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NOTE: GLK's approximate ranking of 5 most important tagged with 
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THIS TODO HAS BEEN MOVED TO THE DIDEROT WIKI: 
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http://diderotwiki.cs.uchicago.edu/index.php/Todo 
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PLEASE USE THAT PAGE TO UPDATE PROBLEMS AND PROGRESS 
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11 

NOTE: GLK's approximate ranking of 8 most important tagged with 
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[GLK:1], [GLK:2], ... 
[GLK:1], [GLK:2], ... 
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14 
======================== 
======================== 
15 
SHORT TERM ============= (*needed* for streamlines & tractography) 
SHORT TERM ============= (*needed* for streamlines & tractography) 
16 
======================== 
======================== 
17 


18 
[GLK:1] Add sequence types (needed for evals & evecs) 
[GLK:2] Add sequence types (needed for evals & evecs) 
19 
syntax 
syntax 
20 
types: ty '{' INT '}' 
types: ty '{' INT '}' 
21 
value construction: '{' e1 ',' … ',' en '}' 
value construction: '{' e1 ',' … ',' en '}' 
22 
indexing: e '{' e '}' 
indexing: e '{' e '}' 
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[GLK:1] evals & evecs for symmetric tensor[3,3] (requires sequences) 

24 

[GLK:3] evals & evecs for symmetric tensor[2,2] and 
25 

tensor[3,3] (requires sequences) 
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27 
ability to emit/track/record variables into dynamically resized 
ability to emit/track/record variables into dynamically resized 
28 
runtime buffer 
runtime output buffer 
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30 
tensor fields: convolution on general tensor images 
[GLK:4] tensor fields from tensor images: Initially need at least 
31 

convolution on tensor[2,2] and tensor[3,3] (the same componentwise 
32 

convolution as for vectors). 
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34 
======================== 
======================== 
35 
SHORTISH TERM ========= (to make using Diderot less annoying/slow) 
SHORTISH TERM ========= (to make using Diderot less annoying to 
36 
======================== 
======================== program in, and slow to execute) 
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38 

Allow ".ddro" file extensions in addition to ".diderot" 
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40 

Be able to output values of type tensor[2,2] and tensor[3,3]; 
41 

(currently only scalars & vectors). Want to add some regression tests 
42 

based on this and currently can't 
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44 

[GLK:1] Proper handling of stabilize method 
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46 

Convolution on general tensor images (order > 2) 
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48 
valuenumbering optimization 
allow "*" to represent "modulate": percomponent multiplication of 
49 

vectors, and vectors only (not tensors of order 2 or higher). Once 
50 

sequences are implemented this should be removed: the operation is not 
51 

invariant WRT basis so it is not a legit vector computation. 
52 


53 
proper handling of stabilize method 
implicit type promotion of integers to reals where reals are 
54 

required (e.g. not exponentiation "^") 
55 


56 
[GLK:2] Save Diderot output to nrrd, instead of "mip.txt" 
[Nick working on this] Save Diderot output to nrrd, instead of "mip.txt" 
57 
For grid of strands, save to similarlyshaped array 
For grid of strands, save to similarlyshaped array 
58 
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 
59 
For ragged things (like tractography output), will need to save both 
For ragged things (like tractography output), will need to save both 
60 
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 
61 
to index into complete list 
to index into complete list 
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63 
[GLK:3] Use of Teem's "hest" commandline parser for getting 
[GLK:6] ability to declare a field so that probe positions are 

any input variables that are not defined in the source file 





[GLK:4] ability to declare a field so that probe positions are 

64 
*always* "inside"; with various ways of mapping the known image values 
*always* "inside"; with various ways of mapping the known image values 
65 
to nonexistant index locations. One possible syntax emphasizes that 
to nonexistant index locations. One possible syntax emphasizes that 
66 
there is a index mapping function that logically precedes convolution: 
there is a index mapping function that logically precedes convolution: 
67 
F = bspln3 ⊛ (img clamp) 
F = bspln3 ⊛ (img ◦ clamp) 
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F = bspln3 ⊛ (img ◦ repeat) 
F = bspln3 ⊛ (img ◦ repeat) 
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F = bspln3 ⊛ (img ◦ mirror) 
F = bspln3 ⊛ (img ◦ mirror) 
70 
where "◦" or "∘" is used to indicate function composition 
where "◦" or "∘" is used to indicate function composition 
71 



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). 




72 
Level of differentiability in field type should be statement about how 
Level of differentiability in field type should be statement about how 
73 
much differentiation the program *needs*, rather than what the kernel 
much differentiation the program *needs*, rather than what the kernel 
74 
*provides*. The needed differentiability can be less than or equal to 
*provides*. The needed differentiability can be less than or equal to 
75 
the provided differentiability. 
the provided differentiability. 
76 


77 

Use ∇⊗ etc. syntax 
78 

syntax [DONE] 
79 

typechecking 
80 

IL and codegen 
81 


82 
Add type aliases for color types 
Add type aliases for color types 
83 
rgb = real{3} 
rgb = real{3} 
84 
rgba = real{4} 
rgba = real{4} 
85 


86 

Revisit how images are created within the language. 
87 

The "load" operator should probably go away, and its strange 
88 

that strings are there only as a way to refer to nrrd filenames 
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90 
============================== 
============================== 
91 
MEDIUM TERM ================== (*needed* for particles) 
MEDIUM TERM ================== (*needed* for particles) 
92 
============================== 
============================== 
93 


94 
runtime birth of strands 
[Lamont working on this] runtime birth of strands 
95 


96 
"initially" supports lists 
"initially" supports lists 
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98 
"initially" supports lists of positions output from 
"initially" supports lists of positions output from different 
99 
different initalization Diderot program 
initalization Diderot program (or output from the same program; 
100 

e.g. using output of iso2d.diderot for one isovalue to seed the input 
101 
Communication between strands: they have to be able to learn each 
to another invocation of the same program) 
102 
other's state (at the previous iteration). Early version of this can 

103 
have the network of neighbors be completely static (for running one 
[Lamont working on this] Communication between strands: they have to 
104 
strand/pixel image computations). Later version with strands moving 
be able to learn each other's state (at the previous iteration). 
105 
through the domain will require some spatial data structure to 
Early version of this can have the network of neighbors be completely 
106 
optimize discovery of neighbors. 
static (for running one strand/pixel image computations). Later 
107 

version with strands moving through the domain will require some 
108 

spatial data structure to optimize discovery of neighbors. 
109 


110 
============================ 
============================ 
111 
MEDIUMISH TERM ============ (to make Diderot more useful/effective) 
MEDIUMISH TERM ============ (to make Diderot more useful/effective) 
112 
============================ 
============================ 
113 


114 

[GLK:5] Want codegeneration working for tensors of order three. 
115 

Order three matters for edge detection in scalar fields (to get 
116 

second derivatives of gradient magnitude), second derivatives 
117 

of vector fields (for some feature extraction), and first 
118 

derivatives of diffusion tensor fields. 
119 


120 
Python/ctypes interface to runtime 
Python/ctypes interface to runtime 
121 


122 
support for Python interop and GUI 
support for Python interop and GUI 
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124 
Alow X *= Y, X /= Y, X += Y, X = Y to mean what they do in C, 
Allow integer exponentiation ("^2") to apply to square matrices, 
125 
provided that X*Y, X/Y, X+Y, XY are already supported. 
to represent repeated matrix multiplication 

Nearly every Diderot program would be simplified by this. 

126 


127 
Put small 1D and 2D fields, when reconstructed specifically by tent 
Put small 1D and 2D fields, when reconstructed specifically by tent 
128 
and when differentiation is not needed, into faster texture buffers. 
and when differentiation is not needed, into faster texture buffers. 
129 
test/illustvr.diderot is good example of program that uses multiple 
test/illustvr.diderot is good example of program that uses multiple 
130 
such 1D fields basically as lookuptablebased function evaluation 
such 1D fields basically as lookuptablebased function evaluation 
131 



expand trace in mid to low translation 




132 
extend norm (exp) to all tensor types [DONE for vectors and matrices] 
extend norm (exp) to all tensor types [DONE for vectors and matrices] 
133 


134 
determinant ("det") for tensor[3,3] 
determinant ("det") for tensor[3,3] 
152 
tensor construction [DONE] 
tensor construction [DONE] 
153 
tensor indexing [DONE] 
tensor indexing [DONE] 
154 
tensor slicing 
tensor slicing 

verify that hessians work correctly [DONE] 

155 


156 
Better handling of variables that determines the scope of a variable 
Better handling of variables that determines the scope of a variable 
157 
based on its actual use, instead of where the user defined it. So, 
based on its actual use, instead of where the user defined it. So, 
165 
(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 
166 
conditional. 
conditional. 
167 


168 
[GLK:5] Want: nontrivial field expressions & functions: 
[GLK:7] Want: nontrivial field expressions & functions. 
169 

scalar fields from scalar fields F and G: 
170 

field#0(2)[] X = (sin(F) + 1.0)/2; 
171 

field#0(2)[] X = F*G; 
172 

scalar field of vector field magnitude: 
173 
image(2)[2] Vimg = load(...); 
image(2)[2] Vimg = load(...); 
174 
field#0(2)[] Vlen = Vimg ⊛ bspln3; 
field#0(2)[] Vlen = Vimg ⊛ bspln3; 
175 
to get a scalar field of vector length, or 
field of normalized vectors (for LIC and vector field feature extraction) 
176 

field#2(2)[2] F = ... 
177 

field#0(2)[2] V = normalize(F); 
178 

scalar field of gradient magnitude (for edge detection)) 
179 
field#2(2)[] F = Fimg ⊛ bspln3; 
field#2(2)[] F = Fimg ⊛ bspln3; 
180 
field#0(2)[] Gmag = ∇F; 
field#0(2)[] Gmag = ∇F; 
181 
to get a scalar field of gradient magnitude, or 
scalar field of squared gradient magnitude (simpler to differentiate): 
182 
field#2(2)[] F = Fimg ⊛ bspln3; 
field#2(2)[] F = Fimg ⊛ bspln3; 
183 
field#0(2)[] Gmsq = ∇F•∇F; 
field#0(2)[] Gmsq = ∇F•∇F; 
184 
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 
185 
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. 

186 


187 
Permit fields composition, especially for warping images by a 
Introduce region types (syntax region(d), where d is the dimension of the 
188 
smooth field of deformation vectors 
region. One useful operator would be 
189 

dom : field#k(d)[s] > region(d) 
190 

Then the inside test could be written as 
191 

pos ∈ dom(F) 
192 

We could further extend this approach to allow geometric definitions of 
193 

regions. It might also be useful to do inside tests in world space, 
194 

instead of image space. 
195 


196 

co vs contra index distinction 
197 


198 

Permit field composition: 
199 
field#2(3)[3] warp = bspln3 ⊛ warpData; 
field#2(3)[3] warp = bspln3 ⊛ warpData; 
200 
field#2(3)[] F = bspln3 ⊛ img; 
field#2(3)[] F = bspln3 ⊛ img; 
201 
field#2(3)[] Fwarp = F ◦ warp; 
field#2(3)[] Fwarp = F ◦ warp; 
202 
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. 
203 

This will be instrumental for expressing nonrigid registration 
204 

methods (but those will require covscontra index distinction) 
205 


206 
Allow the convolution to be specified either as a single 1D kernel 
Allow the convolution to be specified either as a single 1D kernel 
207 
(as we have it now): 
(as we have it now): 
208 
field#2(3)[] F = bspln3 ⊛ img; 
field#2(3)[] F = bspln3 ⊛ img; 
209 
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. 
210 
field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; 
field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; 
211 
This is especially important for things like timevarying data, or 
This is especially important for things like timevarying fields 
212 
other multidimensional fields where one axis of the domain is very 
and the use of scalespace in field visualization: one axis of the 
213 
different from the rest. What is very unclear is how, in such cases, 
must be convolved with a different kernel during probing. 
214 
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 
215 
respect to some of the axes. 
gradient, when we only want to differentiate with respect to some 
216 

subset of the axes. One ambitious idea would be: 
217 
co vs contra index distinction 
field#0(3)[] Ft = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; // 2D timevarying field 
218 

field#0(2)[] F = lambda([x,y], Ft([x,y,42.0])) // restriction to time=42.0 
219 

vec2 grad = ∇F([x,y]); // 2D gradient 
220 


221 
some indication of tensor symmetry 
representation of tensor symmetry 
222 
(have to identify the group of index permutations that are symmetries) 
(have to identify the group of index permutations that are symmetries) 
223 


224 
dot works on all tensors 
dot works on all tensors 
225 


226 
outer works on all tensors 
outer works on all tensors 
227 


228 

Help for debugging Diderot programs: need to be able to uniquely 
229 

identify strands, and for particular strands that are known to behave 
230 

badly, do something like printf or other logging of their computations 
231 

and updates. 
232 


233 

Permit writing dimensionally general code: Have some statement of the 
234 

dimension of the world "W" (or have it be learned from one particular 
235 

field of interest), and then able to write "vec" instead of 
236 

"vec2/vec3", and perhaps "tensor[W,W]" instead of 
237 

"tensor[2,2]/tensor[3,3]" 
238 


239 

Traits: all things things that have boilerplate code (especially 
240 

volume rendering) should be expressed in terms of the unique 
241 

computational core. Different kinds of streamline/tractography 
242 

computation will be another example, as well as particle systems. 
243 


244 
Einstein summation notation 
Einstein summation notation 
245 


246 
"tensor comprehension" (like list comprehension) 
"tensor comprehension" (like list comprehension) 
247 


248 

Fields coming from different sources of data: 
249 

* triangular or tetrahedral meshes over 2D or 3D domains (of the 
250 

source produced by finiteelement codes; these will come with their 
251 

own specialized kinds of reconstruction kernels, called "basis 
252 

functions" in this context) 
253 

* Large point clouds, with some radial basis function around each point, 
254 

which will be tuned by parameters of the point (at least one parameter 
255 

giving some notion of radius) 
256 


257 
====================== 
====================== 
258 
BUGS ================= 
BUGS ================= 
259 
====================== 
====================== 
263 
// uncaught exception Size [size] 
// uncaught exception Size [size] 
264 
// raised at ctarget/ctarget.sml:47.1547.19 
// raised at ctarget/ctarget.sml:47.1547.19 
265 
//field#4(3)[] F = img ⊛ bspln5; 
//field#4(3)[] F = img ⊛ bspln5; 
266 

