lookup_blitset: degrade from braille smoothly #1334

src/lib/blitset.h

@@ -16,6 +16,22 @@ lookup_blitset(const tinfo* tcache, ncblitter_e setid, bool may_degrade) {
       return NULL;
     }
   }
+  // without braille support, NCBLIT_BRAILLE decays to NCBLIT_3x2
+  if(!tcache->braille && setid == NCBLIT_BRAILLE){
+    if(may_degrade){
+      setid = NCBLIT_3x2;
+    }else{
+      return NULL;
+    }
+  }
+  // without sextant support, NCBLIT_3x2 decays to NCBLIT_2x2
+  if(!tcache->sextants && setid == NCBLIT_3x2){
+    if(may_degrade){
+      setid = NCBLIT_2x2;
+    }else{
+      return NULL;
+    }
+  }
   const struct blitset* bset = notcurses_blitters;
   while(bset->egcs){
     if(bset->geom == setid){
@@ -75,4 +91,12 @@ rgba_blitter(const struct notcurses* nc, const struct ncvisual_options* opts) {
   return rgba_blitter_low(&nc->tcache, scale, maydegrade, opts ? opts->blitter : NCBLIT_DEFAULT);
 }
 
+static inline ncblitter_e
+ncplot_defblitter(const notcurses* nc){
+  if(notcurses_canutf8(nc)){
+    return NCBLIT_8x1;
+  }
+  return NCBLIT_1x1;
+}
+
 #endif

src/lib/plot.h

@@ -45,11 +45,7 @@ class ncppplot {
    const notcurses* notc = ncplane_notcurses(n);
    ncblitter_e blitter = opts ? opts->gridtype : NCBLIT_DEFAULT;
    if(blitter == NCBLIT_DEFAULT){
-     if(notcurses_canutf8(ncplane_notcurses(n))){
-       blitter = NCBLIT_8x1;
-     }else{
-       blitter = NCBLIT_1x1;
-     }
+     blitter = ncplot_defblitter(notc);
    }
    bool degrade_blitter = !(opts && (opts->flags & NCPLOT_OPTION_NODEGRADE));
    auto bset = lookup_blitset(&notc->tcache, blitter, degrade_blitter);