Add full set of alternate button mappings

src/linux/port.c

@@ -140,7 +140,7 @@ static const int sdl_action_keycodes[Action_Max] = {
     [Action_Turbo] = SDLK_t,
 };
 
-static const int sdl_button_keycodes[nes_controller_num_buttons] = {
+static const int sdl_button_keycodes[2 * nes_controller_num_buttons] = {
     SDLK_a,
     SDLK_s,
     SDLK_q,
@@ -149,9 +149,16 @@ static const int sdl_button_keycodes[nes_controller_num_buttons] = {
     SDLK_DOWN,
     SDLK_LEFT,
     SDLK_RIGHT,
-};
 
-#define sdl_alt_start_key   (SDLK_RETURN)
+    SDLK_LCTRL,
+    SDLK_LALT,
+    SDLK_TAB,
+    SDLK_RETURN,
+    SDLK_KP_8,
+    SDLK_KP_2,
+    SDLK_KP_4,
+    SDLK_KP_6,
+};
 
 static int keycode_index(int keycode, const int* codes, int n_codes) {
     int index = n_codes - 1;
@@ -173,14 +180,13 @@ static nese_Action process_events(nes* sys) {
                         SDL_KEYUP == event.type) &&
                     0 == event.key.repeat
                 ) {
-            int index = (   sdl_alt_start_key ==
-                            event.key.keysym.sym) ?
-                        Button_Start : keycode_index(
-                                event.key.keysym.sym,
-                                sdl_button_keycodes,
-                                nes_controller_num_buttons
-                            );
+            int index = keycode_index(
+                    event.key.keysym.sym,
+                    sdl_button_keycodes,
+                    2 * nes_controller_num_buttons
+                );
             if (index >= 0) {
+                index %= nes_controller_num_buttons;
                 uint8_t mask = (1 << index);
                 if (SDL_KEYDOWN == event.type) {
                     input->gamepads[0].buttons |= mask;