chrome/android/java/src/org/chromium/chrome/browser/widget/ThumbnailGenerator.java

// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package org.chromium.chrome.browser.widget;

import android.graphics.Bitmap;
import android.text.TextUtils;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.annotation.VisibleForTesting;

import org.chromium.base.ThreadUtils;
import org.chromium.base.annotations.CalledByNative;
import org.chromium.base.annotations.NativeMethods;

/**
 * This class generates thumbnails for a given {@link ThumbnailRequest} by calling the native
 * {@link ThumbnailProviderGenerator}, which is owned and destroyed by the Java class. Multiple
 * {@link ThumbnailProvider.ThumbnailRequest}s may be processed at a time.
 *
 * After {@link ThumbnailGenerator#destroy()}, assume that this class will not be called again.
 */
public class ThumbnailGenerator {
    // The native side pointer that is owned and destroyed by the Java class.
    private long mNativeThumbnailGenerator;

    private long getNativeThumbnailGenerator() {
        if (mNativeThumbnailGenerator == 0) {
            mNativeThumbnailGenerator = ThumbnailGeneratorJni.get().init(ThumbnailGenerator.this);
        }
        return mNativeThumbnailGenerator;
    }

    /**
     * Asynchronously generates the requested thumbnail.
     * @param request The request for a thumbnail.
     * @param callback The class to call back to after thumbnail has been generated.
     */
    public void retrieveThumbnail(
            ThumbnailProvider.ThumbnailRequest request, ThumbnailGeneratorCallback callback) {
        ThreadUtils.assertOnUiThread();
        boolean hasFilePath = !TextUtils.isEmpty(request.getFilePath());
        assert hasFilePath;
        ThumbnailGeneratorJni.get().retrieveThumbnail(getNativeThumbnailGenerator(),
                ThumbnailGenerator.this, request.getContentId(), request.getFilePath(),
                request.getMimeType(), request.getIconSize(), callback);
    }

    /**
     * Destroys the native {@link ThumbnailGenerator}.
     */
    public void destroy() {
        ThreadUtils.assertOnUiThread();
        if (mNativeThumbnailGenerator == 0) return;
        ThumbnailGeneratorJni.get().destroy(mNativeThumbnailGenerator, ThumbnailGenerator.this);
        mNativeThumbnailGenerator = 0;
    }

    /**
     * Called when thumbnail has been generated.
     * @param contentId Content ID of the requested thumbnail.
     * @param requestedIconSizePx Requested size (maximum required dimension (pixel) of the smaller
     * side) of the requested thumbnail.
     * @param bitmap The requested thumbnail.
     * @param callback The class to call back to after thumbnail has been generated.
     */
    @CalledByNative
    @VisibleForTesting
    void onThumbnailRetrieved(@NonNull String contentId, int requestedIconSizePx,
            @Nullable Bitmap bitmap, ThumbnailGeneratorCallback callback) {
        // The bitmap returned here is retrieved from the native side. The image decoder there
        // scales down the image (if it is too big) so that one of its sides is smaller than or
        // equal to the required size. We check here that the returned image satisfies this
        // criteria.
        assert bitmap == null
                || Math.min(bitmap.getWidth(), bitmap.getHeight()) <= requestedIconSizePx;

        callback.onThumbnailRetrieved(contentId, bitmap, requestedIconSizePx);
    }

    @NativeMethods
    interface Natives {
        long init(ThumbnailGenerator caller);
        void destroy(long nativeThumbnailGenerator, ThumbnailGenerator caller);
        void retrieveThumbnail(long nativeThumbnailGenerator, ThumbnailGenerator caller,
                String contentId, String filePath, String mimeType, int thumbnailSize,
                ThumbnailGeneratorCallback callback);
    }
}