reasampler/src/vst/keyboard_strip.h

// keyboard_strip.h — PURE layout + hit-test + drag math for the S10 capture-first
// editor's keyboard strip. NO VST3, NO REAPER, NO SWELL/LICE types at the boundary.
// The mirror of editor_geometry / embed_strip / mode_switch: the fiddly rectangle +
// note-mapping arithmetic lives here so it is unit-tested outside the DAW, while the
// editor shell (reasampler_editor.cpp) draws the strip and marshals mouse events into
// these functions.
//
// The strip maps the full 128-key MIDI span across a horizontal band (the same key-span
// idiom embed_strip uses). It serves TWO faces of the S10 editor:
//   * the SINGLE-CAPTURE fast path (default): one loaded capture with a ROOT MARKER on
//     the strip, click-a-key (or drag the marker) sets the capture's root note; and
//   * the opt-in ZONES panel (S10-Z, demoted): each performance zone drawn as a bar over
//     the keys it covers, with edge-grab resize handles + a body move-handle so a drag
//     sets low/high (edges) or moves the span (body), and a key-click sets the zone root.
//
// All interaction resolves through the pure DRAG-DELTA resolver here: the shell captures
// a grab on WM_LBUTTONDOWN, feeds each WM_MOUSEMOVE's pixel delta back through
// resolveDragNote, and commits the resolved note(s) on WM_LBUTTONUP. Live feedback is the
// shell re-drawing the in-flight note; one coherent edit lands on release.
//
// It reuses the same Rect + contains() as editor_geometry (one shared geometry idiom),
// so this header depends on editor_geometry.h rather than redefining a rectangle type.

#pragma once

#include "editor_geometry.h"  // Rect, contains — one shared geometry idiom

namespace reasampler::vst {

// The full MIDI key span the strip maps across its width: 128 keys (0..127). Named
// distinctly from embed_strip's kEmbedKeyCount (same value) so the two strips stay
// independent — the editor strip may grow octave labels/metrics the embed strip never does.
inline constexpr int kStripKeyCount = 128;

// The width (px) of an edge-grab hit region at each end of a zone bar: a drag started
// within this many pixels of the bar's left/right edge resizes that edge; a drag started
// anywhere else on the bar moves the whole span. A zone narrower than 2*this has no body
// move-handle (both edges win their halves) — deliberate: a 1-key zone is all edges.
inline constexpr int kStripEdgeGrabWidth = 6;

// The strip's regions, derived from the (w x h) band the shell allots it. The keys band
// takes the whole area today (a future octave-label lane can carve a sub-band here without
// changing callers). Clamped so a degenerate (tiny/zero) size never yields an inverted rect.
struct StripLayout {
    Rect keys;  // the key band: the 128-key span maps linearly across keys.width()
};

// Divide a (w x h) strip area into its regions. Pure: same inputs -> same layout. A zero or
// negative size yields empty rects (no inversion).
StripLayout layoutStrip(int w, int h);

// The x pixel (inside the keys band) of the LEFT edge of key `note` (0..127). The 128-key
// span maps linearly across keys.width(); key N occupies the half-open pixel range
// [keyLeftX(N), keyLeftX(N+1)). Notes are clamped to [0,127]; note==128 maps to the band's
// right edge (so a key's right edge is keyLeftX(note+1)). Pure.
int keyLeftX(const StripLayout& layout, int note);

// The half-open pixel rect of a single key `note` (0..127): [keyLeftX(note),
// keyLeftX(note+1)) horizontally, the full keys-band height. A malformed (out-of-range)
// note clamps to [0,127]. Pure.
Rect keyRect(const StripLayout& layout, int note);

// The rect of the ROOT MARKER for the single-capture fast path: the key cell of `rootNote`,
// drawn as a highlighted key. Equivalent to keyRect(layout, rootNote) — a named entry point
// so the shell's intent (this is the root marker, not just any key) reads at the call site,
// and so a future marker shape (a triangle over the key) has one place to change. Pure.
Rect rootMarkerRect(const StripLayout& layout, int rootNote);

// The MIDI note a point (x, y) lands on, or -1 for a point outside the keys band. Backs
// click-to-set-root (single capture) and click-a-key-sets-zone-root (zones). Pure.
int keyAtPoint(const StripLayout& layout, int x, int y);

// The horizontal sub-rect of the keys band for a zone spanning [lowNote, highNote]
// (inclusive): [keyLeftX(low), keyLeftX(high+1)) horizontally, the full band height. Notes
// clamp to [0,127] and low clamps to <= high, so a malformed zone yields an in-band
// (possibly zero-width) rect, never an inverted one. Mirrors embed_strip::zoneSegmentRect.
// Pure.
Rect zoneBarRect(const StripLayout& layout, int lowNote, int highNote);

// Which part of a zone bar a grab landed on. The shell uses this to decide what a drag
// edits: an edge resizes that boundary; the body moves the whole span; none means the grab
// missed the bar entirely (the shell may treat that as a key-click to set the root, or as a
// deselect).
enum class ZoneGrab {
    kNone,      // the point is not on this zone's bar
    kLowEdge,   // within kStripEdgeGrabWidth of the bar's LEFT edge -> resize low
    kHighEdge,  // within kStripEdgeGrabWidth of the bar's RIGHT edge -> resize high
    kBody,      // on the bar but not an edge -> move the whole span
};

// Classify a grab at (x, y) against ONE zone's bar (low..high). Returns kNone when the
// point is off the bar (or off the keys band). On the bar: kLowEdge/kHighEdge when within
// kStripEdgeGrabWidth of that edge, else kBody. A narrow bar (< 2*kStripEdgeGrabWidth)
// resolves the near half to each edge (no body). The LOW edge wins a tie at the exact
// midpoint of a narrow bar (deterministic). Pure.
ZoneGrab zoneGrabAt(const StripLayout& layout, int lowNote, int highNote, int x, int y);

// The zone (index into `lows`/`highs`, draw order) whose bar a grab at (x, y) lands on,
// plus which part of it, or {-1, kNone} for a point off every bar. First covering zone in
// draw order wins (first-match, mirroring the core's Keymap::resolve + embed_strip). The
// arrays are parallel (lows[i]/highs[i] is zone i's inclusive range); `count` is their
// length. Pure — no host containers at the boundary (a raw pointer pair, like
// embed_strip::zoneAtPoint).
struct ZoneBarHit {
    int zoneIndex = -1;
    ZoneGrab grab = ZoneGrab::kNone;
};
ZoneBarHit zoneBarAtPoint(const StripLayout& layout, const int* lows, const int* highs,
                          int count, int x, int y);

// Resolve a drag to a new MIDI note. Given the note the grabbed field held at grab time
// (`startNote`) and the horizontal pixel delta since grab (`dxPixels`), returns the note
// the field should now hold: startNote shifted by round(dxPixels / keyWidth), clamped to
// [0,127]. keyWidth is derived from the layout (band width / 128); a zero-width band pins
// the result to startNote (no motion). This is the single arithmetic behind edge-resize,
// body-move (apply to both edges with the SAME delta so the span is preserved), and
// root-marker drag. Pure — rounding is to the nearest key so a half-key drag flips at the
// key centre. Returns startNote unchanged for dxPixels==0.
int resolveDragNote(const StripLayout& layout, int startNote, int dxPixels);

// Returns true when `note` (0..127) is a NATURAL (white) key in standard 12-tone equal
// temperament; false when it is an ACCIDENTAL (black) key. Notes out of the [0,127]
// range are clamped to [0,127] before classification (i.e. this never throws/UBs on a
// bad input). The 12 semitone positions within an octave:
//   Natural (white):    0(C)  2(D)  4(E)  5(F)  7(G)  9(A)  11(B)
//   Accidental (black): 1(C#) 3(D#) 6(F#) 8(G#) 10(A#)
// Used by the shell to overlay the two-tone bright/dark piano-key pattern over the
// pastel spectral fill (S-VIEW-7). Pure — no layout required, no host types.
bool isNaturalKey(int note);

}  // namespace reasampler::vst