feat: correct MIDI phrases to root-aware major and minor scales

docs/MODERN_EDITING.md

@@ -31,3 +31,7 @@ Select MIDI clips and use Edit/MIDI tools/Swing quantize. Grid is in source tick
 ## Phase 53
 
 Edit/MIDI tools/Note gate scales lengths from 1 to 400 percent, rounded to at least one tick. Legato ends notes at the next strictly later onset in the same clip and channel; notes in a chord end together. The final onset extends to source end. Gate expansion beyond the source rejects the whole edit. Undo restores original durations.
+
+## Phase 54
+
+Edit/MIDI tools/Correct to scale takes a root (0=C through 11=B) and chromatic, major or natural minor. Each pitch moves to the nearest permitted MIDI note; ties choose the lower pitch. Timing, channel and velocity remain unchanged. Corrections can produce unison notes; notes are not merged. This changes MIDI notes, not audio pitch or a live scale filter.

docs/ROADMAP.md

@@ -1423,12 +1423,12 @@ Implemented: atomic gate scaling and same-channel legato over selected MIDI clip
 Snap notes to a chosen root and chromatic, major or minor scale with deterministic nearest-pitch ties.
 
 ### Tasks and acceptance criteria
-- [ ] Provide the control/model behavior and accessible GUI commands.
-- [ ] Validate bounds and failure rollback; preserve existing project compatibility and callback safety.
-- [ ] Test the new workflow and document scope and limitations.
+- [x] Provide the control/model behavior and accessible GUI commands.
+- [x] Validate bounds and failure rollback; preserve existing project compatibility and callback safety.
+- [x] Test the new workflow and document scope and limitations.
 
 ### Implementation status
-Planned.
+Implemented: root-aware nearest-pitch correction to chromatic, major or natural minor scales, with lower-pitch ties and MIDI endpoint bounds. Core root/tie/endpoint/invalid-input and GUI pitch-refresh tests pass; note IDs and timing persist.
 
 ---
 

include/xtc/xtc_editing.h

@@ -22,11 +22,12 @@ xtc_result xtc_project_transform_clips(xtc_project *project,const uint64_t *ids,
  * a grid; strength 0..100 blends toward the nearest swung point (ties later).
  * Swing durations stay fixed. LEGATO ends at the next strictly later onset in
  * the same clip/channel (chords stay together), or source end for the last onset. Out-of-source results reject the complete operation. */
-typedef enum { XTC_MIDI_TRANSFORM_SWING, XTC_MIDI_TRANSFORM_GATE, XTC_MIDI_TRANSFORM_LEGATO } xtc_midi_transform_type;
+typedef enum { XTC_MIDI_TRANSFORM_SWING, XTC_MIDI_TRANSFORM_GATE, XTC_MIDI_TRANSFORM_LEGATO, XTC_MIDI_TRANSFORM_SCALE } xtc_midi_transform_type;
 typedef struct {
     xtc_midi_transform_type type;
     uint64_t grid;
     unsigned int swing,strength;
+    unsigned int root,scale; /* SCALE: root 0..11 (C..B), scale 0 chromatic, 1 major, 2 natural minor; nearest ties lower. */
     unsigned int gate_percent; /* GATE: 1..400, rounded length, minimum 1 tick. */
 } xtc_midi_transform;
 xtc_result xtc_project_transform_midi(xtc_project *project,const uint64_t *ids,size_t count,const xtc_midi_transform *edit);

src/gui/main_window.cpp

@@ -322,6 +322,7 @@ MainWindow::MainWindow(bool prompt_unsaved,const char *configuration)
     Fl_Group::current(parent);
     menu->add("Edit/Nudge selection left",0,[](Fl_Widget *,void *c){static_cast<SequencerWidget *>(c)->nudge_selection(-1);},sequencer_);
     menu->add("Edit/Nudge selection right",0,[](Fl_Widget *,void *c){static_cast<SequencerWidget *>(c)->nudge_selection(1);},sequencer_);
+    menu->add("Edit/MIDI tools/Correct to scale...",0,[](Fl_Widget *,void *c){static_cast<SequencerWidget *>(c)->scale_dialog();},sequencer_);
     menu->add("Edit/MIDI tools/Note gate...",0,[](Fl_Widget *,void *c){static_cast<SequencerWidget *>(c)->gate_dialog();},sequencer_);
     menu->add("Edit/MIDI tools/Legato",0,[](Fl_Widget *,void *c){xtc_midi_transform edit{};edit.type=XTC_MIDI_TRANSFORM_LEGATO;static_cast<SequencerWidget *>(c)->transform_midi(edit);},sequencer_);
     menu->add("Edit/MIDI tools/Swing quantize...",0,[](Fl_Widget *,void *c){static_cast<SequencerWidget *>(c)->swing_dialog();},sequencer_);

src/gui/sequencer_widget.cpp

@@ -562,6 +562,13 @@ xtc_result SequencerWidget::transform_midi(const xtc_midi_transform &edit)
     if(r==XTC_OK)r=xtc_project_transform_midi(project_,ids.data(),ids.size(),&edit);
     changed(r);return r;
 }
+void SequencerWidget::scale_dialog()
+{
+    const char *input=fl_input("Root (0=C..11=B), scale (0=chromatic, 1=major, 2=natural minor)","0 1");if(!input)return;
+    unsigned int root=0,scale=0;char extra;std::istringstream values(input);
+    if(!(values>>root>>scale) || (values>>extra) || root>11 || scale>2){fl_alert("Enter a root from 0 to 11 and scale from 0 to 2.");return;}
+    xtc_midi_transform edit{};edit.type=XTC_MIDI_TRANSFORM_SCALE;edit.root=root;edit.scale=scale;transform_midi(edit);
+}
 void SequencerWidget::gate_dialog()
 {
     const char *input=fl_input("Note length percentage (1..400)","50");if(!input)return;

src/gui/sequencer_widget.hpp

@@ -41,6 +41,7 @@ class SequencerWidget : public Fl_Group {
     xtc_result transform_midi(const xtc_midi_transform &edit);
     void swing_dialog();
     void gate_dialog();
+    void scale_dialog();
     xtc_result repeat_selection(unsigned int copies);
     void repeat_dialog();
     xtc_result copy_selection();

src/project/editing.c

@@ -133,9 +133,10 @@ xtc_result xtc_project_transform_midi(xtc_project *p,const uint64_t *ids,size_t
 {
     xtc_project *copy=NULL;size_t i,j,matched=0;xtc_result r=selection_valid(p,ids,count);
     if(r!=XTC_OK)return r;
-    if(!edit || edit->type<XTC_MIDI_TRANSFORM_SWING || edit->type>XTC_MIDI_TRANSFORM_LEGATO)return XTC_ERR_INVALID_ARGUMENT;
+    if(!edit || edit->type<XTC_MIDI_TRANSFORM_SWING || edit->type>XTC_MIDI_TRANSFORM_SCALE)return XTC_ERR_INVALID_ARGUMENT;
     if(edit->type==XTC_MIDI_TRANSFORM_SWING && (!edit->grid || edit->grid>3840 || edit->swing>100 || edit->strength>100))return XTC_ERR_INVALID_ARGUMENT;
     if(edit->type==XTC_MIDI_TRANSFORM_GATE && (!edit->gate_percent || edit->gate_percent>400))return XTC_ERR_INVALID_ARGUMENT;
+    if(edit->type==XTC_MIDI_TRANSFORM_SCALE && (edit->root>11 || edit->scale>2))return XTC_ERR_INVALID_ARGUMENT;
     for(i=0;i<count;++i){xtc_clip_info c;xtc_project_find_clip(p,ids[i],&c);if(!c.midi)return XTC_ERR_INVALID_STATE;}
     r=xtc_project_clone(p,&copy);if(r!=XTC_OK)return r;
     for(i=0;r==XTC_OK && i<copy->note_count;++i) {
@@ -147,13 +148,21 @@ xtc_result xtc_project_transform_midi(xtc_project *p,const uint64_t *ids,size_t
         else if(edit->type==XTC_MIDI_TRANSFORM_GATE) {
             n->length_tick=(n->length_tick*edit->gate_percent+50)/100;
             if(!n->length_tick)n->length_tick=1;
-        } else {
+        } else if(edit->type==XTC_MIDI_TRANSFORM_LEGATO) {
             uint64_t next=c.source_length_tick;
             for(j=0;j<p->note_count;++j) {
                 const xtc_note_info *other=p->notes+j;
                 if(other->clip_id==n->clip_id && other->channel==n->channel && other->start_tick>n->start_tick && other->start_tick<next)next=other->start_tick;
             }
             n->length_tick=next-n->start_tick;
+        } else if(edit->type==XTC_MIDI_TRANSFORM_SCALE) {
+            static const unsigned int masks[]={4095,2741,1453};
+            unsigned int pitch,best=n->pitch,distance=128;
+            for(pitch=0;pitch<128;++pitch)if(masks[edit->scale] & (1U<<((pitch+12-edit->root)%12))) {
+                unsigned int d=pitch>n->pitch ? pitch-n->pitch : n->pitch-pitch;
+                if(d<distance){distance=d;best=pitch;}
+            }
+            n->pitch=best;
         }
         if(n->start_tick>=c.source_length_tick || n->length_tick>c.source_length_tick-n->start_tick)r=XTC_ERR_INVALID_ARGUMENT;
     }

tests/integration/test_gui.cpp

@@ -1340,6 +1340,8 @@ int main(int argc, char **argv)
         CHECK(xtc_project_get_note(s->project(),0,&quantized)==XTC_OK && quantized.length_tick==60);
         edit.type=XTC_MIDI_TRANSFORM_LEGATO;CHECK(s->transform_midi(edit)==XTC_OK);
         CHECK(xtc_project_get_note(s->project(),0,&quantized)==XTC_OK && quantized.length_tick==3540);
+        edit.type=XTC_MIDI_TRANSFORM_SCALE;edit.root=0;edit.scale=1;CHECK(s->transform_midi(edit)==XTC_OK);
+        CHECK(xtc_project_get_note(s->project(),0,&quantized)==XTC_OK && quantized.pitch==60);
         window.do_callback();
     }
     if (failures != 0) return 1;

tests/unit/test_modern_editing.c

@@ -2,6 +2,21 @@
 #include <assert.h>
 #include <stdio.h>
 
+static void test_scale(void)
+{
+    xtc_project *p=NULL;uint64_t t,c,n;xtc_note_info note;xtc_midi_transform edit={0};
+    assert(xtc_project_create(&p)==XTC_OK && xtc_project_add_track(p,"Track",&t)==XTC_OK);
+    assert(xtc_project_add_midi_clip(p,t,0,960,&c)==XTC_OK);
+    assert(xtc_project_add_note(p,c,0,120,61,100,0,&n)==XTC_OK);
+    edit.type=XTC_MIDI_TRANSFORM_SCALE;edit.scale=1;
+    assert(xtc_project_transform_midi(p,&c,1,&edit)==XTC_OK);
+    assert(xtc_project_get_note(p,0,&note)==XTC_OK && note.pitch==60 && note.id==n);
+    assert(xtc_project_edit_note(p,n,0,120,0,100,0)==XTC_OK);edit.root=11;
+    assert(xtc_project_transform_midi(p,&c,1,&edit)==XTC_OK);
+    assert(xtc_project_get_note(p,0,&note)==XTC_OK && note.pitch==1);
+    edit.root=12;assert(xtc_project_transform_midi(p,&c,1,&edit)==XTC_ERR_INVALID_ARGUMENT);
+    xtc_project_destroy(p);
+}
 static void test_gate_legato(void)
 {
     xtc_project *p=NULL;uint64_t t,c,n;xtc_note_info note;xtc_midi_transform edit={0};
@@ -75,7 +90,7 @@ static void test_repeat(void)
 }
 int main(void)
 {
-    test_repeat();test_align_slip();test_swing();test_gate_legato();
+    test_repeat();test_align_slip();test_swing();test_gate_legato();test_scale();
     xtc_project *p=NULL;uint64_t track,a,b,n,ids[2],out[2]={999,999};xtc_clip_info c;
     size_t tracks,clips,notes;
     assert(xtc_project_create(&p)==XTC_OK);