Add force_ltr

Close #2252

kitty/config_data.py

@@ -223,6 +223,19 @@ def to_font_size(x):
 
 o('font_size', 11.0, long_text=_('Font size (in pts)'), option_type=to_font_size)
 
+o('force_ltr', False, long_text=_("""
+Kitty does not yet support BIDI (bidirectional text), however, for RTL scripts,
+HarfBuzz will "helpfully" shape text as if we were laying it out RTL. That is
+to say, in an RTL script, the words "HELLO WORLD" display in Kitty as "WORLD
+HELLO", and if you try to select a substring of an RTL-shaped string, you will
+get the character that _would_ be there were the string LTR. For example,
+assuming the Hebrew word ירושלים, selecting the character that on the screen
+appears to be ם actually writes into the selection buffer the character י.
+
+Kitty's default behavior is useful in conjunction with a filter to reverse the
+word order, however, if you wish to manipulate RTL glyphs, it can be very
+challenging to work with, so this option is provided to turn it off."""))
+
 
 def adjust_line_height(x):
     if x.endswith('%'):
@@ -315,6 +328,12 @@ Disable the normal ligatures, but keep the :code:`calt` feature which (in this
 font) breaks up monotony::
 
     font_features TT2020StyleB-Regular -liga +calt
+
+In conjunction with :opt:`force_ltr`, you may want to disable Arabic shaping
+entirely, and only look at their isolated forms if they show up in a document.
+You can do this with e.g.::
+
+    font_features UnifontMedium +isol -medi -fina -init
 '''))
 
 

kitty/fonts.c

@@ -689,6 +689,7 @@ load_hb_buffer(CPUCell *first_cpu_cell, GPUCell *first_gpu_cell, index_type num_
         hb_buffer_add_utf32(harfbuzz_buffer, shape_buffer, num, 0, num);
     }
     hb_buffer_guess_segment_properties(harfbuzz_buffer);
+    if (OPT(force_ltr)) hb_buffer_set_direction(harfbuzz_buffer, HB_DIRECTION_LTR);
 }
 
 

kitty/state.c

@@ -527,6 +527,7 @@ PYWRAP1(set_options) {
     S(macos_thicken_font, PyFloat_AsFloat);
     S(tab_bar_min_tabs, PyLong_AsUnsignedLong);
     S(disable_ligatures, PyLong_AsLong);
+    S(force_ltr, PyObject_IsTrue);
     S(resize_draw_strategy, PyLong_AsLong);
     S(resize_in_steps, PyObject_IsTrue);
     S(pointer_shape_when_grabbed, pointer_shape);

kitty/state.h

@@ -42,6 +42,7 @@ typedef struct {
     Edge tab_bar_edge;
     unsigned long tab_bar_min_tabs;
     DisableLigature disable_ligatures;
+    bool force_ltr;
     ResizeDrawStrategy resize_draw_strategy;
     bool resize_in_steps;
     bool sync_to_monitor;