Piano: Rewrite application

Goals:
- Switch to a more typical LibGUI arrangement
- Separate GUI (MainWidget) and audio (AudioEngine)
- Improve on existing features while retaining the same feature set

Improvements:
- Each GUI element is a separate widget
- The wave (WaveWidget) scales with the window
- The piano roll (RollWidget) scales horizontally and scrolls vertically
- The piano (KeysWidget) fits as many notes as possible
- The knobs (KnobsWidget) are now sliders
- All mouse and key events are handled in constant time
- The octave can be changed while playing notes
- The same note can be played with the mouse, keyboard and roll at the
  same time, and the volume of the resulting note is scaled accordingly
- Note frequency constants use the maximum precision available in a
  double

Applications/Piano/WaveWidget.cpp

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2019-2020, William McPherson <willmcpherson2@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "WaveWidget.h"
+#include "AudioEngine.h"
+#include <LibGUI/GPainter.h>
+#include <limits>
+
+WaveWidget::WaveWidget(GWidget* parent, AudioEngine& audio_engine)
+    : GFrame(parent)
+    , m_audio_engine(audio_engine)
+{
+    set_frame_thickness(2);
+    set_frame_shadow(FrameShadow::Sunken);
+    set_frame_shape(FrameShape::Container);
+}
+
+WaveWidget::~WaveWidget()
+{
+}
+
+static const Color wave_colors[] = {
+    // Sine
+    {
+        255,
+        192,
+        0,
+    },
+    // Triangle
+    {
+        35,
+        171,
+        35,
+    },
+    // Square
+    {
+        128,
+        160,
+        255,
+    },
+    // Saw
+    {
+        240,
+        100,
+        128,
+    },
+    // Noise
+    {
+        197,
+        214,
+        225,
+    },
+};
+
+int WaveWidget::sample_to_y(int sample) const
+{
+    constexpr double sample_max = std::numeric_limits<i16>::max();
+    double percentage = sample / sample_max;
+    double portion_of_height = percentage * frame_inner_rect().height();
+    int y = (frame_inner_rect().height() / 2) + portion_of_height;
+    return y;
+}
+
+void WaveWidget::paint_event(GPaintEvent& event)
+{
+    GPainter painter(*this);
+    painter.fill_rect(frame_inner_rect(), Color::Black);
+    painter.translate(frame_thickness(), frame_thickness());
+
+    Color wave_color = wave_colors[m_audio_engine.wave()];
+    auto buffer = m_audio_engine.buffer();
+    double width_scale = static_cast<double>(frame_inner_rect().width()) / buffer.size();
+
+    int prev_x = 0;
+    int prev_y = sample_to_y(buffer[0].left);
+    painter.set_pixel({ prev_x, prev_y }, wave_color);
+
+    for (size_t x = 1; x < buffer.size(); ++x) {
+        int y = sample_to_y(buffer[x].left);
+
+        Point point1(prev_x * width_scale, prev_y);
+        Point point2(x * width_scale, y);
+        painter.draw_line(point1, point2, wave_color);
+
+        prev_x = x;
+        prev_y = y;
+    }
+
+    GFrame::paint_event(event);
+}