glyph-based background spec elision #131

When we emit a glyph that has no background pixels (i.e.
the U+2588 FULL BLOCK glyph), there's no need to emit a
background color change.

Eagle demo currently has hand-coded elision. Results from
80x70 runs using the `-c` parameter:

No optimization: 12.63MiB
Hand-optimized: 12.48MiB
New scheme, no hand-coded optimization: 12.45MiB

w00t!

include/notcurses.h

@@ -3,6 +3,7 @@
 
 #include <time.h>
 #include <uchar.h>
+#include <ctype.h>
 #include <wchar.h>
 #include <stdio.h>
 #include <stdint.h>
@@ -1317,18 +1318,37 @@ cell_set_bg_alpha(cell* c, int alpha){
   return channels_set_bg_alpha(&c->channels, alpha);
 }
 
-// does the cell contain an East Asian Wide codepoint?
+// Does the cell contain an East Asian Wide codepoint?
 static inline bool
 cell_double_wide_p(const cell* c){
   return (c->channels & CELL_WIDEASIAN_MASK);
 }
 
-// is the cell simple (a lone ASCII character, encoded as such)?
+// Is the cell simple (a lone ASCII character, encoded as such)?
 static inline bool
 cell_simple_p(const cell* c){
   return c->gcluster < 0x80;
 }
 
+// return a pointer to the NUL-terminated EGC referenced by 'c'. this pointer
+// is invalidated by any further operation on the plane 'n', so...watch out!
+API const char* cell_extended_gcluster(const struct ncplane* n, const cell* c);
+
+// True if the cell does not generate foreground pixels (i.e., the cell is
+// entirely whitespace or special characters).
+// FIXME do this at cell prep time and set a bit in the channels
+static inline bool
+cell_noforeground_p(const cell* c){
+  return cell_simple_p(c) || isspace(c->gcluster);
+}
+
+// True if the cell does not generate background pixels. Only the FULL BLOCK
+// glyph has this property, AFAIK.
+static inline bool
+cell_nobackground_p(const struct ncplane* n, const cell* c){
+  return !cell_simple_p(c) && !strcmp(cell_extended_gcluster(n, c), "\xe2\x96\x88");
+}
+
 static inline int
 cell_load_simple(struct ncplane* n, cell* c, char ch){
   cell_release(n, c);
@@ -1347,10 +1367,6 @@ cell_egc_idx(const cell* c){
   return c->gcluster - 0x80;
 }
 
-// return a pointer to the NUL-terminated EGC referenced by 'c'. this pointer
-// is invalidated by any further operation on the plane 'n', so...watch out!
-API const char* cell_extended_gcluster(const struct ncplane* n, const cell* c);
-
 // load up six cells with the EGCs necessary to draw a box. returns 0 on
 // success, -1 on error. on error, any cells this function might
 // have loaded before the error are cell_release()d. There must be at least

src/demo/eagle.c

@@ -121,8 +121,6 @@ draw_eagle(struct ncplane* n, const char* sprite){
   size_t s;
   int sbytes;
   uint64_t channels = 0;
-  // optimization so we can elide more color changes, see README's "#perf"
-  channels_set_bg_rgb(&channels, 0x00, 0x00, 0x00);
   ncplane_cursor_move_yx(n, 0, 0);
   for(s = 0 ; sprite[s] ; ++s){
     switch(sprite[s]){

src/lib/render.c

@@ -534,8 +534,16 @@ notcurses_render_internal(notcurses* nc){
       // escapes ourselves, if either is set to default, we first send op, and
       // then a turnon for whichever aren't default.
 
-      // we can elide the default set iff the previous used both defaults
-      if(cell_fg_default_p(&c) || cell_bg_default_p(&c)){
+      // if our cell has a default foreground *or* background, we can elide the
+      // default set iff one of:
+      //  * we are a partial glyph, and the previous was default on both, or
+      //  * we are a no-foreground glyph, and the previous was default background, or
+      //  * we are a no-background glyph, and the previous was default foreground
+
+      // FIXME move these into the cell bits
+      bool noforeground = cell_noforeground_p(&c);
+      bool nobackground = cell_nobackground_p(p, &c);
+      if((!noforeground && cell_fg_default_p(&c)) || (!nobackground && cell_bg_default_p(&c))){
         if(!nc->rstate.defaultelidable){
           ++nc->stats.defaultemissions;
           term_emit("op", nc->op, out, false);
@@ -548,8 +556,11 @@ notcurses_render_internal(notcurses* nc){
         nc->rstate.bgelidable = false;
       }
 
-      // we can elide the foreground set iff the previous used fg and matched
-      if(!cell_fg_default_p(&c)){
+      // if our cell has a non-default foreground, we can elide the non-default
+      // foreground set iff either:
+      //  * the previous was non-default, and matches what we have now, or
+      //  * we are a no-foreground glyph (iswspace() is true)
+      if(/*!noforeground &&*/ !cell_fg_default_p(&c)){
         cell_get_fg_rgb(&c, &r, &g, &b);
         if(nc->rstate.fgelidable && nc->rstate.lastr == r && nc->rstate.lastg == g && nc->rstate.lastb == b){
           ++nc->stats.fgelisions;
@@ -561,7 +572,7 @@ notcurses_render_internal(notcurses* nc){
         nc->rstate.lastr = r; nc->rstate.lastg = g; nc->rstate.lastb = b;
         nc->rstate.defaultelidable = false;
       }
-      if(!cell_bg_default_p(&c)){
+      if(!nobackground && !cell_bg_default_p(&c)){
         cell_get_bg_rgb(&c, &br, &bg, &bb);
         if(nc->rstate.bgelidable && nc->rstate.lastbr == br && nc->rstate.lastbg == bg && nc->rstate.lastbb == bb){
           ++nc->stats.bgelisions;