From fcd57801bd1b6fcdd8dc0c5317cb4074e8f82e3d Mon Sep 17 00:00:00 2001
From: Gregor Richards <hg-yff@gregor.im>
Date: Sat, 24 Sep 2016 08:12:08 -0400
Subject: [PATCH] When we replay, resimulate input so that it doesn't judder
 between remote states

---
 network/netplay/netplay.c         | 16 ++++++++++------
 network/netplay/netplay_net.c     |  7 ++++++-
 network/netplay/netplay_private.h |  2 ++
 3 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/network/netplay/netplay.c b/network/netplay/netplay.c
index db9c03083e..3b0cd659c5 100644
--- a/network/netplay/netplay.c
+++ b/network/netplay/netplay.c
@@ -554,13 +554,17 @@ static int poll_input(netplay_t *netplay, bool block)
    return 0;
 }
 
-/* TODO: Somewhat better prediction. :P */
-static void simulate_input(netplay_t *netplay)
+/**
+ * netplay_simulate_input:
+ * @netplay             : pointer to netplay object
+ * @sim_ptr             : frame index for which to simulate input
+ *
+ * "Simulate" input by assuming it hasn't changed since the last read input.
+ */
+void netplay_simulate_input(netplay_t *netplay, uint32_t sim_ptr)
 {
-   size_t ptr  = netplay->self_ptr;
    size_t prev = PREV_PTR(netplay->read_ptr);
-
-   memcpy(netplay->buffer[ptr].simulated_input_state,
+   memcpy(netplay->buffer[sim_ptr].simulated_input_state,
          netplay->buffer[prev].real_input_state,
          sizeof(netplay->buffer[prev].real_input_state));
 }
@@ -603,7 +607,7 @@ static bool netplay_poll(netplay_t *netplay)
 
    /* Simulate the input if we don't have real input */
    if (!netplay->buffer[netplay->self_ptr].have_remote)
-      simulate_input(netplay);
+      netplay_simulate_input(netplay, netplay->self_ptr);
 
    /* Consider stalling */
    switch (netplay->stall) {
diff --git a/network/netplay/netplay_net.c b/network/netplay/netplay_net.c
index e31f52beb0..4138ca80c9 100644
--- a/network/netplay/netplay_net.c
+++ b/network/netplay/netplay_net.c
@@ -214,9 +214,14 @@ static void netplay_net_post_frame(netplay_t *netplay)
          serial_info.size       = netplay->state_size;
          serial_info.data_const = NULL;
 
+         /* Remember the current state */
          core_serialize(&serial_info);
+         if (netplay->replay_frame_count < netplay->read_frame_count)
+            netplay_handle_frame_hash(netplay, ptr);
 
-         netplay_handle_frame_hash(netplay, ptr);
+         /* Simulate this frame's input */
+         if (netplay->replay_frame_count >= netplay->read_frame_count)
+            netplay_simulate_input(netplay, netplay->replay_ptr);
 
 #if defined(HAVE_THREADS)
          autosave_lock();
diff --git a/network/netplay/netplay_private.h b/network/netplay/netplay_private.h
index 520cf94d55..e792d94788 100644
--- a/network/netplay/netplay_private.h
+++ b/network/netplay/netplay_private.h
@@ -177,6 +177,8 @@ struct netplay_callbacks* netplay_get_cbs_net(void);
 
 struct netplay_callbacks* netplay_get_cbs_spectate(void);
 
+void netplay_simulate_input(netplay_t *netplay, uint32_t sim_ptr);
+
 void   netplay_log_connection(const struct sockaddr_storage *their_addr,
       unsigned slot, const char *nick);