zandronum interpolation patch

diff -r 0f0c92215f57 src/sdl/i_system.cpp
--- a/src/sdl/i_system.cpp  Sat Jan 01 12:49:07 2022 -0800
+++ b/src/sdl/i_system.cpp  Sat Jan 01 14:44:05 2022 -0800
@@ -142,14 +142,13 @@


 static DWORD TicStart;
-static DWORD TicNext;
 static DWORD BaseTime;
 static int TicFrozen;

 // Signal based timer.
 static Semaphore timerWait;
 static int tics;
-static DWORD sig_start, sig_next;
+static DWORD sig_start;

 void I_SelectTimer();

@@ -187,14 +186,7 @@

    if (saveMS)
    {
-       // [Leo] Replaced the expressions for TicStart and TicNext below.
-       /*
        TicStart = tm;
-       TicNext = Scale((Scale (tm, TICRATE, 1000) + 1), 1000, TICRATE);
-       */
-       DWORD CurrentTic = ((tm - BaseTime) * TICRATE) / 1000;
-       TicStart = (CurrentTic * 1000 / TICRATE) + BaseTime;
-       TicNext = ((CurrentTic + 1) * 1000 / TICRATE) + BaseTime;
    }
    return Scale(tm - BaseTime, TICRATE, 1000);
 }
@@ -204,7 +196,6 @@
    if (saveMS)
    {
        TicStart = sig_start;
-       TicNext = sig_next;
    }
    return tics;
 }
@@ -275,7 +266,6 @@
    if(!TicFrozen)
        tics++;
    sig_start = SDL_GetTicks();
-   sig_next = Scale((Scale (sig_start, TICRATE, 1000) + 1), 1000, TICRATE);
    SEMAPHORE_SIGNAL(timerWait)
 }

@@ -318,15 +308,14 @@
 fixed_t I_GetTimeFrac (uint32 *ms)
 {
    DWORD now = SDL_GetTicks ();
-   if (ms) *ms = TicNext;
-   DWORD step = TicNext - TicStart;
-   if (step == 0)
+   if (ms) *ms = TicStart + (1000 / TICRATE);
+   if (TicStart == 0)
    {
        return FRACUNIT;
    }
    else
    {
-       fixed_t frac = clamp<fixed_t> ((now - TicStart)*FRACUNIT/step, 0, FRACUNIT);
+       fixed_t frac = clamp<fixed_t> ((now - TicStart)*FRACUNIT*TICRATE/1000, 0, FRACUNIT);
        return frac;
    }
 }