Add InitReqType to classify FrameRefType by init/reset requirements.

The accumulated `FrameRefType` of the accesses to a resource within a frame
determines how the resource needs to be initialized. The possibilities are:

* `None`: The initial value of the resource is never used within the frame,
  either because it is never read, or because it is only read after being
  cleared
* `InitOnce`: The resource needs to be initialized before replaying the frame
  for the first time, but does not ever need to be reset; this occurs when a
  resource is read within the frame, but not written within the frame.
* `Reset`: The resource needs to be reset each time before replaying the frame.
  This occurs when the resource is read and later written within the frame.

renderdoc/core/resource_manager.h

@@ -114,6 +114,39 @@ FrameRefType ComposeFrameRefsUnordered(FrameRefType first, FrameRefType second);
 
 bool IsDirtyFrameRef(FrameRefType refType);
 
+// Captures the possible initialization/reset requirements for resources.
+// These requirements are entirely determined by the resource's FrameRefType,
+// but this type improves the readability of the code that checks
+// init/reset requirements.
+enum InitReqType
+{
+  // Initial contents of the resource are not used, and need not be initialized.
+  // Corresponds to `None`, `Write` or `Clear` ref types.
+  eInitReq_None,
+
+  // Initial contents of the resource are read, but not overwritten;
+  // the resource needs to be initialized before the first replay, but need not
+  // be reset before subsequent replays.
+  // Corresponds to `Read` ref type.
+  eInitReq_InitOnce,
+
+  // Initial contents of the resource are read, and later overwritten;
+  // the resource needs to be reset before each replay.
+  // Corresponds to `ReadBeforeWrite` ref type.
+  eInitReq_Reset,
+};
+
+// Return the initialization/reset requirements for a FrameRefType
+inline InitReqType InitReq(FrameRefType refType)
+{
+  switch(refType)
+  {
+    case eFrameRef_Read: return eInitReq_InitOnce;
+    case eFrameRef_ReadBeforeWrite: return eInitReq_Reset;
+    default: return eInitReq_None;
+  }
+}
+
 // handle marking a resource referenced for read or write and storing RAW access etc.
 bool MarkReferenced(std::map<ResourceId, FrameRefType> &refs, ResourceId id, FrameRefType refType);