3DS: add circle pad support for scrolling and navigation (Olivier Senn)

Map the circle pad to directional buttons, giving an alternative
input method to the D-pad. Uses a deadzone of 64 to prevent
unintended movement from minor stick drift.

💘 Generated with Crush

Assisted-by: Crush:deepseek-v4-pro

Edited by Vencislav Atanasov: Fixed KEY_SELECT handling.

Change-Id: I34bf7127688423fca209e199d9535e032ad8b753

docs/CREDITS

@@ -766,6 +766,7 @@ Lê Khánh Bình
 Michael McAllister
 Hemant Kumar
 Jerry Shen
+Olivier Senn
 
 The libmad team
 The wavpack team

firmware/target/hosted/ctru/button-ctru.c

@@ -86,6 +86,8 @@ void update_sound_slider_level(void)
       }
 }
 
+#define CPAD_DEADZONE 64
+
 int button_read_device(int* data)
 {
     int key = BUTTON_NONE;
@@ -97,14 +99,26 @@ int button_read_device(int* data)
 
     hidScanInput();
     u32 kDown = hidKeysDown();
-    
+
     if (kDown & KEY_SELECT) {
         touchscreen_set_mode(touchscreen_get_mode() == TOUCHSCREEN_POINT ? TOUCHSCREEN_BUTTON : TOUCHSCREEN_POINT);
         printf("Touchscreen mode: %s\n", touchscreen_get_mode() == TOUCHSCREEN_POINT ? "TOUCHSCREEN_POINT" : "TOUCHSCREEN_BUTTON");
     }
-    
+
     u32 kHeld = hidKeysHeld();
 
+    /* Circle pad → directional buttons (alternative to D-pad) */
+    circlePosition cpad;
+    hidCircleRead(&cpad);
+    if (cpad.dx > CPAD_DEADZONE)
+        kHeld |= KEY_DRIGHT;
+    else if (cpad.dx < -CPAD_DEADZONE)
+        kHeld |= KEY_DLEFT;
+    if (cpad.dy > CPAD_DEADZONE)
+        kHeld |= KEY_DUP;
+    else if (cpad.dy < -CPAD_DEADZONE)
+        kHeld |= KEY_DDOWN;
+
     /* rockbox will handle button repeats */
     kDown |= kHeld;