refactor: table-driven keymap dispatch + auto-derived help list

Replace the global key handling scattered through the main loop with a single
KEYMAP table (key, gate, action, help text) and a DispatchKeymap() pass. The
About/Help overlay now renders its key list straight from the table, so the
on-screen shortcuts can never drift from the actual bindings.

- Order-sensitive keys (Space, Esc) stay inline where their frame ordering
  matters; they carry action==NULL and appear in the table for the help list.
- Adds the F11 fullscreen binding the sidebar button already advertised but
  that was never actually wired up.
- Fix About title em-dash rendering as '?' (font is ASCII-only); use a hyphen.

Launch render verified pixel-identical (AE=0); keys verified via injected input.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/spectrogram.c

@@ -129,6 +129,66 @@ void ResetForNewSignal(void)
     app.visibleTextureValid = false;
 }
 
+// ============================================================================
+// Keymap — handlers + table + dispatcher. See spectrogram_types.h for the
+// KeyBinding contract. Adding a global key = add one row here (and, if it needs
+// to run at a specific point in the frame, leave action NULL and wire it inline).
+// ============================================================================
+
+static void ActionOpenBrowser(void)    { app.showFileBrowser = true; ScanDirectory(GetWorkingDirectory()); }
+static void ActionToggleScope(void)    { app.showScope = !app.showScope; }
+static void ActionToggleAbout(void)    { app.showAbout = !app.showAbout; }
+static void ActionToggleFullscreen(void){ ToggleFullscreen(); }
+static void ActionExport(void)         { ExportPNG(&app, app.exportDir); }
+
+static void ActionResetView(void)
+{
+    app.viewStart = 0.0f; app.viewEnd = 1.0f;
+    app.freqViewStart = 0.0f; app.freqViewEnd = 1.0f;
+    app.visibleTextureValid = false;
+}
+
+static void ActionZoomToStart(void)
+{
+    app.viewStart = 0.0f;
+    app.viewEnd = 0.1f;
+    app.visibleTextureValid = false;
+}
+
+static const KeyBinding KEYMAP[] = {
+    { KEY_O,     KEYGATE_MODAL,                 ActionOpenBrowser,     "O",     "open file browser" },
+    { KEY_P,     KEYGATE_NONE,                  ActionToggleScope,     "P",     "show / hide waveform scope" },
+    { KEY_F1,    KEYGATE_NONE,                  ActionToggleAbout,     "F1",    "about / help" },
+    { KEY_F11,   KEYGATE_NONE,                  ActionToggleFullscreen,"F11",   "toggle fullscreen" },
+    { KEY_HOME,  KEYGATE_MODAL | KEYGATE_LOADED,ActionResetView,       "Home",  "reset view (fit all)" },
+    { KEY_END,   KEYGATE_MODAL | KEYGATE_LOADED,ActionZoomToStart,     "End",   "zoom to start" },
+    { KEY_E,     KEYGATE_MODAL | KEYGATE_STFT,  ActionExport,          "E",     "export PNG" },
+    // Order-sensitive: handled inline (see main loop), listed here for the overlay.
+    { KEY_SPACE, KEYGATE_NONE,                  NULL,                  "Space", "play / stop selection" },
+    { KEY_ESCAPE,KEYGATE_NONE,                  NULL,                  "Esc",   "clear selection / close dialog" },
+};
+
+const KeyBinding* GetKeymap(int* count)
+{
+    *count = (int)(sizeof(KEYMAP) / sizeof(KEYMAP[0]));
+    return KEYMAP;
+}
+
+// Run every gated, dispatchable binding whose key was pressed this frame.
+static void DispatchKeymap(void)
+{
+    int n;
+    const KeyBinding* km = GetKeymap(&n);
+    for (int i = 0; i < n; i++) {
+        const KeyBinding* b = &km[i];
+        if (!b->action) continue;
+        if ((b->gate & KEYGATE_MODAL)  && UiModalOpen())     continue;
+        if ((b->gate & KEYGATE_LOADED) && !app.loaded)       continue;
+        if ((b->gate & KEYGATE_STFT)   && !app.stftComputed) continue;
+        if (IsKeyPressed(b->key)) b->action();
+    }
+}
+
 // ============================================================================
 // Main Application
 // ============================================================================
@@ -253,26 +313,9 @@ int main(int argc, char* argv[])
             UnloadDroppedFiles(dropped);
         }
         
-        // File browser toggle
+        // Global key bindings (table-driven; see KEYMAP/GetKeymap). The
-        if (IsKeyPressed(KEY_O) && !UiModalOpen()) {
+        // order-sensitive keys (Space, Esc) are handled inline further below.
-            app.showFileBrowser = true;
+        DispatchKeymap();
-            ScanDirectory(GetWorkingDirectory());
-        }
-        
-        // Scope view toggle (P key)
-        if (IsKeyPressed(KEY_P)) {
-            app.showScope = !app.showScope;
-        }
-
-        // About / help dialog (F1)
-        if (IsKeyPressed(KEY_F1)) {
-            app.showAbout = !app.showAbout;
-        }
-
-        // File browser update
-        if (app.showFileBrowser) {
-            // Browser handles its own input
-        }
 
         // Check if playback finished naturally
         if (app.isPlaying && AudioPlaybackSound.frameCount > 0) {
@@ -455,18 +498,6 @@ int main(int argc, char* argv[])
                 }
             }
 
-            // Home/End keys
-            if (IsKeyPressed(KEY_HOME)) {
-                app.viewStart = 0.0f; app.viewEnd = 1.0f;
-                app.freqViewStart = 0.0f; app.freqViewEnd = 1.0f;
-                app.visibleTextureValid = false;
-            }
-            if (IsKeyPressed(KEY_END)) {
-                float newWidth = 0.1f;
-                app.viewStart = 0.0f;
-                app.viewEnd = newWidth;
-                app.visibleTextureValid = false;
-            }
         }
 
         // Keyboard shortcuts (SPACE for play/stop toggle, ESC for clear)
@@ -490,11 +521,6 @@ int main(int argc, char* argv[])
             }
         }
 
-        // Export PNG
-        if (IsKeyPressed(KEY_E) && !UiModalOpen() && app.stftComputed) {
-            ExportPNG(&app, app.exportDir);
-        }
-
         if (IsKeyPressed(KEY_ESCAPE)) {
             if (app.showAbout) {
                 app.showAbout = false;

src/spectrogram_types.h

@@ -233,6 +233,32 @@ static inline bool UiModalOpen(void)
     return app.showFileBrowser || app.showAbout;
 }
 
+// ============================================================================
+// Keymap — single source of truth for global key bindings.
+// The dispatcher (DispatchKeymap in spectrogram.c) runs every entry whose
+// `action` is non-NULL and whose gate passes; the About/Help overlay renders
+// the whole table so the on-screen key list can never drift from the bindings.
+// Order-sensitive keys (Space, Esc) carry action==NULL and are handled inline
+// where their frame ordering matters; they appear here for documentation only.
+// ============================================================================
+typedef void (*KeyActionFn)(void);
+
+#define KEYGATE_NONE   0u
+#define KEYGATE_MODAL  1u   // skip while a modal overlay is open (!UiModalOpen())
+#define KEYGATE_LOADED 2u   // require a loaded signal
+#define KEYGATE_STFT   4u   // require a computed STFT
+
+typedef struct {
+    int key;             // raylib key code
+    unsigned gate;       // KEYGATE_* bitmask
+    KeyActionFn action;  // NULL = handled inline / documentation-only
+    const char* label;   // shown in the help overlay, e.g. "O", "Home"
+    const char* help;    // description for the help overlay
+} KeyBinding;
+
+// Returns the keymap table and its entry count (defined in spectrogram.c).
+const KeyBinding* GetKeymap(int* count);
+
 // ============================================================================
 // Small math helpers (header-inline so every module can use them)
 // ============================================================================

src/ui.c

@@ -578,7 +578,7 @@ void DrawAboutDialog(void)
     DrawRectangle(0, 0, sw, sh, Fade(BLACK, 0.7f));
 
     float pw = 560 * scale;
-    float ph = 470 * scale;
+    float ph = 540 * scale;
     Rectangle panel = { (sw - pw) / 2, (sh - ph) / 2, pw, ph };
     DrawRectangleRec(panel, (Color){ 30, 30, 38, 255 });
     DrawRectangleLinesEx(panel, 2, (Color){ 90, 90, 110, 255 });
@@ -586,7 +586,7 @@ void DrawAboutDialog(void)
     float px = panel.x + 24 * scale;
     float py = panel.y + 20 * scale;
 
-    DrawTextScaled("rspektrum — synchrosqueezed spectrogram viewer", px, py, 18, WHITE);
+    DrawTextScaled("rspektrum - synchrosqueezed spectrogram viewer", px, py, 18, WHITE);
     py += 34 * scale;
 
     // Body lines. NULL = blank spacer; headings start with no leading spaces.
@@ -606,10 +606,6 @@ void DrawAboutDialog(void)
         "    spectral magnitudes.",
         "  - Pixels show synchrosqueezed (reassigned) energy, not raw FFT bins.",
         "  Good to ~a dB for visualization; not lab-grade metrology.",
-        "",
-        "Keys",
-        "  O  open file      P  toggle scope      Home/End  reset / fit view",
-        "  F1 / Esc  close this dialog",
     };
     int n = sizeof(lines) / sizeof(lines[0]);
     for (int i = 0; i < n; i++) {
@@ -619,6 +615,20 @@ void DrawAboutDialog(void)
         py += (s[0] == '\0' ? 8 : 18) * scale;
     }
 
+    // Keys — rendered straight from the keymap table so this list can never
+    // drift from the actual bindings.
+    py += 10 * scale;
+    DrawTextScaled("Keys", px, py, 14, (Color){ 150, 200, 255, 255 });
+    py += 20 * scale;
+    int kn;
+    const KeyBinding* km = GetKeymap(&kn);
+    for (int i = 0; i < kn; i++) {
+        DrawTextScaled(TextFormat("  %-5s %s", km[i].label, km[i].help), px, py, 13, LIGHTGRAY);
+        py += 16 * scale;
+    }
+    DrawTextScaled("  Mouse  wheel = zoom, Alt+drag = pan, drag = select box",
+                   px, py, 13, LIGHTGRAY);
+
     DrawTextScaled("F1 / Esc / click to close", panel.x + pw - 196 * scale,
                    panel.y + ph - 26 * scale, 12, GRAY);
     // Note: opening/closing is handled in the main input loop (not here) so the