Add a minimum value for TEXTUAL_FPS (_get_environ_int was extended with new functionality) and set the FPS to 60 if you set the environment value to 0.

src/textual/constants.py

@@ -27,20 +27,29 @@ def _get_environ_bool(name: str) -> bool:
     return has_environ
 
 
-def _get_environ_int(name: str, default: int) -> int:
+def _get_environ_int(name: str, default: int, *, min_value: Optional[int] = None, max_value: Optional[int] = None) -> int:
     """Retrieves an integer environment variable.
 
     Args:
         name: Name of environment variable.
         default: The value to use if the value is not set, or set to something other
             than a valid integer.
 
+    Keyword args:
+        min_value (optional): The minimum value that should be returned by this function.
+        max_value (optional): The maximum value that should be returned by this function.
+
     Returns:
         The integer associated with the environment variable if it's set to a valid int
             or the default value otherwise.
     """
     try:
-        return int(os.environ[name])
+        value = int(os.environ[name])
+        if min_value is not None and value < min_value:
+            return min_value
+        if max_value is not None and value > max_value:
+            return max_value
+        return value
     except KeyError:
         return default
     except ValueError:
@@ -107,9 +116,15 @@ def _get_textual_animations() -> AnimationLevel:
 SHOW_RETURN: Final[bool] = _get_environ_bool("TEXTUAL_SHOW_RETURN")
 """Write the return value on exit."""
 
-MAX_FPS: Final[int] = _get_environ_int("TEXTUAL_FPS", 60)
+MAX_FPS_DEFAULT: Final[int] = 60
+"""The default value for MAX_FPS."""
+
+MAX_FPS: Final[int] = _get_environ_int("TEXTUAL_FPS", MAX_FPS_DEFAULT, min_value=0)
 """Maximum frames per second for updates."""
 
+if MAX_FPS == 0:
+    MAX_FPS = MAX_FPS_DEFAULT
+
 COLOR_SYSTEM: Final[str | None] = get_environ("TEXTUAL_COLOR_SYSTEM", "auto")
 """Force color system override."""