VG3_get_windowpos_on_bgimage()

Positioning the window on a larger background-image: Get x-/y-position of the background-image

SYNTAX

void VG3_get_windowpos_on_bgimage(struct vg3_windowpos_bgimage *wbpos, int xobj, int yobj, int *bgpos_x, int *bgpos_y, int at_once)

FUNCTION PARAMETERS

wbpos	Window-positioning structure
xobj	Central x-position of the player-object-image which shall be centered
yobj	Central y-position of the player-object-image which shall be centered
bgpos_x	For returning x-position of the background on the window
bgpos_y	For returning y-position of the background on the window
at_once	If player-object-image is not in the focus: 0 = move window steadily, 1 = move window immediately to the image

DESCRIPTION

If the game field, presented by a background-image, is larger than the window, only a section shall be shown, which moves according to the position of the player-object on the background-image. This section is generally the window. With this function the position of the background-image is returned. This position, returned in bgpos_x and bgpos_y must be added when copying the background-image or any other image to the window.

EXAMPLE

Positioning the window on a larger background-image according to the image of the player-object:

  struct vg3_window *wstruct;
  struct vg3_image *bg_image, *player_image;
  int win_w, win_h, bg_w, bg_h;
  struct vg3_rect player_rect;
  struct vg3_windowpos_bgimage wbpos;
  int bgpos_x, bgpos_y;

  [... opening window (wstruct), loading bg_image and player_image ...]

  /* getting window-size */
  VG3_window_getsize(wstruct, &win_w, &win_h);

  /* getting size of the background-image */
  VG3_image_getsize(wstruct, bg_image, NULL, &bg_w, &bg_h);

  /* setting position of the player-object into player-rectangle */
  player_rect.x = player_rect.y = 0;
  VG3_image_getsize(wstruct, player_image, NULL, &player_rect.w, &player_rect.h);

  /* initalize window-positioning structure */
  VG3_init_windowpos_on_bgimage(&wbpos, bg_w, bg_h, win_w, win_h, 2, 60);

  /* game-loop */
  for (;;) {
    /* get background-image position according to player_rect into bgpos_x and bgpos_y */
    VG3_get_windowpos_on_bgimage(&wbpos,
                                 player_rect.x + player_rect.w / 2,
                                 player_rect.y + player_rect.h / 2,
                                 &bgpos_x, &bgpos_y, 0);

    /* copy background-image to window using position bgpos_x and bgpos_y */
    VG3_image_copy(wstruct, NULL, bg_image, bgpos_x + bg_w / 2, bgpos_y + bg_w / 2, NULL, 0);

    /* copy player-image to window adding bgpos_x and bgpos_y */
    VG3_image_copy(wstruct, NULL, player_image,
                   player_rect.x + player_rect.w / 2 + bgpos_x,
                   player_rect.y + player_rect.h / 2 + bgpos_y,
                   NULL, 0);

    [...]
  }