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} 
111 


112 
support for Python interop and GUI 
support for Python interop and GUI 
113 


114 

Allow integer exponentiation ("^2") to apply to square matrices, 
115 

to represent repeated matrix multiplication 
116 


117 
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, 
118 
provided that X*Y, X/Y, X+Y, XY are already supported. 
provided that X*Y, X/Y, X+Y, XY are already supported. 
119 
Nearly every Diderot program would be simplified by this. 
Nearly every Diderot program would be simplified by this. 
162 
(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 
163 
conditional. 
conditional. 
164 


165 
[GLK:5] Want: nontrivial field expressions & functions: 
[GLK:8] Want: nontrivial field expressions & functions. 
166 

scalar fields from scalar fields F and G: 
167 

field#0(2)[] X = (sin(F) + 1.0)/2; 
168 

field#0(2)[] X = F*G; 
169 

scalar field of vector field magnitude: 
170 
image(2)[2] Vimg = load(...); 
image(2)[2] Vimg = load(...); 
171 
field#0(2)[] Vlen = Vimg ⊛ bspln3; 
field#0(2)[] Vlen = Vimg ⊛ bspln3; 
172 
to get a scalar field of vector length, or 
field of normalized vectors (for LIC and vector field feature extraction) 
173 

field#2(2)[2] F = ... 
174 

field#0(2)[2] V = normalize(F); 
175 

scalar field of gradient magnitude (for edge detection)) 
176 
field#2(2)[] F = Fimg ⊛ bspln3; 
field#2(2)[] F = Fimg ⊛ bspln3; 
177 
field#0(2)[] Gmag = ∇F; 
field#0(2)[] Gmag = ∇F; 
178 
to get a scalar field of gradient magnitude, or 
scalar field of squared gradient magnitude (simpler to differentiate): 
179 
field#2(2)[] F = Fimg ⊛ bspln3; 
field#2(2)[] F = Fimg ⊛ bspln3; 
180 
field#0(2)[] Gmsq = ∇F•∇F; 
field#0(2)[] Gmsq = ∇F•∇F; 
181 
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 
182 
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. 

183 


184 
Permit fields composition, especially for warping images by a 
Introduce region types (syntax region(d), where d is the dimension of the 
185 
smooth field of deformation vectors 
region. One useful operator would be 
186 

dom : field#k(d)[s] > region(d) 
187 

Then the inside test could be written as 
188 

pos ∈ dom(F) 
189 

We could further extend this approach to allow geometric definitions of 
190 

regions. It might also be useful to do inside tests in world space, 
191 

instead of image space. 
192 


193 

co vs contra index distinction 
194 


195 

Permit field composition: 
196 
field#2(3)[3] warp = bspln3 ⊛ warpData; 
field#2(3)[3] warp = bspln3 ⊛ warpData; 
197 
field#2(3)[] F = bspln3 ⊛ img; 
field#2(3)[] F = bspln3 ⊛ img; 
198 
field#2(3)[] Fwarp = F ◦ warp; 
field#2(3)[] Fwarp = F ◦ warp; 
199 
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. 
200 

This will be instrumental for expressing nonrigid registration 
201 

methods (but those will require covscontra index distinction) 
202 


203 
Allow the convolution to be specified either as a single 1D kernel 
Allow the convolution to be specified either as a single 1D kernel 
204 
(as we have it now): 
(as we have it now): 
205 
field#2(3)[] F = bspln3 ⊛ img; 
field#2(3)[] F = bspln3 ⊛ img; 
206 
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. 
207 
field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; 
field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; 
208 
This is especially important for things like timevarying data, or 
This is especially important for things like timevarying fields 
209 
other multidimensional fields where one axis of the domain is very 
and the use of scalespace in field visualization: one axis of the 
210 
different from the rest. What is very unclear is how, in such cases, 
must be convolved with a different kernel during probing. 
211 
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 
212 
respect to some of the axes. 
gradient, when we only want to differentiate with respect to some 
213 

subset of the axes. One ambitious idea would be: 
214 

field#0(3)[] Ft = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; // 2D timevarying field 
215 

field#0(2)[] F = lambda([x,y], Ft([x,y,42.0])) // restriction to time=42.0 
216 

vec2 grad = ∇F([x,y]); // 2D gradient 
217 


218 

Tensors of order 3 (e.g. gradients of diffusion tensor fields, or 
219 

hessians of vector fields) and order 4 (e.g. Hessians of diffusion 
220 

tensor fields). 
221 


222 
co vs contra index distinction 
representation of tensor symmetry 




some indication of tensor symmetry 

223 
(have to identify the group of index permutations that are symmetries) 
(have to identify the group of index permutations that are symmetries) 
224 


225 
dot works on all tensors 
dot works on all tensors 
226 


227 
outer works on all tensors 
outer works on all tensors 
228 


229 

Help for debugging Diderot programs: need to be able to uniquely 
230 

identify strands, and for particular strands that are known to behave 
231 

badly, do something like printf or other logging of their computations 
232 

and updates. 
233 


234 

Permit writing dimensionally general code: Have some statement of the 
235 

dimension of the world "W" (or have it be learned from one particular 
236 

field of interest), and then able to write "vec" instead of 
237 

"vec2/vec3", and perhaps "tensor[W,W]" instead of 
238 

"tensor[2,2]/tensor[3,3]" 
239 


240 

Traits: all things things that have boilerplate code (especially 
241 

volume rendering) should be expressed in terms of the unique 
242 

computational core. Different kinds of streamline/tractography 
243 

computation will be another example, as well as particle systems. 
244 


245 
Einstein summation notation 
Einstein summation notation 
246 


247 
"tensor comprehension" (like list comprehension) 
"tensor comprehension" (like list comprehension) 
248 


249 

Fields coming from different sources of data: 
250 

* triangular or tetrahedral meshes over 2D or 3D domains (of the 
251 

source produced by finiteelement codes; these will come with their 
252 

own specialized kinds of reconstruction kernels, called "basis 
253 

functions" in this context) 
254 

* Large point clouds, with some radial basis function around each point, 
255 

which will be tuned by parameters of the point (at least one parameter 
256 

giving some notion of radius) 
257 


258 
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259 
BUGS ================= 
BUGS ================= 
260 
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====================== 