Retire the zone system: one capture = one parameter set, and re-seam the engine and Sample face into bands

src/core/instrument/ui/sample_bands.h

@@ -0,0 +1,53 @@
+#pragma once
+// sample_bands.h — THE band-stack allocator for the Sample face: the one module that owns
+// the editor's vertical inventory. Three bands, top to bottom — CHROME (toolbar + control
+// row), WAVEFORM (elastic, sized to hold two stacked channel lanes), DECKS (the knob-deck
+// row). Everything else in the editor fills a band it is handed; nothing else allocates
+// vertical space, so a band's owner can re-lay its interior without moving its neighbours.
+
+#include "core/instrument/ui/editor_geometry.h"  // Rect
+
+namespace reasampler::instrument::ui {
+
+// Shared outer inset every band honours horizontally.
+inline constexpr int kPad = 8;
+
+// Chrome band: the toolbar row (title + nav) stacked over the control row (piano strip,
+// preview, velocity knob, curve button, channel toggle). sample_chrome partitions it.
+inline constexpr int kTitleHeight = 26;
+inline constexpr int kChromeRowHeight = 52;
+
+// Waveform band floor: two stacked lanes plus the seam between them. The band never shrinks
+// below this — a window too short for it clips the bands beneath instead, so the waveform
+// stays a usable two-lane surface at every size.
+inline constexpr int kLaneMinHeight = 74;
+inline constexpr int kLaneGap = 2;
+inline constexpr int kWaveformMinHeight = 2 * kLaneMinHeight + kLaneGap;
+
+// Vertical seam between adjacent bands.
+inline constexpr int kBandGap = 4;
+
+// The vertical inventory. Bands never overlap and are returned top-to-bottom; a band may be
+// empty() on a degenerate window, in which case its owner draws and hit-tests nothing.
+struct SampleBands {
+    Rect chrome;    // full width: toolbar row + control row
+    Rect waveform;  // kPad-inset, elastic, >= kWaveformMinHeight
+    Rect decks;     // kPad-inset, bottom-anchored, height `deckHeight`
+};
+
+// Divide a (w x h) client area into the three bands. `deckHeight` is the knob deck's own
+// wrapped height (from knob_deck) — the only interior measurement the allocator needs, so
+// the deck band is exactly as tall as its content. Pure.
+SampleBands computeSampleBands(int w, int h, int deckHeight);
+
+// The waveform band's two channel lanes: L above R, separated by kLaneGap. In mono only
+// `upper` is populated (it takes the whole band) and `lower` is empty — a mono capture has
+// no second lane to draw, and overlays that ride the waveform draw ONCE across the whole
+// band in either mode, never per lane.
+struct WaveformLanes {
+    Rect upper;
+    Rect lower;  // empty() in mono
+};
+WaveformLanes waveformLanes(const Rect& waveform, bool stereo);
+
+}  // namespace reasampler::instrument::ui