Add stream open to bufferview & image

ReFuel.Gltf/GltfBufferView.cs

@@ -1,4 +1,5 @@
-using System;
+using ReFuel.Gltf.IO;
+using System;
 using System.Text.Json;
 
 namespace ReFuel.Gltf
@@ -26,6 +27,11 @@ namespace ReFuel.Gltf
             buffer = new GltfSmartId<GltfBuffer>(document.Buffers);
         }
 
+        public Stream Open()
+        {
+            return ((StreamWrapper)buffer.Value.Open()).ForkAbs(ByteOffset, ByteOffset + ByteLength);
+        }
+
         internal override void Deserialize(JsonElement element)
         {
             AssertObject(element);

ReFuel.Gltf/GltfImage.cs

@@ -39,7 +39,7 @@ namespace ReFuel.Gltf
         {
             if (Uri == null)
             {
-                throw new Exception("Only images with a URI property are to be opened.");
+                return BufferView!.Open();
             }
 
             if (Uri.IsAbsoluteUri)
@@ -64,9 +64,13 @@ namespace ReFuel.Gltf
             // otherwise
 
             if (provider != null)
+            {
                 return provider.OpenFile(pwd, Uri) ?? throw new FileNotFoundException(Uri.ToString());
+            }
             else
+            {
                 return File.OpenRead(Path.Combine(pwd ?? string.Empty, Uri.LocalPath));
+            }
 
             // throw new Exception("Unrecognized URI scheme.");
         }
@@ -74,7 +78,9 @@ namespace ReFuel.Gltf
         internal override void Deserialize(JsonElement element)
         {
             if (element.ValueKind != JsonValueKind.Object)
+            {
                 throw new Exception("Expected a JSON object for glTF image node.");
+            }
 
             foreach (JsonProperty property in element.EnumerateObject())
             {