fix comment

Author: iskakaushik

impeller/renderer/backend/vulkan/allocator_vk.cc

@@ -132,17 +132,21 @@ static constexpr vk::ImageUsageFlags ToVKImageUsageFlags(PixelFormat format,
 
   if (usage & static_cast<TextureUsageMask>(TextureUsage::kShaderRead)) {
     vk_usage |= vk::ImageUsageFlagBits::eSampled;
-    // unmark the usage as transient if it is used as a sampled image
-    // See: https://github.com/flutter/flutter/issues/121633
+    // Device transient images can only be used as attachments. The caller
+    // specified incorrect usage flags and is attempting to read a device
+    // transient image in a shader. Unset the transient attachment flag. See:
+    // https://github.com/flutter/flutter/issues/121633
     if (mode == StorageMode::kDeviceTransient) {
       vk_usage &= ~vk::ImageUsageFlagBits::eTransientAttachment;
     }
   }
 
   if (usage & static_cast<TextureUsageMask>(TextureUsage::kShaderWrite)) {
     vk_usage |= vk::ImageUsageFlagBits::eStorage;
-    // unmark the usage as transient if it is used as a storage image
-    // See: https://github.com/flutter/flutter/issues/121633
+    // Device transient images can only be used as attachments. The caller
+    // specified incorrect usage flags and is attempting to read a device
+    // transient image in a shader. Unset the transient attachment flag. See:
+    // https://github.com/flutter/flutter/issues/121633
     if (mode == StorageMode::kDeviceTransient) {
       vk_usage &= ~vk::ImageUsageFlagBits::eTransientAttachment;
     }

impeller/renderer/backend/vulkan/swapchain_impl_vk.cc

@@ -84,18 +84,18 @@ static std::optional<vk::SurfaceFormatKHR> ChooseSurfaceFormat(
 
 static std::optional<vk::CompositeAlphaFlagBitsKHR> ChooseAlphaCompositionMode(
     vk::CompositeAlphaFlagsKHR flags) {
-  if (flags & vk::CompositeAlphaFlagBitsKHR::ePreMultiplied) {
-    return vk::CompositeAlphaFlagBitsKHR::ePreMultiplied;
-  }
-  if (flags & vk::CompositeAlphaFlagBitsKHR::eOpaque) {
-    return vk::CompositeAlphaFlagBitsKHR::eOpaque;
-  }
   if (flags & vk::CompositeAlphaFlagBitsKHR::eInherit) {
     return vk::CompositeAlphaFlagBitsKHR::eInherit;
   }
+  if (flags & vk::CompositeAlphaFlagBitsKHR::ePreMultiplied) {
+    return vk::CompositeAlphaFlagBitsKHR::ePreMultiplied;
+  }
   if (flags & vk::CompositeAlphaFlagBitsKHR::ePostMultiplied) {
     return vk::CompositeAlphaFlagBitsKHR::ePostMultiplied;
   }
+  if (flags & vk::CompositeAlphaFlagBitsKHR::eOpaque) {
+    return vk::CompositeAlphaFlagBitsKHR::eOpaque;
+  }
 
   return std::nullopt;
 }