I'm learning directx in a master's degree and they taught us to have a GraphicsLayer class which is the one connecting with the direct3d library. That way this class is completly independent from the other classes (my game classes), meaning changing the renderer to OpenGL wouldn't require much effort but only changing the graphicLayer.

This classe has it's LoadAssets, Paint methods, but I have a question, they told us to load all the assets inside this class. This means all these methods will be in the loadAssets method:

D3DXCreateTextureFromFileEx(g_pD3DDevice,"tiles.png",0,0,1,0,D3DFMT_UNKNOWN,D3DPOOL_DEFAULT,D3DX_FILTER_NONE,D3DX_FILTER_NONE,NULL,NULL,NULL,&texTiles);
// And more resources to load
//...

texTiles as you see is a LPDIRECT3DTEXTURE9 instance which is declared in the graphicLayer.h.

So my question is, how do you manage all the resources? Do I have to declare in the .h all my game textures even if I'm not using them? How would you load only those resources there are in a scene and draw them in a code-strucured way?