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al_set_new_window_position / al_get_window_position mismatch
Member #940
January 2001

I noticed a funny surprise with al_set_new_window_position / al_get_window_position. I wanted to make my program save the window position at exit, so the window can be restored at the same position again the next time.

// at initialization
// read x, y, w, h from a config file
al_set_new_display_flags(ALLEGRO_WINDOWED | ALLEGRO_RESIZABLE);
al_set_new_window_position(x, y);
ALLEGRO_DISPLAY *display = al_create_display(w, h);

// at shutdown

int x, y
al_get_window_position(display, &x, &y);
w = al_get_display_width(display);
h = al_get_display_height(display);
// write x, y, w, h to config file

Full code here:

The surprising thing is that, even if I don't move or resize the window, the coordinates returned by al_get_window_position are not the same as the ones I pass into al_set_new_window_position. The effect is different on windows and linux. Here are repeated invocations of the program without moving the window:

1On Linux: 2 3martijn@siepie:~/prg/alleg/bug-window-position$ ./ex_window_pos 4Reading window position: 2147483647,2147483647: 640x480 5Saving window position: 630,303: 640x480 6 7martijn@siepie:~/prg/alleg/bug-window-position$ ./ex_window_pos 8Reading window position: 630,303: 640x480 9Saving window position: 630,327: 640x480 10 11martijn@siepie:~/prg/alleg/bug-window-position$ ./ex_window_pos 12Reading window position: 630,327: 640x480 13Saving window position: 630,351: 640x480 14 15martijn@siepie:~/prg/alleg/bug-window-position$ ./ex_window_pos 16Reading window position: 630,351: 640x480 17Saving window position: 630,375: 640x480 18 19On Windows: 20 21Martijn@Cheshire MINGW32 /z/prg/ex_window_pos 22$ ./ex_window_pos.exe 23Reading window position: 2147483647,2147483647: 640x480 24Saving window position: 630,267: 640x480 25 26Martijn@Cheshire MINGW32 /z/prg/ex_window_pos 27$ ./ex_window_pos.exe 28Reading window position: 630,267: 640x480 29Saving window position: 620,234: 640x480 30 31Martijn@Cheshire MINGW32 /z/prg/ex_window_pos 32$ ./ex_window_pos.exe 33Reading window position: 620,234: 640x480 34Saving window position: 610,201: 640x480 35 36Martijn@Cheshire MINGW32 /z/prg/ex_window_pos 37$ ./ex_window_pos.exe 38Reading window position: 610,201: 640x480 39Saving window position: 600,168: 640x480

On windows, the window is shifted slightly up and left each time. After a while the window is created in negative territory, which is annoying because you can no longer reach the title bar to move the window. On linux, the window is shifted down each time.

I assume the problem is that al_set_window_position is not properly taking into account the title bar. Is there any way to account for this difference?

Member #16,925
December 2018

I have used below code in my own project before, might fix the issue.

height + GetSystemMetrics(SM_CYSIZE) + GetSystemMetrics(SM_CYFRAME);

Member #940
January 2001

Good suggestion, thanks! I just need something similar for linux too.

Wouldn't it be a good idea to build this into the al_set_new_window_position function itself? I could start working on a patch...

Edgar Reynaldo
Major Reynaldo
May 2007

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