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This is Info file ../../info/internals.info, produced by Makeinfo version 1.68 from the input file internals.texi. Copyright (C) 1992 - 1996 Ben Wing. Copyright (C) 1996, 1997 Sun Microsystems. Copyright (C) 1994, 1995 Free Software Foundation. Copyright (C) 1994, 1995 Board of Trustees, University of Illinois. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English. File: internals.info, Node: Line Start Cache, Prev: Critical Redisplay Sections, Up: The Redisplay Mechanism Line Start Cache ================ The traditional scrolling code in Emacs breaks in a variable height world. It depends on the key assumption that the number of lines that can be displayed at any given time is fixed. This led to a complete separation of the scrolling code from the redisplay code. In order to fully support variable height lines, the scrolling code must actually be tightly integrated with redisplay. Only redisplay can determine how many lines will be displayed on a screen for any given starting point. What is ideally wanted is a complete list of the starting buffer position for every possible display line of a buffer along with the height of that display line. Maintaining such a full list would be very expensive. We settle for having it include information for all areas which we happen to generate anyhow (i.e. the region currently being displayed) and for those areas we need to work with. In order to ensure that the cache accurately represents what redisplay would actually show, it is necessary to invalidate it in many situations. If the buffer changes, the starting positions may no longer be correct. If a face or an extent has changed then the line heights may have altered. These events happen frequently enough that the cache can end up being constantly disabled. With this potentially constant invalidation when is the cache ever useful? Even if the cache is invalidated before every single usage, it is necessary. Scrolling often requires knowledge about display lines which are actually above or below the visible region. The cache provides a convenient light-weight method of storing this information for multiple display regions. This knowledge is necessary for the scrolling code to always obey the First Golden Rule of Redisplay. If the cache already contains all of the information that the scrolling routines happen to need so that it doesn't have to go generate it, then we are able to obey the Third Golden Rule of Redisplay. The first thing we do to help out the cache is to always add the displayed region. This region had to be generated anyway, so the cache ends up getting the information basically for free. In those cases where a user is simply scrolling around viewing a buffer there is a high probability that this is sufficient to always provide the needed information. The second thing we can do is be smart about invalidating the cache. TODO - Be smart about invalidating the cache. Potential places: * Insertions at end-of-line which don't cause line-wraps do not alter the starting positions of any display lines. These types of buffer modifications should not invalidate the cache. This is actually a large optimization for redisplay speed as well. * Buffer modifications frequently only affect the display of lines at and below where they occur. In these situations we should only invalidate the part of the cache starting at where the modification occurs. In case you're wondering, the Second Golden Rule of Redisplay is not applicable. File: internals.info, Node: Extents, Next: Faces and Glyphs, Prev: The Redisplay Mechanism, Up: Top Extents ******* * Menu: * Introduction to Extents:: Extents are ranges over text, with properties. * Extent Ordering:: How extents are ordered internally. * Format of the Extent Info:: The extent information in a buffer or string. * Zero-Length Extents:: A weird special case. * Mathematics of Extent Ordering:: A rigorous foundation. * Extent Fragments:: Cached information useful for redisplay. File: internals.info, Node: Introduction to Extents, Next: Extent Ordering, Up: Extents Introduction to Extents ======================= Extents are regions over a buffer, with a start and an end position denoting the region of the buffer included in the extent. In addition, either end can be closed or open, meaning that the endpoint is or is not logically included in the extent. Insertion of a character at a closed endpoint causes the character to go inside the extent; insertion at an open endpoint causes the character to go outside. Extent endpoints are stored using memory indices (see `insdel.c'), to minimize the amount of adjusting that needs to be done when characters are inserted or deleted. (Formerly, extent endpoints at the gap could be either before or after the gap, depending on the open/closedness of the endpoint. The intent of this was to make it so that insertions would automatically go inside or out of extents as necessary with no further work needing to be done. It didn't work out that way, however, and just ended up complexifying and buggifying all the rest of the code.) File: internals.info, Node: Extent Ordering, Next: Format of the Extent Info, Prev: Introduction to Extents, Up: Extents Extent Ordering =============== Extents are compared using memory indices. There are two orderings for extents and both orders are kept current at all times. The normal or "display" order is as follows: Extent A is ``less than'' extent B, that is, earlier in the display order, if: A-start < B-start, or if: A-start = B-start, and A-end > B-end So if two extents begin at the same position, the larger of them is the earlier one in the display order (`EXTENT_LESS' is true). For the e-order, the same thing holds: Extent A is ``less than'' extent B in e-order, that is, later in the buffer, if: A-end < B-end, or if: A-end = B-end, and A-start > B-start So if two extents end at the same position, the smaller of them is the earlier one in the e-order (`EXTENT_E_LESS' is true). The display order and the e-order are complementary orders: any theorem about the display order also applies to the e-order if you swap all occurrences of "display order" and "e-order", "less than" and "greater than", and "extent start" and "extent end". File: internals.info, Node: Format of the Extent Info, Next: Zero-Length Extents, Prev: Extent Ordering, Up: Extents Format of the Extent Info ========================= An extent-info structure consists of a list of the buffer or string's extents and a "stack of extents" that lists all of the extents over a particular position. The stack-of-extents info is used for optimization purposes - it basically caches some info that might be expensive to compute. Certain otherwise hard computations are easy given the stack of extents over a particular position, and if the stack of extents over a nearby position is known (because it was calculated at some prior point in time), it's easy to move the stack of extents to the proper position. Given that the stack of extents is an optimization, and given that it requires memory, a string's stack of extents is wiped out each time a garbage collection occurs. Therefore, any time you retrieve the stack of extents, it might not be there. If you need it to be there, use the `_force' version. Similarly, a string may or may not have an extent_info structure. (Generally it won't if there haven't been any extents added to the string.) So use the `_force' version if you need the extent_info structure to be there. A list of extents is maintained as a double gap array: one gap array is ordered by start index (the "display order") and the other is ordered by end index (the "e-order"). Note that positions in an extent list should logically be conceived of as referring *to* a particular extent (as is the norm in programs) rather than sitting between two extents. Note also that callers of these functions should not be aware of the fact that the extent list is implemented as an array, except for the fact that positions are integers (this should be generalized to handle integers and linked list equally well). File: internals.info, Node: Zero-Length Extents, Next: Mathematics of Extent Ordering, Prev: Format of the Extent Info, Up: Extents Zero-Length Extents =================== Extents can be zero-length, and will end up that way if their endpoints are explicitly set that way or if their detachable property is nil and all the text in the extent is deleted. (The exception is open-open zero-length extents, which are barred from existing because there is no sensible way to define their properties. Deletion of the text in an open-open extent causes it to be converted into a closed-open extent.) Zero-length extents are primarily used to represent annotations, and behave as follows: 1. Insertion at the position of a zero-length extent expands the extent if both endpoints are closed; goes after the extent if it is closed-open; and goes before the extent if it is open-closed. 2. Deletion of a character on a side of a zero-length extent whose corresponding endpoint is closed causes the extent to be detached if it is detachable; if the extent is not detachable or the corresponding endpoint is open, the extent remains in the buffer, moving as necessary. Note that closed-open, non-detachable zero-length extents behave exactly like markers and that open-closed, non-detachable zero-length extents behave like the "point-type" marker in Mule. File: internals.info, Node: Mathematics of Extent Ordering, Next: Extent Fragments, Prev: Zero-Length Extents, Up: Extents Mathematics of Extent Ordering ============================== The extents in a buffer are ordered by "display order" because that is that order that the redisplay mechanism needs to process them in. The e-order is an auxiliary ordering used to facilitate operations over extents. The operations that can be performed on the ordered list of extents in a buffer are 1. Locate where an extent would go if inserted into the list. 2. Insert an extent into the list. 3. Remove an extent from the list. 4. Map over all the extents that overlap a range. (4) requires being able to determine the first and last extents that overlap a range. NOTE: "overlap" is used as follows: * two ranges overlap if they have at least one point in common. Whether the endpoints are open or closed makes a difference here. * a point overlaps a range if the point is contained within the range; this is equivalent to treating a point P as the range [P, P]. * In the case of an *extent* overlapping a point or range, the extent is normally treated as having closed endpoints. This applies consistently in the discussion of stacks of extents and such below. Note that this definition of overlap is not necessarily consistent with the extents that `map-extents' maps over, since `map-extents' sometimes pays attention to whether the endpoints of an extents are open or closed. But for our purposes, it greatly simplifies things to treat all extents as having closed endpoints. First, define >, <, <=, etc. as applied to extents to mean comparison according to the display order. Comparison between an extent E and an index I means comparison between E and the range [I, I]. Also define e>, e<, e<=, etc. to mean comparison according to the e-order. For any range R, define R(0) to be the starting index of the range and R(1) to be the ending index of the range. For any extent E, define E(next) to be the extent directly following E, and E(prev) to be the extent directly preceding E. Assume E(next) and E(prev) can be determined from E in constant time. (This is because we store the extent list as a doubly linked list.) Similarly, define E(e-next) and E(e-prev) to be the extents directly following and preceding E in the e-order. Now: Let R be a range. Let F be the first extent overlapping R. Let L be the last extent overlapping R. Theorem 1: R(1) lies between L and L(next), i.e. L <= R(1) < L(next). This follows easily from the definition of display order. The basic reason that this theorem applies is that the display order sorts by increasing starting index. Therefore, we can determine L just by looking at where we would insert R(1) into the list, and if we know F and are moving forward over extents, we can easily determine when we've hit L by comparing the extent we're at to R(1). Theorem 2: F(e-prev) e< [1, R(0)] e<= F. This is the analog of Theorem 1, and applies because the e-order sorts by increasing ending index. Therefore, F can be found in the same amount of time as operation (1), i.e. the time that it takes to locate where an extent would go if inserted into the e-order list. If the lists were stored as balanced binary trees, then operation (1) would take logarithmic time, which is usually quite fast. However, currently they're stored as simple doubly-linked lists, and instead we do some caching to try to speed things up. Define a "stack of extents" (or "SOE") as the set of extents (ordered in the display order) that overlap an index I, together with the SOE's "previous" extent, which is an extent that precedes I in the e-order. (Hopefully there will not be very many extents between I and the previous extent.) Now: Let I be an index, let S be the stack of extents on I, let F be the first extent in S, and let P be S's previous extent. Theorem 3: The first extent in S is the first extent that overlaps any range [I, J]. Proof: Any extent that overlaps [I, J] but does not include I must have a start index > I, and thus be greater than any extent in S. Therefore, finding the first extent that overlaps a range R is the same as finding the first extent that overlaps R(0). Theorem 4: Let I2 be an index such that I2 > I, and let F2 be the first extent that overlaps I2. Then, either F2 is in S or F2 is greater than any extent in S. Proof: If F2 does not include I then its start index is greater than I and thus it is greater than any extent in S, including F. Otherwise, F2 includes I and thus is in S, and thus F2 >= F. File: internals.info, Node: Extent Fragments, Prev: Mathematics of Extent Ordering, Up: Extents Extent Fragments ================ Imagine that the buffer is divided up into contiguous, non-overlapping "runs" of text such that no extent starts or ends within a run (extents that abut the run don't count). An extent fragment is a structure that holds data about the run that contains a particular buffer position (if the buffer position is at the junction of two runs, the run after the position is used) - the beginning and end of the run, a list of all of the extents in that run, the "merged face" that results from merging all of the faces corresponding to those extents, the begin and end glyphs at the beginning of the run, etc. This is the information that redisplay needs in order to display this run. Extent fragments have to be very quick to update to a new buffer position when moving linearly through the buffer. They rely on the stack-of-extents code, which does the heavy-duty algorithmic work of determining which extents overly a particular position. File: internals.info, Node: Faces and Glyphs, Next: Specifiers, Prev: Extents, Up: Top Faces and Glyphs **************** Not yet documented. File: internals.info, Node: Specifiers, Next: Menus, Prev: Faces and Glyphs, Up: Top Specifiers ********** Not yet documented. File: internals.info, Node: Menus, Next: Subprocesses, Prev: Specifiers, Up: Top Menus ***** A menu is set by setting the value of the variable `current-menubar' (which may be buffer-local) and then calling `set-menubar-dirty-flag' to signal a change. This will cause the menu to be redrawn at the next redisplay. The format of the data in `current-menubar' is described in `menubar.c'. Internally the data in current-menubar is parsed into a tree of `widget_value's' (defined in `lwlib.h'); this is accomplished by the recursive function `menu_item_descriptor_to_widget_value()', called by `compute_menubar_data()'. Such a tree is deallocated using `free_widget_value()'. `update_screen_menubars()' is one of the external entry points. This checks to see, for each screen, if that screen's menubar needs to be updated. This is the case if 1. `set-menubar-dirty-flag' was called since the last redisplay. (This function sets the C variable menubar_has_changed.) 2. The buffer displayed in the screen has changed. 3. The screen has no menubar currently displayed. `set_screen_menubar()' is called for each such screen. This function calls `compute_menubar_data()' to create the tree of widget_value's, then calls `lw_create_widget()', `lw_modify_all_widgets()', and/or `lw_destroy_all_widgets()' to create the X-Toolkit widget associated with the menu. `update_psheets()', the other external entry point, actually changes the menus being displayed. It uses the widgets fixed by `update_screen_menubars()' and calls various X functions to ensure that the menus are displayed properly. The menubar widget is set up so that `pre_activate_callback()' is called when the menu is first selected (i.e. mouse button goes down), and `menubar_selection_callback()' is called when an item is selected. `pre_activate_callback()' calls the function in activate-menubar-hook, which can change the menubar (this is described in `menubar.c'). If the menubar is changed, `set_screen_menubars()' is called. `menubar_selection_callback()' enqueues a menu event, putting in it a function to call (either `eval' or `call-interactively') and its argument, which is the callback function or form given in the menu's description. File: internals.info, Node: Subprocesses, Next: Interface to X Windows, Prev: Menus, Up: Top Subprocesses ************ The fields of a process are: `name' A string, the name of the process. `command' A list containing the command arguments that were used to start this process. `filter' A function used to accept output from the process instead of a buffer, or `nil'. `sentinel' A function called whenever the process receives a signal, or `nil'. `buffer' The associated buffer of the process. `pid' An integer, the Unix process ID. `childp' A flag, non-`nil' if this is really a child process. It is `nil' for a network connection. `mark' A marker indicating the position of the end of the last output from this process inserted into the buffer. This is often but not always the end of the buffer. `kill_without_query' If this is non-`nil', killing XEmacs while this process is still running does not ask for confirmation about killing the process. `raw_status_low' `raw_status_high' These two fields record 16 bits each of the process status returned by the `wait' system call. `status' The process status, as `process-status' should return it. `tick' `update_tick' If these two fields are not equal, a change in the status of the process needs to be reported, either by running the sentinel or by inserting a message in the process buffer. `pty_flag' Non-`nil' if communication with the subprocess uses a PTY; `nil' if it uses a pipe. `infd' The file descriptor for input from the process. `outfd' The file descriptor for output to the process. `subtty' The file descriptor for the terminal that the subprocess is using. (On some systems, there is no need to record this, so the value is `-1'.) `tty_name' The name of the terminal that the subprocess is using, or `nil' if it is using pipes. File: internals.info, Node: Interface to X Windows, Next: Index, Prev: Subprocesses, Up: Top Interface to X Windows ********************** Not yet documented. File: internals.info, Node: Index, Prev: Interface to X Windows, Up: Top Index ***** * Menu: * Amdahl Corporation: XEmacs. * Andreessen, Marc: XEmacs. * asynchronous subprocesses: Modules for Interfacing with the Operating System. * Baur, Steve: XEmacs. * Benson, Eric: Lucid Emacs. * bridge, playing: XEmacs From the Outside. * Buchholz, Martin: XEmacs. * C vs. Lisp: The Lisp Language. * caller-protects (GCPRO rule): Writing Lisp Primitives. * case table: Modules for Other Aspects of the Lisp Interpreter and Object System. * closer: Lstream Methods. * closure: The XEmacs Object System (Abstractly Speaking). * Common Lisp: The Lisp Language. * conservative garbage collection: GCPROing. * copy-on-write: General Coding Rules. * critical redisplay sections: Critical Redisplay Sections. * Devin, Matthieu: Lucid Emacs. * display order of extents: Mathematics of Extent Ordering. * dynamic array: Low-Level Modules. * dynamic scoping: The Lisp Language. * dynamic types: The Lisp Language. * Energize: Lucid Emacs. * Epoch <1>: XEmacs. * Epoch: Lucid Emacs. * extent fragment: Extent Fragments. * extent mathematics: Mathematics of Extent Ordering. * extent ordering: Mathematics of Extent Ordering. * extents, display order: Mathematics of Extent Ordering. * external widget: Modules for Interfacing with X Windows. * flusher: Lstream Methods. * Free Software Foundation: A History of Emacs. * frob block: Introduction to Allocation. * FSF: A History of Emacs. * FSF Emacs <1>: GNU Emacs 20. * FSF Emacs: GNU Emacs 19. * garbage collection: Garbage Collection. * garbage collection protection: Writing Lisp Primitives. * garbage collection, conservative: GCPROing. * GNU Emacs 19: GNU Emacs 19. * GNU Emacs 20: GNU Emacs 20. * Gosling, James <1>: The Lisp Language. * Gosling, James: Through Version 18. * Great Usenet Renaming: Through Version 18. * Hackers (Steven Levy): A History of Emacs. * hierarchy of windows: Window Hierarchy. * history of Emacs: A History of Emacs. * Illinois, University of: XEmacs. * interactive: Modules for Standard Editing Operations. * interning: The XEmacs Object System (Abstractly Speaking). * ITS (Incompatible Timesharing System): A History of Emacs. * Java: The Lisp Language. * Java vs. Lisp: The Lisp Language. * Kaplan, Simon: XEmacs. * Levy, Steven: A History of Emacs. * line start cache: Line Start Cache. * Lisp vs. C: The Lisp Language. * Lisp vs. Java: The Lisp Language. * lstream: Modules for Interfacing with the File System. * Lstream_close: Lstream Functions. * Lstream_fgetc: Lstream Functions. * Lstream_flush: Lstream Functions. * Lstream_fputc: Lstream Functions. * Lstream_fungetc: Lstream Functions. * Lstream_getc: Lstream Functions. * Lstream_new: Lstream Functions. * Lstream_putc: Lstream Functions. * Lstream_read: Lstream Functions. * Lstream_reopen: Lstream Functions. * Lstream_rewind: Lstream Functions. * Lstream_set_buffering: Lstream Functions. * Lstream_ungetc: Lstream Functions. * Lstream_unread: Lstream Functions. * Lstream_write: Lstream Functions. * Lucid Emacs: Lucid Emacs. * Lucid Inc.: Lucid Emacs. * mark and sweep: Garbage Collection. * mark method <1>: lrecords. * mark method: Modules for Other Aspects of the Lisp Interpreter and Object System. * marker: Lstream Methods. * mathematics of extents: Mathematics of Extent Ordering. * merging attempts: XEmacs. * MIT: A History of Emacs. * Mlynarik, Richard: GNU Emacs 19. * MULE merged XEmacs appears: XEmacs. * NAS: Modules for Interfacing with the Operating System. * native sound: Modules for Interfacing with the Operating System. * network connections: Modules for Interfacing with the Operating System. * network sound: Modules for Interfacing with the Operating System. * pane: Modules for the Basic Displayable Lisp Objects. * permanent objects: The XEmacs Object System (Abstractly Speaking). * pi, calculating: XEmacs From the Outside. * pseudo_closer: Lstream Methods. * pure space: Basic Lisp Modules. * read syntax: The XEmacs Object System (Abstractly Speaking). * read-eval-print: XEmacs From the Outside. * reader: Lstream Methods. * record type: How Lisp Objects Are Represented in C. * relocating allocator: Low-Level Modules. * rename to XEmacs: XEmacs. * rewinder: Lstream Methods. * RMS: A History of Emacs. * scanner: Modules for Other Aspects of the Lisp Interpreter and Object System. * scoping, dynamic: The Lisp Language. * seekable_p: Lstream Methods. * selections: Modules for Interfacing with X Windows. * Sexton, Harlan: Lucid Emacs. * sound, native: Modules for Interfacing with the Operating System. * sound, network: Modules for Interfacing with the Operating System. * SPARCWorks: XEmacs. * Stallman, Richard: A History of Emacs. * subprocesses, asynchronous: Modules for Interfacing with the Operating System. * subprocesses, synchronous: Modules for Interfacing with the Operating System. * Sun Microsystems: XEmacs. * synchronous subprocesses: Modules for Interfacing with the Operating System. * taxes, doing: XEmacs From the Outside. * TECO: A History of Emacs. * temporary objects: The XEmacs Object System (Abstractly Speaking). * Thompson, Chuck: XEmacs. * types, dynamic: The Lisp Language. * University of Illinois: XEmacs. * Win-Emacs: XEmacs. * window (in Emacs): Modules for the Basic Displayable Lisp Objects. * window hierarchy: Window Hierarchy. * window point internals: The Window Object. * Wing, Ben: XEmacs. * writer: Lstream Methods. * XEmacs: XEmacs. * Zawinski, Jamie: Lucid Emacs.