restore nccell_[bf]channel using safe ncchannels_bchannel #2571

NEWS.md

@@ -7,6 +7,7 @@ rearrangements of Notcurses.
     `ncchannels_set_[fb]channel()`, and `ncchannels_[fb]channel()` now
     function only on the 28 alpha + coloring bits of their respective
     channels, which is almost certainly what you wanted in the first place.
+  * Restore `nccell_set_[fb]channel()` and friends, using these semantics.
 
 * 3.0.5 (2022-01-21)
   * The Hyper and Super modifiers are now supported. CapsLock and NumLock

USAGE.md

@@ -2245,13 +2245,15 @@ Helpers are provided to manipulate an `nccell`'s `channels` member. They are
 all implemented in terms of the lower-level [Channels API](#channels).
 
 ```c
-// Extract the 32-bit background channel from a cell.
+// Extract the background alpha and coloring bits from a cell's channels
+// as a single 32-bit value.
 static inline uint32_t
 nccell_bchannel(const nccell* cl){
   return ncchannels_bchannel(cl->channels);
 }
 
-// Extract the 32-bit foreground channel from a cell.
+// Extract the foreground alpha and coloring bits from a cell's channels
+// as a single 32-bit value.
 static inline uint32_t
 nccell_fchannel(const nccell* cl){
   return ncchannels_fchannel(cl->channels);

include/notcurses/notcurses.h

@@ -821,6 +821,20 @@ nccell_wide_left_p(const nccell* c){
 API __attribute__ ((returns_nonnull)) const char*
 nccell_extended_gcluster(const struct ncplane* n, const nccell* c);
 
+// Extract the background alpha and coloring bits from a cell's channels
+// as a single 32-bit value.
+static inline uint32_t
+nccell_bchannel(const nccell* cl){
+  return ncchannels_bchannel(cl->channels);
+}
+
+// Extract the foreground alpha and coloring bits from a cell's channels
+// as a single 32-bit value.
+static inline uint32_t
+nccell_fchannel(const nccell* cl){
+  return ncchannels_fchannel(cl->channels);
+}
+
 // return the number of columns occupied by 'c'. see ncstrwidth() for an
 // equivalent for multiple EGCs.
 static inline unsigned