From e44cc402792d1e2cac15a10f758f34ad3072c4e3 Mon Sep 17 00:00:00 2001
From: askmeaboutloom <askmeaboutlo0m@users.noreply.github.com>
Date: Fri, 30 Aug 2024 23:04:41 +0200
Subject: [PATCH] Assume soft reset when getting stream state

Because the server always does this before asking us to start a streamed
reset, so we now rely on that assumption to avoid rolling back the local
fork twice.
---
 .../libengine/dpengine/canvas_history.c       | 22 +++++++------------
 .../libengine/dpengine/canvas_history.h       |  4 ++--
 .../libengine/dpengine/paint_engine.c         |  2 +-
 3 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/src/drawdance/libengine/dpengine/canvas_history.c b/src/drawdance/libengine/dpengine/canvas_history.c
index a4983753e1..ecfdd69727 100644
--- a/src/drawdance/libengine/dpengine/canvas_history.c
+++ b/src/drawdance/libengine/dpengine/canvas_history.c
@@ -896,23 +896,17 @@ void DP_canvas_history_soft_reset(DP_CanvasHistory *ch, DP_DrawContext *dc,
     }
 }
 
-DP_CanvasState *DP_canvas_history_stream_start_state_inc(DP_CanvasHistory *ch,
-                                                         DP_DrawContext *dc)
+DP_CanvasState *DP_canvas_history_stream_start_state_inc(DP_CanvasHistory *ch)
 {
     DP_ASSERT(ch);
-    bool have_fork = have_local_fork(ch);
-    if (have_fork) {
-        search_and_replay_from(ch, dc, ch->fork.start - ch->offset, false);
-    }
-
-    DP_CanvasState *cs = DP_canvas_state_incref(ch->current_state);
-
-    if (have_fork) {
-        finish_replay(ch, replay_fork_dec(ch, DP_canvas_state_incref(cs), dc),
-                      dc);
+    int used = ch->used;
+    for (int i = 0; i < used; ++i) {
+        DP_CanvasState *cs = ch->entries->state;
+        if (cs) {
+            return DP_canvas_state_incref(cs);
+        }
     }
-
-    return cs;
+    DP_UNREACHABLE();
 }
 
 int DP_canvas_history_undo_depth_limit(DP_CanvasHistory *ch)
diff --git a/src/drawdance/libengine/dpengine/canvas_history.h b/src/drawdance/libengine/dpengine/canvas_history.h
index 26b70e3a54..261a955571 100644
--- a/src/drawdance/libengine/dpengine/canvas_history.h
+++ b/src/drawdance/libengine/dpengine/canvas_history.h
@@ -113,8 +113,8 @@ void DP_canvas_history_soft_reset(DP_CanvasHistory *ch, DP_DrawContext *dc,
                                   unsigned int context_id,
                                   DP_CanvasHistorySoftResetFn fn, void *user);
 
-DP_CanvasState *DP_canvas_history_stream_start_state_inc(DP_CanvasHistory *ch,
-                                                     DP_DrawContext *dc);
+// This must have had a soft reset right before it to return the correct state.
+DP_CanvasState *DP_canvas_history_stream_start_state_inc(DP_CanvasHistory *ch);
 
 int DP_canvas_history_undo_depth_limit(DP_CanvasHistory *ch);
 
diff --git a/src/drawdance/libengine/dpengine/paint_engine.c b/src/drawdance/libengine/dpengine/paint_engine.c
index 76ff0e39e5..6cabe1da0f 100644
--- a/src/drawdance/libengine/dpengine/paint_engine.c
+++ b/src/drawdance/libengine/dpengine/paint_engine.c
@@ -353,7 +353,7 @@ static void handle_internal(DP_PaintEngine *pe, DP_DrawContext *dc,
                     mi, &correlator_length);
             stream_reset_start_fn(
                 pe->stream_reset.user,
-                DP_canvas_history_stream_start_state_inc(pe->ch, dc),
+                DP_canvas_history_stream_start_state_inc(pe->ch),
                 correlator_length, correlator);
         }
         else {