As a result of a recent conversation with David, I would like to propose several changes in the material previsualisation window. The main idea is that the material previsualisation window offers many more posibilities and can by itself partially supply for the lack of interactive rendering capabilities. There are several areas that could be improved in my opinion. The main goals of a good material previsualisation window should be:
1. Ability to set a key light in the previsualisation window. A key light is a dominant light source we can use to produce a clear terminator area on which we can study in a better way effects produced by light sources on relief maps (bump mapping, normal mapping or real displacement). This is part of the whole idea about implementing tools for producing better and more consistent diffuse components in our scenes. This is already done in Blender internal previsualisation result for instance. It would be great also that we can change the key light type. Example below, notice how relief mapping (in this case displacement) is more evident on the terminator area:
2. Ability to change key light incident angle, so we can place the terminator area on the preview object.
3. Ability to focus in the observer's terminator area. Lighting effects accumulate in tangent angles to the scene subject, but this is true either from the key light (previous paragraph) perspective or the observer's standpoint (image below). Many times I set such a scene for material testing so I produce a tangent camera to the subject to study in a better way relief mapping strength and Oren-Nayar gradients. Ideally, the best test scenario is the one in which both key light and the camera view use a tangent angle to the previsualisation subject. Terminator areas and tangent views is where astronomers study planets' surface properties.
This could be achieved in the previsualisation window with a zoom in/out tool so users can focus on such an area and also rotating interactively the previsualisation object. An important feature would be that we can control resolution settings for the previsualisation for detail, but I am not sure whether Blender would allow for these features. In that case maybe we can look for alternatives.
|Same Oren-Nayar object, rendered with different camera angles, notice how standar cube preview is useless to see Oren-Nayar gradients.|
4. Ability to change light power in the material previsualisation window, so we can accomodate its results in line with our scene lighting balance, for instance Grey 18 or Grey 12.
5. Ability to change previsualisation object size according to Blender scene units, so we can define in a better way scale of our relief mapping work, particularly when working with procedural textures. Also with this feature we could better simulate and study effects in every possible scale, from micro to middle and macro levels. This feature is very important for instance if we layer a specular reflections on a surface and and we want them working consistently in different scales. We can set several scale intervals for common scene units or a just a multipliying factor for the standard size.
Viewing scale concepts and terminology are getting more attention in the wake of phisically based shading, for instance at close distance sea water can be modelled as a perfect mirror with displacement for the specular component but at a large distance, it behaves more like a microfacet specular model aka glossy. You don't need such large distances though to observe surface properties change in other common objects, like plaster and matte painted surfaces becoming increasingly specular at bigger viewing scales.
6. Rendering an object from the scene as a previsualisation object, so we can really test more possible cases not accounted for right now, for instance cylindrical objects with anisotropic reflections. This would translate better our results in the material window to the final result in the scene.
7. Material previsualisation render input in the Blender UV/Image windows, so we can study in a better way diffuse detail and specular effects on the material surface.