Initial revision

FossilOrigin-Name: 2bf55ca9aa942b581137b9f474da5ad9c1480de4

1 files changed, 775 insertions, 0 deletions

diff --git a/generic/tkTextMark.c b/generic/tkTextMark.c
new file mode 100644
index 0000000..0d12c98
--- /dev/null
+++ b/generic/tkTextMark.c
@@ -0,0 +1,775 @@
+/* 
+ * tkTextMark.c --
+ *
+ *	This file contains the procedure that implement marks for
+ *	text widgets.
+ *
+ * Copyright (c) 1994 The Regents of the University of California.
+ * Copyright (c) 1994-1997 Sun Microsystems, Inc.
+ *
+ * See the file "license.terms" for information on usage and redistribution
+ * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
+ *
+ * SCCS: @(#) tkTextMark.c 1.18 97/10/20 11:12:50
+ */
+
+#include "tkInt.h"
+#include "tkText.h"
+#include "tkPort.h"
+
+/*
+ * Macro that determines the size of a mark segment:
+ */
+
+#define MSEG_SIZE ((unsigned) (Tk_Offset(TkTextSegment, body) \
+	+ sizeof(TkTextMark)))
+
+/*
+ * Forward references for procedures defined in this file:
+ */
+
+static void		InsertUndisplayProc _ANSI_ARGS_((TkText *textPtr,
+			    TkTextDispChunk *chunkPtr));
+static int		MarkDeleteProc _ANSI_ARGS_((TkTextSegment *segPtr,
+			    TkTextLine *linePtr, int treeGone));
+static TkTextSegment *	MarkCleanupProc _ANSI_ARGS_((TkTextSegment *segPtr,
+			    TkTextLine *linePtr));
+static void		MarkCheckProc _ANSI_ARGS_((TkTextSegment *segPtr,
+			    TkTextLine *linePtr));
+static int		MarkLayoutProc _ANSI_ARGS_((TkText *textPtr,
+			    TkTextIndex *indexPtr, TkTextSegment *segPtr,
+			    int offset, int maxX, int maxChars,
+			    int noCharsYet, Tk_Uid wrapMode,
+			    TkTextDispChunk *chunkPtr));
+static int		MarkFindNext _ANSI_ARGS_((Tcl_Interp *interp,
+			    TkText *textPtr, char *markName));
+static int		MarkFindPrev _ANSI_ARGS_((Tcl_Interp *interp,
+			    TkText *textPtr, char *markName));
+
+
+/*
+ * The following structures declare the "mark" segment types.
+ * There are actually two types for marks, one with left gravity
+ * and one with right gravity.  They are identical except for
+ * their gravity property.
+ */
+
+Tk_SegType tkTextRightMarkType = {
+    "mark",					/* name */
+    0,						/* leftGravity */
+    (Tk_SegSplitProc *) NULL,			/* splitProc */
+    MarkDeleteProc,				/* deleteProc */
+    MarkCleanupProc,				/* cleanupProc */
+    (Tk_SegLineChangeProc *) NULL,		/* lineChangeProc */
+    MarkLayoutProc,				/* layoutProc */
+    MarkCheckProc				/* checkProc */
+};
+
+Tk_SegType tkTextLeftMarkType = {
+    "mark",					/* name */
+    1,						/* leftGravity */
+    (Tk_SegSplitProc *) NULL,			/* splitProc */
+    MarkDeleteProc,				/* deleteProc */
+    MarkCleanupProc,				/* cleanupProc */
+    (Tk_SegLineChangeProc *) NULL,		/* lineChangeProc */
+    MarkLayoutProc,				/* layoutProc */
+    MarkCheckProc				/* checkProc */
+};
+
+/*
+ *--------------------------------------------------------------
+ *
+ * TkTextMarkCmd --
+ *
+ *	This procedure is invoked to process the "mark" options of
+ *	the widget command for text widgets. See the user documentation
+ *	for details on what it does.
+ *
+ * Results:
+ *	A standard Tcl result.
+ *
+ * Side effects:
+ *	See the user documentation.
+ *
+ *--------------------------------------------------------------
+ */
+
+int
+TkTextMarkCmd(textPtr, interp, argc, argv)
+    register TkText *textPtr;	/* Information about text widget. */
+    Tcl_Interp *interp;		/* Current interpreter. */
+    int argc;			/* Number of arguments. */
+    char **argv;		/* Argument strings.  Someone else has already
+				 * parsed this command enough to know that
+				 * argv[1] is "mark". */
+{
+    int c, i;
+    size_t length;
+    Tcl_HashEntry *hPtr;
+    TkTextSegment *markPtr;
+    Tcl_HashSearch search;
+    TkTextIndex index;
+    Tk_SegType *newTypePtr;
+
+    if (argc < 3) {
+	Tcl_AppendResult(interp, "wrong # args: should be \"",
+		argv[0], " mark option ?arg arg ...?\"", (char *) NULL);
+	return TCL_ERROR;
+    }
+    c = argv[2][0];
+    length = strlen(argv[2]);
+    if ((c == 'g') && (strncmp(argv[2], "gravity", length) == 0)) {
+	if (argc < 4 || argc > 5) {
+	    Tcl_AppendResult(interp, "wrong # args: should be \"",
+		    argv[0], " mark gravity markName ?gravity?\"",
+		    (char *) NULL);
+	    return TCL_ERROR;
+	}
+	hPtr = Tcl_FindHashEntry(&textPtr->markTable, argv[3]);
+	if (hPtr == NULL) {
+	    Tcl_AppendResult(interp, "there is no mark named \"",
+		    argv[3], "\"", (char *) NULL);
+	    return TCL_ERROR;
+	}
+	markPtr = (TkTextSegment *) Tcl_GetHashValue(hPtr);
+	if (argc == 4) {
+	    if (markPtr->typePtr == &tkTextRightMarkType) {
+		interp->result = "right";
+	    } else {
+		interp->result = "left";
+	    }
+	    return TCL_OK;
+	}
+	length = strlen(argv[4]);
+	c = argv[4][0];
+	if ((c == 'l') && (strncmp(argv[4], "left", length) == 0)) {
+	    newTypePtr = &tkTextLeftMarkType;
+	} else if ((c == 'r') && (strncmp(argv[4], "right", length) == 0)) {
+	    newTypePtr = &tkTextRightMarkType;
+	} else {
+	    Tcl_AppendResult(interp, "bad mark gravity \"",
+		    argv[4], "\": must be left or right", (char *) NULL);
+	    return TCL_ERROR;
+	}
+	TkTextMarkSegToIndex(textPtr, markPtr, &index);
+	TkBTreeUnlinkSegment(textPtr->tree, markPtr,
+		markPtr->body.mark.linePtr);
+	markPtr->typePtr = newTypePtr;
+	TkBTreeLinkSegment(markPtr, &index);
+    } else if ((c == 'n') && (strncmp(argv[2], "names", length) == 0)) {
+	if (argc != 3) {
+	    Tcl_AppendResult(interp, "wrong # args: should be \"",
+		    argv[0], " mark names\"", (char *) NULL);
+	    return TCL_ERROR;
+	}
+	for (hPtr = Tcl_FirstHashEntry(&textPtr->markTable, &search);
+		hPtr != NULL; hPtr = Tcl_NextHashEntry(&search)) {
+	    Tcl_AppendElement(interp,
+		    Tcl_GetHashKey(&textPtr->markTable, hPtr));
+	}
+    } else if ((c == 'n') && (strncmp(argv[2], "next", length) == 0)) {
+	if (argc != 4) {
+	    Tcl_AppendResult(interp, "wrong # args: should be \"",
+		    argv[0], " mark next index\"", (char *) NULL);
+	    return TCL_ERROR;
+	}
+	return MarkFindNext(interp, textPtr, argv[3]);
+    } else if ((c == 'p') && (strncmp(argv[2], "previous", length) == 0)) {
+	if (argc != 4) {
+	    Tcl_AppendResult(interp, "wrong # args: should be \"",
+		    argv[0], " mark previous index\"", (char *) NULL);
+	    return TCL_ERROR;
+	}
+	return MarkFindPrev(interp, textPtr, argv[3]);
+    } else if ((c == 's') && (strncmp(argv[2], "set", length) == 0)) {
+	if (argc != 5) {
+	    Tcl_AppendResult(interp, "wrong # args: should be \"",
+		    argv[0], " mark set markName index\"", (char *) NULL);
+	    return TCL_ERROR;
+	}
+	if (TkTextGetIndex(interp, textPtr, argv[4], &index) != TCL_OK) {
+	    return TCL_ERROR;
+	}
+	TkTextSetMark(textPtr, argv[3], &index);
+    } else if ((c == 'u') && (strncmp(argv[2], "unset", length) == 0)) {
+	for (i = 3; i < argc; i++) {
+	    hPtr = Tcl_FindHashEntry(&textPtr->markTable, argv[i]);
+	    if (hPtr != NULL) {
+		markPtr = (TkTextSegment *) Tcl_GetHashValue(hPtr);
+		if ((markPtr == textPtr->insertMarkPtr)
+			|| (markPtr == textPtr->currentMarkPtr)) {
+		    continue;
+		}
+		TkBTreeUnlinkSegment(textPtr->tree, markPtr,
+			markPtr->body.mark.linePtr);
+		Tcl_DeleteHashEntry(hPtr);
+		ckfree((char *) markPtr);
+	    }
+	}
+    } else {
+	Tcl_AppendResult(interp, "bad mark option \"", argv[2],
+		"\": must be gravity, names, next, previous, set, or unset",
+		(char *) NULL);
+	return TCL_ERROR;
+    }
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * TkTextSetMark --
+ *
+ *	Set a mark to a particular position, creating a new mark if
+ *	one doesn't already exist.
+ *
+ * Results:
+ *	The return value is a pointer to the mark that was just set.
+ *
+ * Side effects:
+ *	A new mark is created, or an existing mark is moved.
+ *
+ *----------------------------------------------------------------------
+ */
+
+TkTextSegment *
+TkTextSetMark(textPtr, name, indexPtr)
+    TkText *textPtr;		/* Text widget in which to create mark. */
+    char *name;			/* Name of mark to set. */
+    TkTextIndex *indexPtr;	/* Where to set mark. */
+{
+    Tcl_HashEntry *hPtr;
+    TkTextSegment *markPtr;
+    TkTextIndex insertIndex;
+    int new;
+
+    hPtr = Tcl_CreateHashEntry(&textPtr->markTable, name, &new);
+    markPtr = (TkTextSegment *) Tcl_GetHashValue(hPtr);
+    if (!new) {
+	/*
+	 * If this is the insertion point that's being moved, be sure
+	 * to force a display update at the old position.  Also, don't
+	 * let the insertion cursor be after the final newline of the
+	 * file.
+	 */
+
+	if (markPtr == textPtr->insertMarkPtr) {
+	    TkTextIndex index, index2;
+	    TkTextMarkSegToIndex(textPtr, textPtr->insertMarkPtr, &index);
+	    TkTextIndexForwChars(&index, 1, &index2);
+	    TkTextChanged(textPtr, &index, &index2);
+	    if (TkBTreeLineIndex(indexPtr->linePtr)
+		    == TkBTreeNumLines(textPtr->tree))  {
+		TkTextIndexBackChars(indexPtr, 1, &insertIndex);
+		indexPtr = &insertIndex;
+	    }
+	}
+	TkBTreeUnlinkSegment(textPtr->tree, markPtr,
+		markPtr->body.mark.linePtr);
+    } else {
+	markPtr = (TkTextSegment *) ckalloc(MSEG_SIZE);
+	markPtr->typePtr = &tkTextRightMarkType;
+	markPtr->size = 0;
+	markPtr->body.mark.textPtr = textPtr;
+	markPtr->body.mark.linePtr = indexPtr->linePtr;
+	markPtr->body.mark.hPtr = hPtr;
+	Tcl_SetHashValue(hPtr, markPtr);
+    }
+    TkBTreeLinkSegment(markPtr, indexPtr);
+
+    /*
+     * If the mark is the insertion cursor, then update the screen at the
+     * mark's new location.
+     */
+
+    if (markPtr == textPtr->insertMarkPtr) {
+	TkTextIndex index2;
+
+	TkTextIndexForwChars(indexPtr, 1, &index2);
+	TkTextChanged(textPtr, indexPtr, &index2);
+    }
+    return markPtr;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * TkTextMarkSegToIndex --
+ *
+ *	Given a segment that is a mark, create an index that
+ *	refers to the next text character (or other text segment
+ *	with non-zero size) after the mark.
+ *
+ * Results:
+ *	*IndexPtr is filled in with index information.
+ *
+ * Side effects:
+ *	None.
+ *
+ *--------------------------------------------------------------
+ */
+
+void
+TkTextMarkSegToIndex(textPtr, markPtr, indexPtr)
+    TkText *textPtr;		/* Text widget containing mark. */
+    TkTextSegment *markPtr;	/* Mark segment. */
+    TkTextIndex *indexPtr;	/* Index information gets stored here.  */
+{
+    TkTextSegment *segPtr;
+
+    indexPtr->tree = textPtr->tree;
+    indexPtr->linePtr = markPtr->body.mark.linePtr;
+    indexPtr->charIndex = 0;
+    for (segPtr = indexPtr->linePtr->segPtr; segPtr != markPtr;
+	    segPtr = segPtr->nextPtr) {
+	indexPtr->charIndex += segPtr->size;
+    }
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * TkTextMarkNameToIndex --
+ *
+ *	Given the name of a mark, return an index corresponding
+ *	to the mark name.
+ *
+ * Results:
+ *	The return value is TCL_OK if "name" exists as a mark in
+ *	the text widget.  In this case *indexPtr is filled in with
+ *	the next segment whose after the mark whose size is
+ *	non-zero.  TCL_ERROR is returned if the mark doesn't exist
+ *	in the text widget.
+ *
+ * Side effects:
+ *	None.
+ *
+ *--------------------------------------------------------------
+ */
+
+int
+TkTextMarkNameToIndex(textPtr, name, indexPtr)
+    TkText *textPtr;		/* Text widget containing mark. */
+    char *name;			/* Name of mark. */
+    TkTextIndex *indexPtr;	/* Index information gets stored here. */
+{
+    Tcl_HashEntry *hPtr;
+
+    hPtr = Tcl_FindHashEntry(&textPtr->markTable, name);
+    if (hPtr == NULL) {
+	return TCL_ERROR;
+    }
+    TkTextMarkSegToIndex(textPtr, (TkTextSegment *) Tcl_GetHashValue(hPtr),
+	    indexPtr);
+    return TCL_OK;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * MarkDeleteProc --
+ *
+ *	This procedure is invoked by the text B-tree code whenever
+ *	a mark lies in a range of characters being deleted.
+ *
+ * Results:
+ *	Returns 1 to indicate that deletion has been rejected.
+ *
+ * Side effects:
+ *	None (even if the whole tree is being deleted we don't
+ *	free up the mark;  it will be done elsewhere).
+ *
+ *--------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+static int
+MarkDeleteProc(segPtr, linePtr, treeGone)
+    TkTextSegment *segPtr;		/* Segment being deleted. */
+    TkTextLine *linePtr;		/* Line containing segment. */
+    int treeGone;			/* Non-zero means the entire tree is
+					 * being deleted, so everything must
+					 * get cleaned up. */
+{
+    return 1;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * MarkCleanupProc --
+ *
+ *	This procedure is invoked by the B-tree code whenever a
+ *	mark segment is moved from one line to another.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The linePtr field of the segment gets updated.
+ *
+ *--------------------------------------------------------------
+ */
+
+static TkTextSegment *
+MarkCleanupProc(markPtr, linePtr)
+    TkTextSegment *markPtr;		/* Mark segment that's being moved. */
+    TkTextLine *linePtr;		/* Line that now contains segment. */
+{
+    markPtr->body.mark.linePtr = linePtr;
+    return markPtr;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * MarkLayoutProc --
+ *
+ *	This procedure is the "layoutProc" for mark segments.
+ *
+ * Results:
+ *	If the mark isn't the insertion cursor then the return
+ *	value is -1 to indicate that this segment shouldn't be
+ *	displayed.  If the mark is the insertion character then
+ *	1 is returned and the chunkPtr structure is filled in.
+ *
+ * Side effects:
+ *	None, except for filling in chunkPtr.
+ *
+ *--------------------------------------------------------------
+ */
+
+	/*ARGSUSED*/
+static int
+MarkLayoutProc(textPtr, indexPtr, segPtr, offset, maxX, maxChars,
+	noCharsYet, wrapMode, chunkPtr)
+    TkText *textPtr;		/* Text widget being layed out. */
+    TkTextIndex *indexPtr;	/* Identifies first character in chunk. */
+    TkTextSegment *segPtr;	/* Segment corresponding to indexPtr. */
+    int offset;			/* Offset within segPtr corresponding to
+				 * indexPtr (always 0). */
+    int maxX;			/* Chunk must not occupy pixels at this
+				 * position or higher. */
+    int maxChars;		/* Chunk must not include more than this
+				 * many characters. */
+    int noCharsYet;		/* Non-zero means no characters have been
+				 * assigned to this line yet. */
+    Tk_Uid wrapMode;		/* Not used. */
+    register TkTextDispChunk *chunkPtr;
+				/* Structure to fill in with information
+				 * about this chunk.  The x field has already
+				 * been set by the caller. */
+{
+    if (segPtr != textPtr->insertMarkPtr) {
+	return -1;
+    }
+
+    chunkPtr->displayProc = TkTextInsertDisplayProc;
+    chunkPtr->undisplayProc = InsertUndisplayProc;
+    chunkPtr->measureProc = (Tk_ChunkMeasureProc *) NULL;
+    chunkPtr->bboxProc = (Tk_ChunkBboxProc *) NULL;
+    chunkPtr->numChars = 0;
+    chunkPtr->minAscent = 0;
+    chunkPtr->minDescent = 0;
+    chunkPtr->minHeight = 0;
+    chunkPtr->width = 0;
+
+    /*
+     * Note: can't break a line after the insertion cursor:  this
+     * prevents the insertion cursor from being stranded at the end
+     * of a line.
+     */
+
+    chunkPtr->breakIndex = -1;
+    chunkPtr->clientData = (ClientData) textPtr;
+    return 1;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * TkTextInsertDisplayProc --
+ *
+ *	This procedure is called to display the insertion
+ *	cursor.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Graphics are drawn.
+ *
+ *--------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+void
+TkTextInsertDisplayProc(chunkPtr, x, y, height, baseline, display, dst, screenY)
+    TkTextDispChunk *chunkPtr;		/* Chunk that is to be drawn. */
+    int x;				/* X-position in dst at which to
+					 * draw this chunk (may differ from
+					 * the x-position in the chunk because
+					 * of scrolling). */
+    int y;				/* Y-position at which to draw this
+					 * chunk in dst (x-position is in
+					 * the chunk itself). */
+    int height;				/* Total height of line. */
+    int baseline;			/* Offset of baseline from y. */
+    Display *display;			/* Display to use for drawing. */
+    Drawable dst;			/* Pixmap or window in which to draw
+					 * chunk. */
+    int screenY;			/* Y-coordinate in text window that
+					 * corresponds to y. */
+{
+    TkText *textPtr = (TkText *) chunkPtr->clientData;
+    int halfWidth = textPtr->insertWidth/2;
+
+    if ((x + halfWidth) < 0) {
+	/*
+	 * The insertion cursor is off-screen.  Just return.
+	 */
+
+	return;
+    }
+
+    /*
+     * As a special hack to keep the cursor visible on mono displays
+     * (or anywhere else that the selection and insertion cursors
+     * have the same color) write the default background in the cursor
+     * area (instead of nothing) when the cursor isn't on.  Otherwise
+     * the selection might hide the cursor.
+     */
+
+    if (textPtr->flags & INSERT_ON) {
+	Tk_Fill3DRectangle(textPtr->tkwin, dst, textPtr->insertBorder,
+		x - textPtr->insertWidth/2, y, textPtr->insertWidth,
+		height, textPtr->insertBorderWidth, TK_RELIEF_RAISED);
+    } else if (textPtr->selBorder == textPtr->insertBorder) {
+	Tk_Fill3DRectangle(textPtr->tkwin, dst, textPtr->border,
+		x - textPtr->insertWidth/2, y, textPtr->insertWidth,
+		height, 0, TK_RELIEF_FLAT);
+    }
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * InsertUndisplayProc --
+ *
+ *	This procedure is called when the insertion cursor is no
+ *	longer at a visible point on the display.  It does nothing
+ *	right now.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	None.
+ *
+ *--------------------------------------------------------------
+ */
+
+	/* ARGSUSED */
+static void
+InsertUndisplayProc(textPtr, chunkPtr)
+    TkText *textPtr;			/* Overall information about text
+					 * widget. */
+    TkTextDispChunk *chunkPtr;		/* Chunk that is about to be freed. */
+{
+    return;
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * MarkCheckProc --
+ *
+ *	This procedure is invoked by the B-tree code to perform
+ *	consistency checks on mark segments.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	The procedure panics if it detects anything wrong with
+ *	the mark.
+ *
+ *--------------------------------------------------------------
+ */
+
+static void
+MarkCheckProc(markPtr, linePtr)
+    TkTextSegment *markPtr;		/* Segment to check. */
+    TkTextLine *linePtr;		/* Line containing segment. */
+{
+    Tcl_HashSearch search;
+    Tcl_HashEntry *hPtr;
+
+    if (markPtr->body.mark.linePtr != linePtr) {
+	panic("MarkCheckProc: markPtr->body.mark.linePtr bogus");
+    }
+
+    /*
+     * Make sure that the mark is still present in the text's mark
+     * hash table.
+     */
+
+    for (hPtr = Tcl_FirstHashEntry(&markPtr->body.mark.textPtr->markTable,
+	    &search); hPtr != markPtr->body.mark.hPtr;
+	    hPtr = Tcl_NextHashEntry(&search)) {
+	if (hPtr == NULL) {
+	    panic("MarkCheckProc couldn't find hash table entry for mark");
+	}
+    }
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * MarkFindNext --
+ *
+ *	This procedure searches forward for the next mark.
+ *
+ * Results:
+ *	A standard Tcl result, which is a mark name or an empty string.
+ *
+ * Side effects:
+ *	None.
+ *
+ *--------------------------------------------------------------
+ */
+
+static int
+MarkFindNext(interp, textPtr, string)
+    Tcl_Interp *interp;			/* For error reporting */
+    TkText *textPtr;			/* The widget */
+    char *string;			/* The starting index or mark name */
+{
+    TkTextIndex index;
+    Tcl_HashEntry *hPtr;
+    register TkTextSegment *segPtr;
+    int offset;
+
+
+    hPtr = Tcl_FindHashEntry(&textPtr->markTable, string);
+    if (hPtr != NULL) {
+	/*
+	 * If given a mark name, return the next mark in the list of
+	 * segments, even if it happens to be at the same character position.
+	 */
+	segPtr = (TkTextSegment *) Tcl_GetHashValue(hPtr);
+	TkTextMarkSegToIndex(textPtr, segPtr, &index);
+	segPtr = segPtr->nextPtr;
+    } else {
+	/*
+	 * For non-mark name indices we want to return any marks that
+	 * are right at the index.
+	 */
+	if (TkTextGetIndex(interp, textPtr, string, &index) != TCL_OK) {
+	    return TCL_ERROR;
+	}
+	for (offset = 0, segPtr = index.linePtr->segPtr; 
+		segPtr != NULL && offset < index.charIndex;
+		offset += segPtr->size,	segPtr = segPtr->nextPtr) {
+	    /* Empty loop body */ ;
+	}
+    }
+    while (1) {
+	/*
+	 * segPtr points at the first possible candidate,
+	 * or NULL if we ran off the end of the line.
+	 */
+	for ( ; segPtr != NULL ; segPtr = segPtr->nextPtr) {
+	    if (segPtr->typePtr == &tkTextRightMarkType ||
+		    segPtr->typePtr == &tkTextLeftMarkType) {
+		Tcl_SetResult(interp,
+		    Tcl_GetHashKey(&textPtr->markTable, segPtr->body.mark.hPtr),
+		    TCL_STATIC);
+		return TCL_OK;
+	    }
+	}
+	index.linePtr = TkBTreeNextLine(index.linePtr);
+	if (index.linePtr == (TkTextLine *) NULL) {
+	    return TCL_OK;
+	}
+	index.charIndex = 0;
+	segPtr = index.linePtr->segPtr;
+    }
+}
+
+/*
+ *--------------------------------------------------------------
+ *
+ * MarkFindPrev --
+ *
+ *	This procedure searches backwards for the previous mark.
+ *
+ * Results:
+ *	A standard Tcl result, which is a mark name or an empty string.
+ *
+ * Side effects:
+ *	None.
+ *
+ *--------------------------------------------------------------
+ */
+
+static int
+MarkFindPrev(interp, textPtr, string)
+    Tcl_Interp *interp;			/* For error reporting */
+    TkText *textPtr;			/* The widget */
+    char *string;			/* The starting index or mark name */
+{
+    TkTextIndex index;
+    Tcl_HashEntry *hPtr;
+    register TkTextSegment *segPtr, *seg2Ptr, *prevPtr;
+    int offset;
+
+
+    hPtr = Tcl_FindHashEntry(&textPtr->markTable, string);
+    if (hPtr != NULL) {
+	/*
+	 * If given a mark name, return the previous mark in the list of
+	 * segments, even if it happens to be at the same character position.
+	 */
+	segPtr = (TkTextSegment *) Tcl_GetHashValue(hPtr);
+	TkTextMarkSegToIndex(textPtr, segPtr, &index);
+    } else {
+	/*
+	 * For non-mark name indices we do not return any marks that
+	 * are right at the index.
+	 */
+	if (TkTextGetIndex(interp, textPtr, string, &index) != TCL_OK) {
+	    return TCL_ERROR;
+	}
+	for (offset = 0, segPtr = index.linePtr->segPtr; 
+		segPtr != NULL && offset < index.charIndex;
+		offset += segPtr->size, segPtr = segPtr->nextPtr) {
+	    /* Empty loop body */ ;
+	}
+    }
+    while (1) {
+	/*
+	 * segPtr points just past the first possible candidate,
+	 * or at the begining of the line.
+	 */
+	for (prevPtr = NULL, seg2Ptr = index.linePtr->segPtr; 
+		seg2Ptr != NULL && seg2Ptr != segPtr;
+		seg2Ptr = seg2Ptr->nextPtr) {
+	    if (seg2Ptr->typePtr == &tkTextRightMarkType ||
+		    seg2Ptr->typePtr == &tkTextLeftMarkType) {
+		prevPtr = seg2Ptr;
+	    }
+	}
+	if (prevPtr != NULL) {
+	    Tcl_SetResult(interp, 
+		Tcl_GetHashKey(&textPtr->markTable, prevPtr->body.mark.hPtr),
+		TCL_STATIC);
+	    return TCL_OK;
+	}
+	index.linePtr = TkBTreePreviousLine(index.linePtr);
+	if (index.linePtr == (TkTextLine *) NULL) {
+	    return TCL_OK;
+	}
+	segPtr = NULL;
+    }
+}