rendering: lack of term capability is not error #768

If we don't have setaf/setab, then we're not going to set color.
OK, fine. Don't regard it as an error during
notcurses_rasterization(), just don't emit the escape. This is
necessary to run on terminals like vt100, which in turn is
necessary to run unit tests properly on Redhat's koji.
Also, use notcurses_canfade() to avoid just breaking during
fades in intro and trans demos.

src/demo/intro.c

@@ -132,6 +132,9 @@ int intro(struct notcurses* nc){
     demo_nanosleep(nc, &iter);
     clock_gettime(CLOCK_MONOTONIC_RAW, &now);
   }while(timespec_to_ns(&now) < deadline);
+  if(!notcurses_canfade(nc)){
+    return 0;
+  }
   struct timespec fade = demodelay;
   return ncplane_fadeout(ncp, &fade, demo_fader, NULL);
 }

src/demo/trans.c

@@ -258,6 +258,7 @@ int trans_demo(struct notcurses* nc){
       ++x;
     }
   }
+  if(notcurses_canfade(nc)){
     struct ncplane* l = legend(nc, "what say we explore transparency together?");
     DEMO_RENDER(nc);
     struct timespec now;
@@ -267,5 +268,6 @@ int trans_demo(struct notcurses* nc){
       return err;
     }
     ncplane_destroy(l);
+  }
   return slidepanel(nc);
 }

src/lib/internal.h

@@ -538,11 +538,17 @@ term_emit(const char* name __attribute__ ((unused)), const char* seq,
 
 static inline int
 term_bg_palindex(const notcurses* nc, FILE* out, unsigned pal){
+  if(nc->tcache.setab == NULL){
+    return 0;
+  }
   return term_emit("setab", tiparm(nc->tcache.setab, pal), out, false);
 }
 
 static inline int
 term_fg_palindex(const notcurses* nc, FILE* out, unsigned pal){
+  if(nc->tcache.setaf == NULL){
+    return 0;
+  }
   return term_emit("setaf", tiparm(nc->tcache.setaf, pal), out, false);
 }
 

src/lib/render.c

@@ -655,7 +655,7 @@ term_bg_rgb8(bool RGBflag, const char* setab, int colors, FILE* out,
     return term_esc_rgb(out, false, r, g, b);
   }else{
     if(setab == NULL){
-      return -1;
+      return 0;
     }
     // For 256-color indexed mode, start constructing a palette based off
     // the inputs *if we can change the palette*. If more than 256 are used on
@@ -682,7 +682,7 @@ term_fg_rgb8(bool RGBflag, const char* setaf, int colors, FILE* out,
     return term_esc_rgb(out, true, r, g, b);
   }else{
     if(setaf == NULL){
-      return -1;
+      return 0;
     }
     // For 256-color indexed mode, start constructing a palette based off
     // the inputs *if we can change the palette*. If more than 256 are used on
@@ -926,7 +926,9 @@ notcurses_rasterize(notcurses* nc, const struct crender* rvec){
         if((!noforeground && cell_fg_default_p(srccell)) || (!nobackground && cell_bg_default_p(srccell))){
           if(!nc->rstate.defaultelidable){
             ++nc->stats.defaultemissions;
+            if(nc->tcache.op){
               ret |= term_emit("op", nc->tcache.op, out, false);
+            }
           }else{
             ++nc->stats.defaultelisions;
           }