1 
NOTE: GLK's approximate ranking of 5 most important tagged with 
NOTE: GLK's approximate ranking of 8 most important tagged with 
2 
[GLK:1], [GLK:2], ... 
[GLK:1], [GLK:2], ... 
3 


4 
======================== 
======================== 
5 
SHORT TERM ============= (*needed* for streamlines & tractography) 
SHORT TERM ============= (*needed* for streamlines & tractography) 
6 
======================== 
======================== 
7 


8 
[GLK:1] Add sequence types (needed for evals & evecs) 
[GLK:3] Add sequence types (needed for evals & evecs) 
9 
syntax 
syntax 
10 
types: ty '{' INT '}' 
types: ty '{' INT '}' 
11 
value construction: '{' e1 ',' … ',' en '}' 
value construction: '{' e1 ',' … ',' en '}' 
12 
indexing: e '{' e '}' 
indexing: e '{' e '}' 
13 
[GLK:1] evals & evecs for symmetric tensor[3,3] (requires sequences) 

14 

[GLK:4] evals & evecs for symmetric tensor[2,2] and 
15 

tensor[3,3] (requires sequences) 
16 


17 
ability to emit/track/record variables into dynamically resized 
ability to emit/track/record variables into dynamically resized 
18 
runtime buffer 
runtime buffer 
20 
tensor fields: convolution on general tensor images 
tensor fields: convolution on general tensor images 
21 


22 
======================== 
======================== 
23 
SHORTISH TERM ========= (to make using Diderot less annoying/slow) 
SHORTISH TERM ========= (to make using Diderot less annoying to 
24 
======================== 
======================== program in, and slow to execute) 
25 


26 

valuenumbering optimization [DONE] 
27 


28 

Allow ".ddro" file extensions in addition to ".diderot" 
29 


30 

Be able to output values of type tensor[2,2] and tensor[3,3]; 
31 

(currently only scalars & vectors). Want to add some regression tests 
32 

based on this and currently can't 
33 


34 

[GLK:1] Add a clamp function, which takes three arguments; either 
35 

three scalars: 
36 

clamp(lo, hi, x) = max(lo, min(hi, x)) 
37 

or three vectors of the same size: 
38 

clamp(lo, hi, [x,y]) = [max(lo[0], min(hi[0], x)), 
39 

max(lo[1], min(hi[1], y))] 
40 

This would be useful in many current Diderot programs. 
41 

One question: clamp(x, lo, hi) is the argument order used in OpenCL 
42 

and other places, but clamp(lo, hi, x) is much more consistent with 
43 

lerp(lo, hi, x), hence GLK's preference 
44 


45 
valuenumbering optimization 
[GLK:2] Proper handling of stabilize method 
46 


47 
proper handling of stabilize method 
allow "*" to represent "modulate": percomponent multiplication of 
48 

vectors, and vectors only (not tensors of order 2 or higher). Once 
49 

sequences are implemented this should be removed: the operation is not 
50 

invariant WRT basis so it is not a legit vector computation. 
51 


52 
[GLK:2] Save Diderot output to nrrd, instead of "mip.txt" 
implicit type promotion of integers to reals where reals are 
53 

required (e.g. not exponentiation "^") 
54 


55 

[GLK:5] Save Diderot output to nrrd, instead of "mip.txt" 
56 
For grid of strands, save to similarlyshaped array 
For grid of strands, save to similarlyshaped array 
57 
For list of strands, save to long 1D (or 2D for nonscalar output) list 
For list of strands, save to long 1D (or 2D for nonscalar output) list 
58 
For ragged things (like tractography output), will need to save both 
For ragged things (like tractography output), will need to save both 
59 
complete list of values, as well as list of start indices and lengths 
complete list of values, as well as list of start indices and lengths 
60 
to index into complete list 
to index into complete list 
61 


62 
[GLK:3] Use of Teem's "hest" commandline parser for getting 
[GLK:6] Use of Teem's "hest" commandline parser for getting 
63 
any input variables that are not defined in the source file 
any "input" variables that are not defined in the source file. 
64 


65 
[GLK:4] ability to declare a field so that probe positions are 
[GLK:7] ability to declare a field so that probe positions are 
66 
*always* "inside"; with various ways of mapping the known image values 
*always* "inside"; with various ways of mapping the known image values 
67 
to nonexistant index locations. One possible syntax emphasizes that 
to nonexistant index locations. One possible syntax emphasizes that 
68 
there is a index mapping function that logically precedes convolution: 
there is a index mapping function that logically precedes convolution: 
69 
F = bspln3 ⊛ (img clamp) 
F = bspln3 ⊛ (img ◦ clamp) 
70 
F = bspln3 ⊛ (img ◦ repeat) 
F = bspln3 ⊛ (img ◦ repeat) 
71 
F = bspln3 ⊛ (img ◦ mirror) 
F = bspln3 ⊛ (img ◦ mirror) 
72 
where "◦" or "∘" is used to indicate function composition 
where "◦" or "∘" is used to indicate function composition 
73 



Use ∇⊗ etc. syntax 


syntax [DONE] 


typechecking 


IL and codegen 





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). 




74 
Level of differentiability in field type should be statement about how 
Level of differentiability in field type should be statement about how 
75 
much differentiation the program *needs*, rather than what the kernel 
much differentiation the program *needs*, rather than what the kernel 
76 
*provides*. The needed differentiability can be less than or equal to 
*provides*. The needed differentiability can be less than or equal to 
77 
the provided differentiability. 
the provided differentiability. 
78 


79 

Use ∇⊗ etc. syntax 
80 

syntax [DONE] 
81 

typechecking 
82 

IL and codegen 
83 


84 
Add type aliases for color types 
Add type aliases for color types 
85 
rgb = real{3} 
rgb = real{3} 
86 
rgba = real{4} 
rgba = real{4} 
93 


94 
"initially" supports lists 
"initially" supports lists 
95 


96 
"initially" supports lists of positions output from 
"initially" supports lists of positions output from different 
97 
different initalization Diderot program 
initalization Diderot program (or output from the same program; 
98 

e.g. using output of iso2d.diderot for one isovalue to seed the input 
99 

to another invocation of the same program) 
100 


101 
Communication between strands: they have to be able to learn each 
Communication between strands: they have to be able to learn each 
102 
other's state (at the previous iteration). Early version of this can 
other's state (at the previous iteration). Early version of this can 
113 


114 
support for Python interop and GUI 
support for Python interop and GUI 
115 


116 

Allow integer exponentiation ("^2") to apply to square matrices, 
117 

to represent repeated matrix multiplication 
118 


119 
Alow X *= Y, X /= Y, X += Y, X = Y to mean what they do in C, 
Alow X *= Y, X /= Y, X += Y, X = Y to mean what they do in C, 
120 
provided that X*Y, X/Y, X+Y, XY are already supported. 
provided that X*Y, X/Y, X+Y, XY are already supported. 
121 
Nearly every Diderot program would be simplified by this. 
Nearly every Diderot program would be simplified by this. 
164 
(but we should only duplicate over the liverange of the result of the 
(but we should only duplicate over the liverange of the result of the 
165 
conditional. 
conditional. 
166 


167 
[GLK:5] Want: nontrivial field expressions & functions: 
[GLK:8] Want: nontrivial field expressions & functions. 
168 

scalar fields from scalar fields F and G: 
169 

field#0(2)[] X = (sin(F) + 1.0)/2; 
170 

field#0(2)[] X = F*G; 
171 

scalar field of vector field magnitude: 
172 
image(2)[2] Vimg = load(...); 
image(2)[2] Vimg = load(...); 
173 
field#0(2)[] Vlen = Vimg ⊛ bspln3; 
field#0(2)[] Vlen = Vimg ⊛ bspln3; 
174 
to get a scalar field of vector length, or 
field of normalized vectors (for LIC and vector field feature extraction) 
175 

field#2(2)[2] F = ... 
176 

field#0(2)[2] V = normalize(F); 
177 

scalar field of gradient magnitude (for edge detection)) 
178 
field#2(2)[] F = Fimg ⊛ bspln3; 
field#2(2)[] F = Fimg ⊛ bspln3; 
179 
field#0(2)[] Gmag = ∇F; 
field#0(2)[] Gmag = ∇F; 
180 
to get a scalar field of gradient magnitude, or 
scalar field of squared gradient magnitude (simpler to differentiate): 
181 
field#2(2)[] F = Fimg ⊛ bspln3; 
field#2(2)[] F = Fimg ⊛ bspln3; 
182 
field#0(2)[] Gmsq = ∇F•∇F; 
field#0(2)[] Gmsq = ∇F•∇F; 
183 
to get a scalar field of squared gradient magnitude, which is simpler 
There is value in having these, even if the differentiation of them is 
184 
to differentiate. However, there is value in having these, even if 
not supported (hence the indication of "field#0" for these above) 

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. 

185 


186 
Permit fields composition, especially for warping images by a 
Introduce region types (syntax region(d), where d is the dimension of the 
187 
smooth field of deformation vectors 
region. One useful operator would be 
188 

dom : field#k(d)[s] > region(d) 
189 

Then the inside test could be written as 
190 

pos ∈ dom(F) 
191 

We could further extend this approach to allow geometric definitions of 
192 

regions. It might also be useful to do inside tests in world space, 
193 

instead of image space. 
194 


195 

co vs contra index distinction 
196 


197 

Permit field composition: 
198 
field#2(3)[3] warp = bspln3 ⊛ warpData; 
field#2(3)[3] warp = bspln3 ⊛ warpData; 
199 
field#2(3)[] F = bspln3 ⊛ img; 
field#2(3)[] F = bspln3 ⊛ img; 
200 
field#2(3)[] Fwarp = F ◦ warp; 
field#2(3)[] Fwarp = F ◦ warp; 
201 
So Fwarp(x) = F(warp(X)). Chain rule can be used for differentation 
So Fwarp(x) = F(warp(X)). Chain rule can be used for differentation. 
202 

This will be instrumental for expressing nonrigid registration 
203 

methods (but those will require covscontra index distinction) 
204 


205 
Allow the convolution to be specified either as a single 1D kernel 
Allow the convolution to be specified either as a single 1D kernel 
206 
(as we have it now): 
(as we have it now): 
207 
field#2(3)[] F = bspln3 ⊛ img; 
field#2(3)[] F = bspln3 ⊛ img; 
208 
or, as a tensor product of kernels, one for each axis, e.g. 
or, as a tensor product of kernels, one for each axis, e.g. 
209 
field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; 
field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; 
210 
This is especially important for things like timevarying data, or 
This is especially important for things like timevarying fields 
211 
other multidimensional fields where one axis of the domain is very 
and the use of scalespace in field visualization: one axis of the 
212 
different from the rest. What is very unclear is how, in such cases, 
must be convolved with a different kernel during probing. 
213 
we should notate the gradient, when we only want to differentiate with 
What is very unclear is how, in such cases, we should notate the 
214 
respect to some of the axes. 
gradient, when we only want to differentiate with respect to some 
215 

subset of the axes. One ambitious idea would be: 
216 

field#0(3)[] Ft = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; // 2D timevarying field 
217 

field#0(2)[] F = lambda([x,y], Ft([x,y,42.0])) // restriction to time=42.0 
218 

vec2 grad = ∇F([x,y]); // 2D gradient 
219 


220 

Tensors of order 3 (e.g. gradients of diffusion tensor fields, or 
221 

hessians of vector fields) and order 4 (e.g. Hessians of diffusion 
222 

tensor fields). 
223 


224 
co vs contra index distinction 
representation of tensor symmetry 




some indication of tensor symmetry 

225 
(have to identify the group of index permutations that are symmetries) 
(have to identify the group of index permutations that are symmetries) 
226 


227 
dot works on all tensors 
dot works on all tensors 
228 


229 
outer works on all tensors 
outer works on all tensors 
230 


231 

Help for debugging Diderot programs: need to be able to uniquely 
232 

identify strands, and for particular strands that are known to behave 
233 

badly, do something like printf or other logging of their computations 
234 

and updates. 
235 


236 

Permit writing dimensionally general code: Have some statement of the 
237 

dimension of the world "W" (or have it be learned from one particular 
238 

field of interest), and then able to write "vec" instead of 
239 

"vec2/vec3", and perhaps "tensor[W,W]" instead of 
240 

"tensor[2,2]/tensor[3,3]" 
241 


242 

Traits: all things things that have boilerplate code (especially 
243 

volume rendering) should be expressed in terms of the unique 
244 

computational core. Different kinds of streamline/tractography 
245 

computation will be another example, as well as particle systems. 
246 


247 
Einstein summation notation 
Einstein summation notation 
248 


249 
"tensor comprehension" (like list comprehension) 
"tensor comprehension" (like list comprehension) 
250 


251 

Fields coming from different sources of data: 
252 

* triangular or tetrahedral meshes over 2D or 3D domains (of the 
253 

source produced by finiteelement codes; these will come with their 
254 

own specialized kinds of reconstruction kernels, called "basis 
255 

functions" in this context) 
256 

* Large point clouds, with some radial basis function around each point, 
257 

which will be tuned by parameters of the point (at least one parameter 
258 

giving some notion of radius) 
259 


260 
====================== 
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261 
BUGS ================= 
BUGS ================= 
262 
====================== 
====================== 