capture bytes in linux framebuffer graphics to sprixelbytes stat

README.md

@@ -440,6 +440,13 @@ If things break or seem otherwise lackluster, **please** consult the
   returns successfully.
 </details>
 
+<details>
+  <summary>Why do the stats show more Linux framebuffer bitmap bytes written
+  than total bytes written to the terminal?</summary>
+  Linux framebuffer graphics aren't implemented via terminal writes, but instead
+  writes directly into a memory map.
+</details>
+
 ## Useful links
 
 * [BiDi in Terminal Emulators](https://terminal-wg.pages.freedesktop.org/bidi/)

doc/man/man3/notcurses_stats.3.md

@@ -42,6 +42,7 @@ typedef struct ncstats {
   uint64_t sprixelelisions;  // sprixel elision count
   uint64_t sprixelbytes;     // sprixel bytes emitted
   uint64_t appsync_updates;  // application-synchronized updates
+  uint64_t input_events;     // EGC inputs received or synthesized
   uint64_t input_errors;     // errors processing input
 
   // current state -- these can decrease
@@ -120,6 +121,12 @@ malformed control sequences or invalid UTF-8 (see **utf8(7)**).
 
 Unsuccessful render operations do not contribute to the render timing stats.
 
+Linux framebuffer bitmaps are not written through the terminal device, but
+instead directly into the memory-mapped framebuffer (see **mmap(2)**). Bytes
+used for framebuffer graphics are thus independent of bytes written to the
+terminal. This explains why **sprixelbytes** may be surprising given the
+value of **render_bytes**.
+
 # RETURN VALUES
 
 Neither **notcurses_stats** nor **notcurses_stats_reset** can fail. Neither
@@ -128,6 +135,7 @@ object on success, or **NULL** on failure.
 
 # SEE ALSO
 
+**mmap(2)**,
 **notcurses(3)**,
 **notcurses_render(3)**,
 **utf8(7)**

src/lib/linux.c

@@ -106,6 +106,7 @@ int fbcon_scrub(const struct ncpile* p, sprixel* s){
 int fbcon_draw(const struct ncpile *p, sprixel* s, FILE* out, int y, int x){
   (void)out; // we don't write to the stream
   const tinfo* ti = &p->nc->tcache;
+  int wrote = 0;
   for(int l = 0 ; l < s->pixy ; ++l){
     // FIXME pixel size isn't necessarily 4B, line isn't necessarily psize*pixx
     size_t offset = ((l + y * ti->cellpixy) * ti->pixx + x * ti->cellpixx) * 4;
@@ -116,12 +117,13 @@ int fbcon_draw(const struct ncpile *p, sprixel* s, FILE* out, int y, int x){
       memcpy(&pixel, src, 4);
       if(!rgba_trans_p(pixel, 0)){
         memcpy(tl, &pixel, 4);
+        wrote += 4;
       }
       src += 4;
       tl += 4;
     }
   }
-  return 0;
+  return wrote;
 }
 
 #ifdef __linux__