Add tests and repro cases

Author: geoff-powell

paparazzi/src/main/java/app/cash/paparazzi/internal/OffByTwo.kt

@@ -49,6 +49,7 @@ internal object OffByTwo : Differ {
           continue
         }
 
+        val deltaA = (actualRgb and -0x1000000).ushr(24) - (expectedRgb and -0x1000000).ushr(24)
         val deltaR = (actualRgb and 0xFF0000).ushr(16) - (expectedRgb and 0xFF0000).ushr(16)
         val deltaG = (actualRgb and 0x00FF00).ushr(8) - (expectedRgb and 0x00FF00).ushr(8)
         val deltaB = (actualRgb and 0x0000FF) - (expectedRgb and 0x0000FF)
@@ -60,7 +61,8 @@ internal object OffByTwo : Differ {
           ((expectedRgb and -0x1000000).ushr(24) + (actualRgb and -0x1000000).ushr(24)) / 2 shl 24
         val newRGB = avgAlpha or (newR shl 16) or (newG shl 8) or newB
 
-        if (abs(deltaR) <= 2 && abs(deltaG) <= 2 && abs(deltaB) <= 2) {
+        if (abs(deltaR) <= 2 && abs(deltaG) <= 2 && abs(deltaB) <= 2 //* && abs(deltaA) <= 2 *//
+           ) {
           similarPixels++
           deltaImage.setRGB(expectedWidth + x, y, 0xFF0000FF.toInt())
           continue
@@ -84,7 +86,13 @@ internal object OffByTwo : Differ {
 
     // 3 different colors, 256 color levels
     val total = actualHeight.toLong() * actualWidth.toLong() * 3L * 256L
-    val percentDifference = (delta * 100 / total.toDouble()).toFloat()
+    var percentDifference = (delta * 100 / total.toDouble()).toFloat()
+
+    // If the delta diff is all black pixels, the computed difference is 0, but there are still
+    // different pixels. We can fallback to the amount of different pixels to less precise difference to ensure difference is reported.
+    if (differentPixels > 0 && percentDifference == 0f) {
+      percentDifference = differentPixels * 100 / (actualWidth * actualHeight.toDouble()).toFloat()
+    }
 
     return if (differentPixels > 0) {
       DiffResult.Different(

paparazzi/src/main/java/app/cash/paparazzi/internal/PixelPerfect.kt

@@ -78,7 +78,13 @@ internal object PixelPerfect : Differ {
 
     // 3 different colors, 256 color levels
     val total = actualHeight.toLong() * actualWidth.toLong() * 3L * 256L
-    val percentDifference = (delta * 100 / total.toDouble()).toFloat()
+    var percentDifference = (delta * 100 / total.toDouble()).toFloat()
+
+    // If the delta diff is all black pixels, the computed difference is 0, but there are still
+    // different pixels. We can fallback to the amount of different pixels to less precise difference to ensure difference is reported.
+//    if (differentPixels > 0 && percentDifference == 0f) {
+//      percentDifference = differentPixels * 100 / (actualWidth * actualHeight.toDouble()).toFloat()
+//    }
 
     return if (percentDifference == 0f) {
       DiffResult.Identical(delta = deltaImage)

paparazzi/src/test/java/app/cash/paparazzi/internal/OffByTwoTest.kt

@@ -0,0 +1,45 @@
+package app.cash.paparazzi.internal
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.Test
+import java.awt.image.BufferedImage
+import java.awt.image.BufferedImage.TYPE_INT_ARGB
+
+class OffByTwoTest {
+  @Test
+  fun `compare identical images`() {
+    val expected = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val actual = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val result = OffByTwo.compare(expected, actual)
+    assertThat(result).isInstanceOf(Differ.DiffResult.Identical::class.java)
+  }
+
+  @Test
+  fun `compare similar images`() {
+    val expected = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val actual = BufferedImage(1, 1, TYPE_INT_ARGB)
+    expected.setRGB(0, 0, 0xFFFFFFFE.toInt())
+    actual.setRGB(0, 0, 0xFFFFFFFF.toInt())
+    val result = OffByTwo.compare(expected, actual)
+    assertThat(result).isInstanceOf(Differ.DiffResult.Similar::class.java)
+  }
+
+  @Test
+  fun `compare similar images using black actual and alpha expected`() {
+    val expected = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val actual = BufferedImage(1, 1, TYPE_INT_ARGB)
+    expected.setRGB(0, 0, 0x00000000.toInt())
+    actual.setRGB(0, 0, 0xFF000000.toInt())
+    val result = OffByTwo.compare(expected, actual)
+    assertThat(result).isInstanceOf(Differ.DiffResult.Similar::class.java)
+  }
+
+  @Test
+  fun `compare different images`() {
+    val expected = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val actual = BufferedImage(1, 1, TYPE_INT_ARGB)
+    actual.setRGB(0, 0, 0xFFFFFFFF.toInt())
+    val result = OffByTwo.compare(expected, actual)
+    assertThat(result).isInstanceOf(Differ.DiffResult.Different::class.java)
+  }
+}

paparazzi/src/test/java/app/cash/paparazzi/internal/PixelPerfectTest.kt

@@ -0,0 +1,45 @@
+package app.cash.paparazzi.internal
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.Test
+import java.awt.image.BufferedImage
+import java.awt.image.BufferedImage.TYPE_INT_ARGB
+
+class PixelPerfectTest {
+  @Test
+  fun `compare identical images`() {
+    val expected = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val actual = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val result = PixelPerfect.compare(expected, actual)
+    assertThat(result).isInstanceOf(Differ.DiffResult.Identical::class.java)
+  }
+
+  @Test
+  fun `compare similar images`() {
+    val expected = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val actual = BufferedImage(1, 1, TYPE_INT_ARGB)
+    expected.setRGB(0, 0, 0xFFFFFFFE.toInt())
+    actual.setRGB(0, 0, 0xFFFFFFFF.toInt())
+    val result = PixelPerfect.compare(expected, actual)
+    assertThat(result).isInstanceOf(Differ.DiffResult.Different::class.java)
+  }
+
+  @Test
+  fun `compare similar images using black actual and alpha expected`() {
+    val expected = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val actual = BufferedImage(1, 1, TYPE_INT_ARGB)
+    expected.setRGB(0, 0, 0x00000000.toInt())
+    actual.setRGB(0, 0, 0xFF000000.toInt())
+    val result = PixelPerfect.compare(expected, actual)
+    assertThat(result).isInstanceOf(Differ.DiffResult.Identical::class.java)
+  }
+
+  @Test
+  fun `compare different images`() {
+    val expected = BufferedImage(1, 1, TYPE_INT_ARGB)
+    val actual = BufferedImage(1, 1, TYPE_INT_ARGB)
+    actual.setRGB(0, 0, 0xFFFFFFFF.toInt())
+    val result = PixelPerfect.compare(expected, actual)
+    assertThat(result).isInstanceOf(Differ.DiffResult.Different::class.java)
+  }
+}