I decided it would be very handy if I could actually inspect various textures at runtime from within the engine, and chose to use a gui approach to displaying them.
Of course, that's fine for 2D textures, but other types, not so much.
My CubeMap textures, for example, would appear blank, when treated as 2D textures, which they are not. So, how would one go about displaying them, short of applying them to a skybox?
OpenGL does not give us easy access to the 6 individual 'face textures' of a CubeMap texture - we can do it, but it involves copying the image data into a new texture or textures, which is very slow.
A nice fast approach was presented a while back by Scali, whom I credit for my implementation of his solution.
He suggests that we create a flat geometry which happens to have 3D texture coordinates to suit a cubemap, and render it using a shader that samples a cubemap.
Since I was already using a gui widget to display 2D textures, I decided to take a 'render to texture' approach, and noted immediately that since the projection is orthographic, there is no need for 3D positions - 2D positions with 3D texcoords is what I have used to render the tile geometry to a regular 2D texture, which is then handballed to the gui system for display.
In retrospect, given that the geometry is presented in NDC Space, there's no need for a projection transform either, so there is still room for some optimizing and polish, but it works well enough for the purpose, I'm happy, since it performs well on dynamic cubemaps - I'm now able to view both static and dynamic cubemaps in realtime :)
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