there is no room left to push a
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# ball. Explosions will destroy the character above the ball, the ball
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# itself, and the rocket. The character above the ball and the ball will
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# be replaced with smoke (`#'), which will disappear the following frame.
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s|#| |g
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s|[^ ]\(.\{41\}\)o\(.\{41\}\)\^|#\1#\2 |g
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# Rockets leave a trail `:', which needs to be cleaned up in the event of
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# an explosion if no rocket is above it.
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s#\([^^:].\{41\}\):#\1 #g
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# Rockets (^) rise when they have a ball on top of them, but fall
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# otherwise. They leave behind a trail (`:'), which is used as a guide
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# for falling back into its original position.
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s# \(.\{41\}\)o\(.\{41\}\)\^#o\1^\2:#g
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s#\([^o].\{41\}\)\^\(.\{41\}\):#\1 \2^#g
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# Finally, balls will fall if there is nothing beneath them. We do this
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# last so that ball aren't found floating in a frame (e.g. if they fall
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# off of an edge, they do so immediately, not float over the edge until
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# the next frame).
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s#o\(.\{41\}\) # \1o#g
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# If no substitutions were made, exit with a non-zero status so that the
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# animation script will stop animating.
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t
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q1
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# All of the above makes for a pretty interesting animation, but doesn't
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# allow for a whole lot of creativity with regards to world manipulation;
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# it lacks useful primitives. That's the topic of future hacks. Have
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# fun, and happy hacking!
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