关于launcher3中view的坐标计算含义

/**
 * Given a coordinate relative to the descendant, find the coordinate in a parent view's
 * coordinates.
 *
 * @param descendant The descendant to which the passed coordinate is relative.
 * @param ancestor The root view to make the coordinates relative to.
 * @param coord The coordinate that we want mapped.
 * @param includeRootScroll Whether or not to account for the scroll of the descendant:
 *          sometimes this is relevant as in a child's coordinates within the descendant.
 * @return The factor by which this descendant is scaled relative to this DragLayer. Caution
 *         this scale factor is assumed to be equal in X and Y, and so if at any point this
 *         assumption fails, we will need to return a pair of scale factors.
 */
public static float getDescendantCoordRelativeToAncestor(
        View descendant, View ancestor, int[] coord, boolean includeRootScroll) {
    sPoint[0] = coord[0];
    sPoint[1] = coord[1];

    float scale = 1.0f;
    View v = descendant;
    while(v != ancestor && v != null) {
        // For TextViews, scroll has a meaning which relates to the text position
        // which is very strange... ignore the scroll.
        if (v != descendant || includeRootScroll) {
            sPoint[0] -= v.getScrollX();
            sPoint[1] -= v.getScrollY();
        }

        v.getMatrix().mapPoints(sPoint);
        sPoint[0] += v.getLeft();
        sPoint[1] += v.getTop();
        scale *= v.getScaleX();

        v = (View) v.getParent();
    }

    coord[0] = Math.round(sPoint[0]);
    coord[1] = Math.round(sPoint[1]);
    return scale;
}

方法1：将子孙descendant上的坐标coord(相对于descendant的坐标，非祖先)，映射为相对于祖先ancestor的当前屏幕的坐标。


/**
 * Inverse of {@link #getDescendantCoordRelativeToAncestor(View, View, int[], boolean)}.
 */
public static void mapCoordInSelfToDescendant(View descendant, View root, int[] coord) {
    sMatrix.reset();
    View v = descendant;
    while(v != root) {
        sMatrix.postTranslate(-v.getScrollX(), -v.getScrollY());
        sMatrix.postConcat(v.getMatrix());
        sMatrix.postTranslate(v.getLeft(), v.getTop());
        v = (View) v.getParent();
    }
    sMatrix.postTranslate(-v.getScrollX(), -v.getScrollY());
    sMatrix.invert(sInverseMatrix);

    sPoint[0] = coord[0];
    sPoint[1] = coord[1];
    sInverseMatrix.mapPoints(sPoint);
    coord[0] = Math.round(sPoint[0]);
    coord[1] = Math.round(sPoint[1]);
}

方法2：将位于当前子孙descendant上的屏幕坐标coord，映射为最初未进行任何matrix变换的,descendant上的点相对于祖先root的视图坐标(非屏幕坐标)