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/* This file contains the low-level _tek_vector() method, which takes two
integer arguments and writes them, in the format used by a Tektronix
4014 terminal for addresses while in vector or point-plot mode, to a
specified output stream. It is called by several TekPlotter methods.
Original Tek 4014 resolution was 1024 by 1024, with 1024 by 780
displayable, i.e. 0x400 by 0x30c. Extended (EGM) resolution, supported
by 4014's with the Enhanced Graphics Module, is four times that: 4096 by
3120. This is the resolution of the xterm Tektronix emulator.
With EGM, have an allowed range of 12 bits (0 <= x,y <=4095). A Tek
code for a point address (x,y) consists of a sequence of bytes:
[Hi_Y] [EGM] [Lo_Y] [Hi_X] Lo_X.
Since the EGM byte was added later, to improve resolution, it contains
the lowest 2 bits of each of the X and Y bytes, packed into the lowest
four bits of the byte. The remaining 10 bits are subdivided as follows
among the remaining four code bytes. Lo=lowest 5 of the 10 bits,
Hi=highest 5 of the 10 bits, all packed into the lowest 5 bits of the
byte. Code bytes are distinguished from each other by the pattern of
the high three bits. (Hi_Y = ?01, EGM = ?11, Lo_Y = ?11, Hi_X = ?01,
Lo_X = ?10, where ? is ignored [or should be].) If EGM is included then
Lo_Y must be included to prevent ambiguity. Also if Hi_X is included
then Lo_Y must be included.
If a byte is omitted, then its value defaults to the value of the
corresponding byte in the most recently received point. The exception
is the EGM byte; if omitted, it defaults to zero.
Warning: some emulators, the xterm emulator in particular, get this
scheme wrong. The xterm emulator will behave unpredicably if Lo_Y is
omitted. And if EGM is omitted, its value (as far as the xterm emulator
goes) is not zero, but is equal to the value of the EGM byte in the most
recently received point. */
#include "sys-defines.h"
#include "extern.h"
#define FIVEBITS 0x1F
#define TWOBITS 0x03 /* a dollar and six bits for a haircut... */
void
#ifdef _HAVE_PROTOS
_tek_vector (R___(Plotter *_plotter) int xx, int yy)
#else
_tek_vector (R___(_plotter) xx, yy)
S___(Plotter *_plotter;)
int xx, yy;
#endif
{
unsigned char xx_high, yy_high;
unsigned char xx_low, yy_low;
unsigned char xx_topsig, yy_topsig;
unsigned char egm;
unsigned char byte_buf[5];
int num_bytes = 0;
#ifdef NO_WRAP /* could completely restrict to box */
if (xx < 0)
xx = 0;
if (yy < 0)
yy = 0;
#endif
xx_high = (xx>>7) & FIVEBITS; /* bits 11 through 7 of xx */
yy_high = (yy>>7) & FIVEBITS; /* bits 11 through 7 of yy */
xx_low = (xx>>2) & FIVEBITS; /* bits 6 through 2 of xx */
yy_low = (yy>>2) & FIVEBITS; /* bits 6 through 2 of yy */
xx_topsig = xx & TWOBITS; /* bits 1 through 0 of xx */
yy_topsig = yy & TWOBITS; /* bits 1 through 0 of yy */
egm = (yy_topsig<<2) + xx_topsig;
/* The bit patterns 0x20, 0x40, 0x60 are magic */
byte_buf[num_bytes++] = yy_high | 0x20; /* bits 5 through 9 of yy */
#ifdef CAN_OMIT_EGM
if (egm)
#endif
byte_buf[num_bytes++] = egm | 0x60;
byte_buf[num_bytes++] = yy_low | 0x60; /* bits 0 through 4 of yy */
byte_buf[num_bytes++] = xx_high | 0x20; /* bits 5 through 9 of xx */
byte_buf[num_bytes++] = xx_low | 0x40; /* bits 0 through 4 of xx */
/* invoke low-level output routine */
_write_bytes (_plotter->data, num_bytes, byte_buf);
return;
}
/* This version checks whether the supplied x and y coordinates are similar
to the x and y coordinates of another point, presumed to be the most
recently output point. If they are, the Tek code is shortened by the
omission of optional bytes. Hi_Y, Lo_Y and Hi_X are all held in memory,
so need not be transmitted if they did not change. Lo_X must always be
transmitted. EGM is not held in memory; if not transmitted, it defaults
to zero.
The `force' argument will force output even if the vector has zero
length. */
void
#ifdef _HAVE_PROTOS
_tek_vector_compressed (R___(Plotter *_plotter) int xx, int yy, int oldxx, int oldyy, bool force)
#else
_tek_vector_compressed (R___(_plotter) xx, yy, oldxx, oldyy, force)
S___(Plotter *_plotter;)
int xx, yy, oldxx, oldyy;
bool force;
#endif
{
unsigned char xx_high, yy_high, oldxx_high, oldyy_high;
unsigned char xx_low, yy_low, oldyy_low;
unsigned char xx_top, yy_top;
unsigned char egm;
unsigned char byte_buf[5];
int num_bytes = 0;
#ifdef NO_WRAP /* could completely restrict to box */
if (xx < 0)
xx = 0;
if (yy < 0)
yy = 0;
#endif
/* if line segment has zero length, do nothing unless forcing an output */
if (!force && (xx == oldxx) && (yy == oldyy))
return;
xx_high = (xx>>7) & FIVEBITS; /* bits 11 through 7 of xx */
yy_high = (yy>>7) & FIVEBITS; /* bits 11 through 7 of yy */
oldxx_high = (oldxx>>7) & FIVEBITS; /* bits 11 through 7 of oldxx */
oldyy_high = (oldyy>>7) & FIVEBITS; /* bits 11 through 7 of oldyy */
xx_low = (xx>>2) & FIVEBITS; /* bits 6 through 2 of xx */
yy_low = (yy>>2) & FIVEBITS; /* bits 6 through 2 of yy */
oldyy_low = (oldyy>>2) & FIVEBITS; /* bits 4 through 0 of oldyy */
xx_top = xx & TWOBITS; /* bits 1 through 0 of xx */
yy_top = yy & TWOBITS; /* bits 1 through 0 of yy */
egm = (yy_top<<2) + xx_top;
/* The bit patterns 0x20, 0x40, 0x60 are magic */
if (yy_high != oldyy_high)
byte_buf[num_bytes++] = yy_high | 0x20; /* bits 11 through 7 of yy: Hi_Y */
#ifdef CAN_OMIT_EGM
if (egm)
#endif
byte_buf[num_bytes++] = egm | 0x60; /* bits 1 through 0 of xx and yy */
#ifdef CAN_OMIT_LO_Y
if ((yy_low != oldyy_low) || (xx_high != oldxx_high) || egm)
#endif
byte_buf[num_bytes++] = yy_low | 0x60; /* bits 6 through 2 of yy: Lo_Y */
if (xx_high != oldxx_high)
byte_buf[num_bytes++] = xx_high | 0x20; /* bits 11 through 7 of xx: Hi_X */
byte_buf[num_bytes++] = xx_low | 0x40; /* bits 6 through 2 of xx: Lo_X */
/* invoke low-level output routine */
_write_bytes (_plotter->data, num_bytes, byte_buf);
return;
}
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