loop: crossfade the Gate sustain seam, and unshadow the loop handles that made loop points look gone

src/shell/instrument/editor_session.cpp

@@ -17,6 +17,7 @@
 #include "core/ui/bank_grid.h"           // ThumbnailKey / thumbnailKeyString (the pure key)
 #include "core/util/file_bytes.h"        // shared whole-file loader
 #include "ext_keys.h"
+#include "core/instrument/engine/loop/loop_span.h"  // defaultLoopBounds (the shared ghost span)
 #include "core/instrument/ui/browser_scroll.h"  // nameMatchesQuery (type-to-filter)
 #include "shell/instrument/reaper_bridge.h"
 #include "shell/instrument/reasampler_processor.h"
@@ -31,6 +32,8 @@ using capture::WavLayout;
 using capture::extractFloatFrames;
 using capture::parseWavLayout;
 using capture::resolveBankFile;
+using instrument::engine::loop::LoopBounds;
+using instrument::engine::loop::defaultLoopBounds;
 using instrument::ui::nameMatchesQuery;
 using ui::ThumbnailKey;
 using ui::thumbnailKeyString;
@@ -160,10 +163,12 @@ void ReaSamplerEditor::loadSelection(const std::string& id) {
     // loaded, so a load swaps the sound and keeps the settings. The three CAPTURE-ANCHORED
     // overrides are: a root, a loop span and a start frame all name positions in the
     // OUTGOING capture and mean nothing in the new one, so they clear and the new capture
-    // plays from its own bank intrinsics.
+    // plays from its own bank intrinsics. The loop crossfade goes with the span it belongs
+    // to — it is a length in the outgoing capture's frames.
     selectedId_ = id;
     params_.rootOverride.reset();
     params_.loopOverride.reset();
+    params_.loopCrossfadeFrames = 0;
     params_.startPoint.reset();
     commitAndReload();
 }
@@ -196,10 +201,17 @@ ReaSamplerEditor::SetupMarkers ReaSamplerEditor::pickedMarkers(std::int64_t fram
         m.loopEnd = params_.loopOverride->end;
     }
     if (params_.startPoint) m.start = *params_.startPoint;
-    // Default an unset loop's end to the sample length so the loop markers have somewhere sane
-    // to sit before the user drags (loopStart stays 0). The "no loop" state is m.hasLoop==false;
-    // the markers are still drawn (drag one to CREATE a loop).
-    if (!m.hasLoop && m.loopEnd == 0) m.loopEnd = frames > 0 ? frames : 0;
+    m.crossfade = params_.loopCrossfadeFrames;
+    // A collapsed or inverted span is the OFF state (the engine refuses it either way), so
+    // park the handles on the shared default rather than leaving them stacked on each other
+    // where neither could be grabbed apart again. The markers are still drawn at 'no loop'
+    // weight — drag one to CREATE a loop.
+    if (!m.hasLoop || m.loopEnd <= m.loopStart) {
+        m.hasLoop = false;
+        const LoopBounds d = defaultLoopBounds(frames);
+        m.loopStart = d.start;
+        m.loopEnd = d.end;
+    }
     return m;
 }
 
@@ -207,10 +219,13 @@ void ReaSamplerEditor::applyMarkers(const SetupMarkers& m) {
     // Write the edited markers into the parameter set as the loop/start override. The bank
     // intrinsic is never written (read-only bank consumer).
     SampleLoop loop;
-    loop.hasLoop = m.hasLoop;
+    // Collapsing the span onto itself is the OFF gesture — record it as such so the next
+    // pickedMarkers re-offers the default handles instead of two coincident ones.
+    loop.hasLoop = m.hasLoop && m.loopEnd > m.loopStart;
     loop.start = m.loopStart;
     loop.end = m.loopEnd;
     params_.loopOverride = loop;
+    params_.loopCrossfadeFrames = m.crossfade;
     params_.startPoint = m.start;
 }