feat: add alternative get_cell_size() method

textual_image/_terminal.py

@@ -4,6 +4,8 @@
 import os
 import sys
 from contextlib import contextmanager
+from re import search
+from shutil import get_terminal_size
 from types import SimpleNamespace
 from typing import Iterator, NamedTuple, cast
 
@@ -19,6 +21,10 @@
 logger = logging.getLogger(__name__)
 
 
+# VT340 sizes
+FALLBACK_SIZE = (10, 20)
+
+
 class TerminalError(Exception):
     """Error thrown on failing terminal operations."""
 
@@ -35,7 +41,7 @@ class CellSize(NamedTuple):
 
 
 def get_cell_size() -> CellSize:
-    """Get size information from the terminal.
+    """Get the terminal's character cell size in pixels.
 
     This function is querying the terminal only once. For any call after the first, a cached result is returned.
 
@@ -49,46 +55,59 @@ def get_cell_size() -> CellSize:
     if hasattr(get_cell_size, "_result"):
         return cast("CellSize", getattr(get_cell_size, "_result"))
 
-    width = 0
-    height = 0
+    size = None
 
     if sys.__stdout__.isatty():
         # Try to get the cell size via ioctl
         try:
             rows, columns, screen_width, screen_height = get_tiocgwinsz()
             width = int(screen_width / columns)
             height = int(screen_height / rows)
+
+            if width and height:
+                size = (width, height)
         except OSError as e:
             logger.debug("Failed to get cell size via ioctl, falling back to escape sequence", exc_info=e)
 
-    if sys.__stdout__.isatty() and (height == 0 or width == 0):
         # Didn't work, let's try to do it via escape sequence
-        try:
-            with capture_terminal_response("\x1b[", "t", 0.1) as response:
-                sys.__stdout__.write("\x1b[16t")
-                sys.__stdout__.flush()
+        if not size:
+            # CSI 16 t: report character cell size in pixels.
+            # Response: ESC [ 6 ; height ; width t
+            response = query_tty("\x1b[16t")
+
+            if response and (found := search(r"\x1b\[6;(\d+);(\d+)t", response)):
+                height, width = map(int, found.groups())
+                size = (width, height)
 
-            sequence = response.sequence[len("\x1b[") : -len("t")]
-            _, height, width = [int(v) for v in sequence.split(";")]
-        except (TerminalError, TimeoutError) as e:
-            logger.warning("Failed to get cell size via escape sequence, assuming VT340 sizes", exc_info=e)
+        # Didn't work, try an alternate escape code sequence
+        if not size:
+            # CSI 14 t: report terminal dimensions in pixels
+            # Response: ESC [ 4 ; pixel_height ; pixel_width t
+            response = query_tty("\x1b[14t")
 
-    if height == 0 or width == 0:
-        # Try environment variables (set by textual-serve for web terminals)
+            if response and (found := search(r"\x1b\[4;(\d+);(\d+)t", response)):
+                height, width = map(int, found.groups())
+
+                # Note: this can also be done via
+                # CSI 18 t response: ESC [ 8 ; rows ; columns t
+                # query_tty("\x1b[18t")
+                columns, rows = get_terminal_size()
+
+                size = (round(width / columns), round(height / rows))
+
+    # Try environment variables (set by textual-serve for web terminals)
+    if not size:
         match os.environ:
             case {
                 "TEXTUAL_CELL_WIDTH": str(width_str),
                 "TEXTUAL_CELL_HEIGHT": str(height_str),
             } if width_str.isdigit() and height_str.isdigit():
-                width = int(width_str)
-                height = int(height_str)
+                size = (int(width_str), int(height_str))
 
-    if height == 0 or width == 0:
-        # Still didn't work, use VT340 sizes as default
-        width = 10
-        height = 20
+    if not size:
+        size = FALLBACK_SIZE
 
-    cell_size = CellSize(width, height)
+    cell_size = CellSize(*size)
     setattr(get_cell_size, "_result", cell_size)
     return cell_size
 
@@ -133,5 +152,16 @@ def capture_terminal_response(
                 raise TerminalError("Unexpected response from terminal")
 
 
+def query_tty(query: str, timeout: float = 0.1) -> str | None:
+    """Query the terminal using an escape code."""
+    try:
+        with capture_terminal_response("\x1b[", "t", timeout) as response:
+            sys.__stdout__.write(query)
+            sys.__stdout__.flush()
+        return response.sequence
+    except (TimeoutError, TerminalError):
+        ...
+
+
 def prepare_terminal_sequence(data: str) -> str:
     return maybe_tmux_escape(data)