84 lines
3.1 KiB
Plaintext
84 lines
3.1 KiB
Plaintext
X Generic Event Extension
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Peter Hutterer
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peter.hutterer@who-t.net
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1. Introduction
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2. Extension Initialization
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3. Extension Events
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4. Notes
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_____________________________________________________________________________
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1. Introduction
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X was designed to provide 64 event opcodes for all extensions. These events
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are limited to 32 bytes.
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The Generic Event Extension provides a template event for extensions to re-use
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a single event opcode. GE only provide headers and the most basic
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functionality, leaving the extensions to interpret the events in their
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specific context.
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GenericEvents may be longer than 32 bytes. If so, the number of 4 byte units
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following the initial 32 bytes must be specified in the length field of the
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event.
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_____________________________________________________________________________
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2. Extension Initialization
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The name of this extension is "Generic Event Extension"
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┌───
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GEQueryVersion
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client-major-version: CARD16
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client-minor-version: CARD16
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▶
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major-version: CARD16
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minor-version: CARD16
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└───
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The client sends the highest supported version to the server
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and the server sends the highest version it supports, but no
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higher than the requested version. Major versions changes can
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introduce incompatibilities in existing functionality, minor
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version changes introduce only backward compatible changes.
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It is the clients responsibility to ensure that the server
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supports a version which is compatible with its expectations.
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As of version 1.0, no other requests are provided by this extension.
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_____________________________________________________________________________
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3. Extension Events
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GE defines a single event, to be used by all extensions. The event's structure
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is similar to a reply.
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┌───
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GenericEvent
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type: BYTE; always GenericEvent
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extension: CARD8; extension offset
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sequenceNumber: CARD16 low 16 bits of request seq. number
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length: CARD32 length
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evtype: CARD16 event type
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└───
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The field 'extension' is to be set to the major opcode of the
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extension. The 'evtype' field is the actual opcode of the event.
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The length field specifies the number of 4-byte blocks after the
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initial 32 bytes. If length is 0, the event is 32 bytes long.
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_____________________________________________________________________________
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4. Notes
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Although the wire event is of arbitrary length, the actual size of an XEvent
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is restricted to sizeof(XEvent) [96 bytes, see Xlib.h]. If an extension
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converts a wire event to an XEvent > 96 bytes, it will overwrite the space
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allocated for the event. See struct _XSQEvent in Xlibint.h for details.
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Extensions need to malloc additional data and fill the XEvent structure with
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pointers to the malloc'd data. The client then needs to free the data, only
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the XEvent structure will be released by Xlib.
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The server must not send GenericEvents longer than 32 bytes until it has
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verified that the client is able to interpret these events. If a long event is
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sent to a client unable to process GenericEvents, future interpretation of
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replies and events by this client will fail.
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