Render in place: a track's output to a new sibling, source to the bench

src/core/capture/capture_name.cpp

@@ -86,4 +86,17 @@ CaptureName composeCaptureName(const CaptureNameInputs& in) {
     return out;
 }
 
+std::string captureTrackName(const std::string& sourceName) {
+    const std::string prefix(kCaptureTrackPrefix);
+    // A source with no readable name yields the bare word rather than a trailing
+    // space; both spellings are fixed points, which is what makes the whole function
+    // one (a track named exactly "Capture" must not become "Capture Capture").
+    const std::string bare = prefix.substr(0, prefix.size() - 1);
+
+    if (sourceName.empty()) return bare;
+    if (sourceName == bare) return sourceName;
+    if (sourceName.rfind(prefix, 0) == 0) return sourceName;
+    return prefix + sourceName;
+}
+
 } // namespace reasampler::capture

src/core/capture/capture_name.h

@@ -59,4 +59,16 @@ std::string formatCaptureStamp(const CaptureStamp& stamp);
 
 CaptureName composeCaptureName(const CaptureNameInputs& in);
 
+// Prefixed onto a source track's name to name the track a render-in-place created.
+// A display convention, not a persisted key — unlike a lane prefix or an action-id
+// suffix, changing it later strands nothing.
+inline constexpr const char* kCaptureTrackPrefix = "Capture ";
+
+// The new track's name for a render of `sourceName`. IDEMPOTENT — a fixed point on
+// its own output, so a second render over a result track yields "Capture MONEY"
+// again rather than "Capture Capture MONEY". A counter suffix is deliberately not
+// offered: REAPER does not uniquify track names either, and what distinguishes two
+// renders of one source is their position, not their name.
+std::string captureTrackName(const std::string& sourceName);
+
 } // namespace reasampler::capture

src/core/capture/capture_paths.cpp

@@ -45,16 +45,25 @@ std::string sanitizeStem(const std::string& baseName) {
     return out;
 }
 
-BankPaths deriveBankPaths(const std::string& projectDir,
-                          const std::string& baseName,
-                          const std::string& uniqueTag) {
-    const std::string dir = normalizeSlashes(projectDir);
-
+RenderPaths deriveRenderPaths(const std::string& absoluteDir,
+                              const std::string& baseName,
+                              const std::string& uniqueTag) {
     std::string stem = sanitizeStem(baseName);
     if (!uniqueTag.empty()) {
         stem += "_" + sanitizeStem(uniqueTag);
     }
-    const std::string fileName = stem + ".wav";
+
+    RenderPaths r;
+    r.fileStem    = stem;              // stem only — REAPER appends the extension
+    r.fileName    = stem + ".wav";
+    r.absoluteDir = normalizeSlashes(absoluteDir);
+    return r;
+}
+
+BankPaths deriveBankPaths(const std::string& projectDir,
+                          const std::string& baseName,
+                          const std::string& uniqueTag) {
+    const std::string dir = normalizeSlashes(projectDir);
 
     // Precondition: caller must resolve a non-empty project directory — an
     // empty one would otherwise fall back to a bare relative path (forbidden).
@@ -62,18 +71,19 @@ BankPaths deriveBankPaths(const std::string& projectDir,
     // ignores it fails at the render/stat step, not silently onto CWD.
     assert(!dir.empty() && "deriveBankPaths: projectDir must not be empty");
 
+    const RenderPaths r = deriveRenderPaths(
+        dir.empty() ? std::string{} : dir + "/" + kBankSubfolder, baseName, uniqueTag);
+
     BankPaths p;
-    p.fileStem     = stem;                                    // stem only — REAPER appends extension
-    p.fileName     = fileName;
-    p.relativePath = std::string(kBankSubfolder) + "/" + fileName;
-    p.absoluteDir  = dir.empty() ? std::string{}
-                                 : dir + "/" + kBankSubfolder;
+    p.fileStem     = r.fileStem;
+    p.fileName     = r.fileName;
+    p.relativePath = bankRelativeForName(r.fileName);
+    p.absoluteDir  = r.absoluteDir;
     return p;
 }
 
 std::string bankRelativeForName(const std::string& fileName) {
     if (fileName.empty()) return {};
-    // Same expression deriveBankPaths uses, so the two spellings can't drift.
     return std::string(kBankSubfolder) + "/" + fileName;
 }
 

src/core/capture/capture_paths.h

@@ -36,9 +36,29 @@ std::string normalizeSlashes(const std::string& path);
 // "capture" if nothing usable remains. Deterministic.
 std::string sanitizeStem(const std::string& baseName);
 
-// Derives the bank paths for one capture: baseName is the sanitized file-stem
-// source, uniqueTag an optional sanitized disambiguator (timestamp/counter) so
-// repeated captures don't collide. Produces "<stem>[_<tag>].wav".
+// Where one render writes, with no index spelling at all: the directory REAPER is
+// told to render into plus the stem/file name it produces there. `absoluteDir` is
+// taken as given (normalized only) rather than derived, because a render that never
+// enters the bank has no bank subfolder to append — the render-in-place verb points
+// this at the project's own recording path.
+struct RenderPaths {
+    std::string absoluteDir;   // RENDER_FILE   (forward slash, no trailing slash)
+    std::string fileName;      // <stem>.wav
+    std::string fileStem;      // <stem>        (RENDER_PATTERN — REAPER appends the extension)
+};
+
+// The file-stem spelling for one render: baseName is the sanitized file-stem source,
+// uniqueTag an optional sanitized disambiguator (timestamp/counter) so repeated
+// renders don't collide. Produces "<stem>[_<tag>].wav". THE one owner of that
+// spelling — deriveBankPaths is expressed over it, and bankRelativeForName depends
+// on the bank's spelling never drifting from it.
+RenderPaths deriveRenderPaths(const std::string& absoluteDir,
+                              const std::string& baseName,
+                              const std::string& uniqueTag);
+
+// Derives the bank paths for one capture: the same stem spelling as
+// deriveRenderPaths, in the bank subfolder, plus the project-relative path the
+// index stores.
 BankPaths deriveBankPaths(const std::string& projectDir,
                           const std::string& baseName,
                           const std::string& uniqueTag);

src/core/capture/track_topology.cpp

@@ -25,4 +25,38 @@ std::vector<int> directChildIndices(const std::vector<int>& folderDepths,
     return children;
 }
 
+SiblingPlacement siblingPlacement(const std::vector<int>& folderDepths, int srcIndex) {
+    const int count = static_cast<int>(folderDepths.size());
+    if (count == 0) return SiblingPlacement{};
+
+    const int src = srcIndex < 0 ? 0 : (srcIndex >= count ? count - 1 : srcIndex);
+
+    // levels[i] is track i's absolute nesting depth; levels[count] is the depth the
+    // list closes at (0 in a well-formed project). Negative is unrepresentable, so a
+    // malformed over-closing delta clamps here rather than propagating.
+    std::vector<int> levels(static_cast<std::size_t>(count) + 1, 0);
+    for (int i = 0; i < count; ++i) {
+        const int next = levels[static_cast<std::size_t>(i)] +
+                         folderDepths[static_cast<std::size_t>(i)];
+        levels[static_cast<std::size_t>(i) + 1] = next < 0 ? 0 : next;
+    }
+
+    const int L = levels[static_cast<std::size_t>(src)];
+
+    int p = src + 1;
+    if (folderDepths[static_cast<std::size_t>(src)] >= 1) {
+        p = count;  // an unterminated folder swallows the rest of the list
+        for (int j = src + 1; j <= count; ++j) {
+            if (levels[static_cast<std::size_t>(j)] == L) { p = j; break; }
+        }
+    }
+
+    SiblingPlacement out;
+    out.insertIndex    = p;
+    out.precedingIndex = p - 1;
+    out.precedingDepth = L - levels[static_cast<std::size_t>(p - 1)];
+    out.newDepth       = levels[static_cast<std::size_t>(p)] - L;
+    return out;
+}
+
 }  // namespace reasampler::capture

src/core/capture/track_topology.h

@@ -1,8 +1,8 @@
 #pragma once
 // track_topology — pure folder arithmetic over a project's track list: which tracks
-// are the DIRECT children of a folder parent, derived from the I_FOLDERDEPTH deltas
-// alone. NO REAPER types (the shell reads the deltas); unit-tested by
-// tests/test_track_topology.cpp.
+// are the DIRECT children of a folder parent, and where a new SIBLING of a given
+// track goes, both derived from the I_FOLDERDEPTH deltas alone. NO REAPER types
+// (the shell reads the deltas); unit-tested by tests/test_track_topology.cpp.
 
 #include <vector>
 
@@ -21,4 +21,34 @@ namespace reasampler::capture {
 std::vector<int> directChildIndices(const std::vector<int>& folderDepths,
                                     int parentIndex);
 
+// Where a new track goes so it is a SIBLING of `srcIndex` — same nesting level, same
+// folder — and the two I_FOLDERDEPTH writes that put it there.
+struct SiblingPlacement {
+    int insertIndex = 0;      // the index the new track occupies after insertion
+
+    // The track that will PRECEDE the new one (insertIndex - 1), and its rewritten
+    // delta. -1 only for a degenerate empty list, where there is nothing to write.
+    int precedingIndex = -1;
+    int precedingDepth = 0;
+
+    int newDepth = 0;         // the new track's own I_FOLDERDEPTH
+};
+
+// Both naive answers are audibly wrong, which is why this is arithmetic and not
+// `srcIndex + 1`: inserting straight after a folder PARENT makes the new track that
+// folder's first child (its audio re-enters the parent's FX and fader), and inserting
+// straight after the folder's LAST track steals that track's closing delta and drops
+// the new one outside the folder entirely (its audio bypasses the folder bus).
+//
+// Levels are absolute nesting depths recovered from the deltas (level[0] = 0,
+// level[i+1] = level[i] + depth[i]). A folder parent's insert point is the first
+// following track back at the source's own level — i.e. after the whole folder;
+// everything else inserts directly below the source. The two writes preserve the
+// total delta sum, so no track after the insertion changes level.
+//
+// A malformed list (deltas not summing to zero, an out-of-range srcIndex) CLAMPS to
+// the nearest legal placement rather than asserting: the failure mode of a corrupt
+// project must be a track at the wrong nesting level, never a crash.
+SiblingPlacement siblingPlacement(const std::vector<int>& folderDepths, int srcIndex);
+
 }  // namespace reasampler::capture