[WIP] Introduce fast mouse polling for lower lag interpolation

[mikeday0]

This is my humble attempt to port to Crispy the fine work that @ceski-1 did for Woof. It's not ready yet but I thought it might be prudent to go ahead and get it out there for early review and testing.

[ceski-1]

Nice starting point, I tested it briefly. Some issues I noticed:

• Mouselook and mousevert feel off (compare capped and uncapped).
• Combining keyboard turning and mouse turning at the same time has visual glitches (occasional "pops").
• The "mouse threshold" concept in Chocolate/Crispy/Woof assumes each update is a tic in duration (1/35th of a second). So it doesn't work correctly with fast polling and the mouse will feel "slow" at higher fps. I sidestep the issue in Woof by ignoring threshold under certain conditions.
• If you follow the mouse input calculations from start to finish, you'll notice that Crispy has rounding error in several stages. First there's AccelerateMouse() in I_ReadMouse(), then there's *(mouseSensitivity+5)/10 in G_Responder() or G_FastResponder(). By the time the error accumulator runs ("carrying" the error), it's too late and ineffective. I prevent this in Woof by doing the calculations as a single step and using doubles as working variables (see CalcMouseAngle() for example). The rounding only occurs once, in the carry function.

I'll try to give more feedback later, I know it's WIP right now.

[mikeday0]

• Combining keyboard turning and mouse turning at the same time has visual glitches (occasional "pops").

I can repeat this. It appears to be fixed on my end by moving the fractionaltic update back to the end of I_FinishUpdate().

Diff

diff --git a/src/i_video.c b/src/i_video.c
index ab3c7bc9..b5f9f6f1 100644
--- a/src/i_video.c
+++ b/src/i_video.c
@@ -544,9 +544,6 @@ void I_StartDisplay(void) // [crispy]
 {
     SDL_PumpEvents();
 
-    // [AM] Figure out how far into the current tic we're in as a fixed_t.
-    fractionaltic = I_GetFracRealTime();
-
     if (usemouse && !nomouse && window_focused)
     {
         I_ReadMouseUncapped();
@@ -941,6 +938,9 @@ void I_FinishUpdate (void)
                 }
             }
         }
+        // [AM] Figure out how far into the current tic we're in as a fixed_t.
+        fractionaltic = I_GetFracRealTime();
+
     }
 
     // Restore background and undo the disk indicator, if it was drawn.

Does this fix the "pops" for you?

[ceski-1]

Does this fix the "pops" for you?

That seems to work fine, or like Woof:

Diff (Alt)

diff --git a/src/i_video.c b/src/i_video.c
index ab3c7bc9..328e6b1e 100644
--- a/src/i_video.c
+++ b/src/i_video.c
@@ -542,11 +542,11 @@ void I_StartTic (void)
 
 void I_StartDisplay(void) // [crispy]
 {
-    SDL_PumpEvents();
-
     // [AM] Figure out how far into the current tic we're in as a fixed_t.
     fractionaltic = I_GetFracRealTime();
 
+    SDL_PumpEvents();
+
     if (usemouse && !nomouse && window_focused)
     {
         I_ReadMouseUncapped();