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# View of /branches/lamont/TODO

Sun May 8 14:43:30 2011 UTC (8 years, 3 months ago) by glk
Original Path: trunk/TODO
File size: 6989 byte(s)
more ideas
NOTE: GLK's approximate ranking of 5 most important tagged with
[GLK:1], [GLK:2], ...

==============================
other SHORT TERM =============  (including needed for LIC)
==============================

Add a clamp function, which takes three arguments; either three scalars:
clamp(x, minval, maxval)  = max(minval, min(maxval, x))
or three vectors of the same size:
clamp([x,y], minvec, maxvec)  = [max(minvec[0], min(maxvec[0], x)),
max(minvec[1], min(maxvec[1], y))]
This would be useful in many current Diderot programs.
One question: clamp(x, minval, maxval) is the argument order
used in OpenCL and other places, but clamp(minval, maxval, x)
would be more consistent with lerp(minout, maxout, x).

Level of differentiability in field type should be statement about how
much differentiation the program *needs*, rather than what the kernel
*provides*.  The needed differentiability can be less than or equal to
the provided differentiability.

[GLK:1] Add sequence types (needed for evals & evecs)
syntax
types: ty '{' INT '}'
value construction: '{' e1 ',' … ',' en '}'
indexing: e '{' e '}'

IL support for higher-order tensor values (matrices, etc).
tensor construction [DONE]
tensor indexing [DONE]
tensor slicing
verify that hessians work correctly [DONE]

Use ∇⊗ etc. syntax
syntax [DONE]
typechecking
IL and codegen

test/uninit.diderot:
documents need for better compiler error messages when output variables
are not initialized; the current messages are very cryptic

determinant ("det") for tensor[3,3]

expand trace in mid to low translation

value-numbering optimization

Add type aliases for color types
rgb = real{3}
rgba = real{4}

==============================
MEDIUM TERM ================== (including needed for streamlines & tractography)
==============================

[GLK:1] evals & evecs for symmetric tensor[3,3] (requires sequences)

[GLK:2] Save Diderot output to nrrd, instead of "mip.txt"
For grid of strands, save to similarly-shaped array
For list of strands, save to long 1-D (or 2-D for non-scalar output) list
For ragged things (like tractography output), will need to save both
complete list of values, as well as list of start indices and lengths
to index into complete list

[GLK:3] Use of Teem's "hest" command-line parser for getting
any input variables that are not defined in the source file

[GLK:4] ability to declare a field so that probe positions are
*always* "inside"; with various ways of mapping the known image values
to non-existant index locations.  One possible syntax emphasizes that
there is a index mapping function that logically precedes convolution:
F = bspln3 ⊛ (img ◦ clamp)
F = bspln3 ⊛ (img ◦ repeat)
F = bspln3 ⊛ (img ◦ mirror)
where "◦" or "∘" is used to indicate function composition

extend norm (|exp|) to all tensor types [DONE for vectors and matrices]

ability to emit/track/record variables into dynamically re-sized
runtime buffer

Want: allow X *= Y, X /= Y, X += Y, X -= Y to mean what they do in C,
provided that X*Y, X/Y, X+Y, X-Y are already supported.
Nearly every Diderot program would be simplified by this.

[GLK:5] Want: non-trivial field expressions & functions:
field#0(2)[] Vlen = |Vimg ⊛ bspln3|;
to get a scalar field of vector length, or
field#2(2)[] F = Fimg ⊛ bspln3;
field#0(2)[] Gmag = |∇F|;
to get a scalar field of gradient magnitude, or
field#2(2)[] F = Fimg ⊛ bspln3;
field#0(2)[] Gmsq = ∇F•∇F;
to get a scalar field of squared gradient magnitude, which is simpler
to differentiate.  However, there is value in having these, even if
the differentiation of them is not supported (hence the indication
of "field#0" for these above)

Want: ability to apply "normalize" to a field itself, e.g.
field#0(2)[2] V = normalize(Vimg ⊛ ctmr);
so that V(x) = normalize((Vimg ⊛ ctmr)(x)).
Having this would simplify expression of standard LIC method, and
would also help express other vector field expressions that arise
in vector field feature exraction.

tensor fields: convolution on general tensor images

==============================
other MEDIUM TERM ============ (needed for particles)
==============================

Put small 1-D and 2-D fields, when reconstructed specifically by tent
and when differentiation is not needed, into faster texture buffers.
test/illust-vr.diderot is good example of program that uses multiple
such 1-D fields basically as lookup-table-based function evaluation

run-time birth of strands

"initially" supports lists

"initially" supports lists of positions output from
different initalization Diderot program

spatial data structure that permits strands' queries of neighbors

proper handling of stabilize method

test/vr-kcomp2.diderot: Add support for code like

(F1 if x else F2)@pos

This will require duplication of the continuation of the conditional
(but we should only duplicate over the live-range of the result of the
conditional.

add ":" for tensor dot product (contracts out two indices
instead of one like •), valid for all pairs of tensors with
at least two indices

==============================
other MEDIUM TERM ============
==============================

want: warnings when "D" (reserved for differentiation) is declared as
a variable name (get confusing error messages now)

support for Python interop and GUI

Python/ctypes interface to run-time

Allow the convolution to be specified either as a single 1D kernel
(as we have it now):
field#2(3)[] F = bspln3 ⊛ img;
or, as a tensor product of kernels, one for each axis, e.g.
field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img;
This is especially important for things like time-varying data, or
other multi-dimensional fields where one axis of the domain is very
different from the rest.  What is very unclear is how, in such cases,
we should notate the gradient, when we only want to differentiate with
respect to some of the axes.

==============================
LONG TERM ====================
==============================

Better handling of variables that determines the scope of a variable
based on its actual use, instead of where the user defined it.  So,
for example, we should lift strand-invariant variables to global
scope.  Also prune out useless variables, which should include field
variables after the translation to mid-il.

co- vs contra- index distinction

some indication of tensor symmetry
(have to identify the group of index permutations that are symmetries)

dot works on all tensors

outer works on all tensors

Einstein summation notation

"tensor comprehension" (like list comprehension)

======================
BUGS =================
======================

test/zslice2.diderot:
// HEY (bug) bspln5 leads to problems ...
//  uncaught exception Size [size]
//    raised at c-target/c-target.sml:47.15-47.19
//field#4(3)[] F = img ⊛ bspln5;