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
*/

#ifndef _SDL_x11dyn_h
#define _SDL_x11dyn_h

#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/Xatom.h>
#include <X11/Xproto.h>
#include <X11/Xlibint.h>

#if defined(__osf__)
#include <XFree86/extensions/extutil.h>
#else
#include <X11/extensions/extutil.h>
#endif

#ifndef NO_SHARED_MEMORY
#include <sys/ipc.h>
#include <sys/shm.h>
#include <X11/extensions/XShm.h>
#endif

/*
 * Never reference Xlib directly...we might load it dynamically at runtime.
 *  Even if we don't, for readability, we still use the function pointers
 *  (although the symbol resolution will be done by the loader in that case).
 *
 * We define SDL_X11_SYM and include SDL_x11sym.h to accomplish various
 *  goals, without having to duplicate those function signatures.
 */
#ifdef __cplusplus
extern "C" {
#endif

/* evil function signatures... */
typedef Bool (*SDL_X11_XESetWireToEventRetType)(Display*,XEvent*,xEvent*);
typedef int (*SDL_X11_XSynchronizeRetType)(Display*);
typedef Status (*SDL_X11_XESetEventToWireRetType)(Display*,XEvent*,xEvent*);
typedef int (*SDL_X11_XSetExtensionErrorHandlerType)(Display *,char *,char *);

#define SDL_X11_SYM(req,ret,fn,params) extern ret (*p##fn) params;
#include "SDL_x11sym.h"
#undef SDL_X11_SYM

/* Macro in the xlib headers, not an actual symbol... */
#define pXDestroyImage XDestroyImage

/* Workaround code in headers... */
#if !__SDL_NO_REDEFINE_X11_HEADER_SYMS
#define _XFlush p_XFlush
#define _XFlushGCCache p_XFlushGCCache
#define _XReply p_XReply
#define _XSend p_XSend
#define _XData32 p_XData32
#define XFree pXFree
#endif

int SDL_X11_LoadSymbols(void);
void SDL_X11_UnloadSymbols(void);

#ifdef __cplusplus
}
#endif

#endif  /* !defined _SDL_x11dyn_h */