feat: add signal stats panel for selection region

Display Duration, Energy, Peak amplitude, RMS amplitude, and PAPR for
the current time/frequency selection. The stats box:
- Appears next to the selection box (right side, or left if not enough room)
- Centers vertically on the selection box
- Uses a semi-transparent dark background with yellow border
- Updates live while dragging the selection
- Computed in utils.c with ComputeSignalStats()

.qwen/settings.json

@@ -0,0 +1,8 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(make)"
+    ]
+  },
+  "$version": 4
+}

.qwen/settings.json.orig

@@ -0,0 +1,7 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(make)"
+    ]
+  }
+}

rspektrum.make

@@ -120,8 +120,10 @@ OBJECTS :=
 
 GENERATED += $(OBJDIR)/spectrogram.o
 GENERATED += $(OBJDIR)/platform_linux.o
+GENERATED += $(OBJDIR)/utils.o
 OBJECTS += $(OBJDIR)/spectrogram.o
 OBJECTS += $(OBJDIR)/platform_linux.o
+OBJECTS += $(OBJDIR)/utils.o
 
 # Rules
 # #############################################
@@ -193,6 +195,10 @@ $(OBJDIR)/platform_linux.o: src/platform_linux.c
 	@echo "$(notdir $<)"
 	$(SILENT) $(CC) $(ALL_CFLAGS) $(FORCE_INCLUDE) -o "$@" -MF "$(@:%.o=%.d)" -c "$<"
 
+$(OBJDIR)/utils.o: src/utils.c
+	@echo "$(notdir $<)"
+	$(SILENT) $(CC) $(ALL_CFLAGS) $(FORCE_INCLUDE) -o "$@" -MF "$(@:%.o=%.d)" -c "$<"
+
 -include $(OBJECTS:%.o=%.d)
 ifneq (,$(PCH))
   -include $(PCH_PLACEHOLDER).d

src/spectrogram.c

@@ -4,6 +4,7 @@
 #include "raylib.h"
 #include "resource_dir.h"
 #include "platform.h"
+#include "utils.h"
 
 #include <stdlib.h>
 #include <string.h>
@@ -64,14 +65,6 @@ typedef enum {
 // Data Structures
 // ============================================================================
 
-typedef struct {
-    float* samples;
-    int numSamples;
-    int sampleRate;
-    int channels;
-    float duration;
-} AudioSignal;
-
 typedef struct {
     float frequency;
     float amplitude;
@@ -1210,6 +1203,70 @@ static void DrawSelection(Rectangle bounds)
     
     // Draw selection box border
     DrawRectangleLinesEx((Rectangle){ selStartX, selStartY, selEndX - selStartX, selEndY - selStartY }, 2, YELLOW);
+
+    // Display selection stats inside viewport, clamped to fit
+    {
+        int startSample = (int)(app.timeSelectionStart * app.signal.numSamples);
+        int endSample = (int)(app.timeSelectionEnd * app.signal.numSamples);
+        SignalStats stats = ComputeSignalStats(&app.signal, startSample, endSample);
+
+        if (stats.durationSec > 0.0f && app.signal.samples != NULL) {
+            char lines[5][128];
+            int lineCount = 0;
+            int fontSize = 10;
+            int maxTextW = 0;
+
+            sprintf(lines[lineCount++], "Duration: %.3fs", stats.durationSec);
+            sprintf(lines[lineCount++], "Energy: %.2f", stats.energy);
+            sprintf(lines[lineCount++], "Peak: %.3f", stats.peakAmplitude);
+            sprintf(lines[lineCount++], "RMS: %.3f", stats.rmsAmplitude);
+            sprintf(lines[lineCount++], "PAPR: %.1f dB", stats.paprDb);
+
+            // Measure text width
+            for (int i = 0; i < lineCount; i++) {
+                int textW = MeasureText(lines[i], fontSize);
+                if (textW > maxTextW) maxTextW = textW;
+            }
+
+            int boxW = maxTextW + 20;
+            int boxH = lineCount * 14 + 12;
+
+            // Center vertically on the selection box, clamp to viewport
+            float selCenterY = (selStartY + selEndY) / 2.0f;
+            float boxY = selCenterY - boxH / 2.0f;
+            if (boxY < bounds.y) boxY = bounds.y;
+            if (boxY + boxH > bounds.y + bounds.height) boxY = bounds.y + bounds.height - boxH;
+
+            // Place to the right of the selection, or left if not enough room
+            float boxX = selEndX + 10;
+            if (boxX + boxW > bounds.x + bounds.width) {
+                boxX = selStartX - boxW - 10;
+                if (boxX < bounds.x) boxX = bounds.x;
+            }
+
+            // Clamp to viewport bounds
+            if (boxX + boxW > bounds.x + bounds.width) {
+                // Not enough room on right — draw to the left of selection
+                if (selStartX > boxW + 20) {
+                    boxX = selStartX - boxW - 10;
+                } else {
+                    boxX = bounds.x;
+                }
+            }
+            if (boxY + boxH > bounds.y + bounds.height) {
+                boxY = bounds.y + bounds.height - boxH;
+            }
+
+            // Draw background box
+            DrawRectangle((int)boxX, (int)boxY, boxW, boxH, (Color){ 0, 0, 0, 200 });
+            DrawRectangleLines((int)boxX, (int)boxY, boxW, boxH, Fade(YELLOW, 0.6f));
+
+            // Draw text
+            for (int i = 0; i < lineCount; i++) {
+                DrawText(lines[i], (int)boxX + 10, (int)boxY + 8 + i * 14, fontSize, LIGHTGRAY);
+            }
+        }
+    }
 }
 
 static void DrawSelectionDrag(Rectangle bounds)
@@ -1240,6 +1297,70 @@ static void DrawSelectionDrag(Rectangle bounds)
     float h = fabsf(selEndY - selStartY);
     
     DrawRectangleLinesEx((Rectangle){ x, y, w, h }, 2, YELLOW);
+
+    // Display live stats while dragging (inside viewport, clamped to fit)
+    {
+        int startSample = (int)(app.timeSelectionStart * app.signal.numSamples);
+        int endSample = (int)(app.timeSelectionEnd * app.signal.numSamples);
+        SignalStats stats = ComputeSignalStats(&app.signal, startSample, endSample);
+
+        if (stats.durationSec > 0.0f && app.signal.samples != NULL) {
+            char lines[5][128];
+            int lineCount = 0;
+            int fontSize = 10;
+            int maxTextW = 0;
+
+            sprintf(lines[lineCount++], "Duration: %.3fs", stats.durationSec);
+            sprintf(lines[lineCount++], "Energy: %.2f", stats.energy);
+            sprintf(lines[lineCount++], "Peak: %.3f", stats.peakAmplitude);
+            sprintf(lines[lineCount++], "RMS: %.3f", stats.rmsAmplitude);
+            sprintf(lines[lineCount++], "PAPR: %.1f dB", stats.paprDb);
+
+            // Measure text width
+            for (int i = 0; i < lineCount; i++) {
+                int textW = MeasureText(lines[i], fontSize);
+                if (textW > maxTextW) maxTextW = textW;
+            }
+
+            int boxW = maxTextW + 20;
+            int boxH = lineCount * 14 + 12;
+
+            // Center vertically on the selection box, clamp to viewport
+            float selCenterY = (selStartY + selEndY) / 2.0f;
+            float boxY = selCenterY - boxH / 2.0f;
+            if (boxY < bounds.y) boxY = bounds.y;
+            if (boxY + boxH > bounds.y + bounds.height) boxY = bounds.y + bounds.height - boxH;
+
+            // Place to the right of the selection, or left if not enough room
+            float boxX = selEndX + 10;
+            if (boxX + boxW > bounds.x + bounds.width) {
+                boxX = selStartX - boxW - 10;
+                if (boxX < bounds.x) boxX = bounds.x;
+            }
+
+            // Clamp to viewport bounds
+            if (boxX + boxW > bounds.x + bounds.width) {
+                // Not enough room on right — draw to the left of selection
+                if (x > boxW + 20) {
+                    boxX = x - boxW - 10;
+                } else {
+                    boxX = bounds.x;
+                }
+            }
+            if (boxY + boxH > bounds.y + bounds.height) {
+                boxY = bounds.y + bounds.height - boxH;
+            }
+
+            // Draw background box
+            DrawRectangle((int)boxX, (int)boxY, boxW, boxH, (Color){ 0, 0, 0, 200 });
+            DrawRectangleLines((int)boxX, (int)boxY, boxW, boxH, Fade(YELLOW, 0.6f));
+
+            // Draw text
+            for (int i = 0; i < lineCount; i++) {
+                DrawText(lines[i], (int)boxX + 10, (int)boxY + 8 + i * 14, fontSize, LIGHTGRAY);
+            }
+        }
+    }
 }
 
 // ============================================================================

src/utils.c

@@ -0,0 +1,65 @@
+// Signal analysis utilities for spectrogram selection stats
+
+#include <math.h>
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+    float* samples;
+    int numSamples;
+    int sampleRate;
+    int channels;
+    float duration;
+} AudioSignal;
+
+typedef struct {
+    float durationSec;
+    float energy;
+    float peakAmplitude;
+    float rmsAmplitude;
+    float paprDb;      // Peak-to-Average Power Ratio in dB
+    int peakSampleIdx;  // sample index of peak amplitude
+} SignalStats;
+
+SignalStats ComputeSignalStats(const AudioSignal* signal, int startSample, int endSample)
+{
+    SignalStats stats = {0};
+
+    if (!signal || !signal->samples || endSample <= startSample ||
+        startSample < 0 || endSample > signal->numSamples) {
+        return stats;
+    }
+
+    int numSamples = endSample - startSample;
+    float* samples = signal->samples + startSample;
+    float peak = 0.0f;
+    float energy = 0.0f;
+    int peakIdx = 0;
+
+    // Compute energy and find peak
+    for (int i = 0; i < numSamples; i++) {
+        float amp = samples[i];
+        energy += amp * amp;
+        if (fabsf(amp) > peak) {
+            peak = fabsf(amp);
+            peakIdx = i;
+        }
+    }
+
+    stats.energy = energy;
+    stats.peakAmplitude = peak;
+    stats.rmsAmplitude = sqrtf(energy / numSamples);
+    stats.durationSec = (float)numSamples / (float)signal->sampleRate;
+    stats.peakSampleIdx = startSample + peakIdx;
+
+    // PAPR in dB: 10 * log10(peak^2 / avg_power)
+    // avg_power = energy / numSamples = rms^2
+    // So PAPR = 10 * log10(peak^2 / rms^2) = 20 * log10(peak / rms)
+    if (stats.rmsAmplitude > 0.0f) {
+        stats.paprDb = 10.0f * log10f((peak * peak) / (stats.rmsAmplitude * stats.rmsAmplitude));
+    } else {
+        stats.paprDb = 0.0f;
+    }
+
+    return stats;
+}

src/utils.h

@@ -0,0 +1,26 @@
+#ifndef SIGNAL_UTILS_H
+#define SIGNAL_UTILS_H
+
+// Structure mirroring AudioSignal from spectrogram.c
+// (kept separate to avoid circular dependencies and coupling)
+typedef struct {
+    float* samples;
+    int numSamples;
+    int sampleRate;
+    int channels;
+    float duration;
+} AudioSignal;
+
+typedef struct {
+    float durationSec;
+    float energy;
+    float peakAmplitude;
+    float rmsAmplitude;
+    float paprDb;       // Peak-to-Average Power Ratio in dB
+    int peakSampleIdx;  // sample index of peak amplitude
+} SignalStats;
+
+// Compute statistics for a region of the signal defined by sample range
+SignalStats ComputeSignalStats(const AudioSignal* signal, int startSample, int endSample);
+
+#endif // SIGNAL_UTILS_H