Piano: Add sustain

Author: https://github.com/willmcpherson2
Commit: https://github.com/SerenityOS/serenity/commit/5990b3b2e64
Pull-request: https://github.com/SerenityOS/serenity/pull/1178

Applications/Piano/AudioEngine.cpp

@@ -31,6 +31,7 @@
 
 AudioEngine::AudioEngine()
 {
+    set_sustain_impl(0);
     set_decay(0);
 }
 
@@ -48,8 +49,8 @@ void AudioEngine::fill_buffer(FixedArray<Sample>& buffer)
                 continue;
 
             m_power[note] -= m_decay_step;
-            if (m_power[note] < 0)
-                m_power[note] = 0;
+            if (m_power[note] < m_sustain_level)
+                m_power[note] = m_sustain_level;
 
             double val = 0;
             switch (m_wave) {
@@ -212,7 +213,20 @@ void AudioEngine::set_decay(int decay)
 {
     ASSERT(decay >= 0);
     m_decay = decay;
-    m_decay_step = calculate_step(1, m_decay);
+    m_decay_step = calculate_step(1 - m_sustain_level, m_decay);
+}
+
+void AudioEngine::set_sustain_impl(int sustain)
+{
+    ASSERT(sustain >= 0);
+    m_sustain = sustain;
+    m_sustain_level = sustain / 1000.0;
+}
+
+void AudioEngine::set_sustain(int sustain)
+{
+    set_sustain_impl(sustain);
+    set_decay(m_decay);
 }
 
 void AudioEngine::set_delay(int delay)

Applications/Piano/AudioEngine.h

@@ -44,6 +44,7 @@ public:
     int octave_base() const { return (m_octave - octave_min) * 12; }
     int wave() const { return m_wave; }
     int decay() const { return m_decay; }
+    int sustain() const { return m_sustain; }
     int delay() const { return m_delay; }
     int time() const { return m_time; }
     int tick() const { return m_tick; }
@@ -55,6 +56,7 @@ public:
     void set_wave(int wave);
     void set_wave(Direction);
     void set_decay(int decay);
+    void set_sustain(int sustain);
     void set_delay(int delay);
 
 private:
@@ -64,6 +66,8 @@ private:
     double triangle(size_t note);
     double noise() const;
 
+    void set_sustain_impl(int sustain);
+
     FixedArray<Sample> m_front_buffer { sample_count };
     FixedArray<Sample> m_back_buffer { sample_count };
     FixedArray<Sample>* m_front_buffer_ptr { &m_front_buffer };
@@ -79,6 +83,8 @@ private:
     int m_wave { first_wave };
     int m_decay;
     double m_decay_step;
+    int m_sustain;
+    double m_sustain_level;
     int m_delay { 0 };
 
     int m_time { 0 };

Applications/Piano/KnobsWidget.cpp

@@ -51,6 +51,7 @@ KnobsWidget::KnobsWidget(GUI::Widget* parent, AudioEngine& audio_engine, MainWid
     m_octave_label = GUI::Label::construct("Octave", m_labels_container);
     m_wave_label = GUI::Label::construct("Wave", m_labels_container);
     m_decay_label = GUI::Label::construct("Decay", m_labels_container);
+    m_sustain_label = GUI::Label::construct("Sustain", m_labels_container);
     m_delay_label = GUI::Label::construct("Delay", m_labels_container);
 
     m_values_container = GUI::Widget::construct(this);
@@ -61,6 +62,7 @@ KnobsWidget::KnobsWidget(GUI::Widget* parent, AudioEngine& audio_engine, MainWid
     m_octave_value = GUI::Label::construct(String::number(m_audio_engine.octave()), m_values_container);
     m_wave_value = GUI::Label::construct(wave_strings[m_audio_engine.wave()], m_values_container);
     m_decay_value = GUI::Label::construct(String::number(m_audio_engine.decay()), m_values_container);
+    m_sustain_value = GUI::Label::construct(String::number(m_audio_engine.sustain()), m_values_container);
     m_delay_value = GUI::Label::construct(String::number(m_audio_engine.delay() / m_audio_engine.tick()), m_values_container);
 
     m_knobs_container = GUI::Widget::construct(this);
@@ -102,6 +104,17 @@ KnobsWidget::KnobsWidget(GUI::Widget* parent, AudioEngine& audio_engine, MainWid
         m_decay_value->set_text(String::number(new_decay));
     };
 
+    constexpr int max_sustain = 1000;
+    m_sustain_knob = GUI::Slider::construct(Orientation::Vertical, m_knobs_container);
+    m_sustain_knob->set_range(0, max_sustain);
+    m_sustain_knob->set_value(max_sustain - m_audio_engine.sustain());
+    m_sustain_knob->on_value_changed = [this](int value) {
+        int new_sustain = max_sustain - value;
+        m_audio_engine.set_sustain(new_sustain);
+        ASSERT(new_sustain == m_audio_engine.sustain());
+        m_sustain_value->set_text(String::number(new_sustain));
+    };
+
     constexpr int max_delay = 8;
     m_delay_knob = GUI::Slider::construct(Orientation::Vertical, m_knobs_container);
     m_delay_knob->set_range(0, max_delay);

Applications/Piano/KnobsWidget.h

@@ -54,18 +54,21 @@ private:
     RefPtr<GUI::Label> m_octave_label;
     RefPtr<GUI::Label> m_wave_label;
     RefPtr<GUI::Label> m_decay_label;
+    RefPtr<GUI::Label> m_sustain_label;
     RefPtr<GUI::Label> m_delay_label;
 
     RefPtr<GUI::Widget> m_values_container;
     RefPtr<GUI::Label> m_octave_value;
     RefPtr<GUI::Label> m_wave_value;
     RefPtr<GUI::Label> m_decay_value;
+    RefPtr<GUI::Label> m_sustain_value;
     RefPtr<GUI::Label> m_delay_value;
 
     RefPtr<GUI::Widget> m_knobs_container;
     RefPtr<GUI::Slider> m_octave_knob;
     RefPtr<GUI::Slider> m_wave_knob;
     RefPtr<GUI::Slider> m_decay_knob;
+    RefPtr<GUI::Slider> m_sustain_knob;
     RefPtr<GUI::Slider> m_delay_knob;
 
     bool m_change_octave { true };

Applications/Piano/MainWidget.cpp

@@ -60,7 +60,7 @@ MainWidget::MainWidget(AudioEngine& audio_engine)
 
     m_knobs_widget = KnobsWidget::construct(m_keys_and_knobs_container, audio_engine, *this);
     m_knobs_widget->set_size_policy(GUI::SizePolicy::Fixed, GUI::SizePolicy::Fill);
-    m_knobs_widget->set_preferred_size(200, 0);
+    m_knobs_widget->set_preferred_size(250, 0);
 }
 
 MainWidget::~MainWidget()