feat: shape MIDI note gates and create channel-aware legato phrases

docs/MODERN_EDITING.md

@@ -27,3 +27,7 @@ Edit/Align clip starts to cursor places every selected start at the cursor. Slip
 ## Phase 52
 
 Select MIDI clips and use Edit/MIDI tools/Swing quantize. Grid is in source ticks; swing delays alternate subdivisions by 0..half a grid step, while strength blends the old start toward the nearest swung point. Durations stay fixed. All source notes are affected, including notes outside visible trims. Mixed audio/MIDI selections and notes that would exceed source bounds reject the entire edit. This is destructive note editing with undo, not a live groove engine.
+
+## 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.

docs/ROADMAP.md

@@ -1408,12 +1408,12 @@ Implemented: deterministic nearest swung-grid quantization with 0..100 strength
 Set note gates or extend notes to the next onset on the same channel, preserving IDs and validating all notes before publication.
 
 ### 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: atomic gate scaling and same-channel legato over selected MIDI clip sources. Chords share the next distinct onset; final notes extend to source end. Core channel/chord/bounds rollback and GUI duration/refresh tests pass.
 
 ---
 

include/xtc/xtc_editing.h

@@ -20,12 +20,14 @@ xtc_result xtc_project_transform_clips(xtc_project *project,const uint64_t *ids,
  * fields persist. No matching notes returns NOT_FOUND. Edits are atomic.
  * Swing: grid 1..3840, swing 0..100 delays alternate grid points by up to half
  * a grid; strength 0..100 blends toward the nearest swung point (ties later).
- * Durations stay fixed. Out-of-source results reject the complete operation. */
-typedef enum { XTC_MIDI_TRANSFORM_SWING } xtc_midi_transform_type;
+ * 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 struct {
     xtc_midi_transform_type type;
     uint64_t grid;
     unsigned int swing,strength;
+    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);
 /* Repeat the bounding phrase span, including gaps, 1..1024 additional copies.

src/gui/main_window.cpp

@@ -322,6 +322,8 @@ 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/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_);
     menu->add("Edit/Align clip starts to cursor",0,[](Fl_Widget *,void *c){auto *s=static_cast<SequencerWidget *>(c);s->transform_selection(XTC_CLIPS_ALIGN,static_cast<int64_t>(s->position()));},sequencer_);
     menu->add("Edit/Slip sources earlier",0,[](Fl_Widget *,void *c){auto *s=static_cast<SequencerWidget *>(c);s->transform_selection(XTC_CLIPS_SLIP,-static_cast<int64_t>(s->grid()));},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::gate_dialog()
+{
+    const char *input=fl_input("Note length percentage (1..400)","50");if(!input)return;
+    unsigned int percent=0;char extra;std::istringstream values(input);
+    if(!(values>>percent) || (values>>extra) || percent<1 || percent>400){fl_alert("Enter a whole percentage from 1 to 400.");return;}
+    xtc_midi_transform edit{};edit.type=XTC_MIDI_TRANSFORM_GATE;edit.gate_percent=percent;transform_midi(edit);
+}
 void SequencerWidget::swing_dialog()
 {
     const char *input=fl_input("Grid ticks (1..3840), swing (0..100), strength (0..100)","240 50 100");if(!input)return;

src/gui/sequencer_widget.hpp

@@ -40,6 +40,7 @@ class SequencerWidget : public Fl_Group {
     xtc_result transform_selection(xtc_clip_operation operation,int64_t amount);
     xtc_result transform_midi(const xtc_midi_transform &edit);
     void swing_dialog();
+    void gate_dialog();
     xtc_result repeat_selection(unsigned int copies);
     void repeat_dialog();
     xtc_result copy_selection();

src/project/editing.c

@@ -133,7 +133,9 @@ 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->grid || edit->grid>3840 || edit->swing>100 || edit->strength>100)return XTC_ERR_INVALID_ARGUMENT;
+    if(!edit || edit->type<XTC_MIDI_TRANSFORM_SWING || edit->type>XTC_MIDI_TRANSFORM_LEGATO)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;
     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) {
@@ -141,7 +143,18 @@ xtc_result xtc_project_transform_midi(xtc_project *p,const uint64_t *ids,size_t
         for(j=0;j<count;++j)if(n->clip_id==ids[j])break;
         if(j==count)continue;
         ++matched;xtc_project_find_clip(copy,n->clip_id,&c);
-        n->start_tick=swung_start(n->start_tick,edit);
+        if(edit->type==XTC_MIDI_TRANSFORM_SWING)n->start_tick=swung_start(n->start_tick,edit);
+        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 {
+            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;
+        }
         if(n->start_tick>=c.source_length_tick || n->length_tick>c.source_length_tick-n->start_tick)r=XTC_ERR_INVALID_ARGUMENT;
     }
     if(r==XTC_OK && !matched)r=XTC_ERR_NOT_FOUND;

tests/integration/test_gui.cpp

@@ -1336,6 +1336,10 @@ int main(int argc, char **argv)
         xtc_midi_transform edit{};edit.grid=240;edit.swing=50;edit.strength=100;
         CHECK(s->transform_midi(edit)==XTC_OK);xtc_note_info quantized{};
         CHECK(xtc_project_get_note(s->project(),0,&quantized)==XTC_OK && quantized.start_tick==300);
+        edit.type=XTC_MIDI_TRANSFORM_GATE;edit.gate_percent=50;CHECK(s->transform_midi(edit)==XTC_OK);
+        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);
         window.do_callback();
     }
     if (failures != 0) return 1;

tests/unit/test_modern_editing.c

@@ -2,6 +2,27 @@
 #include <assert.h>
 #include <stdio.h>
 
+static void test_gate_legato(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,0,120,60,100,0,&n)==XTC_OK);
+    assert(xtc_project_add_note(p,c,0,120,64,100,0,&n)==XTC_OK);
+    assert(xtc_project_add_note(p,c,240,120,67,100,0,&n)==XTC_OK);
+    assert(xtc_project_add_note(p,c,120,120,72,100,1,&n)==XTC_OK);
+    edit.type=XTC_MIDI_TRANSFORM_LEGATO;assert(xtc_project_transform_midi(p,&c,1,&edit)==XTC_OK);
+    assert(xtc_project_get_note(p,0,&note)==XTC_OK && note.length_tick==240);
+    assert(xtc_project_get_note(p,1,&note)==XTC_OK && note.length_tick==240);
+    assert(xtc_project_get_note(p,2,&note)==XTC_OK && note.length_tick==720);
+    assert(xtc_project_get_note(p,3,&note)==XTC_OK && note.length_tick==840);
+    edit.type=XTC_MIDI_TRANSFORM_GATE;edit.gate_percent=200;
+    assert(xtc_project_transform_midi(p,&c,1,&edit)==XTC_ERR_INVALID_ARGUMENT);
+    assert(xtc_project_get_note(p,0,&note)==XTC_OK && note.length_tick==240);
+    edit.gate_percent=50;assert(xtc_project_transform_midi(p,&c,1,&edit)==XTC_OK);
+    assert(xtc_project_get_note(p,0,&note)==XTC_OK && note.length_tick==120);
+    xtc_project_destroy(p);
+}
 static void test_swing(void)
 {
     xtc_project *p=NULL;uint64_t t,c,n;xtc_note_info note;xtc_midi_transform edit={0};
@@ -54,7 +75,7 @@ static void test_repeat(void)
 }
 int main(void)
 {
-    test_repeat();test_align_slip();test_swing();
+    test_repeat();test_align_slip();test_swing();test_gate_legato();
     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);