NeWS had some spectacular abuses of C preprocessor macros with nested switch statement, loops and gotos.

Especially the conic splines code by Vaughan Pratt and James Gosling, which "flattens" Bezier curves into conic splines (unlike straight lines like most PostScript renderer implementations), which Vaughan Pratt's conix package can draw really fast.

http://www.chilton-computing.org.uk/inf/literature/books/wm/...

SunDew - A Distributed and Extensible Window System

[...] Two pieces of work were done at SUN which provide other key components of the solution to the imaging problems. One is Vaughan Pratt's Conix [53], a package for quickly manipulating curve bounded regions, and the other is Craig Taylor's Pixscene [63], a package for performing graphics operations in overlapped layers of bitmaps. [...]

[...] Pixscene is based on a shape algebra package. The ability, provided by Conix, to do algebra very rapidly on curves should make non-rectangular windows perform well. [...]

[53] Pratt, V., Techniques for Conic Splines, Computer Graphics 19(3), pp.151159 (1985).

[63] Taylor, C. and Pratt, V., A Technique for Representing Layered Images. SUN Microsystems Inc., 2550 Garcia Avenue, Mountain View, CA94043.

Direct Least-Squares Fitting of Algebraic Surfaces:
Vaughan Pratt,
Sun Microsystems Inc.
and
Stanford University.
April 30, 1987.

http://boole.stanford.edu/pub/fit.pdf

http://donhopkins.com/home/code/NeWS/SUN/src/server/graphics...

/*-
Convert a PostScript style path to an arclist
pathtoarc.c, Thu Sep 19 15:45:44 1985
*/

http://donhopkins.com/home/code/NeWS/SUN/src/server/graphics...

/*-
Convert a conic arc to a curve
arctochain.c, Tue Jun 11 14:23:17 1985
"Elegance and truth are inversely related." -- Becker's Razor
Vaughan Pratt
Sun Microsystems
This code is a version of the conix package that has been
heavily massaged by James Gosling.
*/

[...]

/* macros for the conic machines */
#define out(b) {	\
if (b)	\
xpos += dir;	\
else	\
*ypos++ = xpos;	\
}

#define across(rel,q1) {	\
out(1);	\
Fx += Fxx, Fy += Fyx;	\
if ((F += Fx) rel 0)	\
goto q1;	\
}

#define down(rel,q1) {	\
out(0);	\
if (--rem0 < 0)	\
goto final;	\
Fx -= Fxy, Fy -= Fyy;	\
if ((F -= Fy) rel 0)	\
goto q1;	\
}

#define trans1(axis, q1)	\
for (;;)	\
axis(>=, q1);

#define trans2(axis, q1, rel, q2)	\
for (;;) {	\
axis(<, q1);	\
if (Fx rel Fx_err)	\
goto q2;	\
}

[...]

/* enter conic machine at appropriate state */
rem0 = size.y;
if ((size.x > 0) == (side < 0))
goto EOD;
else
goto OED;
/* OE state machine */
ODE:trans1(across, OED);
DOE:trans2(across, ODE, >, OED);
OED:trans2(down, ODE, <, DOE);
/* EO state machine */
EDO:trans1(down, DEO);
DEO:trans2(across, EDO, >, EOD);
EOD:trans2(down, EDO, <, DEO);
final:;
/*-	clearasil(buf0+1, bitlen);	/* clean out 0011/1100 pimples */
assert(ypos <= curve->x + (curve->y1 - curve->y0 + 1));

The main loop of the NeWS PostScript interpreter itself is the realization of Duff's dire warning "Actually, I have another revolting way to use switches to implement interrupt driven state machines but it's too horrid to go into."

http://donhopkins.com/home/code/NeWS/SUN/src/server/nucleus/...

/*
* This is the PostScript interpreter. Its implementation breaks almost every
* rule of structured programming. This is a result of needing to support
* multiple PostScript processes and a paranoia about performance. There are a
* couple of #includes that you should think of as procedure calls. Life is
* tough in the trenches.
*
*/

/*
* The PostScript interpreter has a fairly simple basic structure:
*
* while (1) { 1. Pick up an object to interpret 2. Execute it }
*
* Part 1, picking up an object to interpret is handled by the statement that
* starts "switch (es->type)". es points to the top of the execution stack: a
* stack of sources of executable objects. The switch determines what kind of
* thing the object is being fetched from: an array, a string, ...
*
* Part 2, executing an object, is handled by the code that starts with the label
* "execute_top". It does some tests and switches on the type of the object
* being executed.
*
* All of this is complicated by the mechanism for blocking. If the process
* needs to block, say by needing to read a new buffer from a socket or by
* needing to wait for a message, then the interpreter needs to stop working
* on this process and leave information around that lets it restart. This is
* the "restart_state" variable: it is used as the index to a switch statement
* that is executed when the interpreter starts up, so it won't necessarily be
* intering the main loop of the interpreter at the top. There are cleaner
* ways of doing this, but they can't be written in C!
*/

[...]

/*
* Restart the interpreter where it left off last
*/
switch (ee->restart_state) {
case 1:
goto read_1;

[...]

case 24:
goto read_24;
}

/* The main loop of the interpreter */
while (1) {
struct object new;

[...]

/* Pick up an object to execute */
switch (es->type) {

[...]

case file_execution:{
register PSFILE *f = es->env.file.file;
/* be charitable and think of this as a procedure call */
#ifdef GPROF_HOOKS
/* gP_GetFile defined in parse_file.h */
#endif
#include "parse_file.h"
break;
}

http://donhopkins.com/home/code/NeWS/SUN/src/server/nucleus/...

/*-
*	Parse a PostScript object from a PSFILE
*
*	parse_file.h, Mon Dec 31 09:36:02 1984
*
*	James Gosling,
*	Sun Microsystems
*/

/*
* This is a version of getc that pauses if the buffer is empty and suspends
* the process
*/