Robustify detect_cursor_inversion()

When we're doing cursor querying, whether for detection
of inversion or just straight up localizing ourselves,
we need to talk to a real terminal, or else there's not
much point. When detecting cursor inversion, we need
move the cursor, *and have it reflected in the terminal
feedback*, which means we need write directly to the
terminal (if one exists). This requires ctermfd over
ttyfp, which we now hardcode. Fixes cursor crap when
redirected away from the terminal dankamongmen#1668.

src/lib/direct.c

@@ -140,9 +140,9 @@ int ncdirect_cursor_right(ncdirect* nc, int num){
 }
 
 // if we're on the last line, we need some scrolling action. rather than
-// merely using cud, we emit vertical tabs. this has the peculiar property
-// (in all terminals tested) of scrolling when necessary but performing no
-// carriage return -- a pure line feed.
+// merely using cud (which doesn't reliably scroll), we emit vertical tabs.
+// this has the peculiar property (in all terminals tested) of scrolling when
+// necessary but performing no carriage return -- a pure line feed.
 int ncdirect_cursor_down(ncdirect* nc, int num){
   if(num < 0){
     return -1;
@@ -266,17 +266,32 @@ detect_cursor_inversion(ncdirect* n, int rows, int cols, int* y, int* x){
   if(cursor_yx_get(n->ctermfd, y, x)){
     return -1;
   }
+  // do not use normal ncdirect_cursor_*() commands, because those go to ttyfp
+  // instead of ctermfd. since we always talk directly to the terminal, we need
+  // to move the cursor directly via the terminal.
+  if(!n->tcache.cud || !n->tcache.cub || !n->tcache.cuf || !n->tcache.cuu){
+    return -1;
+  }
+  int movex;
+  int movey;
   if(*x == cols && *y == 1){
-    if(ncdirect_cursor_down(n, 1) || ncdirect_cursor_left(n, 1)){
+    if(tty_emit(tiparm(n->tcache.cud, 1), n->ctermfd)){
       return -1;
     }
+    if(tty_emit(tiparm(n->tcache.cub, 1), n->ctermfd)){
+      return -1;
+    }
+    movex = 1;
+    movey = -1;
   }else{
-    if(ncdirect_cursor_right(n, 1) || ncdirect_cursor_up(n, 1)){
+    if(tty_emit(tiparm(n->tcache.cuu, 1), n->ctermfd)){
       return -1;
     }
-  }
-  if(ncdirect_flush(n)){
-    return -1;
+    if(tty_emit(tiparm(n->tcache.cuf, 1), n->ctermfd)){
+      return -1;
+    }
+    movex = -1;
+    movey = 1;
   }
   int newy, newx;
   if(cursor_yx_get(n->ctermfd, &newy, &newx)){
@@ -288,6 +303,12 @@ detect_cursor_inversion(ncdirect* n, int rows, int cols, int* y, int* x){
     *y = newy;
     newy = 1;
   }
+  if(tty_emit(tiparm(movex == 1 ? n->tcache.cuf : n->tcache.cub, 1), n->ctermfd)){
+    return -1;
+  }
+  if(tty_emit(tiparm(movey == 1 ? n->tcache.cud : n->tcache.cuu, 1), n->ctermfd)){
+    return -1;
+  }
   if(*y == newy && *x == newx){
     return -1; // hopelessly broken
   }else if(*x == newx){
@@ -315,16 +336,18 @@ detect_cursor_inversion(ncdirect* n, int rows, int cols, int* y, int* x){
 
 static int
 detect_cursor_inversion_wrapper(ncdirect* n, int* y, int* x){
+  // if we're not on a real terminal, there's no point in running this
+  if(n->ctermfd < 0){
+    return 0;
+  }
   const int toty = ncdirect_dim_y(n);
   const int totx = ncdirect_dim_x(n);
-  if(ncdirect_cursor_push(n)){
-    return -1; // FIXME work around lack of sc
-  }
-  int ret = detect_cursor_inversion(n, toty, totx, y, x);
-  if(ncdirect_cursor_pop(n)){
-    return -1;
-  }
-  return ret;
+  // there's an argument to be made that this ought be wrapped in sc/rc
+  // (push/pop cursor), rather than undoing itself. problem is, some
+  // terminals lack sc/rc (they need cursor moves to run the detection
+  // algorithm in the first place), and our versions go to ttyfp instead
+  // of ctermfd, as needed by cursor interrogation.
+  return detect_cursor_inversion(n, toty, totx, y, x);
 }
 
 // no terminfo capability for this. dangerous--it involves writing controls to

src/poc/cursor.c

@@ -0,0 +1,21 @@
+#include <notcurses/direct.h>
+
+int main(void){
+  struct ncdirect* n = ncdirect_core_init(NULL, stdout, 0);
+  if(n == NULL){
+    return EXIT_FAILURE;
+  }
+  int y, x;
+  if(ncdirect_cursor_yx(n, &y, &x)){
+    goto err;
+  }
+  int dimx = ncdirect_dim_x(n);
+  int dimy = ncdirect_dim_y(n);
+  printf("Cursor: column %d/%d row %d/%d\n", x, dimx, y, dimy);
+  ncdirect_stop(n);
+  return EXIT_SUCCESS;
+
+err:
+  ncdirect_stop(n);
+  return EXIT_FAILURE;
+}

src/poc/direct.c

@@ -45,12 +45,6 @@ int main(void){
     y += 2; // we just went down two lines
     while(y > 3){
       ret = -1;
-      const int up = y >= 3 ? 3 : y;
-      if(ncdirect_cursor_up(n, up)){
-        break;
-      }
-      fflush(stdout);
-      y -= up;
       int newy;
       if(ncdirect_cursor_yx(n, &newy, NULL)){
         break;
@@ -61,6 +55,12 @@ int main(void){
       }
       printf("\n\tRead cursor position: y: %d x: %d\n", newy, x);
       y += 2;
+      const int up = 3;
+      if(ncdirect_cursor_up(n, up)){
+        break;
+      }
+      fflush(stdout);
+      y -= up;
       ret = 0;
     }
   }else{