perf(gui): skip unchanged repaints and gate updates by tab

Add change detection to Display, WaveformDisplay, FilterDisplay,
EnvelopeDisplay, and LFODisplay so repaint() is only called when
values actually change. Gate updateVisuals() by currentTab so only
the visible tab's displays are updated each timer tick. Similarly
gate updateModList/updateMacroList to their respective tabs.

Manage dynamically created controls via ownedControls
unique_ptr vector instead of raw new leaks. Null-check parameter
lookups before creating attachments. Hold engine control lock
when reading matrix/macros/LFO shape data.

Fix envelope display curve directions (attack rising from bottom,
decay falling toward sustain, release falling toward bottom).
Add tooltip to FilterDisplay noting the approximation. Replace
ToggleButton raw param pointer with ParameterAttachment for proper
gesture handling. Sync preset and scale combos to processor state.

Source/GUI/Display.h

@@ -12,8 +12,8 @@ namespace serum
 class Display : public juce::Component
 {
 public:
-    void setTitle (const juce::String& t) { title = t; repaint(); }
-    void setValue (const juce::String& v) { value = v; repaint(); }
+    void setTitle (const juce::String& t) { if (title != t) { title = t; repaint(); } }
+    void setValue (const juce::String& v) { if (value != v) { value = v; repaint(); } }
 
     void paint (juce::Graphics& g) override;
 

Source/GUI/EnvelopeDisplay.cpp

@@ -5,7 +5,10 @@ namespace serum
 
 void EnvelopeDisplay::setParams (float a, float d, float s, float r, float c)
 {
+    if (attack == a && decay == d && sustain == s && release == r && curve == c)
+        return;
     attack = a; decay = d; sustain = s; release = r; curve = c;
+    repaint();
 }
 
 void EnvelopeDisplay::paint (juce::Graphics& g)
@@ -19,7 +22,7 @@ void EnvelopeDisplay::paint (juce::Graphics& g)
     const float atkShape = 0.3f + curve * 2.7f;
     const float decShape = 3.0f - curve * 2.7f;
 
-    // Normalise durations for display (attack 0..1, decay 0..0.6, release 0..0.6).
+    // Normalise durations for display, allowing a short sustain plateau.
     const float aSec = maps::toSeconds (attack);
     const float dSec = maps::toSeconds (decay);
     const float rSec = maps::toSeconds (release);
@@ -36,7 +39,6 @@ void EnvelopeDisplay::paint (juce::Graphics& g)
 
     juce::Path path;
     path.startNewSubPath (left, bottom);
-    path.lineTo (left, top);
 
     // Attack (curve-shaped).
     const int steps = 48;
@@ -44,7 +46,7 @@ void EnvelopeDisplay::paint (juce::Graphics& g)
     for (int i = 0; i <= steps; ++i)
     {
         const float p = (float) i / steps;
-        const float y = top + (bottom - top) * std::pow (p, atkShape);
+        const float y = bottom - (bottom - top) * std::pow (p, atkShape);
         path.lineTo (left + p * (peakX - left), y);
     }
 
@@ -53,7 +55,7 @@ void EnvelopeDisplay::paint (juce::Graphics& g)
     for (int i = 0; i <= steps; ++i)
     {
         const float p = (float) i / steps;
-        const float y = sustainY + (bottom - sustainY) * std::pow (1.0f - p, decShape);
+        const float y = sustainY + (top - sustainY) * std::pow (1.0f - p, decShape);
         path.lineTo (peakX + p * (decX - peakX), y);
     }
     path.lineTo (decX, sustainY);
@@ -64,7 +66,7 @@ void EnvelopeDisplay::paint (juce::Graphics& g)
     for (int i = 0; i <= steps; ++i)
     {
         const float p = (float) i / steps;
-        const float y = sustainY + (bottom - sustainY) * std::pow (1.0f - p, decShape);
+        const float y = bottom - (bottom - sustainY) * std::pow (1.0f - p, decShape);
         path.lineTo (relStartX + p * (right - relStartX), y);
     }
 

Source/GUI/FilterDisplay.cpp

@@ -37,7 +37,10 @@ float FilterDisplay::magnitude (float freqHz, float cutoffHz, float res, int typ
 
 void FilterDisplay::setParams (int t, float c, float r, float d, int s)
 {
+    if (type == t && cutoff == c && res == r && drive == d && slope == s)
+        return;
     type = t; cutoff = c; res = r; drive = d; slope = s;
+    repaint();
 }
 
 void FilterDisplay::paint (juce::Graphics& g)

Source/GUI/FilterDisplay.h

@@ -8,13 +8,15 @@ namespace serum
 {
 
 // ===========================================================================
-// Filter frequency-response view (magnitude vs log frequency).
+// Approximate filter frequency-response view (magnitude vs log frequency).
 // ===========================================================================
-class FilterDisplay : public juce::Component
+class FilterDisplay : public juce::Component,
+                      public juce::SettableTooltipClient
 {
 public:
+    FilterDisplay() { setTooltip ("Approximate response preview; slope, drive and modulation are not modelled."); }
     void setParams (int type, float cutoff, float res, float drive, int slope);
-    void setEnabled (bool e) { enabled = e; }
+    void setEnabled (bool e) { if (enabled != e) { enabled = e; repaint(); } }
 
     void paint (juce::Graphics& g) override;
 

Source/GUI/LFODisplay.cpp

@@ -5,10 +5,16 @@ namespace serum
 
 void LFODisplay::setShapeData (const std::vector<float>& data, int s)
 {
-    steps = juce::jlimit (2, 64, s);
-    shapeData = data;
-    if ((int) shapeData.size() < 64)
-        shapeData.resize (64, 0.0f);
+    const int newSteps = juce::jlimit (2, 64, s);
+    const size_t dataSize = std::min (data.size(), size_t (64));
+    if (steps == newSteps && shapeData.size() == 64
+        && std::equal (data.begin(), data.begin() + dataSize, shapeData.begin())
+        && std::all_of (shapeData.begin() + dataSize, shapeData.end(), [] (float v) { return v == 0.0f; }))
+        return;
+
+    steps = newSteps;
+    shapeData.assign (data.begin(), data.begin() + dataSize);
+    shapeData.resize (64, 0.0f);
     repaint();
 }
 

Source/GUI/LFODisplay.h

@@ -13,7 +13,7 @@ namespace serum
 class LFODisplay : public juce::Component
 {
 public:
-    void setShape (int s) { shape = s; repaint(); }
+    void setShape (int s) { if (shape != s) { shape = s; repaint(); } }
     void setShapeData (const std::vector<float>& data, int steps);
     void setOnShapeEdited (std::function<void (const std::vector<float>&, int)> cb) { onEdited = std::move (cb); }
 

Source/GUI/ToggleButton.cpp

@@ -10,12 +10,12 @@ ToggleButton::ToggleButton (const juce::String& lbl) : label (lbl)
 
 void ToggleButton::attach (juce::AudioProcessorValueTreeState& apvts, const juce::String& paramId)
 {
-    param = apvts.getParameter (paramId);
-    if (param != nullptr)
+    attachment.reset();
+    if (auto* param = apvts.getParameter (paramId))
     {
-        state = param->getValue() > 0.5f;
         attachment = std::make_unique<juce::ParameterAttachment> (*param,
             [this] (float newValue) { setToggleState (newValue > 0.5f); });
+        attachment->sendInitialUpdate();
     }
 }
 
@@ -60,9 +60,9 @@ void ToggleButton::mouseDown (const juce::MouseEvent&)
     {
         onClick (newState);
     }
-    else if (param != nullptr)
+    else if (attachment != nullptr)
     {
-        param->setValueNotifyingHost (newState ? 1.0f : 0.0f);
+        attachment->setValueAsCompleteGesture (newState ? 1.0f : 0.0f);
     }
 
     setToggleState (newState);

Source/GUI/ToggleButton.h

@@ -35,7 +35,6 @@ public:
 private:
     bool        state = false;
     juce::String label;
-    juce::RangedAudioParameter* param = nullptr;
     std::unique_ptr<juce::ParameterAttachment> attachment;
     std::function<void (bool)> onClick;
     juce::Colour onColour = theme::accent;

Source/GUI/WaveformDisplay.h

@@ -13,10 +13,10 @@ namespace serum
 class WaveformDisplay : public juce::Component
 {
 public:
-    void setWavetables (const WavetableLibrary* lib) { wtLib = lib; }
-    void setWaveIndex (int index) { wave = index; }
-    void setFramePosition (float pos) { wtPos = pos; }
-    void setEnabled (bool e) { enabled = e; }
+    void setWavetables (const WavetableLibrary* lib) { if (wtLib != lib) { wtLib = lib; repaint(); } }
+    void setWaveIndex (int index) { if (wave != index) { wave = index; repaint(); } }
+    void setFramePosition (float pos) { if (wtPos != pos) { wtPos = pos; repaint(); } }
+    void setEnabled (bool e) { if (enabled != e) { enabled = e; repaint(); } }
 
     void paint (juce::Graphics& g) override;