texture_runtime: Add staging buffer lock mechanism

src/common/memory_ref.h

@@ -3,7 +3,7 @@
 // Refer to the license.txt file included.
 
 #pragma once
-
+#include <span>
 #include <memory>
 #include <vector>
 #include <boost/serialization/export.hpp>
@@ -65,8 +65,11 @@ private:
 
 BOOST_CLASS_EXPORT_KEY(BufferMem);
 
-/// A managed reference to host-side memory. Fast enough to be used everywhere instead of u8*
-/// Supports serialization.
+/**
+ * A managed reference to host-side memory.
+ * Fast enough to be used everywhere instead of u8*
+ * Supports serialization.
+ */
 class MemoryRef {
 public:
     MemoryRef() = default;
@@ -75,41 +78,52 @@ public:
         : backing_mem(std::move(backing_mem_)), offset(0) {
         Init();
     }
+
     MemoryRef(std::shared_ptr<BackingMem> backing_mem_, u64 offset_)
         : backing_mem(std::move(backing_mem_)), offset(offset_) {
         ASSERT(offset <= backing_mem->GetSize());
         Init();
     }
+
     explicit operator bool() const {
         return cptr != nullptr;
     }
+
     operator u8*() {
         return cptr;
     }
-    u8* GetPtr() {
-        return cptr;
-    }
-    std::byte* GetBytes() {
-        return reinterpret_cast<std::byte*>(cptr);
-    }
+
     operator const u8*() const {
         return cptr;
     }
+
+    u8* GetPtr() {
+        return cptr;
+    }
+
     const u8* GetPtr() const {
         return cptr;
     }
-    const std::byte* GetBytes() const {
-        return reinterpret_cast<const std::byte*>(cptr);
+
+    std::span<std::byte> GetBytes(std::size_t size) {
+        return std::span{reinterpret_cast<std::byte*>(cptr), size > csize ? csize : size};
     }
+
+    std::span<const std::byte> GetBytes(std::size_t size) const {
+        return std::span{reinterpret_cast<const std::byte*>(cptr), size > csize ? csize : size};
+    }
+
     std::size_t GetSize() const {
         return csize;
     }
+
     MemoryRef& operator+=(u32 offset_by) {
         ASSERT(offset_by < csize);
         offset += offset_by;
         Init();
         return *this;
     }
+
     MemoryRef operator+(u32 offset_by) const {
         ASSERT(offset_by < csize);
         return MemoryRef(backing_mem, offset + offset_by);