android/support/v4/widget/ViewGroupUtils.java

/*
 * Copyright 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.support.v4.widget;

import static android.support.annotation.RestrictTo.Scope.LIBRARY;

import android.graphics.Matrix;
import android.graphics.Rect;
import android.graphics.RectF;
import android.support.annotation.RestrictTo;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;

/**
 * @hide
 */
@RestrictTo(LIBRARY)
public class ViewGroupUtils {
    private static final ThreadLocal<Matrix> sMatrix = new ThreadLocal<>();
    private static final ThreadLocal<RectF> sRectF = new ThreadLocal<>();

    /**
     * This is a port of the common
     * {@link ViewGroup#offsetDescendantRectToMyCoords(View, Rect)}
     * from the framework, but adapted to take transformations into account. The result
     * will be the bounding rect of the real transformed rect.
     *
     * @param descendant view defining the original coordinate system of rect
     * @param rect (in/out) the rect to offset from descendant to this view's coordinate system
     */
    static void offsetDescendantRect(ViewGroup parent, View descendant, Rect rect) {
        Matrix m = sMatrix.get();
        if (m == null) {
            m = new Matrix();
            sMatrix.set(m);
        } else {
            m.reset();
        }

        offsetDescendantMatrix(parent, descendant, m);

        RectF rectF = sRectF.get();
        if (rectF == null) {
            rectF = new RectF();
            sRectF.set(rectF);
        }
        rectF.set(rect);
        m.mapRect(rectF);
        rect.set((int) (rectF.left + 0.5f), (int) (rectF.top + 0.5f),
                (int) (rectF.right + 0.5f), (int) (rectF.bottom + 0.5f));
    }

    /**
     * Retrieve the transformed bounding rect of an arbitrary descendant view.
     * This does not need to be a direct child.
     *
     * @param descendant descendant view to reference
     * @param out rect to set to the bounds of the descendant view
     */
    public static void getDescendantRect(ViewGroup parent, View descendant, Rect out) {
        out.set(0, 0, descendant.getWidth(), descendant.getHeight());
        offsetDescendantRect(parent, descendant, out);
    }

    private static void offsetDescendantMatrix(ViewParent target, View view, Matrix m) {
        final ViewParent parent = view.getParent();
        if (parent instanceof View && parent != target) {
            final View vp = (View) parent;
            offsetDescendantMatrix(target, vp, m);
            m.preTranslate(-vp.getScrollX(), -vp.getScrollY());
        }

        m.preTranslate(view.getLeft(), view.getTop());

        if (!view.getMatrix().isIdentity()) {
            m.preConcat(view.getMatrix());
        }
    }
}