Site hosted by Angelfire.com: Build your free website today!

Hands-on Projects for the Linux Graphics Subsystem
New book from Christos Karayiannis

Available in Amazon Kindle format at:

amazon.com   amazon.co.uk   amazon.de   amazon.es   amazon.fr   amazon.it

The X Protocol messages

At section 1 we have examined the X client-server interaction at the interprocess communication layer between the X client and the X server (mainly Sockets) and also the initial handshake between the X Client and the X Server that allows for the first important info exchange, as the X Protocol determines, for instance the supported color depth of the X Server.

We also statred discussing the stage of the established client-server operation at the X Protocol layer, and more specifically at the X client's requests. As we see from the following figure of the X Window System core protocol Wikipedia article the client sends requests to the X server and receives replies to those requests and also events (for instance a mouse key pressed on the client's window):

In the current section we examine the client request with some more detail and we make some experiments using as example the X Client from the section 1: 


  /*
   Simple Xlib application drawing a box in a window.
   To Compile: gcc -O2 -Wall -o test test.c -L /usr/X11R6/lib -lX11 -lm
 */
 
 #include<X11/Xlib.h>

 #include<stdio.h>
 #include<stdlib.h> // prevents error for exit on line 18 when compiling with gcc

 int main() {
   Display *d;
   int s;
   Window w;
   XEvent e;
 
                        /* open connection with the server */
   d=XOpenDisplay(NULL);
   if(d==NULL) {
     printf("Cannot open display\n");
     exit(1);
   }
   s=DefaultScreen(d);
 
                        /* create window */
   w=XCreateSimpleWindow(d, RootWindow(d, s), 10, 10, 100, 100, 1,
                         BlackPixel(d, s), WhitePixel(d, s));
 
   // Prosses Window Close Event through event handler so XNextEvent does Not fail
        Atom delWindow = XInternAtom( d, "WM_DELETE_WINDOW", 0 );
        XSetWMProtocols(d , w, &delWindow, 1);
 
                        /* select kind of events we are interested in */
   XSelectInput(d, w, ExposureMask | KeyPressMask);
 
                        /* map (show) the window */
   XMapWindow(d, w);
 
                        /* event loop */
   while(1) {
     XNextEvent(d, &e);
                        /* draw or redraw the window */
     if(e.type==Expose) {
       XFillRectangle(d, w, DefaultGC(d, s), 20, 20, 10, 10);
     }
                        /* exit on key press */
     if(e.type==KeyPress)
       break;
 
     // Handle Windows Close Event
     if(e.type==ClientMessage)
        break;
   }
 
                        /* destroy our window */
   XDestroyWindow(d, w);
 
                        /* close connection to server */
   XCloseDisplay(d);
 
   return 0;
 }

We have seen in section 1 that the Xlib routines used by the X client create request structs, that usually are grouped together and finally are flushed to the X server. For instance, as seen in section 1.2 function XCreateSimpleWindow() creates struct xCreateWindowReq. The Xlib functions source code can be examined in the X11 directory as we see in the following figure:

The request structs used by the various Xlib functions to exchange info at the X Protocol layer are defined in Xproto.h . For instance xCreateWindowReq and xChangeWindowAttributesReq are shown bellow: 

typedef struct {
    CARD8 reqType;
    CARD8 depth;
    CARD16 length B16;
    Window wid B32, parent B32;
    INT16 x B16, y B16;
    CARD16 width B16, height B16, borderWidth B16;  
#if defined(__cplusplus) || defined(c_plusplus)
    CARD16 c_class B16;
#else
    CARD16 class B16;
#endif
    VisualID visual B32;
    CARD32 mask B32;
} xCreateWindowReq;

typedef struct {
    CARD8 reqType;
    BYTE pad;
    CARD16 length B16;
    Window window B32;
    CARD32 valueMask B32; 
} xChangeWindowAttributesReq;

As we notice the request struct fields may vary, however two fields are common, namely reqType and length. The first is the id of the specific request, while the latter the size of the request struct in bytes. reqType takes one of the following values, defined in Xproto.h: 

/* Request codes */

#define X_CreateWindow                  1              
#define X_ChangeWindowAttributes        2        
#define X_GetWindowAttributes           3     
#define X_DestroyWindow                 4
#define X_DestroySubwindows             5   
#define X_ChangeSaveSet                 6
#define X_ReparentWindow                7
#define X_MapWindow                     8
#define X_MapSubwindows                 9
#define X_UnmapWindow                  10
#define X_UnmapSubwindows              11  
#define X_ConfigureWindow              12  
#define X_CirculateWindow              13  
#define X_GetGeometry                  14
#define X_QueryTree                    15
#define X_InternAtom                   16
#define X_GetAtomName                  17
#define X_ChangeProperty               18 
#define X_DeleteProperty               19 
#define X_GetProperty                  20
#define X_ListProperties               21 
#define X_SetSelectionOwner            22    
#define X_GetSelectionOwner            23    
#define X_ConvertSelection             24   
#define X_SendEvent                    25
#define X_GrabPointer                  26
#define X_UngrabPointer                27
#define X_GrabButton                   28
#define X_UngrabButton                 29
#define X_ChangeActivePointerGrab      30          
#define X_GrabKeyboard                 31
#define X_UngrabKeyboard               32 
#define X_GrabKey                      33
#define X_UngrabKey                    34
#define X_AllowEvents                  35       
#define X_GrabServer                   36      
#define X_UngrabServer                 37        
#define X_QueryPointer                 38        
#define X_GetMotionEvents              39           
#define X_TranslateCoords              40                
#define X_WarpPointer                  41       
#define X_SetInputFocus                42         
#define X_GetInputFocus                43         
#define X_QueryKeymap                  44       
#define X_OpenFont                     45    
#define X_CloseFont                    46     
#define X_QueryFont                    47
#define X_QueryTextExtents             48     
#define X_ListFonts                    49  
#define X_ListFontsWithInfo    	       50 
#define X_SetFontPath                  51 
#define X_GetFontPath                  52 
#define X_CreatePixmap                 53        
#define X_FreePixmap                   54      
#define X_CreateGC                     55    
#define X_ChangeGC                     56    
#define X_CopyGC                       57  
#define X_SetDashes                    58     
#define X_SetClipRectangles            59             
#define X_FreeGC                       60  
#define X_ClearArea                    61             
#define X_CopyArea                     62    
#define X_CopyPlane                    63     
#define X_PolyPoint                    64     
#define X_PolyLine                     65    
#define X_PolySegment                  66       
#define X_PolyRectangle                67         
#define X_PolyArc                      68   
#define X_FillPoly                     69    
#define X_PolyFillRectangle            70             
#define X_PolyFillArc                  71       
#define X_PutImage                     72    
#define X_GetImage                     73 
#define X_PolyText8                    74     
#define X_PolyText16                   75      
#define X_ImageText8                   76      
#define X_ImageText16                  77       
#define X_CreateColormap               78          
#define X_FreeColormap                 79        
#define X_CopyColormapAndFree          80               
#define X_InstallColormap              81           
#define X_UninstallColormap            82             
#define X_ListInstalledColormaps       83                  
#define X_AllocColor                   84      
#define X_AllocNamedColor              85           
#define X_AllocColorCells              86           
#define X_AllocColorPlanes             87            
#define X_FreeColors                   88      
#define X_StoreColors                  89       
#define X_StoreNamedColor              90           
#define X_QueryColors                  91       
#define X_LookupColor                  92       
#define X_CreateCursor                 93        
#define X_CreateGlyphCursor            94             
#define X_FreeCursor                   95      
#define X_RecolorCursor                96         
#define X_QueryBestSize                97         
#define X_QueryExtension               98          
#define X_ListExtensions               99          
#define X_ChangeKeyboardMapping        100
#define X_GetKeyboardMapping           101
#define X_ChangeKeyboardControl        102                
#define X_GetKeyboardControl           103             
#define X_Bell                         104
#define X_ChangePointerControl         105
#define X_GetPointerControl            106
#define X_SetScreenSaver               107          
#define X_GetScreenSaver               108          
#define X_ChangeHosts                  109       
#define X_ListHosts                    110     
#define X_SetAccessControl             111               
#define X_SetCloseDownMode             112
#define X_KillClient                   113 
#define X_RotateProperties	       114
#define X_ForceScreenSaver	       115
#define X_SetPointerMapping            116
#define X_GetPointerMapping            117
#define X_SetModifierMapping	       118
#define X_GetModifierMapping	       119
#define X_NoOperation                  127

Also length takes one of the following values, also defined in Xproto.h: 

#define sz_xResourceReq 8
#define sz_xCreateWindowReq 32
#define sz_xChangeWindowAttributesReq 12
#define sz_xChangeSaveSetReq 8
#define sz_xReparentWindowReq 16
#define sz_xConfigureWindowReq 12
#define sz_xCirculateWindowReq 8
#define sz_xInternAtomReq 8
#define sz_xChangePropertyReq 24
#define sz_xDeletePropertyReq 12
#define sz_xGetPropertyReq 24
#define sz_xSetSelectionOwnerReq 16
#define sz_xConvertSelectionReq 24
#define sz_xSendEventReq 44
#define sz_xGrabPointerReq 24
#define sz_xGrabButtonReq 24
#define sz_xUngrabButtonReq 12
#define sz_xChangeActivePointerGrabReq 16
#define sz_xGrabKeyboardReq 16
#define sz_xGrabKeyReq 16
#define sz_xUngrabKeyReq 12
#define sz_xAllowEventsReq 8
#define sz_xGetMotionEventsReq 16
#define sz_xTranslateCoordsReq 16
#define sz_xWarpPointerReq 24
#define sz_xSetInputFocusReq 12
#define sz_xOpenFontReq 12
#define sz_xQueryTextExtentsReq 8
#define sz_xListFontsReq 8
#define sz_xSetFontPathReq 8
#define sz_xCreatePixmapReq 16
#define sz_xCreateGCReq 16
#define sz_xChangeGCReq 12
#define sz_xCopyGCReq 16
#define sz_xSetDashesReq 12
#define sz_xSetClipRectanglesReq 12
#define sz_xCopyAreaReq 28
#define sz_xCopyPlaneReq 32
#define sz_xPolyPointReq 12
#define sz_xPolySegmentReq 12
#define sz_xFillPolyReq 16
#define sz_xPutImageReq 24
#define sz_xGetImageReq 20
#define sz_xPolyTextReq 16
#define sz_xImageTextReq 16
#define sz_xCreateColormapReq 16
#define sz_xCopyColormapAndFreeReq 12
#define sz_xAllocColorReq 16
#define sz_xAllocNamedColorReq 12
#define sz_xAllocColorCellsReq 12
#define sz_xAllocColorPlanesReq 16
#define sz_xFreeColorsReq 12
#define sz_xStoreColorsReq 8
#define sz_xStoreNamedColorReq 16
#define sz_xQueryColorsReq 8
#define sz_xLookupColorReq 12
#define sz_xCreateCursorReq 32
#define sz_xCreateGlyphCursorReq 32
#define sz_xRecolorCursorReq 20
#define sz_xQueryBestSizeReq 12
#define sz_xQueryExtensionReq 8
#define sz_xChangeKeyboardControlReq 8
#define sz_xBellReq 4
#define sz_xChangePointerControlReq 12
#define sz_xSetScreenSaverReq 12
#define sz_xChangeHostsReq 8
#define sz_xListHostsReq 4
#define sz_xChangeModeReq 4
#define sz_xRotatePropertiesReq 12
#define sz_xReply 32
#define sz_xGrabKeyboardReply 32
#define sz_xListFontsWithInfoReply 60
#define sz_xSetPointerMappingReply 32
#define sz_xGetKeyboardMappingReply 32
#define sz_xGetPointerMappingReply 32
#define sz_xGetModifierMappingReply 32
#define sz_xListFontsWithInfoReq 8
#define sz_xPolyLineReq 12
#define sz_xPolyArcReq 12
#define sz_xPolyRectangleReq 12
#define sz_xPolyFillRectangleReq 12
#define sz_xPolyFillArcReq 12
#define sz_xPolyText8Req 16
#define sz_xPolyText16Req 16
#define sz_xImageText8Req 16
#define sz_xImageText16Req 16
#define sz_xSetPointerMappingReq 4
#define sz_xForceScreenSaverReq 4
#define sz_xSetCloseDownModeReq 4
#define sz_xClearAreaReq 16
#define sz_xSetAccessControlReq 4
#define sz_xGetKeyboardMappingReq 8
#define sz_xSetModifierMappingReq 4
#define sz_xPropIconSize 24
#define sz_xChangeKeyboardMappingReq 8