[d3d9] Optimize GetCommonTexture

src/d3d9/d3d9_texture.h

@@ -196,17 +196,21 @@ namespace dxvk {
 
   };
 
+  using D3D9TextureGeneric = D3D9BaseTexture<D3D9Surface, IDirect3DBaseTexture9>;
+
+  static_assert(sizeof(D3D9Texture2D) == sizeof(D3D9Texture3D) &&
+                sizeof(D3D9Texture2D) == sizeof(D3D9TextureCube) &&
+                sizeof(D3D9Texture2D) == sizeof(D3D9TextureGeneric));
+
   inline D3D9CommonTexture* GetCommonTexture(IDirect3DBaseTexture9* ptr) {
     if (ptr == nullptr)
       return nullptr;
 
-    D3DRESOURCETYPE type = ptr->GetType();
-    if (type == D3DRTYPE_TEXTURE)
-      return static_cast<D3D9Texture2D*>  (ptr)->GetCommonTexture();
-    else if (type == D3DRTYPE_CUBETEXTURE)
-      return static_cast<D3D9TextureCube*>(ptr)->GetCommonTexture();
-    else //if(type == D3DRTYPE_VOLUMETEXTURE)
-      return static_cast<D3D9Texture3D*>  (ptr)->GetCommonTexture();
+    // We can avoid needing to get the type as m_texture has the same offset
+    // no matter the texture type.
+    // The compiler is not smart enough to eliminate the call to GetType as it is
+    // not marked const.
+    return static_cast<D3D9TextureGeneric*>(ptr)->GetCommonTexture();
   }
 
   inline D3D9CommonTexture* GetCommonTexture(D3D9Surface* ptr) {
@@ -224,13 +228,11 @@ namespace dxvk {
     if (tex == nullptr)
       return;
 
-    D3DRESOURCETYPE type = tex->GetType();
-    if (type == D3DRTYPE_TEXTURE)
-      return CastRefPrivate<D3D9Texture2D>  (tex, AddRef);
-    else if (type == D3DRTYPE_CUBETEXTURE)
-      return CastRefPrivate<D3D9TextureCube>(tex, AddRef);
-    else //if(type == D3DRTYPE_VOLUMETEXTURE)
-      return CastRefPrivate<D3D9Texture3D>  (tex, AddRef);
+    // We can avoid needing to get the type as m_refCount has the same offset
+    // no matter the texture type.
+    // The compiler is not smart enough to eliminate the call to GetType as it is
+    // not marked const.
+    return CastRefPrivate<D3D9TextureGeneric>(tex, AddRef);
   }
 
   inline void TextureChangePrivate(IDirect3DBaseTexture9*& dst, IDirect3DBaseTexture9* src) {