/*
 * square.c
 * this program lets you move the square, with vsync
 */

#include "gba.h"

/* a colored square */
struct square {
    unsigned short x, y, size;
    unsigned char color;
};

/* draw a square onto the screen */
void draw_square(volatile unsigned short* buffer, struct square* s) {
    short row, col;
    /* for each row of the square */
    for (row = s->y; row < (s->y + s->size); row++) {
        /* loop through each column of the square */
        for (col = s->x; col < (s->x + s->size); col++) {
            /* set the screen location to this color */
            put_pixel(buffer, row, col, s->color);
        }
    }
}

/* clear the screen right around the square */
void update_screen(volatile unsigned short* buffer, unsigned short color, struct square* s) {
    short row, col;
    for (row = s->y - 3; row < (s->y + s->size + 3); row++) {
        for (col = s->x - 3; col < (s->x + s->size + 3); col++) {
            put_pixel(buffer, row, col, color);
        }
    }
}

/* handle the buttons which are pressed down */
void handle_buttons(struct square* s) {
    /* move the square with the arrow keys */
    if (button_pressed(BUTTON_DOWN)) {
        s->y += 1;
    }
    if (button_pressed(BUTTON_UP)) {
        s->y -= 1;
    }
    if (button_pressed(BUTTON_RIGHT)) {
        s->x += 1;
    }
    if (button_pressed(BUTTON_LEFT)) {
        s->x -= 1;
    }
}

/* the main function */
int main() {
    /* we set the mode to mode 4 with bg2 on */
    *display_control = MODE4 | BG2;

    /* make a green square */
    struct square s = {10, 10, 15, add_color(0, 20, 2)};

    /* add black to the palette */
    unsigned char black = add_color(0, 0, 0);

    /* the buffer we start with */
    volatile unsigned short* buffer = front_buffer;

    /* clear whole screen first */
    clear_screen(front_buffer, black);
    clear_screen(back_buffer, black);

    /* loop forever */
    while (1) {
        /* clear the screen - only the areas around the square! */
        update_screen(buffer, black, &s);

        /* draw the square */
        draw_square(buffer, &s);

        /* handle button input */
        handle_buttons(&s);

        /* wiat for vblank before switching buffers */
        wait_vblank();

        /* swap the buffers */
        buffer = flip_buffers(buffer);
    }
}