Question

I have code like this to move the player in my game left, right, up, and down:

keysSetRepeat(20, 5);  while (lives) {     scanKeys();      if (keysDownRepeat() & (KEY_LEFT | KEY_RIGHT | KEY_UP | KEY_DOWN)) {         u8 new_x = x;         u8 new_y = y;          if (keysDownRepeat() & KEY_LEFT) {             new_x--;         } else if (keysDownRepeat() & KEY_RIGHT) {             new_x++;         } else if (keysDownRepeat() & KEY_DOWN) {             new_y++;         } else if (keysDownRepeat() & KEY_UP) {             new_y--;         }          // ...     }      // ...      swiWaitForVBlank(); } 

Why are the keys not being detected? If I replace keysDownRepeat() with keysDown() it works (without the repeat rate, of course). The documentation is no help here.

Answer 1

I had to find the libnds source code to figure this out. Look at the implementation of keysDownRepeat():

uint32 keysDownRepeat(void) {     uint32 tmp = keysrepeat;      keysrepeat = 0;      return tmp; } 

It actually returns the keys then resets them back to 0. This wasn’t documented. I solved this by storing the result of keysDownRepeat() into a variable and using the variable to check the keys:

keysSetRepeat(20, 5);  while (lives) {     scanKeys();     u32 keys_down_repeat = keysDownRepeat();      if (keys_down_repeat & (KEY_LEFT | KEY_RIGHT | KEY_UP | KEY_DOWN)) {         u8 new_x = x;         u8 new_y = y;          if (keys_down_repeat & KEY_LEFT) {             new_x--;         } else if (keys_down_repeat & KEY_RIGHT) {             new_x++;         } else if (keys_down_repeat & KEY_DOWN) {             new_y++;         } else if (keys_down_repeat & KEY_UP) {             new_y--;         }          // ...     }      // ...      swiWaitForVBlank(); }