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<HTML><HEAD><TITLE>Xlib Programming Manual: Creating Additional Function Sets</TITLE></HEAD><BODY><H1 ALIGN=center>6.12.9 Creating Additional Function Sets</H1>The creation of additional function sets should berequired only when an output device does not conform to existing function sets or when additional device-dependent color spaces are necessary.A function set consists primarily of a collection of device-dependent<B><A HREF="creating-additional-spaces.html#XcmsColorSpace">XcmsColorSpace</A></B>structures and a means to read and store a screen's color characterization data.This data is stored in an<B>XcmsFunctionSet</B>structure.A handle to this structure (that is, by means of global variable)is usually made accessible to the client program for use with<B><A HREF="XcmsAddFunctionSet.html">XcmsAddFunctionSet()</A></B>.<P>If a function set uses new device-dependent <B><A HREF="creating-additional-spaces.html#XcmsColorSpace">XcmsColorSpace</A></B>structures,they will be transparently processed into the color management system.Function sets can share an <B><A HREF="creating-additional-spaces.html#XcmsColorSpace">XcmsColorSpace</A></B>structure for a device-dependent color space.In addition, multiple <B><A HREF="creating-additional-spaces.html#XcmsColorSpace">XcmsColorSpace</A></B>structures are allowed for a device-dependent color space;however, a function set can reference only one of them.These <B><A HREF="creating-additional-spaces.html#XcmsColorSpace">XcmsColorSpace</A></B>structures will differ in the functions to convert to and from CIE XYZ,thus tailored for the specific function set.<A NAME="XcmsFunctionSet"></A><P><CODE><PRE>typedef struct _XcmsFunctionSet { XcmsColorSpace **DDColorSpaces; XcmsScreenInitProc screenInitProc; XcmsScreenFreeProc screenFreeProc;} XcmsFunctionSet;</PRE></CODE><P>The DDColorSpaces member is a pointer to a NULL terminated listof pointers to <B><A HREF="creating-additional-spaces.html#XcmsColorSpace">XcmsColorSpace</A></B>structures for the device-dependent color spaces that are supportedby the function set.The screenInitProc member is set to the callback procedure (see the followinginterface specification) that initializes the <B>XcmsPerScrnInfo</B>structure for a particular screen.<P>The screen initialization callback must adhere to the following softwareinterface specification:<!.IN "XcmsScreenInitProc" "" "@DEF@"><CODE><PRE>typedef <B><A HREF="../conversion-contexts-and-gamut-mapping.html#cmsStatus">Status</A></B> (*XcmsScreenInitProc)(<B>display</B>, <B>screen_number</B>, <B>screen_info</B>) <A HREF="../../display/opening.html#Display">Display</A> *<B>display</B>; int <B>screen_number</B>; XcmsPerScrnInfo *<B>screen_info</B>;</PRE></CODE><TABLE><TR><TD> <B>display</B><TD> Specifies the connection to the X server.<TR><TD> <B>screen_number</B><TD> Specifies the appropriate screen number on the host server.<TR><TD> <B>screen_info</B><TD> Specifies the <B>XcmsPerScrnInfo</B>structure, which contains the per screen information.</TABLE>The screen initialization callback in the<A HREF="#XcmsFunctionSet">XcmsFunctionSet</A>structure fetches the color characterization data (device profile) forthe specified screen,typically off properties on the screen's root window.It then initializes the specified<B>XcmsPerScrnInfo</B>structure.<!.IN "Device profile"><!.IN "Color Characterization Data">If successful, the procedure fills in the <B>XcmsPerScrnInfo</B>structure as follows:<UL><P><LI>It sets the screenData member to the address of the created device profile data structure (contents known only by the function set).<P><LI>It next sets the screenWhitePoint member.<P><LI>It next sets the functionSet member to the address of the<A HREF="#XcmsFunctionSet">XcmsFunctionSet</A>structure.<P><LI>It then sets the state member to <B>XcmsInitSuccess</B>and finally returns<B>XcmsSuccess</B>.</UL><P>If unsuccessful, the procedure sets the state member to <B>XcmsInitFailure</B>and returns.PN XcmsFailure .<P>The<B>XcmsPerScrnInfo</B>structure contains:<CODE><PRE>typedef struct _XcmsPerScrnInfo { XcmsColor screenWhitePoint; XPointer functionSet; XPointer screenData; unsigned char state; char pad[3];} XcmsPerScrnInfo;</PRE></CODE><P>The screenWhitePoint member specifies the white point inherent tothe screen.The functionSet member specifies the appropriate function set.The screenData member specifies the device profile.The state member is set to one of the following:<UL><P><LI><B>XcmsInitNone</B>indicates initialization has not been previously attempted.<P><LI><B>XcmsInitFailure</B>indicates initialization has been previously attempted but failed.<P><LI><B>XcmsInitSuccess</B>indicates initialization has been previously attempted and succeeded.</UL><P>The screen free callback must adhere to the following softwareinterface specification:<!.IN "XcmsScreenFreeProc" "" "@DEF@"><CODE><PRE>typedef void (*XcmsScreenFreeProc)(<B>screenData</B>) XPointer <B>screenData</B>;</PRE></CODE><TABLE><TR><TD> <B>screenData</B><TD> Specifies the data to be freed.</TABLE>This function is called to free the screenData stored in an<B>XcmsPerScrnInfo</B>structure.<H5 ALIGN=right><I>Next Chapter: <A HREF="../../GC/">Graphics Context Functions</A></I></H5><HR><ADDRESS><A HREF="http://tronche.com/">Christophe Tronche</A>, <A HREF="mailto:ch.tronche@computer.org">ch.tronche@computer.org</A></ADDRESS></BODY></HTML>⌨️ 快捷键说明
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