always send DSRCPR at init, use it to verify u7

for NCOPTION_PRESERVE_CURSOR, we want to know the location
of the cursor at startup. go ahead and always send a DSRCPR
in terminal interrogation. if we get a reply to it, hey, we
just verified that the terminal knows DSRCPR.

if we find a u7 value in terminfo that's different from the
standard DSRCPR, we ought send that in addition. #1816

USAGE.md

@@ -106,6 +106,12 @@ typedef enum {
 // registration of these signal handlers.
 #define NCOPTION_NO_QUIT_SIGHANDLERS 0x0008
 
+// Initialize the standard plane's virtual cursor to match the physical cursor
+// at context creation time. Together with NCOPTION_NO_ALTERNATE_SCREEN and a
+// scrolling standard plane, this facilitates easy scrolling-style programs in
+// rendered mode.
+#define NCOPTION_PRESERVE_CURSOR     0x0010ull
+
 // Notcurses typically prints version info in notcurses_init() and performance
 // info in notcurses_stop(). This inhibits that output.
 #define NCOPTION_SUPPRESS_BANNERS    0x0020

src/info/main.c

@@ -117,7 +117,7 @@ tinfo_debug_styles(struct ncplane* n, const char* indent){
 // notcurses_render() without the alternate screen, no?
 int main(void){
   notcurses_options nopts = {
-    .flags = NCOPTION_NO_ALTERNATE_SCREEN,
+    .flags = NCOPTION_NO_ALTERNATE_SCREEN | NCOPTION_PRESERVE_CURSOR,
   };
   struct notcurses* nc = notcurses_init(&nopts, NULL);
   if(nc == NULL){

src/lib/input.c

@@ -650,6 +650,8 @@ typedef enum {
   STATE_XTSMGRAPHICS_DRAIN, // drain out XTSMGRAPHICS to 'S'
   STATE_APPSYNC_REPORT, // got DECRPT ?2026
   STATE_APPSYNC_REPORT_DRAIN, // drain out decrpt to 'y'
+  STATE_CURSOR, // reading row of cursor location to ';'
+  STATE_CURSOR_COL, // reading col of cursor location to 'R'
 } initstates_e;
 
 typedef struct query_state {
@@ -665,6 +667,7 @@ typedef struct query_state {
   char runstring[80];    // running string
   size_t stridx;         // position to write in string
   uint32_t bg;           // queried default background or 0
+  int cursor_y, cursor_x;// cursor location
   bool xtgettcap_good;   // high when we've received DCS 1
   bool appsync;          // application-synchronized updates advertised
 } query_state;
@@ -879,10 +882,38 @@ pump_control_read(query_state* inits, unsigned char c){
         inits->state = STATE_DA; // could also be DECRPM/XTSMGRAPHICS
       }else if(c == '>'){
         inits->state = STATE_SDA;
+      }else if(isdigit(c)){
+        inits->numeric = 0;
+        inits->state = STATE_CURSOR;
       }else if(c >= 0x40 && c <= 0x7E){
         inits->state = STATE_NULL;
       }
       break;
+    case STATE_CURSOR:
+      if(isdigit(c)){
+        if(ruts_hex(&inits->numeric, c)){
+          return -1;
+        }
+      }else if(c == ';'){
+        inits->cursor_y = inits->numeric;
+        inits->state = STATE_CURSOR_COL;
+        inits->numeric = 0;
+      }else{
+        inits->state = STATE_NULL;
+      }
+      break;
+    case STATE_CURSOR_COL:
+      if(isdigit(c)){
+        if(ruts_hex(&inits->numeric, c)){
+          return -1;
+        }
+      }else if(c == 'R'){
+        inits->cursor_x = inits->numeric;
+        inits->state = STATE_NULL;
+      }else{
+        inits->state = STATE_NULL;
+      }
+      break;
     case STATE_DCS: // terminated by ST
       if(c == '\\'){
 //fprintf(stderr, "terminated DCS\n");
@@ -1168,7 +1199,7 @@ err:
 }
 
 int ncinputlayer_init(tinfo* tcache, FILE* infp, queried_terminals_e* detected,
-                      unsigned* appsync){
+                      unsigned* appsync, int* cursor_y, int* cursor_x){
   ncinputlayer* nilayer = &tcache->input;
   setbuffer(infp, NULL, 0);
   nilayer->inputescapes = NULL;
@@ -1188,6 +1219,8 @@ int ncinputlayer_init(tinfo* tcache, FILE* infp, queried_terminals_e* detected,
         .tcache = tcache,
         .state = STATE_NULL,
         .qterm = TERMINAL_UNKNOWN,
+        .cursor_x = -1,
+        .cursor_y = -1,
       };
       if(control_read(csifd, &inits)){
         input_free_esctrie(&nilayer->inputescapes);
@@ -1198,6 +1231,8 @@ int ncinputlayer_init(tinfo* tcache, FILE* infp, queried_terminals_e* detected,
       tcache->termversion = inits.version;
       *detected = inits.qterm;
       *appsync = inits.appsync;
+      *cursor_x = inits.cursor_x;
+      *cursor_y = inits.cursor_y;
     }
   }
   return 0;

src/lib/input.h

@@ -34,7 +34,8 @@ typedef enum {
 // advertised support for application-sychronized updates, |appsync| will be
 // non-zero.
 int ncinputlayer_init(struct tinfo* tcache, FILE* infp,
-                      queried_terminals_e* detected, unsigned* appsync);
+                      queried_terminals_e* detected, unsigned* appsync,
+                      int* cursor_y, int* cursor_x);
 
 void ncinputlayer_stop(struct ncinputlayer* nilayer);
 

src/lib/termdesc.c

@@ -150,6 +150,46 @@ grow_esc_table(tinfo* ti, const char* tstr, escape_e esc,
   return 0;
 }
 
+// Device Attributes; replies with (depending on decTerminalID resource):
+//   ⇒  CSI ? 1 ; 2 c  ("VT100 with Advanced Video Option")
+//   ⇒  CSI ? 1 ; 0 c  ("VT101 with No Options")
+//   ⇒  CSI ? 4 ; 6 c  ("VT132 with Advanced Video and Graphics")
+//   ⇒  CSI ? 6 c  ("VT102")
+//   ⇒  CSI ? 7 c  ("VT131")
+//   ⇒  CSI ? 1 2 ; Ps c  ("VT125")
+//   ⇒  CSI ? 6 2 ; Ps c  ("VT220")
+//   ⇒  CSI ? 6 3 ; Ps c  ("VT320")
+//   ⇒  CSI ? 6 4 ; Ps c  ("VT420")
+
+// query background, replies in X color https://www.x.org/releases/X11R7.7/doc/man/man7/X.7.xhtml#heading11
+#define CSI_BGQ "\e]11;?\e\\"
+
+// ought be using the u7 terminfo string here, if it exists. the great thing
+// is, if we get a response to this, we know we can use it for u7!
+#define DSRCPR "\e[6n"
+
+// we send an XTSMGRAPHICS to set up 256 color registers (the most we can
+// currently take advantage of; we need at least 64 to use sixel at all.
+// maybe that works, maybe it doesn't. then query both color registers
+// and geometry. send XTGETTCAP for terminal name.
+static int
+send_initial_queries(int fd){
+  const char queries[] = CSI_BGQ
+                         DSRCPR
+                         "\x1b[?2026$p"      // query for App-sync updates
+                         "\x1b[=0c"          // Tertiary Device Attributes
+                         "\x1b[>0q"          // XTVERSION
+                         "\x1bP+q544e\x1b\\" // XTGETTCAP['TN']
+                         "\x1b[?1;3;256S"    // try to set 256 cregs
+                         "\x1b[?2;1;0S"      // XTSMGRAPHICS (cregs)
+                         "\x1b[?1;1;0S"      // XTSMGRAPHICS (geometry)
+                         "\x1b[c";           // Device Attributes
+  if(blocking_write(fd, queries, strlen(queries))){
+    return -1;
+  }
+  return 0;
+}
+
 static int
 init_terminfo_esc(tinfo* ti, const char* name, escape_e idx,
                   size_t* tablelen, size_t* tableused){
@@ -164,14 +204,15 @@ init_terminfo_esc(tinfo* ti, const char* name, escape_e idx,
   return 0;
 }
 
-// older kitty terminfo doesn't include u7. remove this when we can FIXME.
+// if we get a response to the standard cursor locator escape, we know this
+// terminal supports it, hah.
 static int
 add_u7_escape(tinfo* ti, size_t* tablelen, size_t* tableused){
   const char* u7 = get_escape(ti, ESCAPE_DSRCPR);
   if(u7){
     return 0; // already present
   }
-  if(grow_esc_table(ti, "\e[6n", ESCAPE_DSRCPR, tablelen, tableused)){
+  if(grow_esc_table(ti, DSRCPR, ESCAPE_DSRCPR, tablelen, tableused)){
     return -1;
   }
   return 0;
@@ -221,9 +262,6 @@ apply_term_heuristics(tinfo* ti, const char* termname, int fd,
     if(add_smulx_escapes(ti, tablelen, tableused)){
       return -1;
     }
-    if(add_u7_escape(ti, tablelen, tableused)){
-      return -1;
-    }
   }else if(qterm == TERMINAL_ALACRITTY){
     termname = "Alacritty";
     ti->caps.quadrants = true;
@@ -286,41 +324,6 @@ apply_term_heuristics(tinfo* ti, const char* termname, int fd,
   return 0;
 }
 
-// Device Attributes; replies with (depending on decTerminalID resource):
-//   ⇒  CSI ? 1 ; 2 c  ("VT100 with Advanced Video Option")
-//   ⇒  CSI ? 1 ; 0 c  ("VT101 with No Options")
-//   ⇒  CSI ? 4 ; 6 c  ("VT132 with Advanced Video and Graphics")
-//   ⇒  CSI ? 6 c  ("VT102")
-//   ⇒  CSI ? 7 c  ("VT131")
-//   ⇒  CSI ? 1 2 ; Ps c  ("VT125")
-//   ⇒  CSI ? 6 2 ; Ps c  ("VT220")
-//   ⇒  CSI ? 6 3 ; Ps c  ("VT320")
-//   ⇒  CSI ? 6 4 ; Ps c  ("VT420")
-
-// query background, replies in X color https://www.x.org/releases/X11R7.7/doc/man/man7/X.7.xhtml#heading11
-#define CSI_BGQ "\e]11;?\e\\"
-
-// we send an XTSMGRAPHICS to set up 256 color registers (the most we can
-// currently take advantage of; we need at least 64 to use sixel at all.
-// maybe that works, maybe it doesn't. then query both color registers
-// and geometry. send XTGETTCAP for terminal name.
-static int
-send_initial_queries(int fd){
-  const char queries[] = CSI_BGQ
-                         "\x1b[?2026$p"      // query for App-sync updates
-                         "\x1b[=0c"          // Tertiary Device Attributes
-                         "\x1b[>0q"          // XTVERSION
-                         "\x1bP+q544e\x1b\\" // XTGETTCAP['TN']
-                         "\x1b[?1;3;256S"    // try to set 256 cregs
-                         "\x1b[?2;1;0S"      // XTSMGRAPHICS (cregs)
-                         "\x1b[?1;1;0S"      // XTSMGRAPHICS (geometry)
-                         "\x1b[c";           // Device Attributes
-  if(blocking_write(fd, queries, strlen(queries))){
-    return -1;
-  }
-  return 0;
-}
-
 // termname is just the TERM environment variable. some details are not
 // exposed via terminfo, and we must make heuristic decisions based on
 // the detected terminal type, yuck :/.
@@ -501,7 +504,9 @@ int interrogate_terminfo(tinfo* ti, int fd, const char* termname, unsigned utf8,
     }
   }
   unsigned appsync_advertised;
-  if(ncinputlayer_init(ti, stdin, &qterm, &appsync_advertised)){
+  int cursor_x = -1;
+  int cursor_y = -1;
+  if(ncinputlayer_init(ti, stdin, &qterm, &appsync_advertised, &cursor_y, &cursor_x)){
     goto err;
   }
   if(nocbreak){
@@ -512,6 +517,12 @@ int interrogate_terminfo(tinfo* ti, int fd, const char* termname, unsigned utf8,
       }
     }
   }
+  if(cursor_x >= 0 && cursor_y >= 0){
+    if(add_u7_escape(ti, &tablelen, &tableused)){
+      return -1;
+    }
+    // FIXME set cursor up
+  }
   if(appsync_advertised){
     if(add_appsync_escapes(ti, &tablelen, &tableused)){
       goto err;