Add option to select 256 color escape codes (#44)

Fixes #32 
by adding an explicit option to select 256 color escape codes in output. Here's a comparison between true color (top) and 256 color (bottom) outputs in a terminal that has support for both:
![screenshot_2019-01-25_09-18-47](https://user-images.githubusercontent.com/12737903/51751240-6131c600-2082-11e9-81f3-efbb299e2100.png)
In urxvt, where only 256 color is supported, this is what shows up:
![screenshot_2019-01-25_09-13-18](https://user-images.githubusercontent.com/12737903/51751296-8aeaed00-2082-11e9-8aff-845f01a14cf7.png)
Another comparison using image from #32 in urxvt:
![screenshot_2019-01-25_09-24-57](https://user-images.githubusercontent.com/12737903/51751558-1f554f80-2083-11e9-9a34-3eb7bb0964a2.png)

completion/_catimg

@@ -42,6 +42,7 @@ _arguments \
  '-l[specify the amount of loops that catimg should repeat a GIF]' \
  '-r[force the resolution of the image]: :->resolution' \
  '-c[convert colors to a restricted palette]' \
+ '-t[disable true color and use 256 color instead]' \
  '*: :_files' && ret=0
 
 [[ "$state" == 'resolution' ]] && _values 'resolution value' 1 2 && ret=0

man/catimg.1

@@ -28,6 +28,9 @@ Possible values 1 or 2. Force the resolution of the image. By default catimg wil
 .TP
 \fB\-c\fR
 Convert colors to a restricted palette. This is useful when terminal only support a limited set of colors. This transformation should be more accurate than the one performed by the terminal.
+.TP
+\fB\-t\fR
+Disables true color (24-bit) support, falling back to 256 color escape codes instead.
 
 .SH BUGS
 Please report any bugs to https://github.com/posva/catimg/issues.

src/catimg.c

@@ -6,15 +6,16 @@
 #include <unistd.h>
 #include <signal.h>
 
-#define USAGE "Usage: catimg [-h] [-w width] [-l loops] [-r resolution] image-file\n\n" \
+#define USAGE "Usage: catimg [-hct] [-w width] [-l loops] [-r resolution] image-file\n\n" \
  " -h: Displays this message\n" \
  " -w: Terminal width by default\n" \
  " -l: Loops are only useful with GIF files. A value of 1 means that the GIF will " \
  "be displayed twice because it loops once. A negative value means infinite " \
  "looping\n" \
  " -r: Resolution must be 1 or 2. By default catimg checks for unicode support to " \
  "use higher resolution\n" \
- " -c: Convert colors to a restricted palette\n"
+ " -c: Convert colors to a restricted palette\n" \
+ " -t: Disables true color (24-bit) support, falling back to 256 color\n"
 
 // Transparency threshold -- all pixels with alpha below 25%.
 #define TRANSP_ALPHA 64
@@ -68,7 +69,8 @@ int main(int argc, char *argv[])
 
  uint32_t cols = 0, precision = 0;
  uint8_t convert = 0;
- while ((c = getopt (argc, argv, "w:l:r:hc")) != -1)
+ uint8_t true_color = 1;
+ while ((c = getopt (argc, argv, "w:l:r:hct")) != -1)
  switch (c) {
  case 'w':
  cols = strtol(optarg, &num, 0) >> 1;
@@ -84,8 +86,11 @@ int main(int argc, char *argv[])
  exit(0);
  break;
  case 'c':
- convert = 1;
- break;
+ convert = 1;
+ break;
+ case 't':
+ true_color = 0;
+ break;
  default:
  printf(USAGE);
  exit(1);
@@ -145,49 +150,54 @@ int main(int argc, char *argv[])
  for (x = 0; x < img.width; x++) {
  index = y * img.width + x + offset;
  const color_t* upperPixel = &img.pixels[index];
+ uint32_t fgCol = pixelToInt(upperPixel);
  if (precision == 2) {
  if (y < img.height - 1) {
  const color_t* lowerPixel = &img.pixels[index + img.width];
- /* uint32_t bgCol = pixelToInt(&img.pixels[index + img.width]); */
+ uint32_t bgCol = pixelToInt(&img.pixels[index + img.width]);
  if (upperPixel->a < TRANSP_ALPHA) { // first pixel is transparent
  if (lowerPixel->a < TRANSP_ALPHA)
  printf("\e[m ");
  else
- printf("\x1b[0;38;2;%d;%d;%dm\u2584",
- lowerPixel->r, lowerPixel->g, lowerPixel->b
- );
- /* printf("\e[0;38;5;%um\u2584", bgCol); */
+ if (true_color)
+ printf("\x1b[0;38;2;%d;%d;%dm\u2584",
+ lowerPixel->r, lowerPixel->g, lowerPixel->b);
+ else
+ printf("\e[0;38;5;%um\u2584", bgCol);
  } else {
  if (lowerPixel->a < TRANSP_ALPHA)
- /* printf("\e[0;38;5;%um\u2580", fgCol); */
- printf("\x1b[0;38;2;%d;%d;%dm\u2580",
- upperPixel->r, upperPixel->g, upperPixel->b
- );
+ if (true_color)
+ printf("\x1b[0;38;2;%d;%d;%dm\u2580",
+ upperPixel->r, upperPixel->g, upperPixel->b);
+ else
+ printf("\e[0;38;5;%um\u2580", fgCol);
  else
- /* printf("\e[38;5;%u;48;5;%um\u2580", fgCol, bgCol); */
- printf("\x1b[48;2;%d;%d;%dm\x1b[38;2;%d;%d;%dm\u2584",
- upperPixel->r, upperPixel->g, upperPixel->b,
- lowerPixel->r, lowerPixel->g, lowerPixel->b
-  );
-
+ if (true_color)
+  printf("\x1b[48;2;%d;%d;%dm\x1b[38;2;%d;%d;%dm\u2584",
+  upperPixel->r, upperPixel->g, upperPixel->b,
+  lowerPixel->r, lowerPixel->g, lowerPixel->b);
+ else
+ printf("\e[38;5;%u;48;5;%um\u2580", fgCol, bgCol);
  }
  } else { // this is the last line
  if (upperPixel->a < TRANSP_ALPHA)
  printf("\e[m ");
  else
- printf("\x1b[0;38;2;%d;%d;%dm\u2580",
- upperPixel->r, upperPixel->g, upperPixel->b
- );
- /* printf("\e[38;5;%um\u2580", fgCol); */
+ if (true_color)
+ printf("\x1b[0;38;2;%d;%d;%dm\u2580",
+ upperPixel->r, upperPixel->g, upperPixel->b);
+ else
+ printf("\e[38;5;%um\u2580", fgCol);
  }
  } else {
  if (img.pixels[index].a < TRANSP_ALPHA)
  printf("\e[m ");
  else
- printf("\x1b[0;48;2;%d;%d;%dm ",
- img.pixels[index].r, img.pixels[index].g, img.pixels[index].b
- );
- /* printf("\e[48;5;%um ", fgCol); */
+ if (true_color)
+ printf("\x1b[0;48;2;%d;%d;%dm ",
+ img.pixels[index].r, img.pixels[index].g, img.pixels[index].b);
+ else
+ printf("\e[48;5;%um ", fgCol);
  }
  }
  printf("\e[m\n");
@@ -203,4 +213,3 @@ int main(int argc, char *argv[])
  free_hash_colors();
  return 0;
 }
-