Tutorial 2

The body of the game is created, now we add the player-racket. We can move it up and down with the cursor-keys or a gamecontroller. When it collides with the upper or lower border we stop the moving.

At first an overview about the file pingpong.c.

pingpong.c: Overview

/* global declarations */
[CODEBOX]

/* show help-text */
static VG_BOOL show_help(void) { ... (see pingpong.c) ... }

/* main function */
int main(int argc, char **argv) {
  /* variable declaration */
  [CODEBOX]

  /* initializing */
  [...]      /* opening */
  [CODEBOX]  /* set keys */
  [CODEBOX]  /* initialize player-racket */
  [...]      /* show help, start background music */

  /* game loop */
  [...]      /* receive input-events and check the local key-strokes */
  [CODEBOX]  /* check key-strokes for player-racket */
  [CODEBOX]  /* draw out */
  [...]      /* flush and wait */

  /* end game */
  [...]      /* destroy and exit */
}

An overview about the used variables in function main(). We add the player-racket structure.

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pingpong.c: the variables in function main()

const int border_size = 10;  /* size of borders in pixels */

int winw, winh;  /* window's width and height */
int audc_bgmusic;  /* audio descriptors */

struct {  /* player's structure */
  struct VG_Image *imgp;  /* image */
  struct VG_Rect rect;    /* rectangle position */
} player;

/* helper variables */
struct VG_Rect rect;
struct VG_Position posi;

At the beginning of the file pingpong.c we add the keys for the player-racket.

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pingpong.c: global declarations

/* keys */
struct {
  int k_quit_lalt;  /* part of quit: Left-ALT */
  int k_quit_q;     /* part of quit: Q */
  int k_pause;      /* pause */
  int k_up;         /* move up */
  int k_down;       /* move down */
} kref;

When setting the keys we add the player-racket keys: - move the player-racket up with - keyboard: [Cursor UP] - gamecontroller: [Right axis: up] it shall be changeable in a key-change menu - move the player-racket down with - keyboard: [Cursor DOWN] - gamecontroller: [Right axis: down] it shall be changeable in a key-change menu

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pingpong.c: continuing the function main()

/* set keys */

/* quit with ALT+Q, not changeable */
if ((kref.k_quit_lalt = vg4->input->key_insert("Quit-LALT", VG_FALSE, VG_FALSE)) == 0) { VG_dest(); exit(1); }
vg4->input->key_setkbd(kref.k_quit_lalt, VG_INPUT_KBDCODE_LALT);
if ((kref.k_quit_q = vg4->input->key_insert("Quit-Q", VG_FALSE, VG_FALSE)) == 0) { VG_dest(); exit(1); }
vg4->input->key_setkbd(kref.k_quit_q, VG_INPUT_KBDCODE_Q);

/* pause with P, changeable */
if ((kref.k_pause = vg4->input->key_insert("Pause", VG_TRUE, VG_FALSE)) == 0) { VG_dest(); exit(1); }
vg4->input->key_setkbd(kref.k_pause, VG_INPUT_KBDCODE_P);

/* move-up with cursor-key UP, changeable */
if ((kref.k_up = vg4->input->key_insert("Move up", VG_TRUE, VG_FALSE)) == 0) { VG_dest(); exit(1); }
vg4->input->key_setkbd(kref.k_up, VG_INPUT_KBDCODE_UCURS);
vg4->input->key_setgc(kref.k_up, 0, VG_INPUT_GCAXIS_RIGHTY_UP);

/* move-down with cursor-key DOWN, changeable */
if ((kref.k_down = vg4->input->key_insert("Move down", VG_TRUE, VG_FALSE)) == 0) { VG_dest(); exit(1); }
vg4->input->key_setkbd(kref.k_down, VG_INPUT_KBDCODE_DCURS);
vg4->input->key_setgc(kref.k_down, 0, VG_INPUT_GCAXIS_RIGHTY_DOWN);

Furthermove we initialize the player-racket, using the structure-variable player. The racket-image is loaded and the rectangle of the racket is set by the width and height of the image and its position.

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pingpong.c: continuing the function main()

/* initialize player-racket, put it at the left */

/* load image */
player.imgp = vg4->image->load("files/player.bmp");
if (player.imgp == NULL) { VG_dest(); exit(1); }

/* set rectangle */
vg4->image->getsize(player.imgp, NULL, &player.rect.w, &player.rect.h);
player.rect.x = 0;
player.rect.y = (winh - player.rect.h) / 2;

In the game-loop we check the key-strokes for using the player-racket and move it according to the key-stroke at 2 pixels. If it collides with the upper or lower border, whose height is border_size pixels, the moving stops.

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pingpong.c: continuing the game-loop of the function main()

  /* +++ player: check for key-strokes +++ */

  /* moving up */
  if (vg4->input->key_pressed(kref.k_up)) {
    player.rect.y -= 2;
    if (player.rect.y < border_size) { player.rect.y = border_size; }
  }

  /* moving down */
  if (vg4->input->key_pressed(kref.k_down)) {
    player.rect.y += 2;
    if (player.rect.y > winh - border_size - player.rect.h) { player.rect.y = winh - border_size - player.rect.h; }
  }

Additionally the player-racket is drawn out.

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pingpong.c: continuing the game-loop of the function main()

  /* +++ draw out +++ */

  /* clear window */
  vg4->window->clear();

  /* draw background and borders */

  vg4->window->fill(vg4->misc->colorbrightness(VG_COLOR_BLUE, 50));

  /* top border */
  rect.x = rect.y = 0; rect.w = winw; rect.h = border_size;
  vg4->window->draw_rect(&rect, VG_COLOR_RGB(0xb1, 0, 0), VG_TRUE);

  /* bottom border */
  rect.x = 0; rect.y = winh - border_size; rect.w = winw; rect.h = border_size;
  vg4->window->draw_rect(&rect, VG_COLOR_RGB(0xb1, 0, 0), VG_TRUE);

  /* right border */
  rect.x = winw - border_size; rect.y = 0; rect.w = border_size; rect.h = winh;
  vg4->window->draw_rect(&rect, VG_COLOR_RGB(0xb1, 0, 0), VG_TRUE);

  /* draw player */
  vg4->window->copy(player.imgp, vg4->misc->rect2position(&posi, &player.rect), NULL);

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