[a5] drag your window with ALLEGRO

Mark Oates

So, I'm just having some fun here trying to make a window dragable without a frame. Basically, I came up with this simple little technique that actually works, but it's buggy. I can't identify exactly what causes window to go crazy all over the screen and then fly off somewhere.

#SelectExpand
    case ALLEGRO_EVENT_MOUSE_AXES:
      if (mouse.dragging)
      {
        int x, y;
        al_get_window_position(display, &x, &y);
        al_set_window_position(display, x+al_event.mouse.dx, y+al_event.mouse.dy);
        al_set_mouse_xy(al_event.mouse.x - al_event.mouse.dx, al_event.mouse.y - al_event.mouse.dy);
      }
      break;
    case ALLEGRO_EVENT_MOUSE_BUTTON_DOWN:
      mouse.start_drag(al_event.mouse.x, al_event.mouse.y);
      break;
    case ALLEGRO_EVENT_MOUSE_BUTTON_UP:
      mouse.end_drag();
      break;

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I'm surprised it works as well as it does, but it doesn't retain the position of the mouse inside the window (as well as sometimes just flipping out all together.) In the screenshot, the window has been dragged around a bit and you'll notice the red cross hair (drag start) and green cross hair (current mouse position) have different locations. The actual mouse cursor is not visible in the screenshot. This isn't a regular transformation - sometimes they'll still overlap when dragging, and sometimes they won't. Sometimes the window will flip out on a drag with slow mouse movement, other times it's with quick mouse movements.

I tried some other methods like setting al_set_mouse_xy() to the same mouse position when the drag began, but that would only aggravate the window flip outs more. Don't know why.

Here's a complete example (with a few extra lines of code that aren't used) if you wanna try it out. I've attached an MSVC build for Windows, too. Click-drag to drag the window. Press an any key to quit. You may have to hard-close it if it flies off the screen.

#SelectExpand
   1#include <allegro5/allegro.h>
   2#include <allegro5/allegro_font.h>
   3#include <allegro5/allegro_ttf.h>
   4#include <allegro5/allegro_primitives.h>
   5#include <allegro5/allegro_image.h>
   6#include <allegro5/allegro_color.h>
   7#include <allegro5/allegro_audio.h>
   8#include <allegro5/allegro_vorbis.h>
   9#include <allegro5/allegro_native_dialog.h>
  10#include <allegro5/allegro_opengl.h>
  11
  12
  13#include <iostream>
  14using std::cout;
  15using std::endl;
  16
  17
  18
  19
  20
  21
  22class Mouse
  23{
  24public:
  25  bool dragging;
  26  int drag_start_x;
  27  int drag_start_y;
  28  int drag_offset_x;
  29  int drag_offset_y;
  30
  31  int x;
  32  int y;
  33
  34  Mouse():dragging(false), drag_start_x(0), drag_start_y(0) {}
  35
  36  void start_drag(int x, int y)
  37  {
  38    drag_start_x = x;
  39    drag_start_y = y;
  40    this->x = x;
  41    this->y = y;
  42    dragging = true;
  43    cout << "starting drag" << endl;
  44  }
  45
  46  void move_offset(int x, int y)
  47  {
  48    drag_offset_x = x;
  49    drag_offset_y = y;
  50  }
  51
  52  void end_drag()
  53  {
  54    dragging = false;
  55    drag_start_x = 0;
  56    drag_start_y = 0;
  57    cout << "ending drag" << endl;
  58  }
  59};
  60
  61
  62
  63
  64
  65
  66
  67int main(int argc, char *argv[])
  68{
  69  ALLEGRO_DISPLAY *display;
  70  ALLEGRO_EVENT_QUEUE *queue;
  71
  72  al_init();
  73
  74  al_set_new_display_flags(ALLEGRO_NOFRAME);
  75  display = al_create_display(800, 600);
  76
  77  al_install_keyboard();
  78  al_install_mouse();
  79  al_install_joystick();
  80
  81  /* setup event queue */
  82
  83  queue = al_create_event_queue();
  84
  85  ALLEGRO_EVENT_SOURCE *display_source = al_get_display_event_source(display);
  86  al_register_event_source(queue, display_source);
  87
  88  ALLEGRO_EVENT_SOURCE *keyboard_event_source = al_get_keyboard_event_source();
  89  al_register_event_source(queue, keyboard_event_source);
  90
  91  ALLEGRO_EVENT_SOURCE *mouse_event_source = al_get_mouse_event_source();
  92  al_register_event_source(queue, mouse_event_source);
  93
  94  ALLEGRO_TIMER *timer = al_install_timer(ALLEGRO_BPS_TO_SECS(60));
  95  ALLEGRO_EVENT_SOURCE *timer_event_source = al_get_timer_event_source(timer);
  96  al_register_event_source(queue, timer_event_source);
  97
  98  al_start_timer(timer);
  99
 100  bool game_over = false;
 101
 102
 103  Mouse mouse;
 104
 105  while(!game_over)
 106  {
 107    ALLEGRO_EVENT al_event;
 108    al_wait_for_event(queue, &al_event);
 109
 110    switch(al_event.type)
 111    {
 112      case ALLEGRO_EVENT_MOUSE_AXES:
 113        if (mouse.dragging)
 114        {
 115          int x, y;
 116          al_get_window_position(display, &x, &y);
 117          al_set_window_position(display, x+al_event.mouse.dx, y+al_event.mouse.dy);
 118          al_set_mouse_xy(al_event.mouse.x - al_event.mouse.dx, al_event.mouse.y - al_event.mouse.dy);
 119          mouse.x = al_event.mouse.x - al_event.mouse.dx;
 120          mouse.y = al_event.mouse.y - al_event.mouse.dy;
 121        }
 122        break;
 123      case ALLEGRO_EVENT_MOUSE_BUTTON_DOWN:
 124        mouse.start_drag(al_event.mouse.x, al_event.mouse.y);
 125        break;
 126      case ALLEGRO_EVENT_MOUSE_BUTTON_UP:
 127        mouse.end_drag();
 128        break;
 129      case ALLEGRO_EVENT_KEY_DOWN:
 130        game_over = true;
 131        break;
 132      case ALLEGRO_EVENT_TIMER:
 133        al_clear_to_color(al_color_name("black"));
 134        if (mouse.dragging)
 135        {
 136          al_draw_line(mouse.drag_start_x-10, mouse.drag_start_y, mouse.drag_start_x+10, mouse.drag_start_y, al_color_name("red"), 1.0);
 137          al_draw_line(mouse.drag_start_x, mouse.drag_start_y-10, mouse.drag_start_x, mouse.drag_start_y+10, al_color_name("red"), 1.0);
 138          al_draw_line(mouse.x-10, mouse.y, mouse.x+10, mouse.y, al_color_name("green"), 1.0);
 139          al_draw_line(mouse.x, mouse.y-10, mouse.x, mouse.y+10, al_color_name("green"), 1.0);
 140        }
 141        al_flip_display();
 142        break;
 143      default:
 144        break;
 145    }
 146  }
 147
 148
 149
 150  return 0;
 151}

Elias

Did you look at how ex_noframe does it? It seems to work quite well at least under Linux. [edit: yours doesn't seem to work at all in linux, on the other hand]

Mark Oates

Elias said:

Did you look at how ex_noframe does it?

oooahhhmmmmm... let's see...

al_get_mouse_cursor_position();

I was looking for a function that did that... I was so close.

[edit]Any chance we'll get support for a frameless window with an alpha channel?

Elias

Mark Oates said:

Any chance we'll get support for a frameless window with an alpha channel?

Yes, I want that. I think in the API we basically support it already, just nobody has sent a patch implementing it for any platform yet.

BAF

As far as the flip-outs go, my best guess would be when you move the window, more mouse movement events are fired, giving you wonky coordinates, causing it to go apeshit.

wiseguy

A frameless window with alpha would be nice, as I've set my base gui to allow for rectangular, triangular, and circular/elliptical windows but have only implemented the rectangular at the moment.

Evert

Mark Oates said:

Any chance we'll get support for a frameless window with an alpha channel?

Only with the caveat that we may not be able to provide that functionality on all supported platforms (I don't think we can, someone correct me if I'm wrong).

Mark Oates

Probably work on Mac, Windows, and Linux, I imagine.

Elias

Should be easy for Linux/X11 (if supported by your window manager, which is probably only the case with a compositing window manager... but who is still using something else). We won't provide it for ios4 of course since even with the added multi-tasking it's one app at the screen at a time. I have no idea about Windows or OSX.

Evert

Mark Oates said:

Probably work on Mac

That'll depend on the version of OS X that is running, I imagine.

Mark Oates

Elias said:

I have no idea about Windows or OSX

I'm sure it can be done in Windows. I remember almost 10 years ago I did figured it out, and that was in Visual Basic.

Thomas Fjellstrom

Mark Oates said:

I'm sure it can be done in Windows. I remember almost 10 years ago I did figured it out, and that was in Visual Basic.

Back then it was more likely just a window mask rather than an alpha channel.

Mark Oates

True. I remember it being 1 or 0 transparency.

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