Fix errors

CLAUDE.md

@@ -661,11 +661,87 @@ PPIScope : public Scope (abstract) — shared PPI behavior:
   - Cursor range/bearing readout under scope (white text)
   - Bearing offset for boat mode (k/j)
   - Cursor range clamped to max range
-  - Range rings and labels are beam-painted per sweep sector, NOT a static overlay;
-    the sweep shader evaluates ring radii for the CURRENT max range at the moment
-    each beam angle is rendered; the phosphor buffer retains whatever was last
-    written, so old ring positions fade naturally as the sweep overwrites them with
-    new geometry — no special transition code required
+  - Range rings are beam-painted per sweep sector with P7 persistence and decay;
+    however they are stored in the GAIN-INDEPENDENT G channel of the phosphor FBO
+    (see PHOSPHOR FBO ARCHITECTURE below) so operator gain does not dim the rings
+  - renderRingLabels() — virtual method (default no-op); concrete PPI scopes that
+    have labelled range rings override this to render mile-distance text labels in
+    P7 fresh-blue colour at a fixed bearing (RING_LABEL_BRG_DEG = 045°)
+
+  IMPLEMENTER CHECKLIST — required in every new PPIScope subclass:
+    1. computeRingRadii(): multiply each normalised ring radius by
+       GRAT_INNER_RING_FRAC (same as MarinePPIScope).  Omitting this
+       places the outer ring at the scope boundary where it is clipped
+       and hidden behind the graticule.  Target positions are scaled
+       automatically by PhosphorRenderer::update(); ring radii are not.
+    2. Override renderRingLabels() using the same pattern as
+       MarinePPIScope::renderRingLabels() but with the scope's own
+       ring-mile table.  The base-class no-op produces no labels.
+    The p7Color() fix, two-channel FBO gain-separation, and target
+    position scaling are all automatic via the shared PhosphorRenderer
+    and shaders — no per-scope action required for those.
+
+==================================================================
+
+PHOSPHOR FBO ARCHITECTURE
+
+==================================================================
+
+The phosphor FBO is GL_RG32F (two independent float channels):
+
+  R channel — signal energy
+    Written by: target echoes in the sweep shader
+    Multiplied by: u_gain in the display shader
+    Effect: operator gain knob dims/brightens received echoes without
+            affecting the sweep beam or range rings
+
+  G channel — timing/geometry energy
+    Written by: range rings + sweep background glow in the sweep shader
+    NOT multiplied by gain in the display shader
+    Effect: rings always appear at a fixed brightness; the rotating
+            sweep-line glow is always visible even at minimum gain
+
+Both channels decay at the same P7 rate (P7_DECAY_RATE in settings.h).
+The display shader combines them: totalEnergy = max(R * gain, G).
+This produces the correct visual priority: a strong target echo always
+shows above the ring but a dim echo below gain threshold fades away
+while the ring stays steady.
+
+RANGE POSITION NORMALISATION
+
+All ring radii and target range values are normalised so that
+max-range maps to GRAT_INNER_RING_FRAC (0.915), NOT 1.0.
+
+Normalised 1.0 is the outer edge of the phosphor circle (scope boundary).
+The bearing graticule overlay occupies 0.915 to 0.985 of scope radius.
+If max-range mapped to 1.0, the outer ring would sit at the scope
+boundary — half-clipped by the sweep shader's rng > 1.0 early-exit and
+visually hidden behind the graticule outer ring.
+
+Mapping max-range → GRAT_INNER_RING_FRAC keeps all rings and targets
+within the clean active display area inside the bearing scale overlay.
+
+Scale is applied in two places:
+  1. PhosphorRenderer::update()  — target range: × GRAT_INNER_RING_FRAC
+  2. computeRingRadii() in each concrete PPI scope — ring radii: × GRAT_INNER_RING_FRAC
+
+P7 COLOUR FUNCTION
+
+p7Color() in phosphor.frag is a piecewise linear ramp over [0, 1]:
+  e ≥ T_BLUE (0.82) → pure C_BLUE
+  [T_GREEN, T_BLUE)  → mix(C_GREEN, C_BLUE,  normalised within range)
+  [T_YGREE, T_GREEN) → mix(C_YGREE, C_GREEN, normalised within range)
+  [T_DARK,  T_YGREE) → mix(C_YELLW, C_YGREE, normalised within range)
+  [0,       T_DARK)  → mix(C_BLACK, C_YELLW, normalised within range)
+
+Each mix() factor is in [0, 1] and the function is continuous at every
+threshold boundary. An earlier version had each branch using the formula
+of the branch below it (off-by-one), which caused SWEEP_BACKGROUND_ENERGY
+= 0.10 to render as saturated yellow (factor 3.33) instead of dim
+yellow-green, producing an unwanted solid-yellow band behind the sweep.
+
+==================================================================
+
 
 MarinePPIScope : public PPIScope
   - Sweep time: 4 seconds