278 lines
13 KiB
C++
278 lines
13 KiB
C++
// velocity_curve.cpp — see velocity_curve.h. Pure eval + editing/clamp/inverse map; no host types.
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#include "velocity_curve.h"
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#include <algorithm> // std::max, std::min, std::abs, std::stable_sort
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#include <cmath> // std::fabs
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#include <utility> // std::move
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namespace reasampler::vst {
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namespace {
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double clamp(double v, double lo, double hi) {
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if (v < lo) return lo;
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if (v > hi) return hi;
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return v;
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}
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double clampVelocity(double v) { return clamp(v, kVelMin, kVelMax); }
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double clampAmp(double a) { return clamp(a, kAmpMin, kAmpMax); }
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// Pixel<->box maps (mirror of envelope_edit's timeToX/levelToY). X spans the width for [0,127]; Y
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// spans (height-1) rows for amp [0,1] with amp 1 at the TOP (y increases downward).
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double velPerPixel(const VelocityCurve::Box& box) {
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const int w = std::max(0, box.width);
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if (w <= 0) return 0.0;
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return (kVelMax - kVelMin) / static_cast<double>(w);
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}
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double ampPerPixel(const VelocityCurve::Box& box) {
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const int h = std::max(0, box.height);
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if (h <= 1) return 0.0;
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return (kAmpMax - kAmpMin) / static_cast<double>(h - 1);
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}
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int velToX(const VelocityCurve::Box& box, double velocity) {
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const int w = std::max(0, box.width);
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if (w <= 0) return box.left;
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const double frac = (clampVelocity(velocity) - kVelMin) / (kVelMax - kVelMin);
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return box.left + static_cast<int>(frac * static_cast<double>(w) + 0.5);
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}
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int ampToY(const VelocityCurve::Box& box, double amp) {
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const int h = std::max(0, box.height);
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if (h <= 1) return box.top;
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// amp 1 at top (box.top), amp 0 at bottom (box.top + h - 1).
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const double frac = (clampAmp(amp) - kAmpMin) / (kAmpMax - kAmpMin);
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return box.top + static_cast<int>((1.0 - frac) * static_cast<double>(h - 1) + 0.5);
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}
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} // namespace
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VelocityCurve VelocityCurve::flat() {
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VelocityCurve c;
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c.points_ = {{kVelMin, kAmpMax}, {kVelMax, kAmpMax}}; // y = 1 everywhere (R10-F1 Option A)
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return c;
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}
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VelocityCurve VelocityCurve::linear() {
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VelocityCurve c;
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c.points_ = {{kVelMin, kAmpMin}, {kVelMax, kAmpMax}}; // y = velocity/127
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return c;
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}
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VelocityCurve VelocityCurve::fromPoints(std::vector<VelocityPoint> pts) {
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// Box-clamp every point, then stable-sort by velocity (X-order; stable so coincident-X points
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// keep their wire order). A stable sort keeps the eval well-defined for duplicate-X knots.
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for (VelocityPoint& p : pts) {
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p.velocity = clampVelocity(p.velocity);
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p.amp = clampAmp(p.amp);
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}
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std::stable_sort(pts.begin(), pts.end(),
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[](const VelocityPoint& a, const VelocityPoint& b) {
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return a.velocity < b.velocity;
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});
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// Fewer than 2 usable points -> can't span [0,127] as a function; fall back to the flat default.
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if (pts.size() < 2) return flat();
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// Force endpoints present at velocity 0 and 127 (they must exist for eval to be total).
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if (pts.front().velocity > kVelMin) {
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pts.insert(pts.begin(), VelocityPoint{kVelMin, pts.front().amp});
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} else {
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pts.front().velocity = kVelMin; // snap a near-0 first point exactly onto the endpoint
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}
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if (pts.back().velocity < kVelMax) {
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pts.push_back(VelocityPoint{kVelMax, pts.back().amp});
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} else {
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pts.back().velocity = kVelMax; // snap a near-127 last point exactly onto the endpoint
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}
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VelocityCurve c;
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c.points_ = std::move(pts);
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return c;
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}
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namespace {
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// Fritsch–Carlson monotone-cubic tangent for one interior knot i, given the secant slopes of the
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// two adjacent segments (dPrev = secant into knot i, dNext = secant out of knot i). Returns the
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// limited tangent that keeps the cubic Hermite piece monotone and inside the data range.
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//
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// The rule: a tangent whose adjacent secants have opposite signs (or either is flat) is a local
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// extremum — pin the tangent to 0 so the curve does not overshoot past the knot. Otherwise use the
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// weighted-harmonic-mean tangent (Fritsch–Carlson eq. 4), which for COLLINEAR knots (dPrev==dNext)
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// reduces to that common secant — so collinear control points reproduce the straight line to within
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// floating-point rounding (~1e-15), preserving the Option-B / null-response contract for linear().
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double fritschCarlsonTangent(double dPrev, double dNext, double spanPrev, double spanNext) {
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if (dPrev * dNext <= 0.0) return 0.0; // sign change or a flat neighbour -> local extremum
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// Weighted harmonic mean of the two secants (weights = the two segment widths). Collinear case:
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// dPrev==dNext==d makes this (w1+w2)*d / ((w1+w2)/... ) collapse to d exactly.
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const double w1 = 2.0 * spanNext + spanPrev;
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const double w2 = spanNext + 2.0 * spanPrev;
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return (w1 + w2) / (w1 / dPrev + w2 / dNext);
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}
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} // namespace
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double VelocityCurve::eval(double velocity) const {
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if (points_.empty()) return kAmpMax; // degenerate (shouldn't occur) -> flat unity
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if (points_.size() == 1) return clampAmp(points_[0].amp); // 1-point -> that point's amp
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const double v = clampVelocity(velocity);
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// At or before the first point / at or after the last, read the endpoint amp (the endpoints are
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// at 0 and 127, so this only fires exactly at the ends for an in-range velocity).
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if (v <= points_.front().velocity) return clampAmp(points_.front().amp);
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if (v >= points_.back().velocity) return clampAmp(points_.back().amp);
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// Find the segment [points_[i], points_[i+1]] containing v (X-ordered, so a linear scan).
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for (std::size_t i = 0; i + 1 < points_.size(); ++i) {
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const VelocityPoint& a = points_[i];
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const VelocityPoint& b = points_[i + 1];
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if (v >= a.velocity && v <= b.velocity) {
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const double span = b.velocity - a.velocity;
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// Coincident-X neighbours (a step): jump straight to the later point's amp — the segment
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// has zero width so there is no interior to blend.
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if (span <= 0.0) return clampAmp(b.amp);
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// --- Monotone cubic Hermite (Fritsch–Carlson) interpolation on segment [a,b] ---------
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// Curved (spline) response, not straight lines. The interpolant provably stays within
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// [a.amp, b.amp] between the two knots (no bulge below 0 / above 1), and for collinear
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// control points its tangents reduce to the secant slope — so it reproduces the straight
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// line to within floating-point rounding (~1e-15), preserving linear()'s null-response
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// contract (y = velocity/127 to ~1e-15; the test tolerance of 1e-12 is appropriate).
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const double d = (b.amp - a.amp) / span; // secant of THIS segment
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// Tangent at a: 0 if a is the first knot (endpoint), else the FC-limited tangent using
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// the previous segment's secant. Same for the tangent at b (0 at the last knot).
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double mA = d;
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if (i > 0) {
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const VelocityPoint& prev = points_[i - 1];
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const double spanPrev = a.velocity - prev.velocity;
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if (spanPrev > 0.0) {
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const double dPrev = (a.amp - prev.amp) / spanPrev;
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mA = fritschCarlsonTangent(dPrev, d, spanPrev, span);
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} else {
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mA = 0.0; // coincident-X predecessor (a step at a) -> flat tangent
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}
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}
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double mB = d;
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if (i + 2 < points_.size()) {
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const VelocityPoint& next = points_[i + 2];
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const double spanNext = next.velocity - b.velocity;
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if (spanNext > 0.0) {
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const double dNext = (next.amp - b.amp) / spanNext;
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mB = fritschCarlsonTangent(d, dNext, span, spanNext);
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} else {
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mB = 0.0; // coincident-X successor (a step at b) -> flat tangent
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}
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}
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// Cubic Hermite basis on the normalized position t across [a,b]. For collinear knots
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// mA==mB==d, so h00*a + (h10*span)*d + h01*b + (h11*span)*d collapses to the straight
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// line to within floating-point rounding (~1e-15).
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const double t = (v - a.velocity) / span;
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const double t2 = t * t;
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const double t3 = t2 * t;
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const double h00 = 2.0 * t3 - 3.0 * t2 + 1.0;
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const double h10 = t3 - 2.0 * t2 + t;
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const double h01 = -2.0 * t3 + 3.0 * t2;
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const double h11 = t3 - t2;
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const double y = h00 * a.amp + h10 * span * mA + h01 * b.amp + h11 * span * mB;
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return clampAmp(y);
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}
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}
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return clampAmp(points_.back().amp); // unreachable (v is between the endpoints)
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}
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std::size_t VelocityCurve::addPoint(double velocity, double amp) {
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const VelocityPoint p{clampVelocity(velocity), clampAmp(amp)};
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// Insert keeping X-order: first index whose velocity is STRICTLY greater than the new one, so a
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// duplicate-X point lands immediately after the existing one (a later move can separate them).
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std::size_t i = 0;
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while (i < points_.size() && points_[i].velocity <= p.velocity) ++i;
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points_.insert(points_.begin() + static_cast<std::ptrdiff_t>(i), p);
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return i;
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}
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VelocityPoint VelocityCurve::movePoint(std::size_t index, double velocity, double amp) {
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if (index >= points_.size()) return VelocityPoint{}; // no-op (out of range)
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const bool isFirst = (index == 0);
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const bool isLast = (index + 1 == points_.size());
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double newAmp = clampAmp(amp);
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double newVel;
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if (isFirst) {
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newVel = kVelMin; // endpoint pinned in X at 0 — only amp moves
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} else if (isLast) {
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newVel = kVelMax; // endpoint pinned in X at 127 — only amp moves
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} else {
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// Interior point: clamp X strictly within its immediate neighbours so it can't cross them.
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const double lo = points_[index - 1].velocity;
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const double hi = points_[index + 1].velocity;
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newVel = clamp(clampVelocity(velocity), lo, hi);
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}
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points_[index] = VelocityPoint{newVel, newAmp};
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return points_[index];
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}
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bool VelocityCurve::deletePoint(std::size_t index) {
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if (index >= points_.size()) return false;
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if (index == 0 || index + 1 == points_.size()) return false; // endpoints are not deletable
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points_.erase(points_.begin() + static_cast<std::ptrdiff_t>(index));
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return true;
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}
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VelocityCurve::CurvePixel VelocityCurve::pixelFromPoint(const Box& box, const VelocityPoint& p) {
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return CurvePixel{velToX(box, p.velocity), ampToY(box, p.amp)};
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}
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VelocityPoint VelocityCurve::pointFromPixel(const Box& box, int x, int y) {
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// The exact inverse of velToX/ampToY (within the one-pixel rounding quantum). Degenerate
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// dimensions collapse the same way the forward map does: velToX pins to box.left (velocity 0),
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// ampToY pins to box.top (amp 1).
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VelocityPoint p;
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const int w = std::max(0, box.width);
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const int h = std::max(0, box.height);
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p.velocity = (w <= 0)
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? kVelMin
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: clampVelocity(kVelMin + static_cast<double>(x - box.left) / static_cast<double>(w) *
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(kVelMax - kVelMin));
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p.amp = (h <= 1)
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? kAmpMax
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: clampAmp(kAmpMax - static_cast<double>(y - box.top) / static_cast<double>(h - 1) *
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(kAmpMax - kAmpMin));
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return p;
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}
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int VelocityCurve::pointAtPixel(const Box& box, int x, int y) const {
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for (std::size_t i = 0; i < points_.size(); ++i) {
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const int px = velToX(box, points_[i].velocity);
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const int py = ampToY(box, points_[i].amp);
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if (std::abs(x - px) <= kCurveNodeGrabRadius && std::abs(y - py) <= kCurveNodeGrabRadius) {
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return static_cast<int>(i);
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}
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}
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return -1;
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}
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VelocityCurve VelocityCurve::resolvePointDrag(const VelocityCurve& grabCurve, std::size_t index,
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const Box& box, int dxPixels, int dyPixels) {
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VelocityCurve out = grabCurve;
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if (index >= out.points_.size()) return out; // out of range -> no motion
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const double velPerPx = velPerPixel(box);
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const double ampPerPx = ampPerPixel(box);
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if (velPerPx <= 0.0 || ampPerPx <= 0.0) return out; // degenerate box -> no motion
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const VelocityPoint& grab = grabCurve.points_[index];
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const double newVel = grab.velocity + static_cast<double>(dxPixels) * velPerPx;
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// Y increases downward but amp increases upward, so a downward drag (positive dy) LOWERS amp.
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const double newAmp = grab.amp - static_cast<double>(dyPixels) * ampPerPx;
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out.movePoint(index, newVel, newAmp); // applies box + neighbour-X + endpoint-pin clamps
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return out;
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}
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bool VelocityCurve::equals(const VelocityCurve& other, double eps) const {
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if (points_.size() != other.points_.size()) return false;
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for (std::size_t i = 0; i < points_.size(); ++i) {
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if (std::fabs(points_[i].velocity - other.points_[i].velocity) > eps) return false;
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if (std::fabs(points_[i].amp - other.points_[i].amp) > eps) return false;
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}
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return true;
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}
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} // namespace reasampler::vst
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