/*
   keys_demo1 ARM9 Code 
   Chris Double (chris.double@double.co.nz)
   http://www.double.co.nz/nintendo_ds
*/

#include <nds.h>

static int old_x = 0;
static int old_y = 0;
static int shape_x = 0;
static int shape_y = 0;
static int shape_width = 10;
static int shape_height = 10;
static uint16 shape_color = RGB15(31, 0, 0);

void draw_shape(int x, int y, uint16* buffer, uint16 color)
{
  buffer += y * SCREEN_WIDTH + x;
  for(int i = 0; i < shape_height; ++i) {
    uint16* line = buffer + (SCREEN_WIDTH * i);
    for(int j = 0; j < shape_width; ++j) {
      *line++ = color;
    }
  }
}

void on_irq() 
{	
  if(REG_IF & IRQ_VBLANK) {
    draw_shape(old_x, old_y, VRAM_A, RGB15(0, 0, 0));
    draw_shape(shape_x, shape_y, VRAM_A, shape_color);

    // Tell the DS we handled the VBLANK interrupt
    VBLANK_INTR_WAIT_FLAGS |= IRQ_VBLANK;
    REG_IF |= IRQ_VBLANK;
  }
  else {
    // Ignore all other interrupts
    REG_IF = REG_IF;
  }
}

void InitInterruptHandler()
{
  REG_IME = 0;
  IRQ_HANDLER = on_irq;
  REG_IE = IRQ_VBLANK;
  REG_IF = ~0;
  DISP_SR = DISP_VBLANK_IRQ;
  REG_IME = 1;
}

int main(void)
{
  powerON(POWER_ALL);
  videoSetMode(MODE_FB0);
  vramSetBankA(VRAM_A_LCD);
  InitInterruptHandler();

  while(1) {
    old_x = shape_x;
    old_y = shape_y;

    // Read the register containing the data of which
    // keys have been pressed.
    uint16 keysPressed = ~(REG_KEYINPUT);
    uint16 specialKeysPressed = ~IPC->buttons;

    // Based on the key pressed, move the shape.
    if(keysPressed & KEY_UP)
      --shape_y;
    if(keysPressed & KEY_DOWN)
      ++shape_y;
    if(keysPressed & KEY_LEFT)
      --shape_x;
    if(keysPressed & KEY_RIGHT)
      ++shape_x;

    // Change the color of the shape if the relevant key was pressed.
    if(keysPressed & KEY_A)
      shape_color = RGB15(31, 0, 0);

    if(keysPressed & KEY_B)
      shape_color = RGB15(0, 31, 0);

    if(keysPressed & KEY_SELECT)
      shape_color = RGB15(0, 0, 31);

    if(keysPressed & KEY_START)
      shape_color = RGB15(31, 31, 31);

    if(keysPressed & KEY_R)
      shape_color = RGB15(15, 0, 15);

    if(keysPressed & KEY_L)
      shape_color = RGB15(7, 15, 7);

    // Y Key
    if(specialKeysPressed & (1 << 1))
      shape_color = RGB15(7, 7, 7);

    // X Key
    if(specialKeysPressed & (1 << 0))
      shape_color = RGB15(0, 15, 15);

    // Pen Down
    if(specialKeysPressed & (1 << 6))
      shape_color = RGB15(0, 31, 31);

    // Hinge closed
    if(!(specialKeysPressed & (1 << 7)))
      shape_color = RGB15(0, 0, 0);

    // Make sure the shape stays within the correct bounds of the
    // screen.
    if(shape_x + shape_width >= SCREEN_WIDTH) 
      shape_x = 0;
    else if(shape_x < 0) 
      shape_x = SCREEN_WIDTH - shape_width - 1;

    if(shape_y + shape_height >= SCREEN_HEIGHT) 
      shape_y = 0;
    else if(shape_y < 0) 
      shape_y = SCREEN_HEIGHT - shape_height - 1;
    
    swiWaitForVBlank();
  }

  return 0;
}