add ncchannels_reverse, use it in ncmenu, add unit test #1878

NEWS.md

@@ -13,6 +13,8 @@ rearrangements of Notcurses.
     the number of columns consumed, and makes available the number of bytes
     used by the EGC.
   * `ncmenu`s can now be used with any plane, not just the standard plane.
+  * Added `ncchannels_reverse()`, which reverses the color aspects of the
+    two channels, while keeping other elements constant.
 
 * 2.3.8 (2021-07-04)
   * Marked all capability functions `__attribute__ ((pure))`. If you were

USAGE.md

@@ -2940,6 +2940,19 @@ ncchannels_fchannel(uint64_t channels){
   return ncchannels_bchannel(channels >> 32u);
 }
 
+// Returns the channels with the color information swapped, but not
+// alpha, nor other housekeeping bits.
+static inline uint64_t
+ncchannels_reverse(uint64_t channels){
+  const uint64_t raw = ((uint64_t)ncchannels_bchannel(channels) << 32u) +
+                       ncchannels_fchannel(channels);
+  const uint64_t statemask = (CELL_NOBACKGROUND_MASK | CELL_FG_ALPHA_MASK |
+                              CELL_BG_ALPHA_MASK | (CELL_NOBACKGROUND_MASK >> 32u));
+  uint64_t ret = raw & ~statemask;
+  ret |= channels & statemask;
+  return ret;
+}
+
 // Extract 24 bits of foreground RGB from 'channels', shifted to LSBs.
 static inline unsigned
 ncchannels_fg_rgb(uint64_t channels){

doc/man/man3/notcurses_channels.3.md

@@ -83,6 +83,8 @@ notcurses_channels - operations on notcurses channels
 
 **uint64_t ncchannels_set_bg_default(uint64_t* ***channels***);**
 
+**uint64_t ncchannels_reverse(uint64_t ***channels***);**
+
 # DESCRIPTION
 
 
@@ -93,6 +95,10 @@ always due to invalid inputs. Functions returning `bool` are predicates, and
 return the requested value. Functions returning `unsigned` forms return the
 input, modified as requested.
 
+**ncchannels_reverse** inverts the color components of the two channels,
+while holding all other elements constant. It's the Notcurses approximation
+to reverse video.
+
 # SEE ALSO
 
 **notcurses(3)**,

include/notcurses/notcurses.h

@@ -118,6 +118,10 @@ API int notcurses_ucs32_to_utf8(const char32_t* ucs32, unsigned ucs32count,
 #define NCALPHA_BLEND           0x10000000ull
 #define NCALPHA_OPAQUE          0x00000000ull
 
+// Does this glyph completely obscure the background? If so, there's no need
+// to emit a background when rasterizing, a small optimization. These are
+// also used to track regions into which we must not cellblit.
+#define CELL_NOBACKGROUND_MASK  0x8700000000000000ull
 // if this bit is set, we are *not* using the default background color
 #define CELL_BGDEFAULT_MASK     0x0000000040000000ull
 // if this bit is set, we are *not* using the default foreground color
@@ -297,6 +301,19 @@ ncchannels_fchannel(uint64_t channels){
   return ncchannels_bchannel(channels >> 32u);
 }
 
+// Returns the channels with the color information swapped, but not
+// alpha, nor other housekeeping bits.
+static inline uint64_t
+ncchannels_reverse(uint64_t channels){
+  const uint64_t raw = ((uint64_t)ncchannels_bchannel(channels) << 32u) +
+                       ncchannels_fchannel(channels);
+  const uint64_t statemask = (CELL_NOBACKGROUND_MASK | CELL_FG_ALPHA_MASK |
+                              CELL_BG_ALPHA_MASK | (CELL_NOBACKGROUND_MASK >> 32u));
+  uint64_t ret = raw & ~statemask;
+  ret |= channels & statemask;
+  return ret;
+}
+
 // Set the 32-bit background channel of a channel pair.
 static inline uint64_t
 ncchannels_set_bchannel(uint64_t* channels, uint32_t channel){

src/lib/internal.h

@@ -38,10 +38,6 @@ extern "C" {
 struct sixelmap;
 struct ncvisual_details;
 
-// Does this glyph completely obscure the background? If so, there's no need
-// to emit a background when rasterizing, a small optimization.
-#define CELL_NOBACKGROUND_MASK  0x8700000000000000ull
-
 // Was this glyph drawn as part of an ncvisual? If so, we need to honor
 // blitter stacking rather than the standard trichannel solver.
 #define CELL_BLITTERSTACK_MASK  CELL_NOBACKGROUND_MASK

src/lib/menu.c

@@ -452,10 +452,9 @@ int ncmenu_unroll(ncmenu* n, int sectionidx){
         ncplane_set_channels(n->ncp, n->disablechannels);
       }
       if(i == sec->itemselected){
-        ncplane_set_styles(n->ncp, NCSTYLE_REVERSE);
-      }else{
-        ncplane_set_styles(n->ncp, 0);
+        ncplane_set_channels(n->ncp, ncchannels_reverse(ncplane_channels(n->ncp)));
       }
+      ncplane_set_styles(n->ncp, 0);
       int cols = ncplane_putstr_yx(n->ncp, ypos, xpos + 1, sec->items[i].desc);
       if(cols < 0){
         return -1;

src/tests/channel.cpp

@@ -170,3 +170,28 @@ TEST_CASE("ChannelBlendDefaultRight") {
   CHECK(0x20 == b);
   CHECK(2 == blends);
 }
+
+// test that colors are inverted, but nothing else
+TEST_CASE("ChannelsReverse") {
+  uint64_t channels = 0;
+  uint64_t rev = ncchannels_reverse(channels);
+  CHECK(0 == rev);
+  ncchannels_set_fg_palindex(&channels, 8);
+  rev = ncchannels_reverse(channels);
+  CHECK(8 == ncchannels_bg_palindex(rev));
+  CHECK(0 == ncchannels_fg_palindex(rev));
+  ncchannels_set_fg_palindex(&rev, 63);
+  rev = ncchannels_reverse(rev);
+  CHECK(8 == ncchannels_fg_palindex(rev));
+  CHECK(63 == ncchannels_bg_palindex(rev));
+  ncchannels_set_fg_default(&rev);
+  ncchannels_set_bg_alpha(&rev, NCALPHA_TRANSPARENT);
+  rev = ncchannels_reverse(rev);
+  CHECK(63 == ncchannels_fg_palindex(rev));
+  CHECK(ncchannels_bg_default_p(rev));
+  CHECK(NCALPHA_TRANSPARENT == ncchannels_bg_alpha(rev));
+  ncchannels_set_fg_rgb(&rev, 0x2288cc);
+  rev = ncchannels_reverse(rev);
+  CHECK(0x2288cc == ncchannels_bg_rgb(rev));
+  CHECK(ncchannels_fg_default_p(rev));
+}