disable quadrants except where whitelisted #1517

Require a known-good TERM heuristic match to enable
quadrants (NCBLIT_2x2); they otherwise decay to halves
(NCBLIT_2x1). The only terminal that supports quadrants
but does not support sextants is the Linux console, where
we program quadrants directly into the font table,
like a beast. Closes #1517, and #1298 if we're lucky.

src/lib/blit.c

@@ -881,8 +881,8 @@ const struct blitset* lookup_blitset(const tinfo* tcache, ncblitter_e setid, boo
       return NULL;
     }
   }
-  // without pixel support, NCBLIT_PIXEL decays to NCBLIT_3x2
-  if(!tcache->sixel_supported && setid == NCBLIT_PIXEL){
+  // without bitmap support, NCBLIT_PIXEL decays to NCBLIT_3x2
+  if(!tcache->bitmap_supported && setid == NCBLIT_PIXEL){
     if(may_degrade){
       setid = NCBLIT_3x2;
     }else{
@@ -897,6 +897,14 @@ const struct blitset* lookup_blitset(const tinfo* tcache, ncblitter_e setid, boo
       return NULL;
     }
   }
+  // without quadrant support, NCBLIT_2x2 decays to NCBLIT_2x1
+  if(!tcache->quadrants && setid == NCBLIT_2x2){
+    if(may_degrade){
+      setid = NCBLIT_2x1;
+    }else{
+      return NULL;
+    }
+  }
   // the only viable blitters in ASCII are NCBLIT_1x1 and NCBLIT_PIXEL
   if(!tcache->utf8 && (setid != NCBLIT_1x1 && setid != NCBLIT_PIXEL)){
     if(may_degrade){

src/lib/blitset.h

@@ -21,19 +21,23 @@ encoding_x_scale(const tinfo* tcache, const struct blitset* bset) {
   return bset->width;
 }
 
-// Expand NCBLIT_DEFAULT for media blitting, based on environment.
+// Expand NCBLIT_DEFAULT for media blitting, based on environment. We never
+// use NCBLIT_PIXEL for NCBLIT_DEFAULT, though maybe this ought change.
 static inline ncblitter_e 
 rgba_blitter_default(const tinfo* tcache, ncscale_e scale){
   if(!tcache->utf8){
-    return NCBLIT_1x1;
+    return NCBLIT_1x1; // only one that works in ASCII
   }
   if(scale == NCSCALE_NONE || scale == NCSCALE_SCALE){
     return NCBLIT_2x1;
   }
-  if(!tcache->sextants){
+  if(tcache->sextants){
+    return NCBLIT_3x2;
+  }
+  if(tcache->quadrants){
     return NCBLIT_2x2;
   }
-  return NCBLIT_3x2;
+  return NCBLIT_2x1;
 }
 
 static inline ncblitter_e

src/lib/debug.c

@@ -25,7 +25,7 @@ tinfo_debug_caps(const tinfo* ti, FILE* debugfp, int rows, int cols,
   if(!ti->pixel_query_done){
     fprintf(debugfp, "%sno bitmap graphics information yet\n", indent);
   }else{
-    if(!ti->sixel_supported){
+    if(!ti->bitmap_supported){
       fprintf(debugfp, "%sdidn't detect bitmap graphics support\n", indent);
     }else if(ti->sixel_maxy || ti->color_registers){
       fprintf(debugfp, "%smax sixel size: %dx%d colorregs: %u\n",
@@ -34,8 +34,9 @@ tinfo_debug_caps(const tinfo* ti, FILE* debugfp, int rows, int cols,
       fprintf(debugfp, "%sRGBA pixel graphics supported\n", indent);
     }
   }
-  fprintf(debugfp, "%sUTF8: %c sextants: %c braille: %c images: %c videos: %c\n",
-          indent, capbool(ti->utf8), capbool(ti->sextants), capbool(ti->braille),
+  fprintf(debugfp, "%sUTF8: %c quad: %c sex: %c braille: %c images: %c videos: %c\n",
+          indent, capbool(ti->utf8), capbool(ti->quadrants),
+          capbool(ti->sextants), capbool(ti->braille),
           capbool(images), capbool(videos));
   if(ti->bg_collides_default){
     fprintf(debugfp, "%sbackground of 0x%06lx is considered transparent\n", indent, ti->bg_collides_default & 0xfffffful);

src/lib/direct.c

@@ -1112,7 +1112,7 @@ int ncdirect_check_pixel_support(ncdirect* n){
   if(query_term(&n->tcache, n->ctermfd)){
     return -1;
   }
-  if(n->tcache.sixel_supported){
+  if(n->tcache.bitmap_supported){
     return 1;
   }
   return 0;

src/lib/internal.h

@@ -359,7 +359,7 @@ typedef struct tinfo {
   pthread_mutex_t pixel_query; // only query for pixel support once
   int color_registers; // sixel color registers (post pixel_query_done)
   int sixel_maxx, sixel_maxy; // sixel size maxima (post pixel_query_done)
-  bool sixel_supported;  // do we support sixel (post pixel_query_done)?
+  bool bitmap_supported;  // do we support bitmaps (post pixel_query_done)?
   int sprixelnonce;      // next sprixel id
   int (*pixel_destroy)(const struct notcurses* nc, const struct ncpile* p, FILE* out, sprixel* s);
   // wipe out a cell's worth of pixels from within a sprixel. for sixel, this
@@ -369,6 +369,7 @@ typedef struct tinfo {
   int (*pixel_init)(int fd);
   int (*pixel_draw)(const struct notcurses* n, const struct ncpile* p, sprixel* s, FILE* out);
   bool pixel_query_done; // have we yet performed pixel query?
+  bool quadrants; // do we have (good, vetted) Unicode 1 quadrant support?
   bool sextants;  // do we have (good, vetted) Unicode 13 sextant support?
   bool braille;   // do we have Braille support? (linux console does not)
   // alacritty went rather off the reservation for their sixel support. they

src/lib/notcurses.c

@@ -908,7 +908,7 @@ int notcurses_check_pixel_support(notcurses* nc){
   if(query_term(&nc->tcache, nc->ttyfd)){
     return -1;
   }
-  if(nc->tcache.sixel_supported){
+  if(nc->tcache.bitmap_supported){
     return 1;
   }
   return 0;

src/lib/sixel.c

@@ -316,12 +316,12 @@ write_rle(int* printed, int color, FILE* fp, int seenrle, unsigned char crle){
 // Emit the sprixel in its entirety, plus enable and disable pixel mode.
 // Closes |fp| on all paths.
 static int
-write_sixel_data(FILE* fp, int lenx, const sixeltable* stab, int* parse_start){
+write_sixel_data(FILE* fp, int leny, int lenx, const sixeltable* stab, int* parse_start){
   *parse_start = fprintf(fp, "\ePq");
   // Set Raster Attributes - pan/pad=1 (pixel aspect ratio), Ph=lenx, Pv=leny
   // using Ph/Pv causes a background to be drawn using color register 0 for all
   // unspecified pixels, which we do not want.
-//  fprintf(fp, "\"1;1;%d;%d", lenx, leny);
+  fprintf(fp, "\"1;2;%d;%d", lenx, leny);
 
   for(int i = 0 ; i < stab->colors ; ++i){
     const unsigned char* rgb = stab->table + i * CENTSIZE;
@@ -396,7 +396,7 @@ sixel_blit_inner(int leny, int lenx, const sixeltable* stab, int rows, int cols,
   }
   int parse_start = 0;
   // calls fclose() on success
-  if(write_sixel_data(fp, lenx, stab, &parse_start)){
+  if(write_sixel_data(fp, leny, lenx, stab, &parse_start)){
     free(buf);
     return -1;
   }

src/lib/terminfo.c

@@ -58,25 +58,32 @@ apply_term_heuristics(tinfo* ti, const char* termname){
     // be RGB(0, 0, 0) (the default). we could also just set it, i guess.
     ti->bg_collides_default = 0x1000000;
     ti->sextants = true; // work since bugfix in 0.19.3
+    ti->quadrants = true;
     ti->pixel_query_done = true;
-    ti->sixel_supported = true;
+    ti->bitmap_supported = true;
     ti->pixel_cell_wipe = sprite_kitty_cell_wipe;
     ti->pixel_destroy = sprite_kitty_annihilate;
     ti->pixel_init = sprite_kitty_init;
     ti->pixel_draw = kitty_draw;
     set_pixel_blitter(kitty_blit);
-  /*}else if(strstr(termname, "alacritty")){
-    ti->sextants = true; // alacritty https://github.com/alacritty/alacritty/issues/4409 */
   }else if(strstr(termname, "alacritty")){
     ti->alacritty_sixel_hack = true;
+    ti->quadrants = true;
+    // ti->sextants = true; // alacritty https://github.com/alacritty/alacritty/issues/4409 */
   }else if(strstr(termname, "vte") || strstr(termname, "gnome") || strstr(termname, "xfce")){
     ti->sextants = true; // VTE has long enjoyed good sextant support
+    ti->quadrants = true;
   }else if(strncmp(termname, "foot", 4) == 0){
     ti->sextants = true;
+    ti->quadrants = true;
+  }else if(strncmp(termname, "st", 2) == 0){
+    // st had neithersextants nor quadrants last i checked (0.8.4)
   }else if(strcmp(termname, "linux") == 0){
     ti->braille = false; // no braille, no sextants in linux console
+    // FIXME if the NCOPTION_NO_FONT_CHANGES, this isn't true
+    ti->quadrants = true; // we program quadrants on the console
   }
-  // run a wcwidth() to guarantee libc Unicode 13 support
+  // run a wcwidth() to guarantee libc Unicode 13 support, independently of term
   if(wcwidth(L'🬸') < 0){
     ti->sextants = false;
   }
@@ -309,13 +316,14 @@ query_sixel_details(tinfo* ti, int fd){
 
 // we found Sixel support -- set up the API
 static void
-setup_sixel(tinfo* ti){
-  ti->sixel_supported = true;
+setup_sixel(tinfo* ti, int fd){
+  ti->bitmap_supported = true;
   ti->color_registers = 256;  // assumed default [shrug]
   ti->pixel_init = sprite_sixel_init;
   ti->pixel_draw = sixel_draw;
   ti->sixel_maxx = ti->sixel_maxy = 0;
   ti->pixel_destroy = sixel_delete;
+  query_sixel_details(ti, fd);
 }
 
 // query for Sixel support
@@ -364,7 +372,7 @@ fprintf(stderr, "SIXEL QUERY!\n");
       case WANT_VT102_C:
         if(in == 'c'){
           if(ti->alacritty_sixel_hack){
-            setup_sixel(ti);
+            setup_sixel(ti, fd);
           }
           state = DONE;
         }else if(in == ';'){
@@ -375,7 +383,7 @@ fprintf(stderr, "SIXEL QUERY!\n");
         if(in == 'c'){
           state = DONE;
         }else if(in == '4'){
-          setup_sixel(ti);
+          setup_sixel(ti, fd);
           state = DONE;
         }
         break;
@@ -384,9 +392,6 @@ fprintf(stderr, "SIXEL QUERY!\n");
         break;
     }
   }
-  if(ti->sixel_supported){
-    query_sixel_details(ti, fd);
-  }
   return 0;
 }
 
@@ -415,7 +420,7 @@ int query_term(tinfo* ti, int fd){
       }
       ret = query_sixel(ti, fd);
       ti->pixel_query_done = true;
-      if(ti->sixel_supported){
+      if(ti->bitmap_supported){
         ti->pixel_init(fd);
       }
       if(flags & O_NONBLOCK){

src/tests/pixel.cpp

@@ -10,7 +10,7 @@ TEST_CASE("Pixel") {
   REQUIRE(n_);
 
   if(notcurses_check_pixel_support(nc_) <= 0){
-    CHECK(0 == nc_->tcache.sixel_supported);
+    CHECK(0 == nc_->tcache.bitmap_supported);
     CHECK(!notcurses_stop(nc_));
     return;
   }
@@ -18,7 +18,7 @@ TEST_CASE("Pixel") {
   SUBCASE("SprixelTermValues") {
     CHECK(0 < nc_->tcache.cellpixy);
     CHECK(0 < nc_->tcache.cellpixx);
-    CHECK(nc_->tcache.sixel_supported);
+    CHECK(nc_->tcache.bitmap_supported);
   }
 
 #ifdef NOTCURSES_USE_MULTIMEDIA