default to NCBLIT_3x2, unify NCBLIT_DEFAULT selection #1088

include/notcurses/notcurses.h

@@ -3152,11 +3152,11 @@ API extern const struct blitset notcurses_blitters[];
 static inline ncblitter_e
 ncvisual_default_blitter(bool utf8, ncscale_e scale){
   if(utf8){
-    // NCBLIT_2x2 is better image quality, especially for large images, but
+    // NCBLIT_3x2 is better image quality, especially for large images, but
     // it's not the general default because it doesn't preserve aspect ratio.
-    // NCSCALE_STRETCH throws away aspect ratio, and can safely use NCBLIT_2x2.
+    // NCSCALE_STRETCH throws away aspect ratio, and can safely use NCBLIT_3x2.
     if(scale == NCSCALE_STRETCH){
-      return NCBLIT_2x2;
+      return NCBLIT_3x2;
     }
     return NCBLIT_2x1;
   }

src/lib/blit.c

@@ -797,9 +797,15 @@ int ncblit_bgrx(const void* data, int linesize, const struct ncvisual_options* v
   if(begy < 0 || begx < 0 || lenx < -1 || leny < -1){
     return -1;
   }
+  ncblitter_e blitter;
+  if(!vopts || vopts->blitter == NCBLIT_DEFAULT){
+    blitter = ncvisual_default_blitter(nc, NCSCALE_NONE);
+  }else{
+    blitter = vopts->blitter;
+  }
   const bool degrade = !(vopts->flags & NCVISUAL_OPTION_NODEGRADE);
   const struct blitset* bset = lookup_blitset(notcurses_canutf8(nc->nc),
-                                              vopts->blitter, degrade);
+                                              blitter, degrade);
   if(bset == NULL){
     return -1;
   }
@@ -830,9 +836,15 @@ int ncblit_rgba(const void* data, int linesize, const struct ncvisual_options* v
   if(begy < 0 || begx < 0 || lenx < -1 || leny < -1){
     return -1;
   }
+  ncblitter_e blitter;
+  if(!vopts || vopts->blitter == NCBLIT_DEFAULT){
+    blitter = ncvisual_default_blitter(notcurses_canutf8(nc->nc), NCSCALE_NONE);
+  }else{
+    blitter = vopts->blitter;
+  }
   const bool degrade = !(vopts->flags & NCVISUAL_OPTION_NODEGRADE);
   const struct blitset* bset = lookup_blitset(notcurses_canutf8(nc->nc),
-                                              vopts->blitter, degrade);
+                                              blitter, degrade);
   if(bset == NULL){
     return -1;
   }

src/lib/blitset.h

@@ -5,9 +5,8 @@
 
 static inline const struct blitset*
 lookup_blitset(unsigned utf8, ncblitter_e setid, bool may_degrade) {
-  if(setid == NCBLIT_DEFAULT){
-    setid = NCBLIT_2x1;
-    may_degrade = true;
+  if(setid == NCBLIT_DEFAULT){ // ought have resolved NCBLIT_DEFAULT before now
+    return NULL;
   }
   // the only viable blitter in ASCII is NCBLIT_1x1
   if(!utf8 && setid != NCBLIT_1x1){