Reach FPS closer to max_fps on Windows (#109)

Author: almarklein

rendercanvas/_loop.py

@@ -372,7 +372,7 @@ def _rc_call_later(self, delay, callback):
         This method is optional. A subclass must either implement ``_rc_add_task`` or ``_rc_call_later``.
 
         * If you implememt this, make ``_rc_add_task()`` call ``super()._rc_add_task()``.
-        * If delay is zero, this should behave like "call_later".
+        * If delay is zero, this should behave like "call_soon".
         * No need to catch errors from the callback; that's dealt with internally.
         * Return None.
         """

rendercanvas/_scheduler.py

@@ -2,13 +2,17 @@
 The scheduler class/loop.
 """
 
+import sys
 import time
 import weakref
 
 from ._coreutils import BaseEnum
 from .utils.asyncs import sleep, Event
 
 
+IS_WIN = sys.platform.startswith("win")
+
+
 class UpdateMode(BaseEnum):
     """The UpdateMode enum specifies the different modes to schedule draws for the canvas."""
 
@@ -123,14 +127,23 @@ async def __scheduler_task(self):
                 delay = 1 / self._max_fps
                 delay = 0 if delay < 0 else delay  # 0 means cannot keep up
 
-            # Offset delay for time spent on processing events, etc.
-            time_since_tick_start = time.perf_counter() - last_tick_time
-            delay -= time_since_tick_start
-            delay = max(0, delay)
-
-            # Wait. Even if delay is zero, it gives control back to the loop,
-            # allowing other tasks to do work.
-            await sleep(delay)
+            # Determine amount of sleep
+            sleep_time = delay - (time.perf_counter() - last_tick_time)
+
+            if IS_WIN:
+                # On Windows OS-level timers have an in accuracy of 15.6 ms.
+                # This can cause sleep to take longer than intended. So we sleep
+                # less, and then do a few small sync-sleeps that have high accuracy.
+                await sleep(max(0, sleep_time - 0.0156))
+                sleep_time = delay - (time.perf_counter() - last_tick_time)
+                while sleep_time > 0:
+                    time.sleep(min(sleep_time, 0.001))  # sleep hard for at most 1ms
+                    await sleep(0)  # Allow other tasks to run but don't wait
+                    sleep_time = delay - (time.perf_counter() - last_tick_time)
+            else:
+                # Wait. Even if delay is zero, it gives control back to the loop,
+                # allowing other tasks to do work.
+                await sleep(max(0, sleep_time))
 
             # Below is the "tick"
 

rendercanvas/qt.py

@@ -31,7 +31,6 @@
         WA_PaintOnScreen = QtCore.Qt.WidgetAttribute.WA_PaintOnScreen
         WA_DeleteOnClose = QtCore.Qt.WidgetAttribute.WA_DeleteOnClose
         WA_InputMethodEnabled = QtCore.Qt.WidgetAttribute.WA_InputMethodEnabled
-        PreciseTimer = QtCore.Qt.TimerType.PreciseTimer
         KeyboardModifiers = QtCore.Qt.KeyboardModifier
         FocusPolicy = QtCore.Qt.FocusPolicy
         CursorShape = QtCore.Qt.CursorShape
@@ -42,7 +41,6 @@
         WA_PaintOnScreen = QtCore.Qt.WA_PaintOnScreen
         WA_DeleteOnClose = QtCore.Qt.WA_DeleteOnClose
         WA_InputMethodEnabled = QtCore.Qt.WA_InputMethodEnabled
-        PreciseTimer = QtCore.Qt.PreciseTimer
         KeyboardModifiers = QtCore.Qt
         FocusPolicy = QtCore.Qt
         CursorShape = QtCore.Qt

rendercanvas/raw.py

@@ -60,6 +60,7 @@ def _rc_run(self):
                 break
             else:
                 # Wait until its time for it to be called
+                # Note that on Windows, the accuracy of the timeout is 15.6 ms
                 wait_time = wrapper.time - time.perf_counter()
                 self._event.wait(max(wait_time, 0))