lib/tty: Add true color support with ncurses and improve S-Lang color detection

Enable true color support in ncurses. TERM must be set to a relevant
terminfo entry, i.e. *-direct, *-direct16, or *-direct256.

When set to *-direct256, both 256-color and true color mode can be used
at the same time.

Also fix true color detection in S-Lang. S-Lang checks for RGB terminfo
capability to enable true color, so we should check for it as well. This
means the COLORTERM variable doesn't need to be set when using direct
terminfo variants. This also applies to simultaneous 256-color and true
color mode.

We need to access the RGB extended capability. This is supported in both
S-Lang and ncurses, so unify the terminfo access routines to enable it.
Now they should be called with both terminfo and termcap capability
name.

Update FAQ.

Resolves: #4137
Resolves: #4821

Signed-off-by: Jakub Horký <jakub.git@horky.net>

Author: Jakub Horký

doc/FAQ

@@ -403,47 +403,51 @@ Frequently Asked Questions
    If you get colors, be happy.
 
    If your terminal stays black and white, your terminal doesn't support
-   color.  You might want to upgrade to a terminal which compatible with
+   color.  You might want to upgrade to a terminal which is compatible with
    the ANSI color sequences.
 
    If your terminal goes completely black, see the next question.
 
    More detailed answer:
 
-   Check that your terminal supports color.  color_xterm, rxvt and Linux
-   console do support, most other terminals don't.  You can test color
-   support with following simple C program:
+   Check that your terminal supports color.  Most terminals do. You can
+   test color support with the following command:
 
-    #include <stdio.h>
+        printf "\033[32m Hello color world! \033[m\n"
 
-    int main (void){
-        printf ("\033[32m Hello world! \033[m\n");
-        return 0;
-    }
+   You can test 256 color support with the following command:
 
-   Compile and run it.  If you see "Hello world!" text in green your
-   terminal supports color, otherwise not (however, for color_xterm see
-   also the next question).
+        printf "\033[38;5;120m Hello 256-color world! \033[m\n"
 
-   Check whether you are using Ncurses or the S-Lang library (type
-   "mc -V" to find out).
+   You can test true color support with the following command:
 
-   With S-Lang library you can force color support by setting the
-   environment variable COLORTERM to any value.
+        printf "\033[38;2;0;200;0m Hello true color world! \033[m\n"
 
-   If you use ncurses library, check that your terminfo database
-   supports color.  If not, you should install one of the enhanced
-   terminfo databases included in GNU Midnight Commander source
-   distribution.
+   If you see the text in green, your terminal supports the respective
+   color mode.
 
-   You might want to set the TERM environment variable so that you are
-   using the correct terminfo database or termcap entry.
+   Check that you are using the proper TERM variable for your terminal.
+   If not, set it accordingly. You can use the 'toe' command to list all
+   available terminfo entries.
 
-   If you use color_xterm (or rxvt) the correct value might be
-   xterm-color, xtermc or simply xterm.
+   If your terminal supports 256 colors, the correct entry name may be
+   appended with -256color. If your terminal supports true color, it
+   should be appended with -direct, -direct16, or -direct256. The best
+   backwards compatibility option is -direct256 variant, which provides
+   both 256-color and true color support simultaneously. There is no
+   difference between the -direct and -direct16 variants when used by
+   mc, but -direct16 variant offers better compatibility with other
+   programs that are not aware of these enhanced color modes.
 
-   If you use Linux console the correct value for TERM is linux or
-   console.
+   If there is no 256-color or true-color terminfo variant for your
+   terminal, even though your terminal supports it, send an e-mail to
+   ncurses/terminfo maintainers (bug-ncurses@gnu.org) and ask them to
+   add one.
+
+   With the S-Lang library (you can check by 'mc -V'), you can force
+   color support by setting the environment variable COLORTERM to any
+   value, and specifically force true color support by setting it to
+   'truecolor'.
 
 4.5 My color_xterm goes completely (or partially) black!
 

lib/skin/common.c

@@ -164,9 +164,10 @@ mc_skin_init (const gchar *skin_override, GError **mcerror)
     if (is_good_init && mc_skin__default.have_256_colors && !tty_use_256colors (&error))
     {
         mc_propagate_error (mcerror, 0,
-                            _ ("Unable to use '%s' skin with 256 colors support\non non-256 colors "
-                               "terminal.\nDefault skin has been loaded"),
-                            mc_skin__default.name);
+                            _ ("Unable to use '%s' skin with 256 colors support:\n%s\nDefault "
+                               "skin has been loaded"),
+                            mc_skin__default.name, error->message);
+        g_error_free (error);
         mc_skin_try_to_load_default ();
         mc_skin_colors_old_configure (&mc_skin__default);
         (void) mc_skin_ini_file_parse (&mc_skin__default);

lib/tty/color-internal.c

@@ -155,7 +155,7 @@ parse_256_or_true_color_name (const char *color_name)
                 i = (h[0] << 20) | (h[0] << 16) | (h[1] << 12) | (h[1] << 8) | (h[2] << 4) | h[2];
             else
                 i = (h[0] << 20) | (h[1] << 16) | (h[2] << 12) | (h[3] << 8) | (h[4] << 4) | h[5];
-            return (1 << 24) | i;
+            return FLAG_TRUECOLOR | i;
         }
     }
 
@@ -178,7 +178,7 @@ tty_color_get_name_by_index (int idx)
             return color_table[i].name;
 
     // Create and return the strings in "colorNNN" or "#rrggbb" format.
-    if ((idx >= 16 && idx < 256) || (idx & (1 << 24)) != 0)
+    if ((idx >= 16 && idx < 256) || (idx & FLAG_TRUECOLOR) != 0)
     {
         char name[9];
 

lib/tty/color-internal.h

@@ -18,6 +18,9 @@
 
 /*** typedefs(not structures) and defined constants **********************************************/
 
+#define FLAG_TRUECOLOR   (1 << 24)
+#define COLORS_TRUECOLOR (1 << 24)
+
 /*** enums ***************************************************************************************/
 
 typedef enum

lib/tty/color-ncurses.c

@@ -38,6 +38,7 @@
 
 #include "lib/global.h"
 
+#include "tty.h"
 #include "tty-ncurses.h"
 #include "color.h"  // variables
 #include "color-internal.h"
@@ -53,6 +54,7 @@
 /*** file scope variables ************************************************************************/
 
 static GHashTable *mc_tty_color_color_pair_attrs = NULL;
+static int overlay_colors = 0;
 
 /* --------------------------------------------------------------------------------------------- */
 /*** file scope functions ************************************************************************/
@@ -179,23 +181,40 @@ tty_color_try_alloc_lib_pair (tty_color_lib_pair_t *mc_color_pair)
         ibg = mc_color_pair->bg;
         attr = mc_color_pair->attr;
 
-        // In legacy color mode, change bright colors into bold
-        if (!tty_use_256colors (NULL) && !tty_use_truecolors (NULL))
+        // Change basic bright colors into bold
+        if (ifg >= 8 && ifg < 16)
         {
-            if (ifg >= 8 && ifg < 16)
-            {
-                ifg &= 0x07;
-                attr |= A_BOLD;
-            }
-
-            if (ibg >= 8 && ibg < 16)
-            {
-                ibg &= 0x07;
-                // attr | = A_BOLD | A_REVERSE ;
-            }
+            ifg &= 0x07;
+            attr |= A_BOLD;
         }
 
+        if (ibg >= 8 && ibg < 16)
+        {
+            ibg &= 0x07;
+            // attr | = A_BOLD | A_REVERSE ;
+        }
+
+        // Shady trick: if we don't have the exact color, because it is overlaid by backwards
+        // compatibility indexed values, just borrow one degree of red. The user won't notice :)
+        if ((ifg & FLAG_TRUECOLOR) != 0)
+        {
+            ifg &= ~FLAG_TRUECOLOR;
+            if (ifg != 0 && ifg <= overlay_colors)
+                ifg += (1 << 16);
+        }
+
+        if ((ibg & FLAG_TRUECOLOR) != 0)
+        {
+            ibg &= ~FLAG_TRUECOLOR;
+            if (ibg != 0 && ibg <= overlay_colors)
+                ibg += (1 << 16);
+        }
+
+#if NCURSES_VERSION_PATCH >= 20170401
+        init_extended_pair (mc_color_pair->pair_index, ifg, ibg);
+#else
         init_pair (mc_color_pair->pair_index, ifg, ibg);
+#endif
         mc_tty_color_save_attr (mc_color_pair->pair_index, attr);
     }
 }
@@ -231,17 +250,50 @@ tty_use_256colors (GError **error)
 {
     (void) error;
 
-    return (COLORS == 256);
+    overlay_colors = tty_tigetnum ("CO", NULL);
+
+    if (COLORS != 256 && !(COLORS > 256 && overlay_colors == 256))
+    {
+        g_set_error (error, MC_ERROR, -1,
+                     _ ("\nIf your terminal supports 256 colors, you need to set your TERM\n"
+                        "environment variable to match your terminal, perhaps using\n"
+                        "a *-256color or *-direct256 variant. Use the 'toe -a'\n"
+                        "command to list all available variants on your system.\n"));
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 /* --------------------------------------------------------------------------------------------- */
 
 gboolean
 tty_use_truecolors (GError **error)
 {
-    // Not yet supported in ncurses
-    g_set_error (error, MC_ERROR, -1, _ ("True color not supported with ncurses."));
+    // Low level true color is supported since ncurses 6.0 patch 20170401 preceding release
+    // of ncurses 6.1
+#if NCURSES_VERSION_PATCH < 20170401
+    g_set_error (error, MC_ERROR, -1,
+                 _ ("You need version 6.1 or later of the ncurses library\n"
+                    "for true color support. Please upgrade your system.\n"));
     return FALSE;
+#else
+    // We support only bool RGB cap configuration (8:8:8 bits), but the other variants are so rare
+    // that we don't need to bother.
+    if (!(tty_tigetflag ("RGB", NULL) && COLORS == COLORS_TRUECOLOR))
+    {
+        g_set_error (
+            error, MC_ERROR, -1,
+            _ ("\nIf your terminal supports true colors, you need to set your TERM\n"
+               "environment variable to a *-direct256, *-direct16, or *-direct variant.\n"
+               "Use the 'toe -a' command to list all available variants on your system.\n"));
+        return FALSE;
+    }
+
+    overlay_colors = tty_tigetnum ("CO", NULL);
+
+    return TRUE;
+#endif
 }
 
 /* --------------------------------------------------------------------------------------------- */

lib/tty/color-slang.c

@@ -38,6 +38,7 @@
 #include "lib/global.h"
 #include "lib/util.h"  // whitespace()
 
+#include "tty.h"
 #include "tty-slang.h"
 #include "color.h"  // variables
 #include "color-internal.h"
@@ -215,12 +216,19 @@ gboolean
 tty_use_256colors (GError **error)
 {
     gboolean ret;
+    int colors, overlay_colors;
 
-    ret = (SLtt_Use_Ansi_Colors && SLtt_tgetnum ((char *) "Co") == 256);
+    colors = tty_tigetnum ("colors", "Co");
+    overlay_colors = tty_tigetnum ("CO", NULL);
+
+    ret = (SLtt_Use_Ansi_Colors && (colors == 256 || (colors > 256 && overlay_colors == 256)));
 
     if (!ret)
         g_set_error (error, MC_ERROR, -1,
-                     _ ("Your terminal doesn't even seem to support 256 colors."));
+                     _ ("\nIf your terminal supports 256 colors, you need to set your TERM\n"
+                        "environment variable to match your terminal, perhaps using\n"
+                        "a *-256color or *-direct256 variant. Use the 'toe -a'\n"
+                        "command to list all available variants on your system.\n"));
 
     return ret;
 }
@@ -245,11 +253,15 @@ tty_use_truecolors (GError **error)
     /* Duplicate slang's check so that we can pop up an error message
        rather than silently use wrong colors. */
     colorterm = getenv ("COLORTERM");
-    if (colorterm == NULL
-        || (strcmp (colorterm, "truecolor") != 0 && strcmp (colorterm, "24bit") != 0))
+    if (!((tty_tigetflag ("RGB", NULL) && tty_tigetnum ("colors", "Co") == COLORS_TRUECOLOR)
+          || (colorterm != NULL
+              && (strcmp (colorterm, "truecolor") == 0 || strcmp (colorterm, "24bit") == 0))))
     {
         g_set_error (error, MC_ERROR, -1,
-                     _ ("Set COLORTERM=truecolor if your terminal really supports true colors."));
+                     _ ("\nIf your terminal supports true colors, you need to set your TERM\n"
+                        "environment variable to a *-direct256, *-direct16, or *-direct variant.\n"
+                        "Use the 'toe -a' command to list all available variants on your system.\n"
+                        "Alternatively, you can set COLORTERM=truecolor.\n"));
         return FALSE;
     }
 

lib/tty/tty-ncurses.c

@@ -739,12 +739,26 @@ tty_printf (const char *fmt, ...)
 
 /* --------------------------------------------------------------------------------------------- */
 
-char *
-tty_tgetstr (const char *cap)
+int
+tty_tigetflag (const char *terminfo_cap, MC_UNUSED const char *termcap_cap)
 {
-    char *unused = NULL;
+    return tigetflag ((NCURSES_CONST char *) terminfo_cap);
+}
 
-    return tgetstr ((NCURSES_CONST char *) cap, &unused);
+/* --------------------------------------------------------------------------------------------- */
+
+int
+tty_tigetnum (const char *terminfo_cap, MC_UNUSED const char *termcap_cap)
+{
+    return tigetnum ((NCURSES_CONST char *) terminfo_cap);
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
+char *
+tty_tigetstr (const char *terminfo_cap, MC_UNUSED const char *termcap_cap)
+{
+    return tigetstr ((NCURSES_CONST char *) terminfo_cap);
 }
 
 /* --------------------------------------------------------------------------------------------- */

lib/tty/tty-slang.c

@@ -756,10 +756,34 @@ tty_printf (const char *fmt, ...)
 
 /* --------------------------------------------------------------------------------------------- */
 
+/* Although S-Lang uses the terminfo database by default (through its own parser), it expects
+ * termcap codes to access standard capabilities. Nevertheless, it can also access extended
+ * terminfo capabilities (including those that have no termcap equivalent, i.e., whose names
+ * are longer than two characters).
+ */
+
+/* --------------------------------------------------------------------------------------------- */
+
+int
+tty_tigetflag (const char *terminfo_cap, const char *termcap_cap)
+{
+    return SLtt_tgetflag ((SLFUTURE_CONST char *) (termcap_cap ? termcap_cap : terminfo_cap));
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
+int
+tty_tigetnum (const char *terminfo_cap, const char *termcap_cap)
+{
+    return SLtt_tgetnum ((SLFUTURE_CONST char *) (termcap_cap ? termcap_cap : terminfo_cap));
+}
+
+/* --------------------------------------------------------------------------------------------- */
+
 char *
-tty_tgetstr (const char *cap)
+tty_tigetstr (const char *terminfo_cap, const char *termcap_cap)
 {
-    return SLtt_tgetstr ((SLFUTURE_CONST char *) cap);
+    return SLtt_tgetstr ((SLFUTURE_CONST char *) (termcap_cap ? termcap_cap : terminfo_cap));
 }
 
 /* --------------------------------------------------------------------------------------------- */

lib/tty/tty.c

@@ -371,16 +371,9 @@ tty_init_xterm_support (gboolean is_xterm)
     // Check mouse and ca capabilities
     /* terminfo/termcap structures have been already initialized,
        in slang_init() or/and init_curses()  */
-    // Check terminfo at first, then check termcap
-    xmouse_seq = tty_tgetstr ("kmous");
-    if (xmouse_seq == NULL)
-        xmouse_seq = tty_tgetstr ("Km");
-    smcup = tty_tgetstr ("smcup");
-    if (smcup == NULL)
-        smcup = tty_tgetstr ("ti");
-    rmcup = tty_tgetstr ("rmcup");
-    if (rmcup == NULL)
-        rmcup = tty_tgetstr ("te");
+    xmouse_seq = tty_tigetstr ("kmous", "Km");
+    smcup = tty_tigetstr ("smcup", "ti");
+    rmcup = tty_tigetstr ("rmcup", "te");
 
     if (strcmp (termvalue, "cygwin") == 0)
     {

lib/tty/tty.h

@@ -63,7 +63,9 @@ typedef enum
 
 extern int mc_tty_frm[];
 
-extern char *tty_tgetstr (const char *name);
+extern int tty_tigetflag (const char *terminfo_cap, const char *termcap_cap);
+extern int tty_tigetnum (const char *terminfo_cap, const char *termcap_cap);
+extern char *tty_tigetstr (const char *terminfo_cap, const char *termcap_cap);
 
 /*** declarations of public functions ************************************************************/