From 5d623cce9fda36f82448ac97a9c5fa00238f0eaf Mon Sep 17 00:00:00 2001
From: Harald Kuhr <harald.kuhr@gmail.com>
Date: Thu, 20 Oct 2022 16:00:12 +0200
Subject: [PATCH] #707 WebP: Fix Alpha support

(cherry picked from commit 8f44cfc43c9b81e41b8ed34bbc957ac05793c419)
---
 .../imageio/plugins/webp/WebPImageReader.java |  8 ++--
 .../plugins/webp/WebPImageReaderTest.java     | 37 +++++++++++++++----
 2 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/imageio/imageio-webp/src/main/java/com/twelvemonkeys/imageio/plugins/webp/WebPImageReader.java b/imageio/imageio-webp/src/main/java/com/twelvemonkeys/imageio/plugins/webp/WebPImageReader.java
index fb4ab4c2..ad121a99 100644
--- a/imageio/imageio-webp/src/main/java/com/twelvemonkeys/imageio/plugins/webp/WebPImageReader.java
+++ b/imageio/imageio-webp/src/main/java/com/twelvemonkeys/imageio/plugins/webp/WebPImageReader.java
@@ -511,16 +511,16 @@ final class WebPImageReader extends ImageReaderBase {
     }
 
     private void readAlpha(BufferedImage destination, ImageReadParam param, final int width, final int height) throws IOException {
+        int compression = (int) lsbBitReader.readBits(2);
+        int filtering = (int) lsbBitReader.readBits(2);
         int reserved = (int) lsbBitReader.readBits(2);
+        int preProcessing = (int) lsbBitReader.readBits(2);
+
         if (reserved != 0) {
             // Spec says SHOULD be 0
             processWarningOccurred(String.format("Unexpected 'ALPH' chunk reserved value, expected 0: %d", reserved));
         }
 
-        int preProcessing = (int) lsbBitReader.readBits(2);
-        int filtering = (int) lsbBitReader.readBits(2);
-        int compression = (int) lsbBitReader.readBits(2);
-
         if (DEBUG) {
             System.out.println("preProcessing: " + preProcessing);
             System.out.println("filtering: " + filtering);
diff --git a/imageio/imageio-webp/src/test/java/com/twelvemonkeys/imageio/plugins/webp/WebPImageReaderTest.java b/imageio/imageio-webp/src/test/java/com/twelvemonkeys/imageio/plugins/webp/WebPImageReaderTest.java
index 244b89a6..66959421 100644
--- a/imageio/imageio-webp/src/test/java/com/twelvemonkeys/imageio/plugins/webp/WebPImageReaderTest.java
+++ b/imageio/imageio-webp/src/test/java/com/twelvemonkeys/imageio/plugins/webp/WebPImageReaderTest.java
@@ -1,11 +1,8 @@
 package com.twelvemonkeys.imageio.plugins.webp;
 
-import static java.util.Arrays.asList;
+import com.twelvemonkeys.imageio.util.ImageReaderAbstractTest;
 
-import java.awt.*;
-import java.awt.image.BufferedImage;
-import java.io.IOException;
-import java.util.List;
+import org.junit.Test;
 
 import javax.imageio.ImageIO;
 import javax.imageio.ImageReadParam;
@@ -13,10 +10,13 @@ import javax.imageio.ImageTypeSpecifier;
 import javax.imageio.spi.ImageReaderSpi;
 import javax.imageio.stream.ImageInputStream;
 import javax.imageio.stream.MemoryCacheImageInputStream;
+import java.awt.*;
+import java.awt.image.*;
+import java.io.IOException;
+import java.util.List;
 
-import org.junit.Test;
-
-import com.twelvemonkeys.imageio.util.ImageReaderAbstractTest;
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
 
 /**
  * WebPImageReaderTest
@@ -141,4 +141,25 @@ public class WebPImageReaderTest extends ImageReaderAbstractTest<WebPImageReader
             reader.dispose();
         }
     }
+
+    @Test
+    public void testReadAlphaTransparent() throws IOException {
+        WebPImageReader reader = createReader();
+
+        try (ImageInputStream stream = ImageIO.createImageInputStream(getClassLoaderResource("/webp/1_webp_a.webp"))) {
+            reader.setInput(stream);
+            BufferedImage image = reader.read(0);
+
+            assertEquals(Transparency.TRANSLUCENT, image.getTransparency());
+
+            assertRGBEquals("Expected transparent corner (0, 0)", 0x00000000, image.getRGB(0, 0) & 0xFF000000, 8);
+            assertRGBEquals("Expected opaque center (200, 150)", 0xff9a4e01, image.getRGB(200, 150), 8);
+            assertRGBEquals("Expected transparent corner (399, 0)", 0x00000000, image.getRGB(399, 0) & 0xFF000000, 8);
+            assertRGBEquals("Expected transparent corner (0, 300)", 0x00000000, image.getRGB(0, 300) & 0xFF000000, 8);
+            assertRGBEquals("Expected transparent corner (399, 300)", 0x00000000, image.getRGB(399, 300) & 0xFF000000, 8);
+        }
+        finally {
+            reader.dispose();
+        }
+    }
 }