Add an option :opt:disable_ligatures_under_cursor to disable multi-character ligatures under the cursor to make editing easier

Fixes #461

docs/changelog.rst

@@ -20,6 +20,10 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - macOS: Allow opening new kitty tabs/top-level windows from Finder
   (:pull:`1350`)
 
+- Add an option :opt:`disable_ligatures_under_cursor` to disable
+  multi-character ligatures under the cursor to make editing easier
+  (:iss:`461`)
+
 - Allow specifying a value of ``none`` for the :opt:`selection_foreground`
   which will cause kitty to not change text color in selections (:iss:`1358`)
 

kitty/config_data.py

@@ -257,8 +257,8 @@ Syntax is::
 '''))
 
 o('disable_ligatures_under_cursor', False, long_text=_('''
-Render the characters of a ligature under the cursor individually
-to make editing more intuitive.
+Render the characters of a multi-character ligature under the cursor
+individually to make editing more intuitive.
 '''))
 
 

kitty/fonts.c

@@ -58,7 +58,7 @@ typedef struct {
 
 
 static hb_buffer_t *harfbuzz_buffer = NULL;
-static hb_feature_t no_liga_feature;
+static hb_feature_t no_calt_feature = {0};
 static char_type shape_buffer[4096] = {0};
 static size_t max_texture_size = 1024, max_array_len = 1024;
 
@@ -743,10 +743,10 @@ shape(CPUCell *first_cpu_cell, GPUCell *first_gpu_cell, index_type num_cells, hb
     group_state.last_gpu_cell = first_gpu_cell + (num_cells ? num_cells - 1 : 0);
     load_hb_buffer(first_cpu_cell, first_gpu_cell, num_cells);
 
-    if (!disable_ligature) {
-        hb_shape(font, harfbuzz_buffer, NULL, 0);
+    if (disable_ligature) {
+        hb_shape(font, harfbuzz_buffer, &no_calt_feature, 1);
     } else {
-        hb_shape(font, harfbuzz_buffer, &no_liga_feature, 1);
+        hb_shape(font, harfbuzz_buffer, NULL, 0);
     }
 
     unsigned int info_length, positions_length;
@@ -1023,14 +1023,13 @@ render_line(FONTS_DATA_HANDLE fg_, Line *line, index_type lnum, Cursor *cursor)
     bool center_glyph = false;
     bool disable_ligature = false;
     bool disable_ligature_in_line = false;
-    index_type first_cell_in_run, i, cursor_x;
+    index_type first_cell_in_run, i;
     attrs_type prev_width = 0;
     if (cursor != NULL && OPT(disable_ligatures_under_cursor)) {
-        cursor_x = cursor->x;
         if (lnum == cursor->y) disable_ligature_in_line = true;
     }
     for (i=0, first_cell_in_run=0; i < line->xnum; i++) {
-        disable_ligature = disable_ligature_in_line && (first_cell_in_run <= cursor_x && cursor_x <= i);
+        disable_ligature = disable_ligature_in_line && (first_cell_in_run <= cursor->x && cursor->x <= i);
         if (prev_width == 2) { prev_width = 0; continue; }
         CPUCell *cpu_cell = line->cpu_cells + i;
         GPUCell *gpu_cell = line->gpu_cells + i;
@@ -1381,8 +1380,12 @@ init_fonts(PyObject *module) {
     harfbuzz_buffer = hb_buffer_create();
     if (harfbuzz_buffer == NULL || !hb_buffer_allocation_successful(harfbuzz_buffer) || !hb_buffer_pre_allocate(harfbuzz_buffer, 2048)) { PyErr_NoMemory(); return false; }
     hb_buffer_set_cluster_level(harfbuzz_buffer, HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS);
-    const char* feature_str = "-calt";
-    if (!hb_feature_from_string(feature_str, strlen(feature_str), &no_liga_feature)) fatal("hb_feature_from_string() failed");
+#define feature_str "-calt"
+    if (!hb_feature_from_string(feature_str, sizeof(feature_str) - 1, &no_calt_feature)) {
+        PyErr_SetString(PyExc_RuntimeError, "Failed to create -calt harfbuzz feature");
+        return false;
+    }
+#undef feature_str
     if (PyModule_AddFunctions(module, module_methods) != 0) return false;
     current_send_sprite_to_gpu = send_sprite_to_gpu;
     return true;

kitty/screen.c

@@ -1468,7 +1468,7 @@ screen_reset_dirty(Screen *self) {
 }
 
 void
-screen_update_cell_data(Screen *self, void *address, FONTS_DATA_HANDLE fonts_data, bool update_cursor_pos) {
+screen_update_cell_data(Screen *self, void *address, FONTS_DATA_HANDLE fonts_data, bool cursor_has_moved) {
     unsigned int history_line_added_count = self->history_line_added_count;
     index_type lnum;
     bool was_dirty = self->is_dirty;
@@ -1478,8 +1478,7 @@ screen_update_cell_data(Screen *self, void *address, FONTS_DATA_HANDLE fonts_dat
     for (index_type y = 0; y < MIN(self->lines, self->scrolled_by); y++) {
         lnum = self->scrolled_by - 1 - y;
         historybuf_init_line(self->historybuf, lnum, self->historybuf->line);
-        if (self->historybuf->line->has_dirty_text ||
-            (update_cursor_pos && (self->cursor->y == lnum || self->last_rendered_cursor_y == lnum))) {
+        if (self->historybuf->line->has_dirty_text) {
             render_line(fonts_data, self->historybuf->line, lnum, self->cursor);
             historybuf_mark_line_clean(self->historybuf, lnum);
         }
@@ -1489,7 +1488,7 @@ screen_update_cell_data(Screen *self, void *address, FONTS_DATA_HANDLE fonts_dat
         lnum = y - self->scrolled_by;
         linebuf_init_line(self->linebuf, lnum);
         if (self->linebuf->line->has_dirty_text ||
-            (update_cursor_pos && (self->cursor->y == lnum || self->last_rendered_cursor_y == lnum))) {
+            (cursor_has_moved && (self->cursor->y == lnum || self->last_rendered_cursor_y == lnum))) {
             render_line(fonts_data, self->linebuf->line, lnum, self->cursor);
             linebuf_mark_line_clean(self->linebuf, lnum);
         }

kitty/screen.h

@@ -177,7 +177,7 @@ void screen_apply_selection(Screen *self, void *address, size_t size);
 bool screen_is_selection_dirty(Screen *self);
 bool screen_has_selection(Screen*);
 bool screen_invert_colors(Screen *self);
-void screen_update_cell_data(Screen *self, void *address, FONTS_DATA_HANDLE, bool update_cursor_pos);
+void screen_update_cell_data(Screen *self, void *address, FONTS_DATA_HANDLE, bool cursor_has_moved);
 bool screen_is_cursor_visible(Screen *self);
 bool screen_selection_range_for_line(Screen *self, index_type y, index_type *start, index_type *end);
 bool screen_selection_range_for_word(Screen *self, index_type x, index_type *, index_type *, index_type *start, index_type *end);