/*
 * gba.h
 * contains graphic and input definitions and functions for the GBA
 */

#ifndef GBA_H
#define GBA_H

/* the width and height of the screen */
#define WIDTH 240
#define HEIGHT 160

/* these identifiers define different bit positions of the display control */
#define MODE4 0x0004
#define BG2 0x0400

/* this bit indicates whether to display the front or the back buffer
 * this allows us to refer to bit 4 of the display_control register */
#define SHOW_BACK 0x10;

/* the screen is simply a pointer into memory at a specific address this
 *  * pointer points to 16-bit colors of which there are 240x160 */
extern volatile unsigned short* screen;

/* the display control pointer points to the gba graphics register */
extern volatile unsigned long* display_control;

/* the address of the color palette used in graphics mode 4 */
extern volatile unsigned short* palette;

/* pointers to the front and back buffers - the front buffer is the start
 * of the screen array and the back buffer is a pointer to the second half */
extern volatile unsigned short* front_buffer;
extern volatile unsigned short* back_buffer;

/* the button register holds the bits which indicate whether each button has
 * been pressed - this has got to be volatile as well
 */
extern volatile unsigned short* buttons;

/* the bit positions indicate each button - the first bit is for A, second for
 * B, and so on, each constant below can be ANDED into the register to get the
 * status of any one button */
#define BUTTON_A (1 << 0)
#define BUTTON_B (1 << 1)
#define BUTTON_SELECT (1 << 2)
#define BUTTON_START (1 << 3)
#define BUTTON_RIGHT (1 << 4)
#define BUTTON_LEFT (1 << 5)
#define BUTTON_UP (1 << 6)
#define BUTTON_DOWN (1 << 7)
#define BUTTON_R (1 << 8)
#define BUTTON_L (1 << 9)

/* the scanline counter is a memory cell which is updated to indicate how
 * much of the screen has been drawn */
extern volatile unsigned short* scanline_counter;

/* wait for the screen to be fully drawn so we can do something during vblank */
void wait_vblank();

/* this function checks whether a particular button has been pressed */
unsigned char button_pressed(unsigned short button);

/*
 * function which adds a color to the palette and returns the
 * index to it
 */
unsigned char add_color(unsigned char r, unsigned char g, unsigned char b);

/* put a pixel on the screen in mode 4 */
void put_pixel(volatile unsigned short* buffer, int row, int col, unsigned char color);

/* this function takes a video buffer and returns to you the other one */
volatile unsigned short* flip_buffers(volatile unsigned short* buffer);

/* clear the screen to black */
void clear_screen(volatile unsigned short* buffer, unsigned short color);

#endif