CSG Virtual Machine

csgvm.txt

CSG virtual machine:

each register represents a 3D space with unspecified bounds, and has two parts:
    D: signed distance
        - typically internally stored as an interval over the selected region
          the program is applied to. holds a floating-point lower and upper bound.
    M: material
        - an N-element vector of linear interpolable floating-point values
            typically:
                - albedo: red, green, blue
                - roughness
                - metallic
                - emissive
                - etc.

for clarity, we'll refer to registers as spaces from now on.

the machine has at least three spaces, S0 as the main and S1 and S2 as spare 
spaces, to allow temporary creation and accumulation of shapes created using 
CSG intersection.

requirements for operations:
    each operation, or a contiguous list of operations must be cullable
    by an optimization process; while operations are always executed in order
    of declaration, culling optimizations test this list against repeatedly
    subdivided axis-aligned bounding boxes, and remove operations that do not
    contribute to surface creation or material changes.
    
    this means that operation output must always describe a surface and material;
    spaces should never store anything but intervals over a surface
    function and their associated materials. this is something to keep in mind 
    when designing new operations.

    it would also be useful to keep all operations in L2 metric, so the output
    of blending union / difference / intersection operations remains predictable
    for the user. this is however not a requirement of the VM.

these are known operand attribute names and associated types:
    SOURCE: register
    TARGET: register
    PRIMITIVE: integer
        typical choices:
            BOX
            ELLIPSOID
            CYLINDER
            TORUS
            etc.
    ORIGIN: 3 x float
    SIZE: 3 x float
    BASIS: 3 x float packed versor (|q| = 1)
    MATERIAL: N x float
    FEATHER: float

IR operations

%o = empty
%o = full
%o = primitive [prim size origin basis]
%o = material %x [material]
%o = add %a %b
%o = sub %a %b
%o = and %a %b
%o = sadd %a %b [feather]
%o = ssub %a %b [feather]
%o = sand %a %b [feather]