Hands-on Projects for the Linux Graphics Subsystem
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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 |