[Gnu3dkit-discuss] How do RenderKit and Renderer communicate?

[Brent Gulanowski]

Phil,

I've cleaned up a bunch of the introductory parts of the white paper, 
and will be working on expanding your point form additions into full 
discussions soon. But I'm concerned that I really do not have a good 
grasp on your preferred model for RenderKit - Renderer communication.

I believe that we established that the RenderKit is the active party, 
while the Renderer is subservient. I mean, rendering happens due to 
instructions and data sent by RenderKit to the Renderer, as opposed to 
the Renderer producing instructions and requesting data from RenderKit. 
Is this correct? It seems logical, if I consider that a view is 
conceptually instigated by a viewer, in this case a camera object 
inside RenderKit.

I have a conceptualization question, which arises from my definition of 
3D rendering (part of my definition of all processing tasks). Rendered 
images are transformations of one set of data (3D object data) into 
another (pixel data). Geometric and projection transformations are just 
some of the transformations applied. Culling, texturing, anti-aliasing, 
blurring, and all sorts of others could be grouped into a general 
category.

My feeling is that some of these would sensibly arise in relation to 
the camera or synthetic viewer, but others would originate from the 
god-like controls of the user (or programmer) of the particular 
application -- and not just pixel filters (which are the leastrelated 
to RenderKit -- e.g. Cel animation-style shading). Wireframe view is 
one that I often think of as being applied "from outside", as is 
occlusion culling, and others. But what about (non-volumetric) fog? 
Does it complicate the issue if the renderer were able to post-filter 
the data (unless such filters were embedded into the renderer)? Because 
then the application would have to do one set of transformations 
through Actions and another set through whatever interaction were 
exposed from the renderer.

Have you specified or assumed a very strict flow of commands for 
various data transformations from the application, through RenderKit, 
and then into the renderer? Can we define different categories of such 
transformations to help us define current and future Actions, and how 
they are similar or different (depending upon when the actions' effects 
come into play)?

Should we provide a sharp contrast between transformations which affect 
the world geometry and those which only affect the way the geometry is 
rendered? I can't see where to draw such a line, but if it exists, it 
seems essential to recognize it and incorporate it. Viewing the world 
orthographically doesn't affect the world per se, but it is a result of 
a camera. Perhaps camera qualities like ortho, depth of field, angle of 
view and such are a special case.

Brent Gulanowski
--
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