Utility method to truncate formatted lines to specified width

kittens/diff/main.py

@@ -80,7 +80,7 @@ class DiffHandler(Handler):
             else:
                 text = self.diff_lines[lpos].text
             self.write(text)
-            self.write('\n\r')
+            self.write('\x1b[0m\n\r')
 
     def on_key(self, key_event):
         if self.state is INITIALIZING:

kittens/diff/render.py

@@ -5,7 +5,7 @@
 import re
 from gettext import gettext as _
 
-from kitty.fast_data_types import wcswidth
+from kitty.fast_data_types import truncate_point_for_length
 
 from .collect import data_for_path, path_name_map
 from .config import formats
@@ -60,13 +60,16 @@ def sanitize(text):
 
 
 def fit_in(text, count):
-    w = wcswidth(text)
-    if w <= count:
+    p = truncate_point_for_length(text, count)
+    if p >= len(text):
         return text
-    text = text[:count-1]
-    while wcswidth(text) > count - 1:
-        text = text[:-1]
-    return text + '…'
+    if count > 1:
+        p = truncate_point_for_length(text, count - 1)
+    return text[:p] + '…'
+
+
+def place_in(text, sz):
+    return fit_in(text, sz).ljust(sz)
 
 
 def format_func(which):
@@ -82,10 +85,6 @@ title_format = format_func('title')
 margin_format = format_func('margin')
 
 
-def place_in(text, sz):
-    return fit_in(text, sz).ljust(sz)
-
-
 def title_lines(left_path, right_path, args, columns, margin_size):
     name = fit_in(sanitize(path_name_map[left_path]), columns - 2 * margin_size)
     yield title_format((' ' + name).ljust(columns))
@@ -99,13 +98,23 @@ def binary_lines(path, other_path, columns, margin_size):
     def fl(path):
         text = template.format(human_readable(len(data_for_path(path))))
         text = place_in(text, columns // 2 - margin_size)
-        return margin_format(' ' * margin_size) + text_format(text)
+        return margin_format(' ' * margin_size) + text_format(text) + '\x1b[0m'
 
     return fl(path) + fl(other_path)
 
 
+def split_to_size(line, width):
+    while line:
+        p = truncate_point_for_length(line, width)
+        yield line[:p]
+        line = line[p:]
+
+
 def lines_for_diff(left_path, right_path, hunks, args, columns, margin_size):
-    return iter(())
+    available_cols = columns // 2 - margin_size
+    for hunk_num, hunk in enumerate(hunks):
+        for line_num, (left, right) in enumerate(zip(hunk.left_lines, hunk.right_lines)):
+            pass
 
 
 def render_diff(collection, diff_map, args, columns):

kitty/screen.c

@@ -1516,6 +1516,52 @@ screen_wcswidth(PyObject UNUSED *self, PyObject *str) {
     return PyLong_FromUnsignedLong(ans);
 }
 
+
+static PyObject*
+screen_truncate_point_for_length(PyObject UNUSED *self, PyObject *args) {
+    PyObject *str; unsigned int num_cells;
+    if (!PyArg_ParseTuple(args, "OI", &str, &num_cells)) return NULL;
+    if (PyUnicode_READY(str) != 0) return NULL;
+    int kind = PyUnicode_KIND(str);
+    void *data = PyUnicode_DATA(str);
+    Py_ssize_t len = PyUnicode_GET_LENGTH(str), i;
+    char_type prev_ch = 0;
+    int prev_width = 0;
+    bool in_sgr = false;
+    unsigned long width_so_far = 0;
+    for (i = 0; i < len && width_so_far < num_cells; i++) {
+        char_type ch = PyUnicode_READ(kind, data, i);
+        if (in_sgr) {
+            if (ch == 'm') in_sgr = false;
+            continue;
+        }
+        if (ch == 0x1b && i + 1 < len && PyUnicode_READ(kind, data, i + 1) == '[') { in_sgr = true; continue; }
+        if (ch == 0xfe0f) {
+            if (is_emoji_presentation_base(prev_ch) && prev_width == 1) {
+                width_so_far += 1;
+                prev_width = 2;
+            } else prev_width = 0;
+        } else {
+            int w = wcwidth_std(ch);
+            switch(w) {
+                case -1:
+                case 0:
+                    prev_width = 0; break;
+                case 2:
+                    prev_width = 2; break;
+                default:
+                    prev_width = 1; break;
+            }
+            if (width_so_far + prev_width > num_cells) { break; }
+            width_so_far += prev_width;
+        }
+        prev_ch = ch;
+
+    }
+    return PyLong_FromUnsignedLong(i);
+}
+
+
 static PyObject*
 line(Screen *self, PyObject *val) {
     unsigned long y = PyLong_AsUnsignedLong(val);
@@ -1987,6 +2033,7 @@ PyTypeObject Screen_Type = {
 static PyMethodDef module_methods[] = {
     {"wcwidth", (PyCFunction)wcwidth_wrap, METH_O, ""},
     {"wcswidth", (PyCFunction)screen_wcswidth, METH_O, ""},
+    {"truncate_point_for_length", (PyCFunction)screen_truncate_point_for_length, METH_VARARGS, ""},
     {NULL}  /* Sentinel */
 };
 

kitty_tests/datatypes.py

@@ -5,7 +5,7 @@
 from kitty.config import build_ansi_color_table, defaults
 from kitty.fast_data_types import (
     REVERSE, ColorProfile, Cursor as C, HistoryBuf, LineBuf,
-    parse_input_from_terminal, wcswidth, wcwidth
+    parse_input_from_terminal, wcswidth, wcwidth, truncate_point_for_length
 )
 from kitty.rgb import to_color
 from kitty.utils import sanitize_title
@@ -338,7 +338,15 @@ class TestDataTypes(BaseTest):
         self.ae(tuple(map(w, 'a1\0コニチ ✔')), (1, 1, 0, 2, 2, 2, 1, 1))
         self.ae(wcswidth('\u2716\u2716\ufe0f\U0001f337'), 5)
         self.ae(wcswidth('\033a\033[2mb'), 2)
+        tpl = truncate_point_for_length
+        self.ae(tpl('abc', 4), 3)
+        self.ae(tpl('abc', 2), 2)
+        self.ae(tpl('abc', 0), 0)
+        self.ae(tpl('a\U0001f337', 2), 1)
+        self.ae(tpl('a\U0001f337', 3), 2)
+        self.ae(tpl('a\U0001f337b', 4), 3)
         self.ae(sanitize_title('a\0\01 \t\n\f\rb'), 'a b')
+        self.ae(tpl('a\x1b[31mbc', 2), 7)
 
         def tp(*data, leftover='', text='', csi='', apc='', ibp=False):
             text_r, csi_r, apc_r, rest = [], [], [], []