2011-04-13 Xiaomei Ji <xji@chromium.org>

2011-04-13  Xiaomei Ji  <xji@chromium.org>

        Reviewed by Ryosuke Niwa.

        Continue (3rd) experiment with moving caret by word in visual order.
        https://bugs.webkit.org/show_bug.cgi?id=58294

        * editing/selection/move-by-word-visually-expected.txt:
        * editing/selection/move-by-word-visually.html:
2011-04-13  Xiaomei Ji  <xji@chromium.org>

        Reviewed by Ryosuke Niwa.

        Continue (3rd) experiment with moving caret by word in visual order.
        https://bugs.webkit.org/show_bug.cgi?id=58294

        This patch along with r82588 and r83483 implements moving caret by
        word in visual order.

        The overall algorithm is:
        1. First get the InlineBox and offset of the pass-in VisiblePosition.
        2. Based on the position (left boundary, middle, right boundary) of the offset and the
           direction of the movement, look for visually adjacent word breaks.
        2.1 If the offset is the minimum offset of the box,
            return the rightmost word boundary in previous boxes if moving left.
            return the leftmost word boundary in box and next boxes if moving right.
        2.2 Similar for the case when offset is at the maximum offset of the box.
        2.3 When offset is inside the box (not at boundaries), first find the previousWordPosition
            or nextWordPosition based on the directionality of the box. If this word break position
            is also inside the same box, return it. Otherwise (the nextWordPosition or
            previousWordPosition is not in the same box or is at the box boundary), collect all the
            word breaks in the box and search for the one closest to the input "offset" based on
            box directionality, block directionality, and movement direction. Continue search in
            adjacent boxes if needed.

        Notes:
        1. Word boundaries are collected one box at a time. Only when a boundary that is closest to
           the input position (in the moving direction) is not available in current box, word
           boundaries in adjacent box will be collected. So, there is no need to save InlineBox in
           word boundaries. Instead, the word boundaries are saved as a pair
           (VisiblePosition, offset) to avoid recomputing VisiblePosition.

        2. We only collect boundaries of the right kind (i.e. left boundary of a word in LTR block
           and right boundary of a word in RTL block). And word boundaries are collected using
           previousWordPosition() and nextWordPosition(). So when box directionality is the same as
           block directionality, word boundaries are collected from right to left visually in a LTR
           box, and word boundaries are collected from left to right visually in a RTL box. It is
           the other way around when box directionality is different from block directionality.

        3. To find the right kinds of word boundaries, we must move back and forth between words
           in some situations. For example, if we're moving to the right in a LTR box in LTR block,
           we cannot simply return nextWordPosition() because it would return the right boundary
           of a word. Instead, we return nextWordPosition()'s nextWordPosition()'s previousWordPosition().

        4. When collecting word breaks inside a box, it first computes a start position, then
           collect the right kind of word breaks until it reaches the end of (or beyond) the box.
           In the meanwhile, it might need special handling on the rightmost or leftmost position
           based on the directionality of the box and block. These computations do not consider the
           box's bidi level.

        * editing/visible_units.cpp:
        (WebCore::nextWordBreakInBoxInsideBlockWithDifferentDirectionality):
        (WebCore::collectWordBreaksInBox):
        (WebCore::previousWordBoundaryInBox):
        (WebCore::nextWordBoundaryInBox):
        (WebCore::visuallyLastWordBoundaryInBox):
        (WebCore::leftWordBoundary):
        (WebCore::rightWordBoundary):
        (WebCore::leftWordPosition):
        (WebCore::rightWordPosition):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@83996 268f45cc-cd09-0410-ab3c-d52691b4dbfc