make
The current status of this entry is:
STATUS: INABIAF - please **DO NOT** fix
For more detailed information see 2012 blakely bugs.
./blakely "RPN formula" resolution > output.gif
./try.sh
Several IOCCC themes (RPN calculator, animated GIF generator, ray tracing) in one package! Very impressive!
The checkerboard pattern in the output can be broken. Could you figure out how?
Larger GIF files confuse some image viewers.
This program renders a generic
RPN expression in
ray-traced animated
GIF form. The expression in spatial
variables x
and y
is specified on the command-line with the required
resolution, and an animated GIF showing a fly-around of the resulting surface is
output to stdout
.
The program should be run as:
./blakely xy* 32 > pic.gif
where the first parameter is a RPN expression, and the second is the width of the required GIF, up to a maximum of 250.
The expressions are written in Reverse Polish Notation with the following characters recognised:
+, -, *, / - usual arithmetic operations
^ - Exponentiation; valid for constant exponent only
s - sin
c - cos
0-9 - single digit integers
d - duplicate number on stack
t - transpose top two elements on stack
x - x coordinate value
y - y coordinate value
NB: all arithmetic is done in double precision, so 23/
is two-thirds, rather
than 0.
The surface plotted corresponds to -1 <= x,y <= 1
and for best results, the
generated z
value should lie between -1
and 1
.
If there is a division by zero, square-root of a negative number, or similar operation, then the results are undefined.
For test-runs, use a resolution of 32. For simple expressions, the
GIF generation should take only
a few seconds with a modern processor and full optimization. Runtime scales as
O(N^3) with resolution N
,
and more complex expressions take longer to compute. For example, increasing the
resolution of ripple.gif
to 250 took ~35 minutes to render on an i7
processor.
./blakely xy* 32 > saddle.gif
./blakely xx*yy*1++d5*ct/ 64 > ripple.gif
A generic root-finding algorithm to find the point of intersection between a ray
and the surface is done using a simple forward search from the eye. In order to
make the rendering realistic, both the value of the expression, and its
derivative with respect to x
and y
must be tracked. This is done using an
obvious stack-based approach.
Much of the obfuscation is achieved through the use of single-letter variables
and #define
s. The characters output for the GIF
format are generated in myriad
and wonderful ways, making use of
XOR, return values from
putchar()
, and odd expressions. The layout is in the form of X Y Z
.
ASCII is assumed since many bytes for the
GIF output are generated from characters
given in the source code. On compilation a few warnings about parentheses come
up when using gcc 4.6.3, and one about no return value from main()
(who uses
exit codes anyway?), but clang 3.1 emits no warnings.
b[0]
?NETSCAPE
and GIF
hidden in the source?(Note that the author may or may not be able to answer all of the above questions.)