--- /dev/null
+#include "nonlinear_fader.h"
+
+#include <assert.h>
+#include <math.h>
+#include <QPainter>
+#include <QPoint>
+#include <QRect>
+#include <QStyle>
+#include <QStyleOption>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "piecewise_interpolator.h"
+
+class QPaintEvent;
+class QWidget;
+
+using namespace std;
+
+namespace {
+
+PiecewiseInterpolator interpolator({
+ // The main area is from +6 to -12 dB (18 dB), and we use half the slider range for it.
+ // Adjust slightly so that the MIDI controller value of 106 becomes exactly 0.0 dB
+ // (cf. map_controller_to_float()); otherwise, we'd miss ever so slightly, which is
+ // really frustrating.
+ { 6.0, 1.0 },
+ { -12.0, 1.0 - (1.0 - 106.5/127.0) * 3.0 }, // About 0.492.
+
+ // -12 to -21 is half the range (9 dB). Halve.
+ { -21.0, 0.325 },
+
+ // -21 to -30 (9 dB) gets the same range as the previous one.
+ { -30.0, 0.25 },
+
+ // -30 to -48 (18 dB) gets half of half.
+ { -48.0, 0.125 },
+
+ // -48 to -84 (36 dB) gets half of half of half.
+ { -84.0, 0.0 },
+});
+
+} // namespace
+
+NonLinearFader::NonLinearFader(QWidget *parent)
+ : QSlider(parent)
+{
+ update_slider_position();
+}
+
+void NonLinearFader::setDbValue(double db)
+{
+ db_value = db;
+ update_slider_position();
+ emit dbValueChanged(db);
+}
+
+void NonLinearFader::paintEvent(QPaintEvent *event)
+{
+ QStyleOptionSlider opt;
+ this->initStyleOption(&opt);
+ QRect gr = this->style()->subControlRect(QStyle::CC_Slider, &opt, QStyle::SC_SliderGroove, this);
+ QRect sr = this->style()->subControlRect(QStyle::CC_Slider, &opt, QStyle::SC_SliderHandle, this);
+
+ // FIXME: Where does the slider_length / 2 come from? I can't really find it
+ // in the Qt code, but it seems to match up with reality.
+ int slider_length = sr.height();
+ int slider_max = gr.top() + (slider_length / 2);
+ int slider_min = gr.bottom() + (slider_length / 2) - slider_length + 1;
+
+ QPainter p(this);
+
+ // Draw some ticks every 6 dB.
+ // FIXME: Find a way to make the slider wider, so that we have more space for tickmarks
+ // and some dB numbering.
+ int x_margin = 5;
+ p.setPen(Qt::darkGray);
+ for (int db = -84; db <= 6; db += 6) {
+ int y = slider_min + lrint(interpolator.db_to_fraction(db) * (slider_max - slider_min));
+ p.drawLine(QPoint(0, y), QPoint(gr.left() - x_margin, y));
+ p.drawLine(QPoint(gr.right() + x_margin, y), QPoint(width() - 1, y));
+ }
+
+ QSlider::paintEvent(event);
+}
+
+void NonLinearFader::sliderChange(SliderChange change)
+{
+ QSlider::sliderChange(change);
+ if (change == QAbstractSlider::SliderValueChange && !inhibit_updates) {
+ if (value() == 0) {
+ db_value = -HUGE_VAL;
+ } else {
+ double frac = double(value() - minimum()) / (maximum() - minimum());
+ db_value = interpolator.fraction_to_db(frac);
+ }
+ emit dbValueChanged(db_value);
+ }
+}
+
+void NonLinearFader::update_slider_position()
+{
+ inhibit_updates = true;
+ double val = interpolator.db_to_fraction(db_value) * (maximum() - minimum()) + minimum();
+ setValue(lrint(val));
+ inhibit_updates = false;
+}