Vulkan: unused resolve attachments must be marked as such

Change-Id: I61e1e6469c20149df5c6296ee237efced36a163c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/28145
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/dawn_native/vulkan/RenderPassCache.cpp

@@ -161,6 +161,13 @@ namespace dawn_native { namespace vulkan {
             ++resolveAttachmentIndex;
         }
 
+        // All color attachments without a corresponding resolve attachment must be set to VK_ATTACHMENT_UNUSED
+        for (; resolveAttachmentIndex < colorAttachmentIndex; resolveAttachmentIndex++) {
+            auto& attachmentRef = resolveAttachmentRefs[resolveAttachmentIndex];
+            attachmentRef.attachment = VK_ATTACHMENT_UNUSED;
+            attachmentRef.layout = VK_IMAGE_LAYOUT_COLOR_ATTACHMENT_OPTIMAL; // The Khronos Vulkan validation layer will complain if not set
+        }
+
         VkAttachmentReference* resolveTargetAttachmentRefs =
             query.resolveTargetMask.any() ? resolveAttachmentRefs.data() : nullptr;