Subregion renders #293 (#404)

Add four new fields to notcurses_options: margin_{tblr}, which requests margins to the top, right, bottom, and left. Render only within those margins, leaving the screen otherwise untouched (well, cleared if using the alternate screen). #293

README.md

@@ -35,7 +35,7 @@ Packages for Debian Unstable and Ubuntu Focal are available from [DSSCAW](https:
   * [Features missing relative to NCURSES](#features-missing-relative-to-ncurses)
   * [Adapting NCURSES programs](#adapting-ncurses-programs)
 * [Environment notes](#environment-notes)
-  * [DirectColor detection](#DirectColor-detection)
+  * [TrueColor detection](#TrueColor-detection)
   * [Fonts](#fonts)
   * [FAQs](#faqs)
 * [Supplemental material](#supplemental-material)
@@ -57,9 +57,9 @@ Packages for Debian Unstable and Ubuntu Focal are available from [DSSCAW](https:
 
 notcurses abandons the X/Open Curses API bundled as part of the Single UNIX
 Specification. The latter shows its age, and seems not capable of making use of
-terminal functionality such as unindexed 24-bit color ("DirectColor", not to be
-confused with 8-bit indexed 24-bit color, aka "TrueColor" or (by NCURSES) as
-"extended color"). For some necessary background, consult Thomas E. Dickey's
+terminal functionality such as unindexed 24-bit color ("TrueColor", not to be
+confused with the 8-bit indexed 24-bit "extended color" of NCURSES).
+For some necessary background, consult Thomas E. Dickey's
 superb and authoritative [NCURSES FAQ](https://invisible-island.net/ncurses/ncurses.faq.html#xterm_16MegaColors).
 As such, notcurses is not a drop-in Curses replacement. It is almost certainly
 less portable, and definitely tested on less hardware. Sorry about that.
@@ -212,6 +212,11 @@ typedef struct notcurses_options {
   // Progressively higher log levels result in more logging to stderr. By
   // default, nothing is printed to stderr once fullscreen service begins.
   ncloglevel_e loglevel;
+  // Desirable margins. If all are 0 (default), we will render to the entirety
+  // of the screen. If the screen is too small, we do what we can--this is
+  // strictly best-effort. Absolute coordinates are relative to the rendering
+  // area ((0, 0) is always the origin of the rendering area).
+  int margin_t, margin_r, margin_b, margin_l;
 } notcurses_options;
 
 // Initialize a notcurses context on the connected terminal at 'fp'. 'fp' must
@@ -2498,12 +2503,12 @@ These are pretty obvious, implementation-wise.
 * The unit tests assume dimensions of at least 80x24. They might work in a
   smaller terminal. They might not. Don't file bugs on it.
 
-### DirectColor detection
+### TrueColor detection
 
-notcurses aims to use only information found in the terminal's terminfo entry to detect capabilities, DirectColor
+notcurses aims to use only information found in the terminal's terminfo entry to detect capabilities, TrueColor
 being one of them. Support for this is indicated by terminfo having a flag, added in NCURSES 6.1, named `RGB` set
 to `true`. However, as of today there are few and far between terminfo entries which have the capability in their
-database entry and so DirectColor won't be used in most cases. Terminal emulators have had for years a kludge to
+database entry and so TrueColor won't be used in most cases. Terminal emulators have had for years a kludge to
 work around this limitation of terminfo in the form of the `COLORTERM` environment variable which, if set to either
 `truecolor` or `24bit` does the job of indicating the capability of sending the escapes 48 and 38 together with a
 tripartite RGB (0 ≤ c ≤ 255 for all three components) to specify fore- and background colors.
@@ -2590,7 +2595,7 @@ up someday **FIXME**.
     I study the history of NCURSES, primarily using Thomas E. Dickey's FAQ and
     the mailing list archives.
     * 2019-11-14: I file [Outcurses issue #56](https://github.com/dankamongmen/ncreels/issues/56)
-      regarding use of DirectColor in outcurses. This is partially inspired by
+      regarding use of TrueColor in outcurses. This is partially inspired by
       Lexi Summer Hale's essay [everything you ever wanted to know about terminals](http://xn--rpa.cc/irl/term.html).
       I get into contact with Thomas E. Dickey and confirm that what I'm hoping
       to do doesn't really fit in with the codified Curses API.

doc/man/man1/notcurses-demo.1.md

@@ -9,13 +9,14 @@ notcurses-demo - Show off some notcurses features
 # SYNOPSIS
 
 **notcurses-demo** [**-h|--help**] [**-p path**] [**-d delaymult**]
- [**-l loglevel**] [**-f renderfile**] [**-J jsonfile**] [**-ikVc**] demospec
+ [**-l loglevel**] [**-f renderfile**] [**-J jsonfile**] [**-m margins**]
+ [**-ikVc**] demospec
 
 # DESCRIPTION
 
 **notcurses-demo** demonstrates the capabilities of the notcurses library. It
 can be run in any terminal emulator or console with a correct terminfo(5)
-database, but is at is best in a "DirectColor" 24bpp RGB environment. If
+database, but is at is best in a 24bpp TrueColor RGB environment. If
 **notcurses-demo** seems to generate garbage, something is likely configured in
 a way that is going to prevent notcurses from working.
 
@@ -53,6 +54,8 @@ At any time, press 'q' to quit. The demo is best run in at least an 80x45 termin
 
 **-J jsonfile**: Emit JSON summary of run to **jsonfile**.
 
+**-m margins**: Define rendering margins (see below).
+
 **-k**: Inhibit use of the alternate screen. Necessary if you want the output left on your terminal after the program exits.
 
 **-c**: Do not attempt to seed the PRNG. This is useful when benchmarking.
@@ -65,6 +68,11 @@ At any time, press 'q' to quit. The demo is best run in at least an 80x45 termin
 
 demospec: Select which demos to run, and what order to run them in. The default is **ixethbcgrwuvlfsjo**. See above for a list of demos.
 
+Default margins are all 0, and thus the full screen will be rendered. Using
+**-m**, margins can be supplied. Provide a single number to set all four margins
+to the same value, or four comma-delimited values for the top, right, bottom,
+and left margins respectively. Negative margins are illegal.
+
 # NOTES
 
 Proper display requires:

doc/man/man3/notcurses.3.md

@@ -17,7 +17,7 @@ notcurses - TUI library for modern terminal emulators
 notcurses builds atop the **terminfo(5)** abstraction layer to provide
 reasonably portable vivid character displays. It is an intellectual descendant
 of **ncurses(3NCURSES)**, but goes beyond that library (and the X/Open Curses
-API it implements). notcurses is capable of subregion fades, 24bpp DirectColor,
+API it implements). notcurses is capable of subregion fades, 24bpp TrueColor,
 transparency, multimedia, and safe multithreaded use.
 
 A program wishing to use notcurses will need to link it, ideally using the

doc/man/man3/notcurses_init.3.md

@@ -19,6 +19,7 @@ typedef struct notcurses_options {
   bool no_quit_sighandlers;
   bool no_winch_sighandler;
   FILE* renderfp;
+  int margin_t, margin_r, margin_b, margin_l;
 } notcurses_options;
 ```
 
@@ -58,6 +59,16 @@ information and some details of the configured terminal. This can be inhibited
 with **suppress_banner**. This will also inhibit the performance summary normally
 printed by **notcurses_stop(3)**.
 
+Notcurses can render to a subregion of the terminal by specifying desired
+margins on all four sides. By default, all margins are zero, and thus rendering
+will be performed on the entirety of the viewing area. This is orthogonal to
+use of the alternate screen; using the alternate screen plus margins will see
+the full screen cleared, followed by rendering to a subregion. Inhibiting the
+alternate screen plus margins will see rendering to a subregion, with the screen
+outside this region not cleared. This is the only means by which existing
+output can be undisturbed by notcurses. Margins are best-effort. Supplying any
+negative margin is an error.
+
 ## Fatal signals
 
 It is important to reset the terminal before exiting, whether terminating due

include/notcurses/notcurses.h

@@ -107,8 +107,6 @@ mbswidth(const char* mbs){
   return cols;
 }
 
-#define NCPALETTESIZE 256
-
 // A cell corresponds to a single character cell on some plane, which can be
 // occupied by a single grapheme cluster (some root spacing glyph, along with
 // possible combining characters, which might span multiple columns). At any
@@ -232,6 +230,11 @@ typedef struct notcurses_options {
   // Progressively higher log levels result in more logging to stderr. By
   // default, nothing is printed to stderr once fullscreen service begins.
   ncloglevel_e loglevel;
+  // Desirable margins. If all are 0 (default), we will render to the entirety
+  // of the screen. If the screen is too small, we do what we can--this is
+  // strictly best-effort. Absolute coordinates are relative to the rendering
+  // area ((0, 0) is always the origin of the rendering area).
+  int margin_t, margin_r, margin_b, margin_l;
 } notcurses_options;
 
 // Initialize a notcurses context on the connected terminal at 'fp'. 'fp' must
@@ -953,6 +956,7 @@ API int ncplane_stain(struct ncplane* n, int ystop, int xstop, uint64_t ul,
 // excluding the base cell.
 API void ncplane_erase(struct ncplane* n);
 
+#define NCPALETTESIZE 256
 #define CELL_WIDEASIAN_MASK     0x8000000080000000ull
 #define CELL_BGDEFAULT_MASK     0x0000000040000000ull
 #define CELL_FGDEFAULT_MASK     (CELL_BGDEFAULT_MASK << 32u)

python/src/notcurses/build_notcurses.py

@@ -72,6 +72,11 @@ typedef struct notcurses_options {
   // Progressively higher log levels result in more logging to stderr. By
   // default, nothing is printed to stderr once fullscreen service begins.
   ncloglevel_e loglevel;
+  // Desirable margins. If all are 0 (default), we will render to the entirety
+  // of the screen. If the screen is too small, we do what we can--this is
+  // strictly best-effort. Absolute coordinates are relative to the rendering
+  // area ((0, 0) is always the origin of the rendering area).
+  int margin_t, margin_r, margin_b, margin_l;
 } notcurses_options;
 struct notcurses* notcurses_init(const notcurses_options*, FILE*);
 int notcurses_stop(struct notcurses*);
@@ -322,7 +327,7 @@ typedef struct multiselector_options {
   uint64_t bgchannels;   // background channels, used only in body
 } multiselector_options;
 struct ncmultiselector* ncmultiselector_create(struct ncplane* n, int y, int x, const multiselector_options* opts);
-int ncmultiselector_selected(struct ncmultiselector* n, bool* selected, unsigned n);
+int ncmultiselector_selected(struct ncmultiselector* n, bool* selected, unsigned count);
 struct ncplane* ncmultiselector_plane(struct ncmultiselector* n);
 bool ncmultiselector_offer_input(struct ncmultiselector* n, const struct ncinput* nc);
 void ncmultiselector_destroy(struct ncmultiselector* n, char** item);

rust/libnotcurses-sys/build.rs

@@ -21,7 +21,7 @@ fn main() {
     // to bindgen, and lets you build up options for
     // the resulting bindings.
     let bindings = bindgen::Builder::default()
-        .clang_arg("-I../../include") // FIXME pass via envvar?
+        .clang_arg("-I../../include -D_XOPEN_SOURCE") // FIXME pass via envvar?
         // The input header we would like to generate
         // bindings for.
         .header("wrapper.h")

rust/notcurses/Cargo.toml

@@ -11,3 +11,4 @@ homepage = "https://nick-black.com/dankwiki/index.php/Notcurses"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+libnotcurses-sys = "^1.2.3"

src/demo/demo.c

@@ -10,9 +10,9 @@
 #include <stdatomic.h>
 #include "demo.h"
 
-// ansi terminal definition-4-life
+// (non-)ansi terminal definition-4-life
 static const int MIN_SUPPORTED_ROWS = 24;
-static const int MIN_SUPPORTED_COLS = 80;
+static const int MIN_SUPPORTED_COLS = 76; // allow a bit of margin, sigh
 
 static int democount;
 static demoresult* results;
@@ -120,7 +120,7 @@ static struct {
 static void
 usage(const char* exe, int status){
   FILE* out = status == EXIT_SUCCESS ? stdout : stderr;
-  fprintf(out, "usage: %s [ -hVikc ] [ -p path ] [ -l loglevel ] [ -d mult ] [ -J jsonfile ] [ -f renderfile ] demospec\n", exe);
+  fprintf(out, "usage: %s [ -hVikc ] [ -m margins ] [ -p path ] [ -l loglevel ] [ -d mult ] [ -J jsonfile ] [ -f renderfile ] demospec\n", exe);
   fprintf(out, " -h: this message\n");
   fprintf(out, " -V: print program name and version\n");
   fprintf(out, " -l: logging level (%d: silent..%d: manic)\n", NCLOGLEVEL_SILENT, NCLOGLEVEL_TRACE);
@@ -131,6 +131,7 @@ usage(const char* exe, int status){
   fprintf(out, " -J: emit JSON summary to file\n");
   fprintf(out, " -c: constant PRNG seed, useful for benchmarking\n");
   fprintf(out, " -p: data file path (default: %s)\n", NOTCURSES_SHARE);
+  fprintf(out, " -m: margin, or 4 comma-separated margins\n");
   fprintf(out, "if no specification is provided, run %s\n", DEFAULT_DEMO);
   for(size_t i = 0 ; i < sizeof(demos) / sizeof(*demos) ; ++i){
     if(demos[i].name){
@@ -140,6 +141,53 @@ usage(const char* exe, int status){
   exit(status);
 }
 
+// extract an integer, which must be non-negative, and followed by either a
+// comma or a NUL terminator.
+static int
+lex_long(const char* op, int* i, char** endptr){
+  errno = 0;
+  long l = strtol(op, endptr, 10);
+  if(l < 0 || (l == LONG_MAX && errno == ERANGE) || (l > INT_MAX)){
+    fprintf(stderr, "Invalid margin: %s\n", op);
+    return -1;
+  }
+  if((**endptr != ',' && **endptr) || *endptr == op){
+    fprintf(stderr, "Invalid margin: %s\n", op);
+    return -1;
+  }
+  *i = l;
+  return 0;
+}
+
+static int
+lex_margins(const char* op, notcurses_options* opts){
+  if(opts->margin_t || opts->margin_r || opts->margin_b || opts->margin_l){
+    fprintf(stderr, "Provided margins twice!\n");
+    return -1;
+  }
+  char* eptr;
+  if(lex_long(op, &opts->margin_t, &eptr)){
+    return -1;
+  }
+  if(!*eptr){ // allow a single value to be specified for all four margins
+    opts->margin_r = opts->margin_l = opts->margin_b = opts->margin_t;
+    return 0;
+  }
+  op = ++eptr; // once here, we require four values
+  if(lex_long(op, &opts->margin_r, &eptr) || !*eptr){
+    return -1;
+  }
+  op = ++eptr;
+  if(lex_long(op, &opts->margin_b, &eptr) || !*eptr){
+    return -1;
+  }
+  op = ++eptr;
+  if(lex_long(op, &opts->margin_l, &eptr) || *eptr){ // must end in NUL
+    return -1;
+  }
+  return 0;
+}
+
 static demoresult*
 ext_demos(struct notcurses* nc, const char* spec, bool ignore_failures){
   int ret = 0;
@@ -189,7 +237,7 @@ handle_opts(int argc, char** argv, notcurses_options* opts, bool* ignore_failure
   *json_output = NULL;
   int c;
   memset(opts, 0, sizeof(*opts));
-  while((c = getopt(argc, argv, "VhickJ:l:r:d:f:p:")) != EOF){
+  while((c = getopt(argc, argv, "VhickJ:l:r:d:f:p:m:")) != EOF){
     switch(c){
       case 'h':
         usage(*argv, EXIT_SUCCESS);
@@ -206,6 +254,11 @@ handle_opts(int argc, char** argv, notcurses_options* opts, bool* ignore_failure
           usage(*argv, EXIT_FAILURE);
         }
         break;
+      }case 'm':{
+        if(lex_margins(optarg, opts)){
+          usage(*argv, EXIT_FAILURE);
+        }
+        break;
       }case 'V':
         printf("notcurses-demo version %s\n", notcurses_version());
         exit(EXIT_SUCCESS);

src/demo/eagle.c

@@ -181,7 +181,8 @@ eagles(struct notcurses* nc){
       }else if(e[i].yoff + height >= truey){
         e[i].yoff = truey - height - 1;
       }
-      e[i].xoff += (random() % (truex / 80)) + 1;
+      int scale = truex >= 80 ? truex / 80 : 1;
+      e[i].xoff += (random() % scale) + 1;
       ncplane_move_yx(e[i].n, e[i].yoff, e[i].xoff);
       ++eaglesmoved;
     }

src/demo/whiteout.c

@@ -211,7 +211,7 @@ message(struct ncplane* n, int maxy, int maxx, int num, int total,
   ncplane_printf_yx(n, 1, 4, " %03dx%03d (%d/%d) ", maxx, maxy, num + 1, total);
   ncplane_styles_off(n, NCSTYLE_ITALIC);
   ncplane_set_fg_rgb(n, 224, 128, 224);
-  ncplane_putstr_yx(n, 3, 1, "  🔥 unicode 13, resize awareness, 24b directcolor…🔥  ");
+  ncplane_putstr_yx(n, 3, 1, "   🔥 unicode 13, resize awareness, 24b truecolor…🔥   ");
   ncplane_set_fg_rgb(n, 255, 255, 255);
   return 0;
 }

src/lib/internal.h

@@ -227,7 +227,7 @@ typedef struct ncdirect {
   char* initc;    // set a palette entry's RGB value
   char* oc;       // restore original colors
   char* clear;    // clear the screen
-  bool RGBflag;   // terminfo-reported "RGB" flag for 24bpc directcolor
+  bool RGBflag;   // terminfo-reported "RGB" flag for 24bpc truecolor
   bool CCCflag;   // terminfo-reported "CCC" flag for palette set capability
   FILE* ttyfp;    // FILE* for controlling tty, from opts->ttyfp
   palette256 palette; // 256-indexed palette can be used instead of/with RGB
@@ -284,7 +284,7 @@ typedef struct notcurses {
   char* getm;     // get mouse events
   char* initc;    // set a palette entry's RGB value
   char* oc;       // restore original colors
-  bool RGBflag;   // terminfo-reported "RGB" flag for 24bpc directcolor
+  bool RGBflag;   // terminfo-reported "RGB" flag for 24bpc truecolor
   bool CCCflag;   // terminfo-reported "CCC" flag for palette set capability
   bool AMflag;    // ti-reported "AM" flag for automatic movement to next line
 
@@ -307,6 +307,9 @@ typedef struct notcurses {
   // be reset (semantics are relied upon by widgets for mouse click detection).
   uint64_t input_events;
 
+  // desired margins (best-effort only), copied in from notcurses_options
+  int margin_t, margin_b, margin_r, margin_l;
+
   palette256 palette; // 256-indexed palette can be used instead of/with RGB
   bool palette_damage[NCPALETTESIZE];
   struct esctrie* inputescapes; // trie of input escapes -> ncspecial_keys

src/lib/notcurses.c

@@ -283,8 +283,8 @@ ncplane_create(notcurses* nc, int rows, int cols, int yoff, int xoff){
   p->leny = rows;
   p->lenx = cols;
   p->x = p->y = 0;
-  p->absx = xoff;
-  p->absy = yoff;
+  p->absx = xoff + nc->margin_l;
+  p->absy = yoff + nc->margin_t;
   p->attrword = 0;
   p->channels = 0;
   egcpool_init(&p->pool);
@@ -301,7 +301,8 @@ ncplane_create(notcurses* nc, int rows, int cols, int yoff, int xoff){
 // the z-buffer. clear out all cells. this is for a wholly new context.
 static ncplane*
 create_initial_ncplane(notcurses* nc, int dimy, int dimx){
-  nc->stdscr = ncplane_create(nc, dimy, dimx, 0, 0);
+  nc->stdscr = ncplane_create(nc, dimy - (nc->margin_t + nc->margin_b),
+                              dimx - (nc->margin_l + nc->margin_r), 0, 0);
   return nc->stdscr;
 }
 
@@ -497,6 +498,15 @@ int notcurses_resize(notcurses* n, int* rows, int* cols){
   if(update_term_dimensions(n->ttyfd, rows, cols)){
     return -1;
   }
+  // FIXME can we emerge from the previous call with rows/cols <= 0?
+  *rows -= n->margin_t + n->margin_b;
+  if(*rows <= 0){
+    *rows = 1;
+  }
+  *cols -= n->margin_l + n->margin_r;
+  if(*cols <= 0){
+    *cols = 1;
+  }
   if(*rows == oldrows && *cols == oldcols){
     return 0; // no change
   }
@@ -551,7 +561,7 @@ query_rgb(void){
   if(!rgb){
     // RGB terminfo capability being a new thing (as of ncurses 6.1), it's not commonly found in
     // terminal entries today. COLORTERM, however, is a de-facto (if imperfect/kludgy) standard way
-    // of indicating DirectColor support for a terminal. The variable takes one of two case-sensitive
+    // of indicating TrueColor support for a terminal. The variable takes one of two case-sensitive
     // values:
     //
     //   truecolor
@@ -567,8 +577,7 @@ query_rgb(void){
 }
 
 static int
-interrogate_terminfo(notcurses* nc, const notcurses_options* opts,
-                     int* dimy, int* dimx){
+interrogate_terminfo(notcurses* nc, const notcurses_options* opts, int* dimy, int* dimx){
   update_term_dimensions(nc->ttyfd, dimy, dimx);
   char* shortname_term = termname();
   char* longname_term = longname();
@@ -826,6 +835,10 @@ notcurses* notcurses_init(const notcurses_options* opts, FILE* outfp){
   if(!opts){
     opts = &defaultopts;
   }
+  if(opts->margin_t < 0 || opts->margin_b < 0 || opts->margin_l < 0 || opts->margin_r < 0){
+    fprintf(stderr, "Provided an illegal negative margin, refusing to start\n");
+    return NULL;
+  }
   const char* encoding = nl_langinfo(CODESET);
   if(encoding == NULL || (strcmp(encoding, "ANSI_X3.4-1968") && strcmp(encoding, "UTF-8"))){
     fprintf(stderr, "Encoding (\"%s\") was neither ANSI_X3.4-1968 nor UTF-8, refusing to start\n",
@@ -837,6 +850,10 @@ notcurses* notcurses_init(const notcurses_options* opts, FILE* outfp){
   if(ret == NULL){
     return ret;
   }
+  ret->margin_t = opts->margin_t;
+  ret->margin_b = opts->margin_b;
+  ret->margin_l = opts->margin_l;
+  ret->margin_r = opts->margin_r;
   ret->stats.fbbytes = 0;
   ret->stashstats.fbbytes = 0;
   reset_stats(&ret->stats);
@@ -921,9 +938,9 @@ notcurses* notcurses_init(const notcurses_options* opts, FILE* outfp){
   if(!opts->suppress_banner){
     char prefixbuf[BPREFIXSTRLEN + 1];
     term_fg_palindex(ret, ret->ttyfp, ret->colors <= 256 ? 50 % ret->colors : 0x20e080);
-    fprintf(ret->ttyfp, "\n notcurses %s by nick black et al", notcurses_version());
+    printf("\n notcurses %s by nick black et al", notcurses_version());
     term_fg_palindex(ret, ret->ttyfp, ret->colors <= 256 ? 12 % ret->colors : 0x2080e0);
-    fprintf(ret->ttyfp, "\n  %d rows, %d columns (%sB), %d colors (%s)\n"
+    printf("\n  %d rows, %d columns (%sB), %d colors (%s)\n"
           "  compiled with gcc-%s\n"
           "  terminfo from %s\n",
           ret->stdscr->leny, ret->stdscr->lenx,
@@ -931,25 +948,26 @@ notcurses* notcurses_init(const notcurses_options* opts, FILE* outfp){
           ret->colors, ret->RGBflag ? "direct" : "palette",
           __VERSION__, curses_version());
 #ifdef USE_FFMPEG
-    fprintf(ret->ttyfp, "  avformat %u.%u.%u\n  avutil %u.%u.%u\n  swscale %u.%u.%u\n",
+    printf("  avformat %u.%u.%u\n  avutil %u.%u.%u\n  swscale %u.%u.%u\n",
           LIBAVFORMAT_VERSION_MAJOR, LIBAVFORMAT_VERSION_MINOR, LIBAVFORMAT_VERSION_MICRO,
           LIBAVUTIL_VERSION_MAJOR, LIBAVUTIL_VERSION_MINOR, LIBAVUTIL_VERSION_MICRO,
           LIBSWSCALE_VERSION_MAJOR, LIBSWSCALE_VERSION_MINOR, LIBSWSCALE_VERSION_MICRO);
+    fflush(stdout);
 #else
     term_fg_palindex(ret, ret->ttyfp, ret->colors <= 88 ? 1 % ret->colors : 0xcb);
-    fprintf(ret->ttyfp, "\n Warning! Notcurses was built without ffmpeg support\n");
+    fprintf(stderr, "\n Warning! Notcurses was built without ffmpeg support\n");
 #endif
     term_fg_palindex(ret, ret->ttyfp, ret->colors <= 88 ? 1 % ret->colors : 0xcb);
     if(!ret->RGBflag){ // FIXME
-      fprintf(ret->ttyfp, "\n Warning! Colors subject to https://github.com/dankamongmen/notcurses/issues/4");
-      fprintf(ret->ttyfp, "\n  Specify a (correct) DirectColor TERM, or COLORTERM=24bit.\n");
+      fprintf(stderr, "\n Warning! Colors subject to https://github.com/dankamongmen/notcurses/issues/4");
+      fprintf(stderr, "\n  Specify a (correct) TrueColor TERM, or COLORTERM=24bit.\n");
     }else{
       if(!ret->CCCflag){
-        fprintf(ret->ttyfp, "\n Warning! Advertised DirectColor but no 'ccc' flag\n");
+        fprintf(stderr, "\n Warning! Advertised TrueColor but no 'ccc' flag\n");
       }
     }
-    if(strcmp(encoding, "UTF-8")){
-      fprintf(ret->ttyfp, "\n Warning! Encoding is not UTF-8.\n");
+    if(strcmp(encoding, "UTF-8")){ // it definitely exists, but could be ASCII
+      fprintf(stderr, "\n Warning! Encoding is not UTF-8.\n");
     }
   }
   // flush on the switch to alternate screen, lest initial output be swept away

src/lib/render.c

@@ -212,8 +212,8 @@ paint(notcurses* nc, ncplane* p, struct crender* rvec, cell* fb){
   // don't use ncplane_dim_yx()/ncplane_yx() here, lest we deadlock
   dimy = p->leny;
   dimx = p->lenx;
-  offy = p->absy;
-  offx = p->absx;
+  offy = p->absy - nc->stdscr->absy;
+  offx = p->absx - nc->stdscr->absx;
 //fprintf(stderr, "PLANE %p %d %d %d %d %d %d\n", p, dimy, dimx, offy, offx, nc->stdscr->leny, nc->stdscr->lenx);
   // skip content above or to the left of the physical screen
   int starty, startx;
@@ -764,19 +764,23 @@ notcurses_rasterize(notcurses* nc, const struct crender* rvec){
   // we only need to emit a coordinate if it was damaged. the damagemap is a
   // bit per coordinate, rows by rows, column by column within a row, with the
   // MSB being the first coordinate.
-  size_t damageidx = 0;
   // don't write a clearscreen. we only update things that have been changed.
   // we explicitly move the cursor at the beginning of each output line, so no
   // need to home it expliticly.
   update_palette(nc, out);
-  for(y = 0 ; y < nc->stdscr->leny ; ++y){
+  // FIXME need to track outer{x,y} (position on screen) and inner{x,y}
+  // (position within lastframe/rvec, which is lfdimx-sized)
+  for(y = nc->stdscr->absy ; y < nc->stdscr->leny + nc->stdscr->absy ; ++y){
+    const int innery = y - nc->stdscr->absy;
     // how many characters have we elided? it's not worthwhile to invoke a
     // cursor movement with cup if we only elided one or two. set to INT_MAX
     // whenever we're on a new line. leave room to avoid overflow.
     int needmove = INT_MAX - nc->stdscr->lenx;
-    for(x = 0 ; x < nc->stdscr->lenx ; ++x){
+    for(x = nc->stdscr->absx ; x < nc->stdscr->lenx + nc->stdscr->absx ; ++x){
+      const int innerx = x - nc->stdscr->absx;
+      const size_t damageidx = innery * nc->lfdimx + innerx;
       unsigned r, g, b, br, bg, bb, palfg, palbg;
-      const cell* srccell = &nc->lastframe[y * nc->lfdimx + x];
+      const cell* srccell = &nc->lastframe[innery * nc->lfdimx + innerx];
 //      cell c;
 //      memcpy(c, srccell, sizeof(*c)); // unsafe copy of gcluster
 //fprintf(stderr, "COPYING: %d from %p\n", c->gcluster, &nc->pool);
@@ -907,9 +911,8 @@ fprintf(stderr, "RAST %u [%s] to %d/%d\n", srccell->gcluster, egcpool_extended_g
       }
       if(cell_double_wide_p(srccell)){
         ++x;
-        ++damageidx;
       }
-      ++damageidx;
+//fprintf(stderr, "damageidx: %ld\n", damageidx);
     }
   }
   ret |= fflush(out);