content: /*
   * Copyright 2022 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 com.google.android.exoplayer2.transformer;
  
  import static androidx.test.core.app.ApplicationProvider.getApplicationContext;
  import static com.google.common.truth.Truth.assertThat;
  
  import android.graphics.Bitmap;
  import android.graphics.BitmapFactory;
  import android.graphics.Color;
  import androidx.annotation.ColorInt;
  import androidx.test.ext.junit.runners.AndroidJUnit4;
  import java.io.IOException;
  import java.io.InputStream;
  import org.junit.Test;
  import org.junit.runner.RunWith;
  
  /** Unit test for {@link MssimCalculator}. */
  @RunWith(AndroidJUnit4.class)
  public class MssimCalculatorTest {
  
    @Test
    public void calculateSsim_sameImage() throws Exception {
      Bitmap bitmap = readBitmap("media/bitmap/sample_mp4_first_frame/linear_colors/original.png");
      byte[] imageLuminosities = bitmapToLuminosityArray(bitmap);
  
      // SSIM equals 1 if the two images match.
      assertThat(
              MssimCalculator.calculate(
                  imageLuminosities, imageLuminosities, bitmap.getWidth(), bitmap.getHeight()))
          .isEqualTo(1);
    }
  
    @Test
    public void calculateSsim_increasedBrightness() throws Exception {
      Bitmap refBitmap = readBitmap("media/bitmap/sample_mp4_first_frame/linear_colors/original.png");
      Bitmap distBitmap =
          readBitmap("media/bitmap/sample_mp4_first_frame/linear_colors/increase_brightness.png");
  
      // SSIM as calculated by ffmpeg: 0.526821 = 52%
  
      assertThat(
              (int)
                  (MssimCalculator.calculate(
                          bitmapToLuminosityArray(refBitmap),
                          bitmapToLuminosityArray(distBitmap),
                          refBitmap.getWidth(),
                          refBitmap.getHeight())
                      * 100))
          .isEqualTo(52);
    }
  
    @Test
    public void calculateSsim_withWindowSkipping_similarToWithout() throws Exception {
      Bitmap referenceBitmap =
          readBitmap("media/bitmap/sample_mp4_first_frame/linear_colors/original.png");
      Bitmap distortedBitmap =
          readBitmap("media/bitmap/sample_mp4_first_frame/linear_colors/increase_brightness.png");
      byte[] referenceLuminosity = bitmapToLuminosityArray(referenceBitmap);
      byte[] distortedLuminosity = bitmapToLuminosityArray(distortedBitmap);
  
      assertThat(
              (int)
                  (MssimCalculator.calculate(
                          referenceLuminosity,
                          distortedLuminosity,
                          referenceBitmap.getWidth(),
                          referenceBitmap.getHeight(),
                          /* enableWindowSkipping= */ false)
                      * 100))
          .isEqualTo(
              (int)
                  (MssimCalculator.calculate(
                          referenceLuminosity,
                          distortedLuminosity,
                          referenceBitmap.getWidth(),
                          referenceBitmap.getHeight(),
                          /* enableWindowSkipping= */ true)
                      * 100));
    }
  
    private static Bitmap readBitmap(String assetString) throws IOException {
      try (InputStream inputStream = getApplicationContext().getAssets().open(assetString)) {
        return BitmapFactory.decodeStream(inputStream);
      }
    }
  
    private static byte[] bitmapToLuminosityArray(Bitmap bitmap) {
      int width = bitmap.getWidth();
      int height = bitmap.getHeight();
      @ColorInt int[] pixels = new int[width * height];
      byte[] luminosities = new byte[width * height];
      bitmap.getPixels(
          pixels, /* offset= */ 0, /* stride= */ width, /* x= */ 0, /* y= */ 0, width, height);
      for (int i = 0; i < pixels.length; i++) {
        luminosities[i] = (byte) (getLuminosity(pixels[i]) & 0xFF);
      }
      return luminosities;
    }
  
    /**
     * Gets the intensity of a given RGB {@link ColorInt pixel} using the luminosity formula
     *
     * <pre>l = 0.2126R + 0.7152G + 0.0722B
     */
    private static int getLuminosity(@ColorInt int pixel) {
      double l = 0;
      l += (0.2126f * Color.red(pixel));
      l += (0.7152f * Color.green(pixel));
      l += (0.0722f * Color.blue(pixel));
      return (int) l;
    }
  }
  