kitty: tripartite blit implementation #1900

src/lib/sprite.h

@@ -172,6 +172,7 @@ int kitty_rebuild(sprixel* s, int ycell, int xcell, uint8_t* auxvec);
 int iterm_rebuild(sprixel* s, int ycell, int xcell, uint8_t* auxvec);
 int fbcon_rebuild(sprixel* s, int ycell, int xcell, uint8_t* auxvec);
 int kitty_rebuild_animation(sprixel* s, int ycell, int xcell, uint8_t* auxvec);
+int kitty_rebuild_selfref(sprixel* s, int ycell, int xcell, uint8_t* auxvec);
 int sixel_draw(const tinfo* ti, const struct ncpile *p, sprixel* s,
                FILE* out, int y, int x);
 int kitty_draw(const tinfo* ti, const struct ncpile *p, sprixel* s,
@@ -199,11 +200,29 @@ int iterm_blit(struct ncplane* nc, int linesize, const void* data,
                int leny, int lenx, const struct blitterargs* bargs);
 int kitty_blit_animated(struct ncplane* n, int linesize, const void* data,
                         int leny, int lenx, const struct blitterargs* bargs);
+int kitty_blit_selfref(struct ncplane* nc, int linesize, const void* data,
+                       int leny, int lenx, const struct blitterargs* bargs);
 int fbcon_blit(struct ncplane* nc, int linesize, const void* data,
                int leny, int lenx, const struct blitterargs* bargs);
 int fbcon_draw(const tinfo* ti, const struct ncpile *p, sprixel* s,
                FILE* out, int y, int x);
 
+typedef enum {
+  // C=1 (disabling scrolling) was only introduced in 0.20.0, at the same
+  // time as animation. prior to this, graphics had to be entirely redrawn
+  // on any change, and it wasn't possible to use the bottom line.
+  KITTY_ALWAYS_SCROLLS,
+  // until 0.21.3's introduction of 't=z' for self-reference, we had to
+  // keep a complete copy of the RGBA data, in case a wiped cell needed to
+  // be rebuilt. we'd otherwise have to unpack the glyph and store it into
+  // the auxvec on the fly.
+  KITTY_ANIMATION,
+  // with 0.21.3, we only ever write transparent cells after writing the
+  // original image (which we now deflate, since we needn't unpack it later).
+  // the only data we need keep is the auxvecs.
+  KITTY_SELFREF,
+} kitty_graphics_e;
+
 #ifdef __cplusplus
 }
 #endif

src/lib/termdesc.c

@@ -85,26 +85,32 @@ setup_iterm_bitmaps(tinfo* ti, int fd){
 }
 
 // kitty 0.19.3 didn't have C=1, and thus needs sixel_maxy_pristine. it also
-// lacked animation, and thus requires the older interface.
+// lacked animation, and must thus redraw the complete image every time it
+// changes. requires the older interface.
 static inline void
-setup_kitty_bitmaps(tinfo* ti, int fd, int sixel_maxy_pristine){
+setup_kitty_bitmaps(tinfo* ti, int fd, kitty_graphics_e level){
   ti->pixel_scrub = kitty_scrub;
   ti->pixel_remove = kitty_remove;
   ti->pixel_draw = kitty_draw;
   ti->pixel_commit = kitty_commit;
   ti->pixel_move = kitty_move;
   ti->pixel_shutdown = kitty_shutdown;
   ti->pixel_clear_all = kitty_clear_all;
-  ti->sixel_maxy_pristine = sixel_maxy_pristine;
-  if(sixel_maxy_pristine){
+  if(level == KITTY_ALWAYS_SCROLLS){
     ti->pixel_wipe = kitty_wipe;
     ti->pixel_trans_auxvec = kitty_trans_auxvec;
     ti->pixel_rebuild = kitty_rebuild;
+    ti->sixel_maxy_pristine = INT_MAX;
     set_pixel_blitter(kitty_blit);
   }else{
     ti->pixel_wipe = kitty_wipe_animation;
-    ti->pixel_rebuild = kitty_rebuild_animation;
-    set_pixel_blitter(kitty_blit_animated);
+    if(level == KITTY_ANIMATION){
+      ti->pixel_rebuild = kitty_rebuild_animation;
+      set_pixel_blitter(kitty_blit_animated);
+    }else{
+      ti->pixel_rebuild = kitty_rebuild_selfref;
+      set_pixel_blitter(kitty_blit_selfref);
+    }
   }
   sprite_init(ti, fd);
 }
@@ -501,11 +507,12 @@ apply_term_heuristics(tinfo* ti, const char* termname, int fd,
     if(add_smulx_escapes(ti, tablelen, tableused)){
       return -1;
     }
-    // kitty only introduced C=1 in 0.20.0
-    if(compare_versions(ti->termversion, "0.20.0") < 0){
-      setup_kitty_bitmaps(ti, fd, INT_MAX);
+    if(compare_versions(ti->termversion, "0.21.3") >= 0){
+      setup_kitty_bitmaps(ti, fd, KITTY_SELFREF);
+    }else if(compare_versions(ti->termversion, "0.20.0") >= 0){
+      setup_kitty_bitmaps(ti, fd, KITTY_ANIMATION);
     }else{
-      setup_kitty_bitmaps(ti, fd, 0);
+      setup_kitty_bitmaps(ti, fd, KITTY_ALWAYS_SCROLLS);
     }
     if(add_pushcolors_escapes(ti, tablelen, tableused)){
       return -1;