Fix garbage frame flash on cinematic camera cuts (#720)

* Fix garbage frame flash on cinematic camera cuts

Frame interpolation blended matrices across instant camera teleports in
attract/demo and post-race cameras, flashing 1-2 frames of sheared
geometry. Complete the existing camera-epoch mechanism: flag a cut in
func_80019890 when the camera moves >100 units, and have the
interpolator snap that frame to the new view instead of blending.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Retrigger CI (transient 502 downloading libogg from gitlab.xiph.org)

* Name the cinematic shot dispatcher

Review feedback on #720: func_80019890 -> camera_start_cinematic_shot.
It starts whichever shot D_80164680 has selected for a camera, dispatching
to the per-shot setup that teleports the camera to the shot's opening
position, which is why the cut detection lives there.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Apply fix to freecam

Added FrameInterpolation_DontInterpolateCamera calls to improve camera behavior when changing target players.

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: MegaMech <MegaMech@users.noreply.github.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/port/interpolation/FrameInterpolation.cpp b/src/port/interpolation/FrameInterpolation.cpp
index 981ef3fa6..51d411c95 100644
--- a/src/port/interpolation/FrameInterpolation.cpp
+++ b/src/port/interpolation/FrameInterpolation.cpp
@@ -253,6 +253,7 @@ bool is_recording;
 vector<Path*> current_path;
 uint32_t camera_epoch;
 uint32_t previous_camera_epoch;
+bool frame_had_camera_cut;
 Recording current_recording;
 Recording previous_recording;
 
@@ -599,8 +600,10 @@ struct InterpolateCtx {
 
 unordered_map<Mtx*, MtxF> FrameInterpolation_Interpolate(float step) {
     InterpolateCtx ctx;
-    ctx.step = step;
-    ctx.w = 1.0f - step;
+    // On a camera cut, blending the two frames would mix unrelated views;
+    // snap every sub-frame to the new frame instead (hard cut, like hardware).
+    ctx.step = frame_had_camera_cut ? 1.0f : step;
+    ctx.w = 1.0f - ctx.step;
     ctx.interpolate_branch(&previous_recording.root_path, &current_recording.root_path);
     return ctx.mtx_replacements;
 }
@@ -633,6 +636,7 @@ void FrameInterpolation_StartRecord(void) {
 }
 
 void FrameInterpolation_StopRecord(void) {
+    frame_had_camera_cut = camera_epoch != previous_camera_epoch;
     previous_camera_epoch = camera_epoch;
     is_recording = false;
 }