perf(core): enable rendering of substrings to avoid slicing

core/embed/extmod/modtrezorui/display.c

@@ -594,7 +594,7 @@ static uint8_t convert_char(const uint8_t c) {
     return c;
   }
 
-  // UTF-8 handling: https://en.wikipedia.org/wiki/UTF-8#Description
+  // UTF-8 handling: https://en.wikipedia.org/wiki/UTF-8#Encoding
 
   // bytes 11xxxxxx are first bytes of UTF-8 characters
   if (c >= 0xC0) {
@@ -867,3 +867,38 @@ void display_fade(int start, int end, int delay) {
   }
   display_backlight(end);
 }
+
+#define UTF8_IS_CONT(ch) (((ch)&0xC0) == 0x80)
+
+void display_utf8_substr(const char *buf_start, size_t buf_len, int char_off,
+                         int char_len, const char **out_start, int *out_len) {
+  size_t i = 0;
+
+  for (; i < buf_len; i++) {
+    if (char_off == 0) {
+      break;
+    }
+    if (!UTF8_IS_CONT(buf_start[i])) {
+      char_off--;
+    }
+  }
+  size_t i_start = i;
+
+  for (; i < buf_len; i++) {
+    if (char_len == 0) {
+      break;
+    }
+    if (!UTF8_IS_CONT(buf_start[i])) {
+      char_len--;
+    }
+  }
+
+  for (; i < buf_len; i++) {
+    if (!UTF8_IS_CONT(buf_start[i])) {
+      break;
+    }
+  }
+
+  *out_start = buf_start + i_start;
+  *out_len = i - i_start;
+}

core/embed/extmod/modtrezorui/display.h

@@ -113,4 +113,8 @@ int display_orientation(int degrees);
 int display_backlight(int val);
 void display_fade(int start, int end, int delay);
 
+// helper for locating a substring in buffer with utf-8 string
+void display_utf8_substr(const char *buf_start, size_t buf_len, int char_off,
+                         int char_len, const char **out_start, int *out_len);
+
 #endif

core/embed/extmod/modtrezorui/modtrezorui-display.h

@@ -317,11 +317,16 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorui_Display_print_obj,
 ///     font: int,
 ///     fgcolor: int,
 ///     bgcolor: int,
+///     text_offset: int = None,
+///     text_len: int = None,
 /// ) -> None:
 ///     """
 ///     Renders left-aligned text at position (x,y) where x is left position and
 ///     y is baseline. Font font is used for rendering, fgcolor is used as
 ///     foreground color, bgcolor as background.
+///
+///     Arguments text_offset and text_len can be used to render a substring of
+///     the text.
 ///     """
 STATIC mp_obj_t mod_trezorui_Display_text(size_t n_args, const mp_obj_t *args) {
   mp_int_t x = mp_obj_get_int(args[1]);
@@ -331,10 +336,25 @@ STATIC mp_obj_t mod_trezorui_Display_text(size_t n_args, const mp_obj_t *args) {
   mp_int_t font = mp_obj_get_int(args[4]);
   mp_int_t fgcolor = mp_obj_get_int(args[5]);
   mp_int_t bgcolor = mp_obj_get_int(args[6]);
-  display_text(x, y, text.buf, text.len, font, fgcolor, bgcolor);
+
+  const char *buf_start = text.buf;
+  int buf_len = text.len;
+  if (n_args > 7) {
+    mp_int_t off = mp_obj_get_int(args[7]);
+    mp_int_t len = n_args > 8 ? mp_obj_get_int(args[8]) : text.len - off;
+    if (off < 0 || off > text.len) {
+      mp_raise_ValueError("Invalid text_offset");
+    }
+    if (len < 0 || len + off > text.len) {
+      mp_raise_ValueError("Invalid text_len");
+    }
+    display_utf8_substr(text.buf, text.len, off, len, &buf_start, &buf_len);
+  }
+
+  display_text(x, y, buf_start, buf_len, font, fgcolor, bgcolor);
   return mp_const_none;
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorui_Display_text_obj, 7, 7,
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorui_Display_text_obj, 7, 9,
                                            mod_trezorui_Display_text);
 
 /// def text_center(
@@ -397,19 +417,44 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorui_Display_text_right_obj,
                                            7, 7,
                                            mod_trezorui_Display_text_right);
 
-/// def text_width(self, text: str, font: int) -> int:
+/// def text_width(
+///     self,
+///     text: str,
+///     font: int,
+///     text_offset: int = None,
+///     text_len: int = None,
+/// ) -> int:
 ///     """
 ///     Returns a width of text in pixels. Font font is used for rendering.
+///
+///     Arguments text_offset and text_len can be used to render a substring of
+///     the text.
 ///     """
-STATIC mp_obj_t mod_trezorui_Display_text_width(mp_obj_t self, mp_obj_t text,
+STATIC mp_obj_t mod_trezorui_Display_text_width(size_t n_args,
-                                                mp_obj_t font) {
+                                                const mp_obj_t *args) {
   mp_buffer_info_t txt = {0};
-  mp_get_buffer_raise(text, &txt, MP_BUFFER_READ);
+  mp_get_buffer_raise(args[1], &txt, MP_BUFFER_READ);
-  mp_int_t f = mp_obj_get_int(font);
+  mp_int_t f = mp_obj_get_int(args[2]);
-  int w = display_text_width(txt.buf, txt.len, f);
+
+  const char *buf_start = txt.buf;
+  int buf_len = txt.len;
+  if (n_args > 3) {
+    mp_int_t off = mp_obj_get_int(args[3]);
+    mp_int_t len = n_args > 4 ? mp_obj_get_int(args[4]) : txt.len - off;
+    if (off < 0 || off > txt.len) {
+      mp_raise_ValueError("Invalid text_offset");
+    }
+    if (len < 0 || len + off > txt.len) {
+      mp_raise_ValueError("Invalid text_len");
+    }
+    display_utf8_substr(txt.buf, txt.len, off, len, &buf_start, &buf_len);
+  }
+
+  int w = display_text_width(buf_start, buf_len, f);
   return mp_obj_new_int(w);
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_3(mod_trezorui_Display_text_width_obj,
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorui_Display_text_width_obj,
+                                           3, 5,
                                            mod_trezorui_Display_text_width);
 
 /// def text_split(self, text: str, font: int, requested_width: int) -> int:

core/mocks/generated/trezorui.pyi

@@ -114,11 +114,15 @@ class Display:
         font: int,
         fgcolor: int,
         bgcolor: int,
+        text_offset: int = None,
+        text_len: int = None,
     ) -> None:
         """
         Renders left-aligned text at position (x,y) where x is left position and
         y is baseline. Font font is used for rendering, fgcolor is used as
         foreground color, bgcolor as background.
+        Arguments text_offset and text_len can be used to render a substring of
+        the text.
         """
 
     def text_center(
@@ -151,9 +155,17 @@ class Display:
         foreground color, bgcolor as background.
         """
 
-    def text_width(self, text: str, font: int) -> int:
+    def text_width(
+        self,
+        text: str,
+        font: int,
+        text_offset: int = None,
+        text_len: int = None,
+    ) -> int:
         """
         Returns a width of text in pixels. Font font is used for rendering.
+        Arguments text_offset and text_len can be used to render a substring of
+        the text.
         """
 
     def text_split(self, text: str, font: int, requested_width: int) -> int:

core/tests/test_trezor.ui.display.py

@@ -25,6 +25,17 @@ class TestDisplay(unittest.TestCase):
 
     def test_text(self):
         display.text(120, 120, 'Test', 0, 0xFFFF, 0x0000)
+        display.text(120, 120, 'Test', 0, 0xFFFF, 0x0000, 2)
+        display.text(120, 120, 'Test', 0, 0xFFFF, 0x0000, 2, 1)
+        display.text(120, 120, 'Těst', 0, 0xFFFF, 0x0000, 2, 2)
+
+        display.text(120, 120, "ǑǑǑǑǑǑǑǑ", 0, 0xFFFF, 0x0000)
+        for off in (0, 2, 3, 8, 16):
+            display.text(120, 120, "ǑǑǑǑǑǑǑǑ", 0, 0xFFFF, 0x0000, off)
+            display.text(120, 120, "ǑǑǑǑǑǑǑǑ", 0, 0xFFFF, 0x0000, off, 0)
+
+        for off, tlen in ((2, 5), (2, 14), (3, 5), (3, 13), (8, 1), (8, 8)):
+            display.text(120, 120, "ǑǑǑǑǑǑǑǑ", 0, 0xFFFF, 0x0000, off, tlen)
 
     def test_text_center(self):
         display.text_center(120, 120, 'Test', 0, 0xFFFF, 0x0000)
@@ -34,6 +45,24 @@ class TestDisplay(unittest.TestCase):
 
     def test_text_width(self):
         display.text_width('Test', 0)
+        display.text_width('Test', 0, 2)
+        display.text_width('Test', 0, 2, 1)
+        display.text_width('Těst', 0, 2, 2)
+
+        display.text_width("ǑǑǑǑǑǑǑǑ", 0)
+        for off in (0, 2, 3, 8, 16):
+            display.text_width("ǑǑǑǑǑǑǑǑ", 0, off)
+            self.assertEqual(display.text_width("ǑǑǑǑǑǑǑǑ", 0, off, 0), 0)
+
+        for off, tlen in ((0, 8), (0, 16), (2, 5), (2, 14), (3, 5), (3, 13)):
+            display.text_width("ǑǑǑǑǑǑǑǑ", 0, off, tlen)
+
+        self.assertEqual(display.text_width("ǑǑǑǑǑǑǑǑ", 8), 0)
+        self.assertEqual(display.text_width("ǑǑǑǑǑǑǑǑ", 8, 1), 0)
+        self.assertEqual(display.text_width("ǑǑǑǑǑǑǑǑ", 8, 8), 0)
+        self.assertEqual(display.text_width("ǑǑǑǑǑǑǑǑ", 9), 0)
+        self.assertEqual(display.text_width("ǑǑǑǑǑǑǑǑ", 9, 1), 0)
+        self.assertEqual(display.text_width("ǑǑǑǑǑǑǑǑ", 15, 1), 0)
 
     def test_qrcode(self):
         display.qrcode(0, 0, 'Test', 4)