Vulkan: Simplify image read barrier necessity check

src/libANGLE/renderer/vulkan/ContextVk.cpp

@@ -4444,8 +4444,17 @@ angle::Result ContextVk::onImageRead(VkImageAspectFlags aspectFlags,
     ASSERT(!image->isReleasedToExternal());
     ASSERT(image->getImageSerial().valid());
 
+    // Layout transitions for images used in the render pass are handled especially.  This function
+    // is only called when the image is used outside the render pass.  As such, if the image is used
+    // inside the render pass, its layout is necessarily different from imageLayout, and thus a
+    // layout transition is necessary (and the render pass has to break).
+    ASSERT(image->isReadBarrierNecessary(imageLayout) ||
+           !(mRenderPassCommands->started() && mRenderPassCommands->usesImageInRenderPass(*image)));
+
     // Note that different read methods are not compatible. A shader read uses a different layout
     // than a transfer read. So we cannot support simultaneous read usage as easily as for Buffers.
+    // TODO: Don't close the render pass if the image was only used read-only in the render pass.
+    // http://anglebug.com/4984
     ANGLE_TRY(endRenderPassIfImageUsed(*image));
 
     image->recordReadBarrier(aspectFlags, imageLayout,

src/libANGLE/renderer/vulkan/SurfaceVk.cpp

@@ -1194,7 +1194,7 @@ angle::Result WindowSurfaceVk::present(ContextVk *contextVk,
         ANGLE_TRY(drawOverlay(contextVk, &image));
     }
 
-    // This does nothing if it already in the requested layout
+    // This does nothing if it's already in the requested layout
     image.image.recordReadBarrier(VK_IMAGE_ASPECT_COLOR_BIT, vk::ImageLayout::Present,
                                   commandBuffer);
 

src/libANGLE/renderer/vulkan/vk_helpers.cpp

@@ -692,7 +692,7 @@ void CommandBufferHelper::imageRead(ResourceUseList *resourceUseList,
 
     if (mIsRenderPassCommandBuffer)
     {
-        // As noted in the header we don't support multiple layouts reads for Images.
+        // As noted in the header we don't support multiple read layouts for Images.
         // We allow duplicate uses in the RP to accomodate for normal GL sampler usage.
         if (!usesImageInRenderPass(*image))
         {
@@ -720,7 +720,7 @@ void CommandBufferHelper::imageWrite(ResourceUseList *resourceUseList,
 
     if (mIsRenderPassCommandBuffer)
     {
-        // When used as a storage buffer we allow for aliased writes.
+        // When used as a storage image we allow for aliased writes.
         if (aliasingMode == AliasingMode::Disallowed)
         {
             ASSERT(!usesImageInRenderPass(*image));
@@ -3373,19 +3373,6 @@ bool ImageHelper::isDepthOrStencil() const
     return mFormat->actualImageFormat().hasDepthOrStencilBits();
 }
 
-bool ImageHelper::isReadBarrierNecessary(ImageLayout newLayout) const
-{
-    // If transitioning to a different layout, we need always need a barrier.
-    if (mCurrentLayout != newLayout)
-    {
-        return true;
-    }
-
-    // RAW (read-after-write) hazards always requires a memory barrier.
-    const ImageMemoryBarrierData &layoutData = kImageMemoryBarrierData[mCurrentLayout];
-    return layoutData.type == BarrierType::Write;
-}
-
 void ImageHelper::changeLayoutAndQueue(VkImageAspectFlags aspectMask,
                                        ImageLayout newLayout,
                                        uint32_t newQueueFamilyIndex,

src/libANGLE/renderer/vulkan/vk_helpers.h

@@ -1432,7 +1432,12 @@ class ImageHelper final : public Resource, public angle::Subject
     }
 
     // This function can be used to prevent issuing redundant layout transition commands.
-    bool isReadBarrierNecessary(ImageLayout newLayout) const;
+    bool isReadBarrierNecessary(ImageLayout newLayout) const
+    {
+        // If transitioning to a different layout, we always need a barrier.  Otherwise RAR
+        // (read-after-read) is not a hazard and doesn't require a barrier.
+        return mCurrentLayout != newLayout;
+    }
 
     void recordReadBarrier(VkImageAspectFlags aspectMask,
                            ImageLayout newLayout,