Are projected light reflections strange?

[Drongle McMahon]

I wonder whether anyone else has found the interaction of materials with projected lights confusing, and whether any of it might be considered unexpected enough to be called a bug. Here are my observations. I would welcome the views of others.

Specular reflection...
Controlled by spec map, spec colour, spec exponent map and gloss spinner.
Not affected by env map or env spinner.

Environmental reflection...
Controlled by env map and env spinner.
Not affected by spec map, spec colour, spec exponent map or gloss spinner.

In other words, these are exclusive.

Legacy local lights give only specular reflection, that behaves as above.

However, with projectors the situation is different. It depends whether alpha blending is on or not. It it's on, they behave just like legacy lights, not even being affected by the colour of the projected image. If it's off, we get two kinds of reflection. 

First, where the projected image impinges on the surface, there is specular reflection that responds to the above controls exactly as does the specular reflection from the sun or legacy local lights. As with legacy local lights, the area of the specular reflection (the range of normals over which it is reflected) is greater than for the sun, presumably because the impinging light is spread over a range of angles (like an area light). Sunlight is parallel (as is a point light). This makes the specular highlights much more prominent than those from the sun.

Then the projected image appears to be incorporated into the environmental lighting, producing a smaller reflected image, as if we are seeing the reflection of the projection image at some distance from the camera. If the focus is set high, this is a precise copy of the projected image. In some respects, it behaves like the rest of the environmental light (from the sky), but in others it does not...

Like the environmental light from the sky, its intensity is controlled by the environmental map (spec map alpha).

It is affected by the environment spinner, but in a rather different way - it's off at 0, but comes on suddenly quite bright and then doesn't change until about 75. This contrasts to the smooth increase in the rest of the environmental reflection. At higher values, instead of continuing increase in intensity, it shrinks and becomes a more and more sharply focused version of the projected image.

As expected, it is not affected at all by the specular exponent map (normal map alpha) or the glossiness spinner. However, unlike the normal environmental reflection, it's intensity and colour are affected by the specular map and by the specular colour selector. The usual environmental lighting is not affected by those. Thus the behavior of this reflection seems a bit paradoxical.

Having both these reflections seems to me a bit confusing. With the added oddities in behavior, it discourages me from trying to use both kinds of reflection together on objects that might be seen near projected lights.

Here is a picture of the two effects from a projected light with an orange checkerboard, falling on a black sphere that is set up to give both specular and environmental reflections. Maps all blank, glossiness = 70, environment = 80 on the left, 160 on the right.

[Jenni Darkwatch]

That's indeed an odd artefact you discovered there. It's intuitively not logical, but I don't know enough about implementation in OpenGL to know whether that's normal or not.