Currently, TSFTextStore::GetTextExt() checks the offset with mContentForTSF.MinOffsetOfLayoutChanged() as "the first offset of modified characters", however, TSFTextStore::Content::IsLayoutChangedAfter() needs actual offset - 1. This is really not useful. So, we should rename it to IsLayoutChangedAt() and check the offset simply. Additonally, TSFTextStore::GetTextExt() should set previous offset of MinOffsetOfLayoutChanged() when it hacks the queried range for avoiding bug of active TIP since setting offsets to the result of MinOffsetOfLayoutChanged() means the offset's layout is always not computed yet. Review commit: https://reviewboard.mozilla.org/r/71750/diff/#index_header See other reviews: https://reviewboard.mozilla.org/r/71750/

When TSFTextStore::GetTextExt() needs to hack the queried range, it means that the method should not return TS_E_NOLAYOUT since the hacks are implemented for that. However, currently, if hacked offset is still at modified offset, it returns TS_E_NOLAYOUT. This causes flicking IME windows. For avoiding that, this patch adjust the hacked offset to the last unmodified offset or offset of the start of composition string. Even if there is no modified character in the composition string, we can use the offset since even if there is no character at the offset, query content event returns caret rect at the offset and if there are old characters, it returns its rect which the user still see. So, the rect at the composition start is useful until layout is modified actually. Review commit: https://reviewboard.mozilla.org/r/71752/diff/#index_header See other reviews: https://reviewboard.mozilla.org/r/71752/

ContentEventHandler and ContentCache allow 0 length text rect query. However, if selection is collapsed and caret is at the queried offset, they return actual caret rect whose height (in horizontal layout, width in vertical layout) may be different from actual font height of the line. Therefore, it may cause "dancing" of candidate or suggest window of TIP. Therefore, we should query text rect at least 1 length. Then, even if there is no character at the offset, they computes caret rect with previous character. Review commit: https://reviewboard.mozilla.org/r/71754/diff/#index_header See other reviews: https://reviewboard.mozilla.org/r/71754/