Reduce data sent to GPU per draw by 30%

Split up the Cell structure into a CPUCell and a GPUCell. Only the
GPUCell part needs to be sent to the GPU. Should make kitty use even
less system resources and make a performance difference on systems where
the GPU bandwidth is constrained.

Also allows adding more CPU only data in the future without affecting
GPU bandwidth. For example, hyperlinks or more combining characters.

Author: kovidgoyal

kitty/core_text.m

@@ -178,7 +178,7 @@
 }
 
 PyObject*
-create_fallback_face(PyObject *base_face, Cell* cell, bool UNUSED bold, bool UNUSED italic, bool emoji_presentation, FONTS_DATA_HANDLE fg UNUSED) {
+create_fallback_face(PyObject *base_face, CPUCell* cell, bool UNUSED bold, bool UNUSED italic, bool emoji_presentation, FONTS_DATA_HANDLE fg UNUSED) {
     CTFace *self = (CTFace*)base_face;
     CTFontRef new_font;
     if (emoji_presentation) new_font = CTFontCreateWithName((CFStringRef)@"AppleColorEmoji", self->scaled_point_sz, NULL);

kitty/cursor.c

@@ -136,7 +136,7 @@ END_ALLOW_CASE_RANGE
 }
 
 void
-apply_sgr_to_cells(Cell *first_cell, unsigned int cell_count, unsigned int *params, unsigned int count) {
+apply_sgr_to_cells(GPUCell *first_cell, unsigned int cell_count, unsigned int *params, unsigned int count) {
 #define RANGE for(unsigned c = 0; c < cell_count; c++, cell++)
 #define SET(shift) RANGE { cell->attrs |= (1 << shift); } break;
 #define RESET(shift) RANGE { cell->attrs &= ~(1 << shift); } break;
@@ -148,7 +148,7 @@ apply_sgr_to_cells(Cell *first_cell, unsigned int cell_count, unsigned int *para
     unsigned int i = 0, attr;
     if (!count) { params[0] = 0; count = 1; }
     while (i < count) {
-        Cell *cell = first_cell;
+        GPUCell *cell = first_cell;
         attr = params[i++];
         switch(attr) {
             case 0:

kitty/data-types.h

@@ -80,7 +80,7 @@ typedef enum MouseShapes { BEAM, HAND, ARROW } MouseShape;
     (c)->reverse = (a >> REVERSE_SHIFT) & 1; (c)->strikethrough = (a >> STRIKE_SHIFT) & 1; (c)->dim = (a >> DIM_SHIFT) & 1;
 
 #define COPY_CELL(src, s, dest, d) \
-    (dest)->cells[d] = (src)->cells[s];
+    (dest)->cpu_cells[d] = (src)->cpu_cells[s]; (dest)->gpu_cells[d] = (src)->gpu_cells[s];
 
 #define COPY_SELF_CELL(s, d) COPY_CELL(self, s, self, d)
 
@@ -140,15 +140,19 @@ typedef struct {
     color_type fg, bg, decoration_fg;
     sprite_index sprite_x, sprite_y, sprite_z;
     attrs_type attrs;
-    // The following are only needed on the CPU, not the GPU
+} GPUCell;
+
+typedef struct {
     char_type ch;
     combining_type cc_idx[2];
-} Cell;
+} CPUCell;
+
 
 typedef struct {
     PyObject_HEAD
 
-    Cell *cells;
+    GPUCell *gpu_cells;
+    CPUCell *cpu_cells;
     index_type xnum, ynum;
     bool continued, needs_free, has_dirty_text;
 } Line;
@@ -157,14 +161,16 @@ typedef struct {
 typedef struct {
     PyObject_HEAD
 
-    Cell *buf;
+    GPUCell *gpu_cell_buf;
+    CPUCell *cpu_cell_buf;
     index_type xnum, ynum, *line_map, *scratch;
     line_attrs_type *line_attrs;
     Line *line;
 } LineBuf;
 
 typedef struct {
-    Cell *cells;
+    GPUCell *gpu_cells;
+    CPUCell *cpu_cells;
     line_attrs_type *line_attrs;
 } HistoryBufSegment;
 
@@ -226,10 +232,10 @@ typedef struct {FONTS_DATA_HEAD} *FONTS_DATA_HANDLE;
     for(index_type __i__ = (at); __i__ < (line)->xnum - (num); __i__++) { \
         COPY_CELL(line, __i__ + (num), line, __i__) \
     } \
-    if ((((line)->cells[(at)].attrs) & WIDTH_MASK) != 1) { \
-        (line)->cells[(at)].ch = BLANK_CHAR; \
-        (line)->cells[(at)].attrs = BLANK_CHAR ? 1 : 0; \
-        clear_sprite_position((line)->cells[(at)]); \
+    if ((((line)->gpu_cells[(at)].attrs) & WIDTH_MASK) != 1) { \
+        (line)->cpu_cells[(at)].ch = BLANK_CHAR; \
+        (line)->gpu_cells[(at)].attrs = BLANK_CHAR ? 1 : 0; \
+        clear_sprite_position((line)->gpu_cells[(at)]); \
     }\
 }
 
@@ -260,7 +266,7 @@ Cursor* cursor_copy(Cursor*);
 void cursor_copy_to(Cursor *src, Cursor *dest);
 void cursor_reset_display_attrs(Cursor*);
 void cursor_from_sgr(Cursor *self, unsigned int *params, unsigned int count);
-void apply_sgr_to_cells(Cell *first_cell, unsigned int cell_count, unsigned int *params, unsigned int count);
+void apply_sgr_to_cells(GPUCell *first_cell, unsigned int cell_count, unsigned int *params, unsigned int count);
 const char* cursor_as_sgr(Cursor*, Cursor*);
 
 double monotonic();

kitty/fontconfig.c

@@ -194,7 +194,7 @@ specialize_font_descriptor(PyObject *base_descriptor, FONTS_DATA_HANDLE fg) {
 }
 
 PyObject*
-create_fallback_face(PyObject UNUSED *base_face, Cell* cell, bool bold, bool italic, bool emoji_presentation, FONTS_DATA_HANDLE fg) {
+create_fallback_face(PyObject UNUSED *base_face, CPUCell* cell, bool bold, bool italic, bool emoji_presentation, FONTS_DATA_HANDLE fg) {
     PyObject *ans = NULL;
     FcPattern *pat = FcPatternCreate();
     if (pat == NULL) return PyErr_NoMemory();