Function TextScanCmd

micropolis-activity/src/tk/tktext.c:1461–1516

(textPtr, interp, argc, argv)

 *
 * TextScanCmd --
 *
 *	This procedure is invoked to process the "scan" 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.
 *
 *--------------------------------------------------------------
 */

static int
TextScanCmd(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 "tag". */
{
    int length, y, line, lastLine;
    char c;

    if (argc != 4) {
	Tcl_AppendResult(interp, "wrong # args: should be \"",
		argv[0], " scan mark|dragto y\"", (char *) NULL);
	return TCL_ERROR;
    }
    if (Tcl_GetInt(interp, argv[3], &y) != TCL_OK) {
	return TCL_ERROR;
    }
    c = argv[2][0];
    length = strlen(argv[2]);
    if ((c == 'd') && (strncmp(argv[2], "dragto", length) == 0)) {
	/*
	 * Amplify the difference between the current y position and the
	 * mark position to compute how many lines up or down the view
	 * should shift, then update the mark position to correspond to
	 * the new view.  If we run off the top or bottom of the text,
	 * reset the mark point so that the current position continues
	 * to correspond to the edge of the window.  This means that the
	 * picture will start dragging as soon as the mouse reverses
	 * direction (without this reset, might have to slide mouse a
	 * long ways back before the picture starts moving again).
	 */

	line = textPtr->scanMarkLine + (10*(textPtr->scanMarkY - y))
		/ (textPtr->fontPtr->ascent + textPtr->fontPtr->descent);
	lastLine = TkBTreeNumLines(textPtr->tree) - 1;
	if (line < 0) {
	    textPtr->scanMarkLine = line = 0;
	    textPtr->scanMarkY = y;
	} else if (line > lastLine) {
	    textPtr->scanMarkLine = line = lastLine;
	    textPtr->scanMarkY = y;