Piano: Create controller widgets for processor parameters

These widgets attach to a processor parameter and keep the two sides in
sync. They will become very useful for smart processor interfaces.

Userland/Applications/Piano/ProcessorParameterWidget/Dropdown.h

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+/*
+ * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include "WidgetWithLabel.h"
+#include <AK/Vector.h>
+#include <LibDSP/ProcessorParameter.h>
+#include <LibGUI/ComboBox.h>
+#include <LibGUI/ItemListModel.h>
+#include <LibGUI/Label.h>
+#include <LibGUI/ModelIndex.h>
+
+template<typename EnumT>
+requires(IsEnum<EnumT>) class ProcessorParameterDropdown : public GUI::ComboBox {
+    C_OBJECT(ProcessorParameterDropdown);
+
+public:
+    ProcessorParameterDropdown(LibDSP::ProcessorEnumParameter<EnumT>& parameter, Vector<String> modes)
+        : ComboBox()
+        , m_parameter(parameter)
+        , m_modes(move(modes))
+    {
+        auto model = GUI::ItemListModel<EnumT, Vector<String>>::create(m_modes);
+        set_model(model);
+        set_only_allow_values_from_model(true);
+        set_model_column(0);
+        set_selected_index(0);
+        m_parameter.set_value(static_cast<EnumT>(0));
+
+        on_change = [this]([[maybe_unused]] auto name, GUI::ModelIndex model_index) {
+            auto value = static_cast<EnumT>(model_index.row());
+            m_parameter.set_value_sneaky(value, LibDSP::Detail::ProcessorParameterSetValueTag {});
+        };
+        m_parameter.did_change_value = [this](auto new_value) {
+            set_selected_index(static_cast<int>(new_value));
+        };
+    }
+
+    // Release focus when escape is pressed
+    virtual void keydown_event(GUI::KeyEvent& event) override
+    {
+        if (event.key() == Key_Escape) {
+            if (is_focused())
+                set_focus(false);
+            event.accept();
+        } else {
+            GUI::ComboBox::keydown_event(event);
+        }
+    }
+
+private:
+    LibDSP::ProcessorEnumParameter<EnumT>& m_parameter;
+    Vector<String> m_modes;
+};

Userland/Applications/Piano/ProcessorParameterWidget/Slider.cpp

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+/*
+ * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Slider.h"
+#include "WidgetWithLabel.h"
+
+ProcessorParameterSlider::ProcessorParameterSlider(Orientation orientation, LibDSP::ProcessorRangeParameter& parameter, RefPtr<GUI::Label> value_label)
+    : Slider(orientation)
+    , WidgetWithLabel(move(value_label))
+    , m_parameter(parameter)
+{
+    set_range(m_parameter.min_value().raw(), m_parameter.max_value().raw());
+    set_value(m_parameter.value().raw());
+    set_step((m_parameter.min_value() - m_parameter.max_value()).raw() / 128);
+    set_tooltip(m_parameter.name());
+    m_value_label->set_text(String::formatted("{:.2f}", static_cast<double>(m_parameter)));
+
+    on_change = [this](auto value) {
+        LibDSP::ParameterFixedPoint real_value;
+        real_value.raw() = value;
+        m_parameter.set_value_sneaky(real_value, LibDSP::Detail::ProcessorParameterSetValueTag {});
+        if (m_value_label) {
+            double value = static_cast<double>(m_parameter);
+            String label_text = String::formatted("{:.2f}", value);
+            // FIXME: This is a magic value; we know that with normal font sizes, the label will disappear starting from approximately this length.
+            //        Can we do this dynamically?
+            if (label_text.length() > 7)
+                m_value_label->set_text(String::formatted("{:.0f}", value));
+            else
+                m_value_label->set_text(label_text);
+        }
+    };
+    m_parameter.did_change_value = [this](auto value) {
+        set_value(value.raw());
+    };
+}

Userland/Applications/Piano/ProcessorParameterWidget/Slider.h

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+/*
+ * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include "WidgetWithLabel.h"
+#include <LibDSP/ProcessorParameter.h>
+#include <LibGUI/Label.h>
+#include <LibGUI/Slider.h>
+#include <LibGfx/Orientation.h>
+
+class ProcessorParameterSlider
+    : public GUI::Slider
+    , public WidgetWithLabel {
+    C_OBJECT(ProcessorParameterSlider);
+
+public:
+    ProcessorParameterSlider(Orientation, LibDSP::ProcessorRangeParameter&, RefPtr<GUI::Label>);
+
+protected:
+    LibDSP::ProcessorRangeParameter& m_parameter;
+};

Userland/Applications/Piano/ProcessorParameterWidget/WidgetWithLabel.h

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+/*
+ * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/RefPtr.h>
+#include <LibGUI/Label.h>
+
+class WidgetWithLabel {
+public:
+    WidgetWithLabel(RefPtr<GUI::Label> value_label)
+        : m_value_label(move(value_label))
+    {
+    }
+    RefPtr<GUI::Label> value_label() { return m_value_label; }
+
+protected:
+    RefPtr<GUI::Label> m_value_label;
+};