main.c

// Reference to the .rsrc file ID
#define GUI_IMAGE_ID 128

short quitting = 0;

void draw_window(void);

int
main() {
  // Counter-clockwise, reverse of CSS
  Rect win_bounds = {
    50,
    30,
    0,
    0
  };

  WindowPtr win;
  char title[] = "GUI App Example";

  // If we use a Pascal string, we need to structure it like this
  //Str255 title = "\pOur app";

  // These are all initializations of built-in libraries we need from MacTrap, etc.
  InitGraf( & thePort);
  InitFonts();
  FlushEvents(everyEvent, 0);
  InitWindows();
  InitMenus();
  TEInit();
  InitDialogs(0);
  InitCursor();
  MaxApplZone();

  win_bounds.right = screenBits.bounds.right - 30;
  win_bounds.bottom = screenBits.bounds.bottom - 10;

  // Definition of our new window. CtoPstr converts our C char to a Pascal title
  win = NewWindow(0 L, & win_bounds, CtoPstr(title), true,
    documentProc, (WindowPtr) - 1 L, true, 0);

  if (!win)
    ExitToShell();

  SetPort(win);

  draw_window();

  while (!quitting) {
    EventRecord event;
    WindowPtr event_win;
    short event_in;

    WaitNextEvent(everyEvent, & event, 10 L, 0);
    event_in = FindWindow(event.where, & event_win);

    switch (event.what) {
    case mouseDown:
      switch (event_in) {
      case inSysWindow:
        SystemClick( & event, event_win);
        break;
      case inDrag:
        // Handles dragging the window
        DragWindow(event_win, event.where, & screenBits.bounds);
        break;
      case inGoAway:
        // Handles if you click and hold on the close button, but drag away, cancelling the action
        if (TrackGoAway(event_win, event.where))
          quitting = 1;
        break;
      }
      break;
    case updateEvt:
      BeginUpdate(event_win);
      // tells the system that you're going to redraw the window
      draw_window();
      EndUpdate(event_win);
      break;
    }
  }
}

// This is a function that handles redrawing the window if you draw it off-screen, then back on-screen
void
draw_window(void) {
  // Handles are a pointer to a pointer.
  // You get a pointer to memory, but memory can move around. The data for pic
  // will move around, such as with new memory allocation, or defragmentation
  PicHandle pic;
  Rect pic_rect = {
    0
  };

  pic = GetPicture(GUI_IMAGE_ID);
  if (!pic) {
    quitting = 1;
    return;
    // We could also call ExitToShell here, but this ends the function more cleanly
  }

  // Windows don't actually exist, you're just drawing wherever the window's coordinates happen to be.
  // Coords are relative to the port

  pic_rect.right = ( ** (pic)).picFrame.right;
  pic_rect.bottom = ( ** (pic)).picFrame.bottom;

  DrawPicture(pic, & pic_rect);
}