Show arrow indicating order of sorted process column

CRT.c

@@ -48,6 +48,8 @@ static const char* const CRT_treeStrAscii[LAST_TREE_STR] = {
    [TREE_STR_TEND] = ",",
    [TREE_STR_OPEN] = "+",
    [TREE_STR_SHUT] = "-",
+   [TREE_STR_ASC]  = "+",
+   [TREE_STR_DESC] = "-",
 };
 
 #ifdef HAVE_LIBNCURSESW
@@ -61,6 +63,8 @@ static const char* const CRT_treeStrUtf8[LAST_TREE_STR] = {
                                      // WITH VERTICAL STROKE' (U+1FBAF, "\xf0\x9f\xae\xaf") when
                                      // Unicode 13 is common
    [TREE_STR_SHUT] = "\xe2\x94\x80", // ─
+   [TREE_STR_ASC]  = "\xe2\x96\xb3", // △
+   [TREE_STR_DESC] = "\xe2\x96\xbd", // ▽
 };
 
 bool CRT_utf8 = false;

CRT.h

@@ -22,6 +22,8 @@ typedef enum TreeStr_ {
    TREE_STR_TEND,
    TREE_STR_OPEN,
    TREE_STR_SHUT,
+   TREE_STR_ASC,
+   TREE_STR_DESC,
    LAST_TREE_STR
 } TreeStr;
 

ProcessList.c

@@ -112,6 +112,13 @@ void ProcessList_printHeader(ProcessList* this, RichString* header) {
       }
 
       RichString_appendWide(header, color, alignedProcessFieldTitle(fields[i]));
+      if (key == fields[i] && RichString_getCharVal(*header, RichString_size(header) - 1) == ' ') {
+         header->chlen--;  // rewind to override space
+         RichString_appendnWide(header,
+                                CRT_colors[PANEL_SELECTION_FOCUS],
+                                CRT_treeStr[Settings_getActiveDirection(this->settings) == 1 ? TREE_STR_DESC : TREE_STR_ASC],
+                                1);
+      }
       if (COMM == fields[i] && settings->showMergedCommand) {
          RichString_appendAscii(header, color, "(merged)");
       }