nick black



notcurses_stats - notcurses runtime statistics


#include <notcurses/notcurses.h>

typedef struct ncstats {
  // purely increasing stats
  uint64_t renders;          // successful ncpile_render() runs
  uint64_t writeouts;        // successful ncpile_rasterize() runs
  uint64_t failed_renders;   // aborted renders, should be 0
  uint64_t failed_writeouts; // aborted writes
  uint64_t render_bytes;     // bytes emitted to ttyfp
  int64_t render_max_bytes;  // max bytes emitted for a frame
  int64_t render_min_bytes;  // min bytes emitted for a frame
  uint64_t render_ns;        // nanoseconds spent rendering
  int64_t render_max_ns;     // max ns spent for a frame
  int64_t render_min_ns;     // min ns spent for a frame
  uint64_t raster_ns;        // nanoseconds spent rasterizing
  int64_t raster_max_ns;     // max ns spent in raster for a frame
  int64_t raster_min_ns;     // min ns spent in raster for a frame
  uint64_t writeout_ns;      // ns spent writing frames to terminal
  int64_t writeout_max_ns;   // max ns spent writing out a frame
  int64_t writeout_min_ns;   // min ns spent writing out a frame
  uint64_t cellelisions;     // cells elided entirely
  uint64_t cellemissions;    // cells emitted
  uint64_t fgelisions;       // RGB fg elision count
  uint64_t fgemissions;      // RGB fg emissions
  uint64_t bgelisions;       // RGB bg elision count
  uint64_t bgemissions;      // RGB bg emissions
  uint64_t defaultelisions;  // default color was emitted
  uint64_t defaultemissions; // default color was elided
  uint64_t refreshes;        // refreshes (unoptimized redraws)
  uint64_t sprixelemissions; // sprixel draw count
  uint64_t sprixelelisions;  // sprixel elision count
  uint64_t sprixelbytes;     // sprixel bytes emitted
  uint64_t appsync_updates;  // application-synchronized updates
  uint64_t input_events;     // inputs received or synthesized
  uint64_t input_errors;     // errors processing input
  uint64_t hpa_gratuitous;   // gratuitous HPAs issued

  // current state -- these can decrease
  uint64_t fbbytes;          // bytes devoted to framebuffers
  unsigned planes;           // planes currently in existence
} ncstats;

ncstats* notcurses_stats_alloc(struct notcurses* nc);

void notcurses_stats(struct notcurses* nc, ncstats* stats);

void notcurses_stats_reset(struct notcurses* nc, ncstats* stats);


notcurses_stats_alloc allocates an ncstats object. This should be used rather than allocating the object in client code, to future-proof against the struct being enlarged by later Notcurses versions.

notcurses_stats acquires an atomic snapshot of statistics, primarily related to notcurses_render(3). notcurses_stats_reset does the same, but also resets all cumulative stats (immediate stats such as fbbytes are not reset).

renders is the number of successful calls to notcurses_render(3) or ncpile_render_to_buffer(3). failed_renders is the number of unsuccessful calls to these functions. failed_renders should be 0; renders are not expected to fail except under exceptional circumstances. should notcurses_render(3) fail while writing out a frame to the terminal, it counts as a failed render.

render_max_bytes and render_min_bytes track the maximum and minimum number of bytes used rasterizing a frame. A given state of Notcurses does not correspond to a unique number of bytes; the size is also dependent on the existing terminal state. As a first approximation, the time a terminal takes to ingest and reflect a frame is dependent on the size of the rasterized frame.

render_ns, render_max_ns, and render_min_ns track the total amount of time spent rendering frames in nanoseconds. Rendering takes place in ncpile_render (called by notcurses_render(3) and ncpile_render_to_buffer). This step is independent of the terminal.

raster_ns, raster_max_ns, and raster_min_ns track the total amount of time spent rasterizing frames in nanoseconds. Rasterizing takes place in ncpile_raster (called by notcurses_raster(3) and ncpile_render_to_buffer). This step depends on the terminal definitions. The same frame might not rasterize to the same bytes for different terminals.

writeout_ns, writeout_max_ns, and writeout_min_ns track the total amount of time spent writing frames to the terminal. This takes place in ncpile_rasterize (called by notcurses_render(3)).

cellemissions reflects the number of EGCs written to the terminal. cellelisions reflects the number of cells which were not written, due to damage detection.

refreshes is the number of times notcurses_refresh has been successfully executed.

fbbytes is the total number of bytes devoted to framebuffers throughout the struct notcurses context. planes is the number of planes in the context. Neither of these stats can reach 0, due to the mandatory standard plane.

sprixelemissions is the number of sprixel draws. sprixelelisions is the number of times a sprixel was elided--essentially, the number of times a sprixel appeared in a rendered frame without freshly drawing it. sprixelbytes is the number of bytes used for sprixel drawing. It does not include move/delete operations, nor glyphs used to erase sprixels.

input_errors is the number of errors while processing input, e.g. malformed control sequences or invalid UTF-8 (see utf8(7)).

hpa_gratuitous is the number of hpa (horizontal position absolute, see terminfo(5)) control sequences issued where not strictly necessary. This is done to cope with fundamental ambiguities regarding glyph width. It is not generally possible to know how wide a glyph will be rendered on a given combination of font, font rendering engine, and terminal. Indeed, it is not even generally possible to know how many glyphs will result from a sequence of EGCs. As a result, Notcurses sometimes issues "gratuitous" hpa controls.


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.


Neither notcurses_stats nor notcurses_stats_reset can fail. Neither returns any value. notcurses_stats_alloc returns a valid ncstats object on success, or NULL on failure.


mmap(2), notcurses(3), notcurses_render(3), terminfo(5), utf8(7)