ncchannels_bchannel: operate only on alpha+coloring bits #2571

NEWS.md

@@ -2,7 +2,11 @@ This document attempts to list user-visible changes and any major internal
 rearrangements of Notcurses.
 
 * 3.0.6 (not yet released)
-  * Remove the unsafe `ncplane_set_bchannel()` and `ncplane_set_fchannel()`.
+  * `ncplane_set_[fb]channel()`, `ncplane_[fb]channel()`,
+    `ncplane_channels()`, `ncplane_set_channels()`,
+    `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.
 
 * 3.0.5 (2022-01-21)
   * The Hyper and Super modifiers are now supported. CapsLock and NumLock

USAGE.md

@@ -3124,13 +3124,16 @@ ncchannel_set_default(uint32_t* channel){
   return *channel &= ~NC_BGDEFAULT_MASK;
 }
 
-// Extract the 32-bit background channel from a channel pair.
+// Extract the background alpha and coloring bits from a 64-bit channel
+// pair as a single 32-bit value.
 static inline unsigned
 ncchannels_bchannel(uint64_t channels){
-  return channels & 0xfffffffflu;
+  return channels & (NC_BG_RGB_MASK | NC_BG_PALETTE |
+                     NC_BGDEFAULT_MASK | NC_BG_ALPHA_MASK);
 }
 
-// Extract the 32-bit foreground channel from a channel pair.
+// Extract the foreground alpha and coloring bits from a 64-bit channel
+// pair as a single 32-bit value.
 static inline uint32_t
 ncchannels_fchannel(uint64_t channels){
   return ncchannels_bchannel(channels >> 32u);

include/notcurses/notcurses.h

@@ -296,13 +296,16 @@ ncchannel_set_rgb8_clipped(uint32_t* channel, int r, int g, int b){
   *channel = (*channel & ~(NC_BG_RGB_MASK | NC_BG_PALETTE)) | NC_BGDEFAULT_MASK | c;
 }
 
-// Extract the 32-bit background channel from a channel pair.
+// Extract the background alpha and coloring bits from a 64-bit channel
+// pair as a single 32-bit value.
 static inline uint32_t
 ncchannels_bchannel(uint64_t channels){
-  return channels & 0xfffffffflu;
+  return channels & (NC_BG_RGB_MASK | NC_BG_PALETTE |
+                     NC_BGDEFAULT_MASK | NC_BG_ALPHA_MASK);
 }
 
-// Extract the 32-bit foreground channel from a channel pair.
+// Extract the foreground alpha and coloring bits from a 64-bit channel
+// pair as a single 32-bit value.
 static inline uint32_t
 ncchannels_fchannel(uint64_t channels){
   return ncchannels_bchannel(channels >> 32u);