Date: Tue, 15 Feb 2005 21:28:48 +0900 (JST) From: "Michael Leonhard" Subject: [SDL] resize bug on Win32 and patch This is my first post to this mailing list. In this email I will detail a bug in the behavior of resizable SDL windows on Win32. Then I will explain the solution and provide a patch. Symptoms: Under Windows, an SDL display created with the SDL_RESIZABLE flag exhibits quirky behavior when being maximized. The window is resized to the proper size, but it is shifted upwards about half the height of the title bar. Similarly, a window whose origin is above the top of the screen will spontaneously move its upper-left origin upon being resized. After two such resize-induced moves, the title bar will be entirely off the top edge of the screen. Subsequently, when the mouse is clicked and released on the window border, the window will shrink its height spontaneously. This height shrinkage occurs even if the user did not resize the border. To observe this curious situation, please invoke: SDL-1.2.8/test/testwm.exe -resize Cause: A pair of integers, SDL_windowX and SDL_windowY, are defined in video/wincommon/SDL_sysevents.c. They are used by the DirectX video driver and the DIB video driver: video/windx5/SDL_dx5video.c video/windib/SDL_dibvideo.c As I understand the source code, the primary use of these variables is to create a rectangle that represents the surface area in CLIENT SPACE. Client space refers to a coordinate system that originates at the upper left corner of a Win32 Window's drawable area. This is just inside the window border and title bar. This client space rectangle, called bounds, is subsequently converted to screen space with a call to AdjustWindowRectEx. The problem is found in SDL's handling of the WM_WINDOWPOSCHANGED message. According to MSDN, "The WM_WINDOWPOSCHANGED message is sent to a window whose size, position, or place in the Z order has changed as a result of a call to the SetWindowPos function or another window-management function." I have confirmed that this message is indeed being sent to the SDL window when the mouse is clicked on the window border, even if the window border is not dragged. In video/wincommon/SDL_sysevents.c, on line 464, in response to the WM_WINDOWPOSCHANGED message, the (potentially) new client rectangle is obtained. This rectangle is translated into screen coordinates and THEN assigned to the SDL_windowX and Y variables. Thus screen coordinates are being assigned to client coordinate variables. Once this is understood, the solution is apparent: assign SDL_windowX and Y before translating the rectangle to screen coordinates. This is accomplished by the following patch. -Mike_L

/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2004 Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public
    License along with this library; if not, write to the Free
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

    Sam Lantinga
    slouken@libsdl.org
*/

#ifdef SAVE_RCSID
static char rcsid =
 "@(#) $Id$";
#endif

#ifndef VK_0
#define VK_0	'0'
#define VK_1	'1'
#define VK_2	'2'
#define VK_3	'3'
#define VK_4	'4'
#define VK_5	'5'
#define VK_6	'6'
#define VK_7	'7'
#define VK_8	'8'
#define VK_9	'9'
#define VK_A	'A'
#define VK_B	'B'
#define VK_C	'C'
#define VK_D	'D'
#define VK_E	'E'
#define VK_F	'F'
#define VK_G	'G'
#define VK_H	'H'
#define VK_I	'I'
#define VK_J	'J'
#define VK_K	'K'
#define VK_L	'L'
#define VK_M	'M'
#define VK_N	'N'
#define VK_O	'O'
#define VK_P	'P'
#define VK_Q	'Q'
#define VK_R	'R'
#define VK_S	'S'
#define VK_T	'T'
#define VK_U	'U'
#define VK_V	'V'
#define VK_W	'W'
#define VK_X	'X'
#define VK_Y	'Y'
#define VK_Z	'Z'
#endif /* VK_0 */

/* These keys haven't been defined, but were experimentally determined */
#define VK_SEMICOLON	0xBA
#define VK_EQUALS	0xBB
#define VK_COMMA	0xBC
#define VK_MINUS	0xBD
#define VK_PERIOD	0xBE
#define VK_SLASH	0xBF
#define VK_GRAVE	0xC0
#define VK_LBRACKET	0xDB
#define VK_BACKSLASH	0xDC
#define VK_RBRACKET	0xDD
#define VK_APOSTROPHE	0xDE
#define VK_BACKTICK	0xDF
#define VK_OEM_102	0xE2