[feat](trx-frontend-http): add waterfall contrast gamma curve slider

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js

@@ -1025,7 +1025,7 @@ function overviewWfResetTextureCache() {
 }
 
 function overviewWfPaletteKey(pal, viewKey = "") {
-  return `${pal.waterfallHue}|${pal.waterfallSat}|${pal.waterfallLight}|${pal.waterfallAlpha}|${spectrumFloor}|${spectrumRange}|${viewKey}`;
+  return `${pal.waterfallHue}|${pal.waterfallSat}|${pal.waterfallLight}|${pal.waterfallAlpha}|${spectrumFloor}|${spectrumRange}|${waterfallGamma}|${viewKey}`;
 }
 
 function resizeHeaderSignalCanvas() {
@@ -1401,7 +1401,8 @@ function waterfallColorRgba(db, pal, minDb, maxDb) {
   const safeDb = Number.isFinite(db) ? db : lo;
   const clamped = Math.max(lo, Math.min(hi, safeDb));
   const span = Math.max(1, hi - lo);
-  const t = (clamped - lo) / span;
+  const tLinear = (clamped - lo) / span;
+  const t = waterfallGamma === 1.0 ? tLinear : Math.pow(tLinear, waterfallGamma);
   const hue = pal.waterfallHue[0] + t * (pal.waterfallHue[1] - pal.waterfallHue[0]);
   const light = pal.waterfallLight[0] + t * (pal.waterfallLight[1] - pal.waterfallLight[0]);
   const alpha = pal.waterfallAlpha[0] + t * (pal.waterfallAlpha[1] - pal.waterfallAlpha[0]);
@@ -8137,6 +8138,7 @@ let spectrumPanFrac = 0.5;
 // Y-axis level: floor = bottom dB value shown; range = total dB span.
 let spectrumFloor = -115;
 let spectrumRange = 90;
+let waterfallGamma = 1.0;
 const SPECTRUM_HEADROOM_DB = 20;
 const SPECTRUM_SMOOTH_ALPHA = 0.42;
 
@@ -9786,4 +9788,17 @@ if (spectrumCenterRightBtn) {
       scheduleSpectrumDraw();
     });
   }
+
+  const gammaInput = document.getElementById("spectrum-gamma-input");
+  const gammaValue = document.getElementById("spectrum-gamma-value");
+  if (gammaInput) {
+    gammaInput.addEventListener("input", () => {
+      const v = Number(gammaInput.value);
+      if (Number.isFinite(v) && v > 0) {
+        waterfallGamma = v;
+        if (gammaValue) gammaValue.textContent = v.toFixed(1);
+        if (lastSpectrumData) scheduleSpectrumDraw();
+      }
+    });
+  }
 })();

src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html

@@ -146,6 +146,7 @@
             </label>
             <label id="spectrum-floor-label">Floor <input type="number" id="spectrum-floor-input" value="-115" step="5" /> dB</label>
             <button id="spectrum-auto-btn" type="button">Auto</button>
+            <label id="spectrum-gamma-label">Contrast <input type="range" id="spectrum-gamma-input" min="0.2" max="3.0" step="0.1" value="1.0" /><span id="spectrum-gamma-value">1.0</span></label>
           </div>
         </div>
         <div id="spectrum-hint" class="spectrum-hint-mouse">Scroll to zoom &middot; Ctrl+Scroll to tune &middot; Drag to pan &middot; Drag BW edges to resize</div>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/style.css

@@ -2573,6 +2573,7 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   }
   #spectrum-bw-label,
   #spectrum-floor-label,
+  #spectrum-gamma-label,
   #spectrum-peak-hold-label {
     width: 100%;
     justify-content: space-between;
@@ -3113,6 +3114,23 @@ button:focus-visible, input:focus-visible, select:focus-visible {
   padding: 0 8px;
   font-size: 0.73rem;
 }
+#spectrum-gamma-label {
+  display: flex;
+  align-items: center;
+  gap: 0.3rem;
+  font-size: 0.75rem;
+  color: var(--text-muted);
+}
+#spectrum-gamma-input {
+  width: 5rem;
+  height: 1.5rem;
+  cursor: pointer;
+}
+#spectrum-gamma-value {
+  font-size: 0.72rem;
+  min-width: 1.6rem;
+  text-align: right;
+}
 .spectrum-hint-mouse,
 .spectrum-hint-touch {
   font-size: 0.68rem;