Original source: Jacek Piszczek <jacek.piszczek@runbox.com>

diff --git a/Source/WebCore/platform/graphics/PixelBufferConversion.cpp b/Source/WebCore/platform/graphics/PixelBufferConversion.cpp
index 9acf304d..618b7b26 100644
--- a/Source/WebCore/platform/graphics/PixelBufferConversion.cpp
+++ b/Source/WebCore/platform/graphics/PixelBufferConversion.cpp
@@ -140,9 +140,17 @@ static void convertImagePixelsAccelerated(const ConstPixelBufferConversionView&
 enum class PixelFormatConversion { None, Permute };
 
 template<PixelFormatConversion pixelFormatConversion>
+#if CPU(BIG_ENDIAN)
+static void convertSinglePixelPremultipliedToPremultiplied(PixelFormat sourcePixelFormat, const uint8_t* sourcePixel, PixelFormat destinationPixelFormat, uint8_t* destinationPixel)
+#else
 static void convertSinglePixelPremultipliedToPremultiplied(const uint8_t* sourcePixel, uint8_t* destinationPixel)
+#endif
 {
+#if CPU(BIG_ENDIAN)
+    uint8_t alpha = sourcePixel[sourcePixelFormat == PixelFormat::ARGB8 ? 0 : 3];
+#else
     uint8_t alpha = sourcePixel[3];
+#endif
     if (!alpha) {
         reinterpret_cast<uint32_t*>(destinationPixel)[0] = 0;
         return;
@@ -151,23 +158,81 @@ static void convertSinglePixelPremultipliedToPremultiplied(const uint8_t* source
     if constexpr (pixelFormatConversion == PixelFormatConversion::None)
         reinterpret_cast<uint32_t*>(destinationPixel)[0] = reinterpret_cast<const uint32_t*>(sourcePixel)[0];
     else {
+#if CPU(BIG_ENDIAN)
+        // Swap pixel channels ARGB <-> RGBA.
+        if (destinationPixelFormat == PixelFormat::ARGB8)
+        {
+            destinationPixel[0] = sourcePixel[3];
+            destinationPixel[1] = sourcePixel[0];
+            destinationPixel[2] = sourcePixel[1];
+            destinationPixel[3] = sourcePixel[2];
+        }
+        else
+        {
+            destinationPixel[0] = sourcePixel[1];
+            destinationPixel[1] = sourcePixel[2];
+            destinationPixel[2] = sourcePixel[3];
+            destinationPixel[3] = sourcePixel[0];
+        }
+#else
         // Swap pixel channels BGRA <-> RGBA.
         destinationPixel[0] = sourcePixel[2];
         destinationPixel[1] = sourcePixel[1];
         destinationPixel[2] = sourcePixel[0];
         destinationPixel[3] = sourcePixel[3];
+#endif
     }
 }
 
 template<PixelFormatConversion pixelFormatConversion>
+#if CPU(BIG_ENDIAN)
+static void convertSinglePixelPremultipliedToUnpremultiplied(PixelFormat sourcePixelFormat, const uint8_t* sourcePixel, PixelFormat destinationPixelFormat, uint8_t* destinationPixel)
+#else
 static void convertSinglePixelPremultipliedToUnpremultiplied(const uint8_t* sourcePixel, uint8_t* destinationPixel)
+#endif
 {
+#if CPU(BIG_ENDIAN)
+    uint8_t alpha = sourcePixel[sourcePixelFormat == PixelFormat::ARGB8 ? 0 : 3];
+#else
     uint8_t alpha = sourcePixel[3];
+#endif
     if (!alpha || alpha == 255) {
+#if CPU(BIG_ENDIAN)
+        convertSinglePixelPremultipliedToPremultiplied<pixelFormatConversion>(sourcePixelFormat, sourcePixel, destinationPixelFormat, destinationPixel);
+#else
         convertSinglePixelPremultipliedToPremultiplied<pixelFormatConversion>(sourcePixel, destinationPixel);
+#endif
         return;
     }
 
+#if CPU(BIG_ENDIAN)
+    UNUSED_PARAM(destinationPixelFormat);
+    if constexpr (pixelFormatConversion == PixelFormatConversion::None) {
+        if (sourcePixelFormat == PixelFormat::ARGB8) {
+            destinationPixel[0] = alpha;
+            destinationPixel[1] = (sourcePixel[1] * 255) / alpha;
+            destinationPixel[2] = (sourcePixel[2] * 255) / alpha;
+            destinationPixel[3] = (sourcePixel[3] * 255) / alpha;
+        } else {
+            destinationPixel[0] = (sourcePixel[0] * 255) / alpha;
+            destinationPixel[1] = (sourcePixel[1] * 255) / alpha;
+            destinationPixel[2] = (sourcePixel[2] * 255) / alpha;
+            destinationPixel[3] = alpha;
+        }
+    } else {
+        if (sourcePixelFormat == PixelFormat::ARGB8) {
+            destinationPixel[0] = (sourcePixel[1] * 255) / alpha;
+            destinationPixel[1] = (sourcePixel[2] * 255) / alpha;
+            destinationPixel[2] = (sourcePixel[3] * 255) / alpha;
+            destinationPixel[3] = alpha;
+        } else {
+            destinationPixel[0] = alpha;
+            destinationPixel[1] = (sourcePixel[0] * 255) / alpha;
+            destinationPixel[2] = (sourcePixel[1] * 255) / alpha;
+            destinationPixel[3] = (sourcePixel[2] * 255) / alpha;
+        }
+    }
+#else
     if constexpr (pixelFormatConversion == PixelFormatConversion::None) {
         destinationPixel[0] = (sourcePixel[0] * 255) / alpha;
         destinationPixel[1] = (sourcePixel[1] * 255) / alpha;
@@ -180,17 +245,58 @@ static void convertSinglePixelPremultipliedToUnpremultiplied(const uint8_t* sour
         destinationPixel[2] = (sourcePixel[0] * 255) / alpha;
         destinationPixel[3] = alpha;
     }
+#endif
 }
 
 template<PixelFormatConversion pixelFormatConversion>
+#if CPU(BIG_ENDIAN)
+static void convertSinglePixelUnpremultipliedToPremultiplied(PixelFormat sourcePixelFormat, const uint8_t* sourcePixel, PixelFormat destinationPixelFormat, uint8_t* destinationPixel)
+#else
 static void convertSinglePixelUnpremultipliedToPremultiplied(const uint8_t* sourcePixel, uint8_t* destinationPixel)
+#endif
 {
+#if CPU(BIG_ENDIAN)
+    uint8_t alpha = sourcePixel[sourcePixelFormat == PixelFormat::ARGB8 ? 0 : 3];
+#else
     uint8_t alpha = sourcePixel[3];
+#endif
     if (!alpha || alpha == 255) {
+#if CPU(BIG_ENDIAN)
+        convertSinglePixelPremultipliedToPremultiplied<pixelFormatConversion>(sourcePixelFormat, sourcePixel, destinationPixelFormat, destinationPixel);
+#else
         convertSinglePixelPremultipliedToPremultiplied<pixelFormatConversion>(sourcePixel, destinationPixel);
+#endif
         return;
     }
 
+#if CPU(BIG_ENDIAN)
+    UNUSED_PARAM(destinationPixelFormat);
+    if constexpr (pixelFormatConversion == PixelFormatConversion::None) {
+        if (sourcePixelFormat == PixelFormat::ARGB8) {
+            destinationPixel[0] = alpha;
+            destinationPixel[1] = (sourcePixel[1] * alpha + 254) / 255;
+            destinationPixel[2] = (sourcePixel[2] * alpha + 254) / 255;
+            destinationPixel[3] = (sourcePixel[3] * alpha + 254) / 255;
+        } else {
+            destinationPixel[0] = (sourcePixel[0] * alpha + 254) / 255;
+            destinationPixel[1] = (sourcePixel[1] * alpha + 254) / 255;
+            destinationPixel[2] = (sourcePixel[2] * alpha + 254) / 255;
+            destinationPixel[3] = alpha;
+        }
+    } else {
+        if (sourcePixelFormat == PixelFormat::ARGB8) {
+            destinationPixel[0] = (sourcePixel[1] * alpha + 254) / 255;
+            destinationPixel[1] = (sourcePixel[2] * alpha + 254) / 255;
+            destinationPixel[2] = (sourcePixel[3] * alpha + 254) / 255;
+            destinationPixel[3] = alpha;
+        } else {
+            destinationPixel[0] = alpha;
+            destinationPixel[1] = (sourcePixel[0] * alpha + 254) / 255;
+            destinationPixel[2] = (sourcePixel[1] * alpha + 254) / 255;
+            destinationPixel[3] = (sourcePixel[2] * alpha + 254) / 255;
+        }
+    }
+#else
     if constexpr (pixelFormatConversion == PixelFormatConversion::None) {
         destinationPixel[0] = (sourcePixel[0] * alpha + 254) / 255;
         destinationPixel[1] = (sourcePixel[1] * alpha + 254) / 255;
@@ -203,23 +309,49 @@ static void convertSinglePixelUnpremultipliedToPremultiplied(const uint8_t* sour
         destinationPixel[2] = (sourcePixel[0] * alpha + 254) / 255;
         destinationPixel[3] = alpha;
     }
+#endif
 }
 
 template<PixelFormatConversion pixelFormatConversion>
+#if CPU(BIG_ENDIAN)
+static void convertSinglePixelUnpremultipliedToUnpremultiplied(PixelFormat sourcePixelFormat, const uint8_t* sourcePixel, PixelFormat destinationPixelFormat, uint8_t* destinationPixel)
+#else
 static void convertSinglePixelUnpremultipliedToUnpremultiplied(const uint8_t* sourcePixel, uint8_t* destinationPixel)
+#endif
 {
     if constexpr (pixelFormatConversion == PixelFormatConversion::None)
         reinterpret_cast<uint32_t*>(destinationPixel)[0] = reinterpret_cast<const uint32_t*>(sourcePixel)[0];
     else {
+#if CPU(BIG_ENDIAN)
+        UNUSED_PARAM(sourcePixelFormat);
+        // Swap pixel channels ARGB <-> RGBA.
+        if (destinationPixelFormat == PixelFormat::ARGB8) {
+            destinationPixel[0] = sourcePixel[3];
+            destinationPixel[1] = sourcePixel[0];
+            destinationPixel[2] = sourcePixel[1];
+            destinationPixel[3] = sourcePixel[2];
+        }
+        else {
+            destinationPixel[0] = sourcePixel[1];
+            destinationPixel[1] = sourcePixel[2];
+            destinationPixel[2] = sourcePixel[3];
+            destinationPixel[3] = sourcePixel[0];
+        }
+#else
         // Swap pixel channels BGRA <-> RGBA.
         destinationPixel[0] = sourcePixel[2];
         destinationPixel[1] = sourcePixel[1];
         destinationPixel[2] = sourcePixel[0];
         destinationPixel[3] = sourcePixel[3];
+#endif
     }
 }
 
+#if CPU(BIG_ENDIAN)
+template<void (*convertFunctor)(PixelFormat, const uint8_t*, PixelFormat, uint8_t*)>
+#else
 template<void (*convertFunctor)(const uint8_t*, uint8_t*)>
+#endif
 static void convertImagePixelsUnaccelerated(const ConstPixelBufferConversionView& source, const PixelBufferConversionView& destination, const IntSize& destinationSize)
 {
     const uint8_t* sourceRows = source.rows;
@@ -228,7 +360,11 @@ static void convertImagePixelsUnaccelerated(const ConstPixelBufferConversionView
     size_t bytesPerRow = destinationSize.width() * 4;
     for (int y = 0; y < destinationSize.height(); ++y) {
         for (size_t x = 0; x < bytesPerRow; x += 4)
+#if CPU(BIG_ENDIAN)
+            convertFunctor(source.format.pixelFormat, &sourceRows[x], destination.format.pixelFormat, &destinationRows[x]);
+#else
             convertFunctor(&sourceRows[x], &destinationRows[x]);
+#endif
         sourceRows += source.bytesPerRow;
         destinationRows += destination.bytesPerRow;
     }
@@ -237,6 +373,7 @@ static void convertImagePixelsUnaccelerated(const ConstPixelBufferConversionView
 void convertImagePixels(const ConstPixelBufferConversionView& source, const PixelBufferConversionView& destination, const IntSize& destinationSize)
 {
     // We don't currently support converting pixel data with non-8-bit buffers.
+    // BGRA8 is actually ARGB8 on BIG_ENDIAN.
     ASSERT(source.format.pixelFormat == PixelFormat::RGBA8 || source.format.pixelFormat == PixelFormat::BGRA8);
     ASSERT(destination.format.pixelFormat == PixelFormat::RGBA8 || destination.format.pixelFormat == PixelFormat::BGRA8);
 
diff --git a/Source/WebCore/platform/graphics/PixelFormat.h b/Source/WebCore/platform/graphics/PixelFormat.h
index 1ca711b8..4a7168f8 100644
--- a/Source/WebCore/platform/graphics/PixelFormat.h
+++ b/Source/WebCore/platform/graphics/PixelFormat.h
@@ -33,6 +33,9 @@ namespace WebCore {
 enum class PixelFormat : uint8_t {
     RGBA8,
     BGRA8,
+#if CPU(BIG_ENDIAN)
+    ARGB8 = BGRA8, // BGRA will actually be ARGB on BIG_ENDIAN
+#endif
     RGB10,
     RGB10A8,
 };