diff options
| -rw-r--r-- | xembed/xembed-spec.xml | 1407 |
1 files changed, 0 insertions, 1407 deletions
diff --git a/xembed/xembed-spec.xml b/xembed/xembed-spec.xml deleted file mode 100644 index b60a2e1..0000000 --- a/xembed/xembed-spec.xml +++ /dev/null @@ -1,1407 +0,0 @@ -<?xml version="1.0"?> -<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" -"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [ -]> -<article id="index"> - <articleinfo> - <title>XEmbed Protocol Specification</title> - <releaseinfo>Version 0.5</releaseinfo> - <date>15 April 2002</date> - <authorgroup> - <author> - <firstname>Mathias</firstname> - <surname>Ettrich</surname> - <affiliation> - <address> - <email>ettrich@trolltech.com</email> - </address> - </affiliation> - </author> - <author> - <firstname>Owen</firstname> - <surname>Taylor</surname> - <affiliation> - <address> - <email>otaylor@redhat.com</email> - </address> - </affiliation> - </author> - </authorgroup> - </articleinfo> - - <sect1 id="overview"> - <title>Overview</title> - <para> - XEmbed is a protocol that uses basic X mechanisms such as client - messages and reparenting windows to provide embedding of a - control from one application into another application. Some - of the goals of the XEmbed design are: - </para> - <orderedlist> - <listitem> - <para> - Support for out-of process controls, written in any toolkit - or even plain Xlib. - </para> - </listitem> - <listitem> - <para> - Support for in-process-controls when mixing different - toolkits in one process. - </para> - </listitem> - <listitem> - <para> - Smooth integration of the embedding application and embedded client - in areas such as input device handling and visual feedback. - </para> - </listitem> - <listitem> - <para> - Easy implementation. A full implementation supporting all - details correctly may require minor toolkit modifications, - but it should be possible to get basic functionality going - in less than 1000 lines of code. - </para> - </listitem> - </orderedlist> - <para> - Goal 1 is the most urgent one. A embedding specification allows - developers to write applets for whatever desktop the user is - using in whatever toolkit they prefer. Goal 2 is more of - something to keep in mind than a immediate requirement. While - there are other ways to mix two or more toolkits, using XEmbed - might be the easiest and thus most comfortable way. Goal 3 - describes the targeted level of integration. The users should - not necessarily notice that they work with embedded controls; - devices like the keyboard and the mouse should work as expected, - inactive windows should look like they are inactive, and so - forth. The level of integration may, however, be limited by goal - 4. In order for the protocol to be successful, it's crucial to - get implementations for the most important toolkits. Thus, the - implementation should not require too much coding and no or only - few modifications to the toolkit's kernel. - </para> - <para> - At the time of writing, an implementation of XEmbed is included - in GTK+-2.0 that mostly conforms to this version of the - specification. The main area of divergence is in the area of - accelerators, where a simpler scheme is implemented than the - XEMBED_REGISTER_ACCELERATOR, XEMBED_UNREGISTER_ACCELERATOR - accelerator scheme described here. The KDE libraries (libkdeui) - include QXEmbed, a mostly-complete implementation for Qt of an - earlier version of the protocol. - </para> - </sect1> - <sect1 id="definitions"> - <title>Definitions</title> - <variablelist> - <varlistentry> - <term>Active</term> - <listitem> - <para> - A toplevel window is <firstterm>active</firstterm> if it - currently is receiving keyboard events. (The window or a - descendent has the X keyboard focus.) A widget within the - toplevel is active if the toplevel is active, regardless - of whether that widget has the input focus within the - toplevel. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Client</term> - <listitem> - <para> - In an embedding situation, the <firstterm>client</firstterm> is - the window that is embedded into an embedder. Sometimes also - called a plug. (Note that the usage here should not be - confused with the typical X usage of "client" to mean an application - connecting to the X server. That is always referred to as - an application in this document) - </para> - <remark> - [ Should we replace client by some other term in - this document to avoid the confusion? ] - </remark> - </listitem> - </varlistentry> - <varlistentry> - <term>Embedder</term> - <listitem> - <para> - In an embedding situation, the <firstterm>embedder</firstterm> - is the graphical location that embeds an external - client. Sometimes also called a socket or site. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Focused</term> - <listitem> - <para> - A widget is <firstterm>focused</firstterm> if it receives - keyboard events within its toplevel. This is without - regard to whether the toplevel is active, and has nothing - to do with the X keyboard focus. - </para> - </listitem> - </varlistentry> - </variablelist> - </sect1> - <sect1 id="rationale"> - <title>Rationale and discussion</title> - <para> - The basis for handling embedding is that the embedder acts like - a "window manager" for the client. (The window management - protocol is defined in the X Inter-Client Communications Manual - or ICCCM). The embedder selects with SubstructureRedirectMask - on its window so that it can intercept, and then the client - window is reparented (using - <function>XReparentWindow()</function>) - as a child of the embedder window. Because of the substructure redirect, the - embedder is able to intercept calls to move or resize the client - window, and handle them as appropriate to the location in the - embedding application. (Map requests are also redirected, but - XEmbed actually handles map requests separately... see the - description of the XEMBED_MAPPED flag.) - </para> - <para> - The window management protocol is sufficient to handle the - basics of visual embedding, but has deficiencies in other areas - that prevent it from providing natural integration between - toolkits. These areas include: - </para> - - <simplelist> - <member>window activation state</member> - <member>keyboard focus</member> - <member>tab focus chain</member> - <member>keyboard short cuts / accelerators</member> - <member>modality</member> - <member>drag and drop (XDND)</member> - </simplelist> - - <para> - The XEmbed protocol is mainly concerned with communicating - additional information between embedder and client to handle - these areas. Communication in XEmbed is done by forwarding - slightly modified XEvents using - <function>XSendEvent()</function>, - by sending special xembed messages, and by setting X properties. In addition, - standard ICCCM features like WMNormalHints are used where - appropriate. - </para> - <para> - The next sections explain why these problems occur with the - simple "window management" approach and how XEmbed solves them. - </para> - - <sect2> - <title>Window activation state</title> - <para> - A widget has to know the activation state of its toplevel - window. This enables input widgets like a line editor, to display - a blinking cursor only when the user can actually type into it. In - addition, certain GUI styles choose to display inactive windows - differently, typically with a lighter and less contrasting color - palette. - </para> - <para> - Unfortunately, there are no such messages like WindowActivate - or WindowDeactivate in the X protocol. Instead, a window knows - that it is active when it receives keyboard focus (XFocusInEvent - with certain modes) or looses it (XFocusOutEvent with certain - modes). This applies to embedded child windows only, when the - mouse pointer points onto one of the child's subwindows in the very - moment the window manager puts the X focus on the toplevel - window. For that reason, XEmbed requires the embedders to pass - XEMBED_WINDOW_ACTIVATE and XEMBED_WINDOW_DEACTIVATE messages to - their respective clients whenever they get or loose X keyboard - </para> - </sect2> - - <sect2> - <title>Keyboard focus</title> - <para> - The delivery of keyboard events in X is designed in a way that - does not correspond to the typical operation of modern - toolkits; instead it seems designed to allow things to allow - things to work without either a window manager or a focus - handling in the toolkit. Typically, key events are sent to the - window which has the X input focus (set with - XSetInputFocus()). However, if the mouse pointer is inside - that focus window, the event is sent to the subwindow of the - focus window that is under the moues pointer. In modern toolkits, - the X input focus is typically left on the toplevel window and - a separate logical input focus is implemented within the - toolkit. The toolkit ignores the window that the key event is - actually sent to (which might be a scrollbar or other random - widget within the toplevel, depending on where the mouse - pointer is), and distributes key events to widget with the - logical input focus. - </para> - <para> - So, for standard operation, the behavior where key events are sent - to the window with the mouse pointer is simply ignored. But - with embedded windows, it causes problems, since, if the - mouse pointer is within the embedded window, the outer toolkit - doesn't see any key events, even if the logical keyboard focus - is elsewhere within the outer toolkits toplevel window. - </para> - <para> - Previous embedding techniques therefore required clients to - forward any key event they receive (KeyPress and KeyRelease) to - their respective embedder. In order to support multiple levels of - embedding, events that stem from a SendEvent request had to be - forwarded as well. While this is a possible solution, it adds both - race conditions and inefficency - </para> - <para> - The solution proposed by XEmbed is is to beat X11 with its own - weapons: The topmost toolkit is <emphasis>required</emphasis> - to keep the X input focus on one of its own windows without - any embedded children. Keeping the focus on such a window - ensures that key events are always delivered to the outer - toolkit and thus can be forwarded easily to any embedded - window. This also makes it possible to use this part of XEmbed - with clients that do not support the protocol at all, without - breaking keyboard input for the embedding application. - </para> - <para> - In detail, the topmost embedder creates a not-visible X Window to - hold the focus, the focus proxy. (It might be a 1x1 child - window of toplevel located at -1,-1.) Since the focus proxy isn't - an ancestor of the client window, the X focus can never move - into the client window because of the mouse pointer location. - In other words, whenever the outer window is activated - (receives the X input focus), it has to put the X focus on the - FocusProxy by calling <function>XSetInputFocus()</function>. - </para> - <para> - The trouble with this is, that you should not use <function>XSetInputFocus()</function> - without a proper time stamp from the Server, to avoid race - conditions. Unfortunately, the XFocusIn even does not carry a - timestamp. The solution to this is, to ask the window manager for - the WM_TAKE_FOCUS window protocol. Thus, whenever the window is - activated, it will receive a WM_PROTOCOLS client message with - data.l[0] being WM_TAKE_FOCUS and data.l[1] being a proper - timestamp. This timestamp can be used safely for the call to - <function>XSetInputFocus()</function>. - </para> - <para> - If an embedder widget gets the logical input focus, it sends - an XEMBED_FOCUS_IN message to its client. The client that - receives this messages knows that its logical focus is now - also the logical focus of the application window and will - react accordingly. If its logical focus lies on the line - editor control mentioned above, and the window is active, the - editor will show a blinking cursor after processing this - message. - </para> - <para> - In a similar fashion, if the embedder looses focus, it sends - an XEMBED_FOCUS_OUT message. - </para> - </sect2> - <sect2> - <title>Tab focus chain</title> - <para> - X does not have a concept of a tab focus chain, it is up to the - toolkit or the application to implement it. Since the concept - is standard among almost all toolkits, XEmbed supports it. An - XEmbed client integrates perfectly in the embedder's tab focus - chain, i.e. the user can tab onto the client, through all its - widgets and back to the outer world without noticing that they - traversed an external window. - </para> - <para> - As explained in the previous section, an embedder sends an - XEMBED_FOCUS_IN message to its client when it gets focus. The - detail code of this message is per default 0, that is, - XEMBED_FOCUS_CURRENT. It indicates that the clients keeps its own - logical focus where it was. To support tabbing, XEmbed provides - two more detail codes, namely XEMBED_FOCUS_FIRST and - XEMBED_FOCUS_LAST, that indicate that the client should move - its focus to the beginning or end of the focus chain. - </para> - <para> - When the user tabs to the very end of a client's tab chain, the - client follows the request (i.e. it puts its logical focus back to - the beginning its tab chain) and sends an XEMBED_FOCUS_NEXT - message to the embedder. If the embedder has siblings that accept - tab focus, it will do a virtual tab forward. As a result, it will - loose focus itself and consequently send an XEMBED_FOCUS_OUT - message to the client. As expected, the client's line edit control - from the previous example will stop blinking. - </para> - <para> - Backward tabbing is done exactly in the same manner, using the - XEMBED_FOCUS_PREV message. - </para> - </sect2> - <sect2> - <title>Keyboard short cuts / accelerators</title> - <para> - XEmbed is designed in such a way, that keyboard events are - received by the toplevel window, and then sent down the focus - focus chain. Toolkits will usually check for shortcuts or - accelerators before sending the event to the focus widget. If - such a shortcut is defined, the respective action is taken - rather than passing the event through to the focus - widget. This means, accelerators in the outmost window always - work properly, whereas accelerators defined inside an embedded - client only work if that client actually has focus. XEmbed - solves this problem with two messages, - XEMBED_REGISTER_ACCELERATOR and XEMBED_UNREGISTER_ACCELERATOR. - With XEMBED_REGISTER_ACCELERATOR, a client can reserve a - certain key/modifier combination as shortcut or - accelerator. The message is passed through to the topmost - embedder, where the key combination is stored. An - XEMBED_UNREGISTER_ACCELERATOR message releases the key again. - </para> - </sect2> - <sect2> - <title>Modality</title> - <para> - If an application window is shadowed by a modal dialog, no user - input is supposed to get through. The XEmbed design ensures this - for keyboard input, because the toplevel window knows about its - modal state and will not pass key events through. Embedded clients - thus inherit the modality from the topmost embedder. Mouse input, - however, is sent directly to the embedded clients by the X-Server, - unaffected by the modality of the application window. To give - clients the possibility to behave correctly when being shadowed by - a modal dialog, an embedder can choose to send an - XEMBED_MODALITY_ON message to its client when it becomes shadowed, - and an XEMBED_MODALITY_OFF message when it leaves modality - again. If the client contains embedders itself, those have to pass - both messages through to their clients. - </para> - </sect2> - <sect2> - <title>Drag and drop (XDND)</title> - <para> - XDND drag-and-drop does not work with reparented external - windows, since messages are exchanged with the toplevel window - only. This is done for performance reasons. While it is cheap to - get the window under the mouse pointer, it is very expensive to - get a window under another window. Unfortunately, this is required - quite often when dragging objects around, since the pointer - may overlap the drag icon. - </para> - <para> - Solving the drag-and-drop problem, however, is quite easy, - since the XDND protocol was carefully designed in a way that - makes it possible to support embedded windows. Basically, the - embedder has to operate as drag-and-drop proxy for the client. Any - XDND messages like XdndEnter, Xdnd,Leave, etc. simply have to be - passed through. A toollkit's XDND implementation has to take this - situation in consideration. - </para> - </sect2> - </sect1> - <sect1 id="lifecycle"> - <title>Embedding life cycle</title> - <para> - The protocol is started by the embedder. The window ID of - the client window is passed (by unspecified means) to the - embedding application, and the embedder calls - <function>XReparentWindow()</function> to reparent the client - window into the embedder window. - </para> - <para> - Implementations may choose to support an alternate method of - beginning the protocol where the window ID of the embedder - is passed to client application and the client creates a window - within the embedder, or reparents an existing window into - the embedder's window. Which method of starting XEmbed is - used a matter up to higher level agreement and outside the - scope of this specification. - </para> - <para> - In either case the client window must have a property called - _XEMBED_INFO on it. This property has type _XEMBED_INFO - and format 32. The contents of the property are: - </para> - <table> - <title>_XEMBED_INFO</title> - <tgroup cols="3"> - <thead> - <row> - <entry>Field</entry><entry>Type</entry><entry>Comments</entry> - </row> - </thead> - <tbody> - <row> - <entry>version</entry><entry>CARD32</entry><entry>The protocol version</entry> - </row> - <row> - <entry>flags</entry><entry>CARD32</entry><entry>A bitfield of flags</entry> - </row> - </tbody> - </tgroup> - </table> - <para> - The <structfield>version</structfield> field indicates the - maximum version of the protocol that the client supports. - The embedder should retrieve this field and set the data2 field - of the XEMBED_EMBEDDED_NOTIFY to - Min (<structfield>version</structfield>, <replaceable>max version supported by embedder</replaceable>). - The version number corresponding to the current version of the - protocol is 0. - <remark>[Should the version be defined as (Major << 16 | Minor) ?]</remark> - </para> - <para> - The currently defined bit in the - <structfield>flags</structfield> field is: - </para> - <programlisting><!-- --->/* Flags for _XEMBED_INFO */ -#define XEMBED_MAPPED (1 << 0)<!-- - --></programlisting> - <variablelist> - <varlistentry> - <term>XEMBED_MAPPED</term> - <listitem> - <para> - If set the client should be mapped. The embedder must - track the flags field by selecting for PropertyNotify - events on the client and map and unmap the client - appropriately. (The embedder can leave the client unmapped - when this bit is set, but should immediately unmap the - client upon detecting that the bit has been unset.) - </para> - <remark> - Rationale: the reason for using this bit rather than - MapRequest events is so that the client can reliably - control it's map state before the inception of the - protocol without worry that the client window will - become visible as a child of the root window. - </remark> - </listitem> - </varlistentry> - </variablelist> - <para> - To support future expansion, all fields not currently defined - must be set to zero. To add proprietary extensions to the - XEMBED protocol, an application must use a separate property, rather - than using unused bits in the struct field or extending the - _XEMBED_INFO property. - </para> - <para> - At the start of the protocol, the embedder first sends an - XEMBED_EMBEDDED_NOTIFY message, then sends - XEMBED_FOCUS_IN, XEMBED_WINDOW_ACTIVATE, and XEMBED_MODALITY_ON - messages as necessary to synchronize the state of the - client with that of the embedder. Before any of these messages - received, the state of the client is: - <simplelist> - <member>Not focused</member> - <member>Not active</member> - <member>Modality off</member> - </simplelist> - </para> - <para> - If the embedder is geometry managed and can change its size, it - should obey the client's WMNormalHints settings. Note that - most toolkits will not have equivalents for all the hints in - the WMNormalHints settings, clients must not assume that the - requested hints will be obeyed exactly. The - <structfield>width_inc</structfield>, - <structfield>height_inc</structfield>, - <structfield>min_aspect</structfield>, and - <structfield>max_aspect</structfield> fields are examples of - fields from WMNormalHints that are unlikely to be supported - by embedders. - </para> - <para> - The protocol ends in one of three ways: - </para> - <orderedlist> - <listitem> - <para> - The embedder can unmap the client and reparent the client - window to the root window. If the client receives an - ReparentNotify event, it should check the - <structfield>parent</structfield> field of the - <structname>XReparentEvent</structname> structure. If this - is the root window of the window's screen, then the protocol - is finished and there is no further interaction. If it - is a window other than the root window, then the protocol - continues with the new parent acting as the embedder window. - </para> - </listitem> - <listitem> - <para> - The client can reparent its window out of the embedder - window. If the embedder receives a ReparentNotify signal - with the <structfield>window</structfield> field being the - current client and the <structfield>parent</structfield> - field being a different window, this indicates the end - of the protocol. - </para> - <remark> - [ GTK+ doesn't currently handle this; but it seems useful - to allow the protocol to be ended in a non-destructive - fashion from either end. ] - </remark> - </listitem> - <listitem> - <para> - The client can destroy its window. - </para> - </listitem> - </orderedlist> - </sect1> - <sect1 id="messages"> - <title>Message Specifications</title> - <para> - An XEmbed message is an X11 client message with message type - "_XEMBED". The format is 32, the first three data longs carry the - toolkit's X time (l[0]), the message's major opcode (l[1]) and the - message's detail code (l[2]). If no detail is required, the value - passed has to be 0. The remaining two data longs (l[3] and l[4]) - are reserved for data1 and data2. Unused bytes of the client - message are set to 0. The event is sent to the target window with - no event mask and propagation turned off. - </para> - <para> - The valid XEmbed messages are: - </para> - <programlisting><!-- --->/* XEMBED messages */ -#define XEMBED_EMBEDDED_NOTIFY 0 -#define XEMBED_WINDOW_ACTIVATE 1 -#define XEMBED_WINDOW_DEACTIVATE 2 -#define XEMBED_REQUEST_FOCUS 3 -#define XEMBED_FOCUS_IN 4 -#define XEMBED_FOCUS_OUT 5 -#define XEMBED_FOCUS_NEXT 6 -#define XEMBED_FOCUS_PREV 7 -/* 8-9 were used for XEMBED_GRAB_KEY/XEMBED_UNGRAB_KEY */ -#define XEMBED_MODALITY_ON 10 -#define XEMBED_MODALITY_OFF 11 -#define XEMBED_REGISTER_ACCELERATOR 12 -#define XEMBED_UNREGISTER_ACCELERATOR 13 -#define XEMBED_ACTIVATE_ACCELERATOR 14<!-- - --></programlisting> - <para> - A detail code is required for XEMBED_FOCUS_IN. The following values - are valid: - </para> - <programlisting><!-- --->/* Details for XEMBED_FOCUS_IN: */ -#define XEMBED_FOCUS_CURRENT 0 -#define XEMBED_FOCUS_FIRST 1 -#define XEMBED_FOCUS_LAST 2<!-- - --></programlisting> - <sect2> - <title>XEMBED_EMBEDDED_NOTIFY</title> - <para> - Sent from the embedder to the client on embedding, after - reparenting and mapping the client's X window. A client that - receives this messages knows that its window was embedded by an - XEmbed site and not simply reparented by a window manager. To support toolkits - that do not keep track of reparenting events, the message carries - the embedder's window handle as data1: - </para> - <table> - <title>XEMBED_EMBEDDED_NOTIFY</title> - <tgroup cols="2"> - <tbody> - <row> - <entry>data1</entry><entry>The embedder's window handle.</entry> - </row> - <row> - <entry>data2</entry><entry>The protocol version in use - (see the description of _XEMBED_INFO).</entry> - </row> - </tbody> - </tgroup> - </table> - </sect2> - <sect2> - <title>XEMBED_WINDOW_ACTIVATE / XEMBED_WINDOW_DEACTIVATE</title> - <para> - Sent from the embedder to the client when the window becomes - active or inactive, i.e. when the window gets or looses the - keyboard input focus. If the client contains embedders itself, - those have to pass the message through to their clients. - </para> - <para> - Note that no XEMBED_FOCUS_IN or XEMBED_FOCUS_OUT messages - should be sent when the toplevel window gains or loses - focus. The XEMBED_FOCUS_IN and XEMBED_FOCUS_OUT messages - refer only to focus <firstterm>within</firstterm> the - toplevel window and are independent of toplevel activation - state. This independence is necessary so that input focus - within a toplevel can be moved programmatically when the - toplevel doesn't have input focus. - </para> - <remark> - [ GTK+ is currently in violation of the preceding note, - and sends FOCUS_IN and FOCUS_OUT only when the toplevel - is active. See - <ulink - url="http://bugzilla.gnome.org/show_bug.cgi?id=67943">GNOME bug #67943</ulink> ] - </remark> - <para> - Widgets within the client should typically be displayed with - the focus only when the client both has focus and is active. - </para> - </sect2> - <sect2> - <title>XEMBED_REQUEST_FOCUS</title> - <para> - Sent from the client to the embedder when the client wants - focus. The most common ocassion is when the user clicks into one - of the client's child widgets, for example a line editor, in order - to type something in. - </para> - <para> - The message is passed along to the topmost embedder that - eventually responds with a XEMBED_FOCUS_IN message. The focus in - message is passed all the way back until it reaches the original - focus requestor. In the end, not only the original client has - focus, but also all its ancestor embedders. - </para> - </sect2> - <sect2> - <title>XEMBED_FOCUS_IN</title> - <para> - Sent from the embedder to the client when it gets focus. The - detail code determines, where the client shall move its own - logical focus to. Three possibilities exist: - </para> - <variablelist> - <varlistentry> - <term>XEMBED_FOCUS_CURRENT</term> - <listitem> - <para> - Normal activation, does not move the clients logical - focus. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>XEMBED_FOCUS_FIRST</term> - <listitem> - <para> - Used when the user tabs onto a client. It indicates that - the client should put its logical focus onto the widget - that comes first in its own tab focus chain. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>XEMBED_FOCUS_LIST</term> - <listitem> - <para> - Used when the user tabs onto a client. It indicates that - the client should put its logical focus onto the widget - that comes first in its own tab focus chain. - </para> - </listitem> - </varlistentry> - </variablelist> - </sect2> - <sect2> - <title>XEMBED_FOCUS_OUT</title> - <para> - Sent from the embedder to the client when it looses focus. - </para> - </sect2> - <sect2> - <title>XEMBED_FOCUS_NEXT</title> - <para> - Sent from the client to the embedder when it reaches the end of - its logical tab chain after the user tabbed forwards. If the - embedder has siblings that accept tab focus, it will do a virtual - tab forward. As a result, it will loose focus itself and - consequently send an XEMBED_FOCUS_OUT message to the client - </para> - </sect2> - <sect2> - <title>XEMBED_FOCUS_PREV</title> - <para> - Sent from the client to the embedder when it reaches the - beginning of its logical tab chain after the user tabbed - backwards. If the embedder has siblings that accept tab focus, it - will do a virtual tab backward. As a result, it will loose focus - itself and consequently send an XEMBED_FOCUS_OUT message to the - client - </para> - </sect2> - <sect2> - <title>XEMBED_REGISTER_ACCELERATOR / XEMBED_UNREGISTER_ACCELERATOR</title> - <para> - A client that needs to reserve a certain key/modifier - combination as shortcut or accelerators, sends a XEMBED_REGISTER_ACCELERATOR - message to its embedder. As long as the embedder itself is a child - of a client, the accelerator will be propagated up to the toplevel. - </para> - <table> - <title>XEMBED_REGISTER_ACCELERATOR</title> - <tgroup cols="2"> - <tbody> - <row> - <entry>detail</entry><entry>accelerator_id</entry> - </row> - <row> - <entry>data1</entry><entry>X key symbol</entry> - </row> - <row> - <entry>data2</entry><entry>bit field of modifier values</entry> - </row> - </tbody> - </tgroup> - </table> - <para> - The accelerator_id is used to identify the accelerator when - activating the accelerator. The reason for using an - accelerator ID instead of identifying accelerators simply by - key symbol and modifiers is to allow the correct handling of - overloaded accelerators with embedded widgets. (An accelerator - is overloaded if there multiple accelerators on the same key, - usually because of accidental collisions.) When an overloaded - accelerator is pressed repeatedly, the toplevel activates - accelerators on that key in round-robin fashion. If this - round-robin behavior is not supported by the embedding - toolkit, picking an arbitrary accelerator for the key and - activating it is acceptable. Well designed applications should - avoid collisions in any case. - </para> - <note> - <para> - Ordering the round-robin of conflicting accelerators - in a predictable (geometric or in focus chain) order - is desirable. This can be achieved if the toplevel sorts - the conflicting accelerators as if they applied to the - client instead of widgets within the client and then - each client does the same sort on the subset of conflicting - accelerators within it. To get this to work properly - if there are conflicting accelerators within a client, say widget - A and B both have the same mnemonic, then instead of - registering one accelerator for widget A and one for - widget B, the client should register two accelerators that - corresponds to both A and B, and then when - XEMBED_ACTIVATE_ACCELERATOR is received for either - accelerator, implement round robin between A and B - with the correct sorting. - </para> - </note> - <para> - The modified bit field is a bitwise OR of values indicating - various accelerators; these indicate logical accelerator - keys rather than corresponding directly to the bits in - the XKeyEvent state field. - </para> - <programlisting><!-- --->/* Modifiers field for XEMBED_REGISTER_ACCELERATOR */ -#define XEMBED_MODIFIER_SHIFT (1 << 0) -#define XEMBED_MODIFIER_CONTROL (1 << 1) -#define XEMBED_MODIFIER_ALT (1 << 2) -#define XEMBED_MODIFIER_SUPER (1 << 3) -#define XEMBED_MODIFIER_HYPER (1 << 4)<!-- - --></programlisting> - <para> - (Meta is intentionally left out here because if you try to separate - Alt and Meta, a large fraction of users will experience problems - with their keyboard setups... there is no reliably standard - of which one is the primary modifier key and on the Alt key.) - </para> - <para> - On activation, the topmost embedder will send - XEMBED_ACTIVATE_ACCELERATOR to its client; if the - accelerator was registered by an embedder inside that - client, the embedder will send XEMBED_ACTIVATE_ACCELERATOR - to its client and so forth. - </para> - <para> - Note that the assignment of ID's is private for each pair - of client and embedder and when accelerators are being - propagated through multiple client/embedder pairs, a - different accelerator ID may be used for each pair. - </para> - <para> - The XEMBED_UNREGISTER_ACCELERATOR message releases the key - combination again. - </para> - <table> - <title>XEMBED_UNREGISTER_ACCELERATOR</title> - <tgroup cols="2"> - <tbody> - <row> - <entry>detail</entry><entry>integer ID passed - to XEMBED_REGISTER_ACCELERATOR</entry> - </row> - </tbody> - </tgroup> - </table> - <para> - Hint to implementators: It is the responsibility of the - embedder to keep track of all forwarded accelerators - and to remove them when the client window dies. - </para> - </sect2> - <sect2> - <title>XEMBED_ACTIVATE_ACCELERATOR</title> - <para> - The XEMBED_ACTIVATE_ACCELERATOR message is sent when a - accelerator previously registered with - XEMBED_REGISTER_ACCELERATOR is activated on the toplevel - containing the embedder. - </para> - <table> - <title>XEMBED_ACTIVATE_ACCELERATOR</title> - <tgroup cols="2"> - <tbody> - <row> - <entry>detail</entry><entry>integer ID passed - when registering the accelerator</entry> - </row> - <row> - <entry>data1</entry><entry>flags.</entry> - </row> - </tbody> - </tgroup> - </table> - <para> - The following bit is defined for the flags field; all - other bits must be zero. - </para> - <programlisting><!-- --->/* Flags for XEMBED_ACTIVATE_ACCELERATOR */ -#define XEMBED_ACCELERATOR_OVERLOADED (1 << 0)<!-- - --> - </programlisting> - <variablelist> - <varlistentry> - <term>XEMBED_ACCELERATOR_OVERLOADED</term> - <listitem> - <para> - This flag indicates that multiple accelerators exist for - the key combination within the toplevel. The toolkit - may modify the behavior of the accelerator based on - this value. For instance, if the accelerator is a - mnemonic for a button, it might activate the the button - immediately if the accelerator is not overloaded, but - when overloaded, it would only focus the button. - </para> - </listitem> - </varlistentry> - </variablelist> - </sect2> - <sect2> - <title>XEMBED_MODALITY_ON / XEMBED_MODALITY_OFF</title> - <para> - Sent from the embedder to the client when the window becomes - shadowed by a modal dialog, or when it is released again. If the - client contains embedders itself, those have to pass the message - through to their clients. An embedded control should ignore - mouse input while modality is active. Note that that keyboard - input is blocked anyway by XEmbed, since the topmost embedder will - not pass keyboard events through in modal state. - </para> - </sect2> - </sect1> - - <sect1 id="techniques"> - <title>Techniques</title> - - <sect2> - <title>Handling errors</title> - <para> - Implementors of the XEmbed protocol should handle the other - party disappearing at any point. For this reason X errors - must be trapped when performing any operation with a window - not created by the application. This is done by using - <function>XSetErrorHandler()</function>. - A sample implementation of trapping errors in C looks like: - </para> - <programlisting><!-- --->#include <X11/Xlib.h> - -static int trapped_error_code = 0; -static int (*old_error_handler) (Display *, XErrorEvent *); - -static int -error_handler(Display *display, - XErrorEvent *error) -{ - trapped_error_code = error->error_code; - return 0; -} - -void -trap_errors(void) -{ - trapped_error_code = 0; - old_error_handler = XSetErrorHandler(error_handler); -} - -int -untrap_errors(void) -{ - XSetErrorHandler(old_error_handler); - return trapped_error_code; -}<!-- - --></programlisting> - </sect2> - <sect2> - <title>Forwarding X Events</title> - <para> - An XEmbed embedder has to forward key-press and key-release - events to its respective client. - </para> - <para> - Key events are forwarded by changing the event's window field - to the window handle of the client and sending the modifed - message via <function>XSendEvent()</function> to the embedder, - with no event mask and propagation turned off. - </para> - <para> - Note: XEmbed requires toolkits to handle key-events that come - from a SendEvent request. That means, if somebody can access - your X-Server, it's possible to fake keyboard input. Given - that most toolkits accept sent key events today anyway and the - X Server is typically protected through magic cookie - authorization, this is not considered to be an - issue. Applications with higher security requirements may - choose not to use embedded components, though, and to filter - out any events coming from <function>XSendEvent()</function>. - </para> - <para> - Given that Window client is the client's window handle, - here is a piece of code of an imaginary event-loop in C that does - the forwarding. - </para> - <programlisting><!-- --->#include <X11/Xlib.h> - -void handle_event( - Display* dpy, /* display */ - XEvent* ev /* event */ -){ - if ( ev->type == KeyPress || ev->type == KeyRelease ) { - ev->xkey.window = client; - trap_errors(); - XSendEvent( dpy, client, False, NoEventMask, ev ); - XSync( dpy, False ); - if (untrap_errors()) { - /* Handle failure */ - } - - return; - } - ... /* normal event handling */ -}<!-- - --></programlisting> - </sect2> - <sect2> - <title>Sending XEmbed messages</title> - <para> - Given that Time x_time contains the timestamp from the event - currently being processed. (CurrentTime is generally the best - choice if no event is being processed), here is a valid - implementation in C of sending an XEMBED message: - </para> - <programlisting><!-- --->#include <X11/Xlib.h> - -void send_xembed_message( - Display* dpy, /* display */ - Window w, /* receiver */ - long message, /* message opcode */ - long detail /* message detail */ - long data1 /* message data 1 */ - long data2 /* message data 2 */ -){ - XEvent ev; - memset(&ev, 0, sizeof(ev)); - ev.xclient.type = ClientMessage; - ev.xclient.window = w; - ev.xclient.message_type = XInternAtom( dpy, "_XEMBED", False ); - ev.xclient.format = 32; - ev.xclient.data.l[0] = x_time; - ev.xclient.data.l[1] = message; - ev.xclient.data.l[2] = detail; - ev.xclient.data.l[3] = data1; - ev.xclient.data.l[4] = data2; - trap_errors(); - XSendEvent(dpy, w, False, NoEventMask, &ev); - XSync(dpy, False); - if (untrap_errors()) { - /* Handle failure */ - } -}<!-- - --></programlisting> - </sect2> - </sect1> - <sect1 id="issues"> - <title>Issues</title> - <sect2> - <title>Implementation of modality</title> - <para> - The protocol could be simplified by removing the - XEMBED_MODALITY_ON and XEMBED_MODALITY_OFF messages in favor - of requiring the embedder to map an input-only window over - it's child when it beings shadowed by a modal grab. - </para> - <para> - One possible reason for the current protocol is that a toolkit - might want to have elements such as scrollbars that remain - active even when grab shadowed. (I know of no toolkit that - actually implements this.) - </para> - </sect2> - <sect2> - <title>Clarify function of timestamps</title> - <para> - The function of the timestamp arguments needs to be clarified, - as well as the requirements for what should be passed - in the field. The original draft of the specification - contained the text about the determining the timestamp. - </para> - <blockquote> - <para> - The x time is to be updated whenever the toolkit receives an - event from the server that carries a timestamp. XEmbed client - messages qualify for that. - </para> - <para> - Hint to implementators: Check that the xembed time stamp - is actually later than your current x time. While this cannot - happen with ordinary XEvents, delayed client messages may have - this effect. Be prepared that evil implementations may even - pass CurrentTime sometimes. - </para> - </blockquote> - <para> - But I [OWT] wouldn't agree with this advice. The point - of a timestamp is to make sure that when events are processed - out of order, the event generated last by the user wins - for shared resources such as input focus, selections, and - grabs. An example of where this can matter is if you have - </para> - <programlisting><!-- ---> Toplevel Window - Embedder - Client - Text Entry 1 - Embedder - Client - Text Entry 2<!-- - --></programlisting> - <para> - If the entries are set to select the text on focus in, and the - user hits TAB in quick succession, then the timestamps on the - FOCUS_IN events are what makes sure that Entry 2 actually ends - up owning the PRIMARY selection, instead of it being a race - between the two clients. But in situations like this having - the correct timestamp only matters if a user action triggers - the behavior. - </para> - <para> - Hence the advice that the timestamp should be the time from - the event currently being processed. - </para> - <para> - If no explicit user action is involved, then the - best thing to do is to use CurrentTime; using the timestamp - from the last X event received can cause problems if the - ultimate trigger of the behavior is a timeout or network - and the last X event happened some time in the distant past. - </para> - </sect2> - <sect2> - <title>Complexity of accelerator handling</title> - <para> - The current specification for accelerator handling is a little - complex. Most of the complexity (the accelerator IDs) comes - from the need to handle conflicting accelerators. - GTK+ currently implements a simpler scheme where grabs are - identified only by key symbol and modifier and conflicting - mnemonic resolution doesn't work across embedder/client - interfaces. - </para> - </sect2> - <sect2> - <title>Infinite loops in focusing</title> - <para> - There is the potential for infinite loops of focusing - - Consider the case: - </para> - <programlisting><!-- ---> Toplevel Window - Embedder - Client<!-- - --></programlisting> - <para> - Where there are no focusable sites in the client or in the - toplevel window. Then if <keysym>Tab</keysym> is pressed, the embedder - will send: FOCUS_IN/FOCUS_FIRST to the client, the client will - send FOCUS_NEXT to the embedder, the toplevel window will - wrap the focus around and send FOCUS_IN/FOCUS_FIRST to the - client... - </para> - <para> - The minimum mechanism that seems necessary to prevent this - loop is a serial number in the FOCUS_IN/FOCUS_FIRST message - that is repeated in a resulting FOCUS_NEXT message. - </para> - <para> - A possibly better way of handling this could be to make FOCUS_IN have - an explicit response; that, is, add a XEMBED_FOCUS_IN_RESPONSE - that the client must send to the embedder after receipt - of a FOCUS_IN message. - </para> - - <table> - <title>XEMBED_FOCUS_IN_RESPONSE</title> - <tgroup cols="2"> - <tbody> - <row> - <entry>detail</entry><entry>1 if the client accepted the focus, 0 otherwise</entry> - </row> - <row> - <entry>data1</entry><entry>serial number from XEMBED_FOCUS_IN</entry> - </row> - </tbody> - </tgroup> - </table> - <para> - The main problem with requiring a response here is that caller - needs to wait for the return event, and to handle cases like - parent (client 1) => child (client 2) => grandchild (client 1), - it probably needs to process all sorts of incoming events at - this point. If the user hits <keysym>Tab</keysym><keysym>Tab</keysym> - in quick succession things could get very complicated. - </para> - </sect2> - <sect2> - <title>Robustness</title> - <para> - The protocol, as currently constituted, is not robust against - the embedder crashing. This will result in the embedder - window being destroyed by the X server, and, as a consequence - client's window being unexpectedly destroyed, which will likely cause the - client to die with a BadWindow error. - </para> - <para> - To fix this requires an X protocol extension which extends - the functionality of <function>XChangeSaveSet()</function> in - two areas: - </para> - <itemizedlist> - <listitem> - <para> - Allow it to be specified that the saved window should be - reparented to the root window rather than to the nearest - parent. (The nearest parent typically being the window - manager's frame window, reparenting to the nearest - parent only saves the client until the window manager - cleans up and destroys the frame window.) - </para> - </listitem> - <listitem> - <para> - Allow it to be specified that the saved window should be - unmapped rather than then mapped. (Without this capability - the client will mapped as a child of the root window, - which will be confusing to the user.) - </para> - </listitem> - </itemizedlist> - </sect2> - <sect2> - <title>Sensitivity</title> - <para> - Toolkits such as Qt and GTK+ have a concept of disabled - widgets. This notion is typically hierarchical, so if - the embedder or a ancestory of the embedder becomes - insensitive, widgets inside the client should be displayed as, - and act insensitive as well. - </para> - </sect2> - <sect2> - <title>Directional focusing</title> - <para> - Some toolkits, such as GTK+, support, along with the standard - concept of a focus chain, the idea of <firstterm>directional - focusing</firstterm>; it's possible in some cases to navigate - focus using the arrow keys. To do this perfectly, you need - to have information about the coordinates of the original - focus window, which is hard to do in an embedding context, - but a good approximation is to, when focusing into a - container, provide the side of the container where focus - is coming from and to focus the "middle widget" on this side. - </para> - <para> - This could be supported by adding an extra data field to - to the XEMBED_FOCUS_FIRST/XEMBED_FOCUS_LAST subtypes - of XEMBED_FOCUS_IN and to XEMBED_FOCUS_NEXT and - XEMBED_FOCUS_PREV, which would contain: - </para> - <programlisting><!-- --->/* Directions for focusing */ -#define XEMBED_DIRECTION_DEFAULT 0 -#define XEMBED_DIRECTION_UP_DOWN 1 -#define XEMBED_DIRECTION_LEFT_RIGHT 2<!-- - --></programlisting> - <para> - Applications supporting only normal tab focusing would always - pass XEMBED_DIRECTION_DEFAULT and treat all received - directions as XEMBED_DIRECTION_DEFAULT. - </para> - <para> - The argument against supporting this is that it's a rather - confusing feature to start with (many widgets eat arrow keys - for other purposes), and becomes more confusing if you have - a application containing widgets from different toolkits, - some of which support it, some of which don't. - </para> - </sect2> - <sect2> - <title>Modal dialogs</title> - <para> - The specification doesn't have any provisions for handling the - case where an embedded client wants to put up a dialog. Such a - dialog should be transient-for the real toplevel window, and, - if modal, should block the entire toplevel window. To fully - implement this, you would need some concept of an application - that spanned multiple toplevel windows in multiple clients. - </para> - </sect2> - <sect2> - <title>Propagation of key presses</title> - <para> - It's frequently useful to have keybindings that trigger on - a widget if the focus is on a child of that widget. For - instance, <keysym>Control</keysym><keysym>PageUp</keysym> - and <keysym>Control</keysym><keysym>PageUp</keysym> switch - pages in a notebook widget when the focus is on a child - of the notebook. The XEmbed spec currently has no handling - of this situation. - </para> - <para> - The simplest solution would be to specify that if the client - widget doesn't handle a key press sent to it, it then sends - the event back to the embedder. Some care would be required - in the embedder handle infinite loops, but it shouldn't - be that bad. - </para> - </sect2> - <sect2> - <title>Handling of toplevel modes</title> - <para> - GTK+-2.0 contains a feature for key navigation of tooltips - where Control-F1 toggles a "tooltips keyboard mode" where - the tooltip for the currently focused window is displayed. - There is no way of propagating this across XEMBED. - This feature could clearly be implemented the same - way as XEMBED_WINDOW_ACTIVATE, but adding a pair of - messages for every feature of this type seems excessive. - </para> - <para> - A possible alternate idea would be to add a _XEMBED_STATE - property that the embedder sets on the client window which - is a list of atoms. This could actually be used to - replace XEMBED_WINDOW_ACTIVATE, and XEMBED_MODALITY_ON, - simplifying the protocol. - </para> - <para> - There are some race conditions in maintaining this property - if the client is allowed to reparent itself out of the - embedder that would have to be considered. - </para> - </sect2> - </sect1> - <appendix id="changes"> - <title>Change history</title> - <formalpara> - <title>"Version 1.0 DRAFT 1", 22 April 2000, Matthias Ettrich</title> - <para> - </para> - </formalpara> - <formalpara> - <title>"Version 1.0 DRAFT 2", 15 August 2000, Matthias Ettrich</title> - <para> - </para> - </formalpara> - <formalpara> - <title>Version 0.5, 19 April 2002, Owen Taylor</title> - <para> - <itemizedlist> - <listitem> - <para> - Add the life-cycle chapter, including _XEMBED_INFO - property, and the XEMBED_MAPPED flags. - </para> - </listitem> - <listitem> - <para> - Define the data2 for XEMBED_EMBEDDED_NOTIFY to be the - protocol version in use. - </para> - </listitem> - <listitem> - <para> - Replaced XEMBED_GRAB_KEY scheme for handling accelerators - with XEMBED_REGISTER_ACCELERATOR. - </para> - </listitem> - <listitem> - <para> - Removed text "This also means that the client has to - prepare for becoming visible anytime without filing a map - request itself" from the description of - XEMBED_EMBEDDED_NOTIFY". - </para> - </listitem> - <listitem> - <para> - Added text about the independence of FOCUS_IN/OUT and - ACTIVATE/DEACTIVE to the description of - XEMBED_WINDOW_ACTIVATE / XEMBED_WINDOW_DEACTIVATE. - </para> - </listitem> - <listitem> - <para> - Added note about fields in WMNormalHints not necessarily - being obeyed by embedders. - </para> - </listitem> - <listitem> - <para> - Removed mention of XEMBED_PROCESS_NEXT_EVENT, which is - no longer part of the protocol. - </para> - </listitem> - <listitem> - <para> - Added definitions of "Active" and "Focused" to the - definitions section. - </para> - </listitem> - <listitem> - <para> - Added issues and change history sections. - </para> - </listitem> - <listitem> - <para> - Lots of textual editing for clarity, style consistency. - </para> - </listitem> - <listitem> - <para> - Converted to docbook format. - </para> - </listitem> - </itemizedlist> - </para> - </formalpara> - </appendix> -</article> |