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 
other SHORT TERM ============= (including needed for LIC) 
SHORT TERM ============= (*needed* for streamlines & tractography) 
6 
============================== 
======================== 
7 


8 
Add a clamp function, which takes three arguments; either three scalars: 
Remove CL from compiler 

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). 

9 


10 
Level of differentiability in field type should be statement about how 
[GLK:3] Add sequence types (needed for evals & evecs) 

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) 

11 
syntax 
syntax 
12 
types: ty '{' INT '}' 
types: ty '{' INT '}' 
13 
value construction: '{' e1 ',' … ',' en '}' 
value construction: '{' e1 ',' … ',' en '}' 
14 
indexing: e '{' e '}' 
indexing: e '{' e '}' 
15 


16 
IL support for higherorder tensor values (matrices, etc). 
[GLK:4] evals & evecs for symmetric tensor[2,2] and 
17 
tensor construction [DONE] 
tensor[3,3] (requires sequences) 

tensor indexing [DONE] 


tensor slicing 


verify that hessians work correctly [DONE] 

18 


19 
Use ∇⊗ etc. syntax 
ability to emit/track/record variables into dynamically resized 
20 
syntax [DONE] 
runtime buffer 

typechecking 


IL and codegen 

21 


22 
test/uninit.diderot: 
tensor fields: convolution on general tensor images 

documents need for better compiler error messages when output variables 


are not initialized; the current messages are very cryptic 

23 


24 
determinant ("det") for tensor[3,3] 
======================== 
25 

SHORTISH TERM ========= (to make using Diderot less annoying to 
26 

======================== program in, and slow to execute) 
27 


28 
expand trace in mid to low translation 
valuenumbering optimization [DONE] 
29 


30 
valuenumbering optimization 
Allow ".ddro" file extensions in addition to ".diderot" 
31 


32 
Add type aliases for color types 
Be able to output values of type tensor[2,2] and tensor[3,3]; 
33 
rgb = real{3} 
(currently only scalars & vectors). Want to add some regression tests 
34 
rgba = real{4} 
based on this and currently can't 
35 


36 
============================== 
[GLK:1] Add a clamp function, which takes three arguments; either 
37 
MEDIUM TERM ================== (including needed for streamlines & tractography) 
three scalars: 
38 
============================== 
clamp(lo, hi, x) = max(lo, min(hi, x)) 
39 

or three vectors of the same size: 
40 

clamp(lo, hi, [x,y]) = [max(lo[0], min(hi[0], x)), 
41 

max(lo[1], min(hi[1], y))] 
42 

This would be useful in many current Diderot programs. 
43 

One question: clamp(x, lo, hi) is the argument order used in OpenCL 
44 

and other places, but clamp(lo, hi, x) is much more consistent with 
45 

lerp(lo, hi, x), hence GLK's preference 
46 

[DONE] 
47 


48 

[GLK:2] Proper handling of stabilize method 
49 


50 

allow "*" to represent "modulate": percomponent multiplication of 
51 

vectors, and vectors only (not tensors of order 2 or higher). Once 
52 

sequences are implemented this should be removed: the operation is not 
53 

invariant WRT basis so it is not a legit vector computation. 
54 


55 
[GLK:1] evals & evecs for symmetric tensor[3,3] (requires sequences) 
implicit type promotion of integers to reals where reals are 
56 

required (e.g. not exponentiation "^") 
57 


58 
[GLK:2] Save Diderot output to nrrd, instead of "mip.txt" 
[GLK:5] Save Diderot output to nrrd, instead of "mip.txt" 
59 
For grid of strands, save to similarlyshaped array 
For grid of strands, save to similarlyshaped array 
60 
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 
61 
For ragged things (like tractography output), will need to save both 
For ragged things (like tractography output), will need to save both 
62 
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 
63 
to index into complete list 
to index into complete list 
64 


65 
[GLK:3] Use of Teem's "hest" commandline parser for getting 
[GLK:6] Use of Teem's "hest" commandline parser for getting 
66 
any input variables that are not defined in the source file 
any "input" variables that are not defined in the source file. 
67 


68 
[GLK:4] ability to declare a field so that probe positions are 
[GLK:7] ability to declare a field so that probe positions are 
69 
*always* "inside"; with various ways of mapping the known image values 
*always* "inside"; with various ways of mapping the known image values 
70 
to nonexistant index locations. One possible syntax emphasizes that 
to nonexistant index locations. One possible syntax emphasizes that 
71 
there is a index mapping function that logically precedes convolution: 
there is a index mapping function that logically precedes convolution: 
74 
F = bspln3 ⊛ (img ◦ mirror) 
F = bspln3 ⊛ (img ◦ mirror) 
75 
where "◦" or "∘" is used to indicate function composition 
where "◦" or "∘" is used to indicate function composition 
76 


77 
extend norm (exp) to all tensor types [DONE for vectors and matrices] 
Level of differentiability in field type should be statement about how 
78 

much differentiation the program *needs*, rather than what the kernel 
79 
ability to emit/track/record variables into dynamically resized 
*provides*. The needed differentiability can be less than or equal to 
80 
runtime buffer 
the provided differentiability. 




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, XY are already supported. 


Nearly every Diderot program would be simplified by this. 

81 


82 
Want: nontrivial field expressions & functions: 
Use ∇⊗ etc. syntax 
83 
image(2)[2] Vimg = load(...); 
syntax [DONE] 
84 
field#0(2)[] Vlen = Vimg ⊛ bspln3; 
typechecking 
85 
to get a scalar field of vector length, or 
IL and codegen 

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. 

86 


87 
tensor fields: convolution on general tensor images 
Add type aliases for color types 
88 

rgb = real{3} 
89 

rgba = real{4} 
90 


91 
============================== 
============================== 
92 
other MEDIUM TERM ============ (needed for particles) 
MEDIUM TERM ================== (*needed* for particles) 
93 
============================== 
============================== 
94 



Put small 1D and 2D fields, when reconstructed specifically by tent 


and when differentiation is not needed, into faster texture buffers. 


test/illustvr.diderot is good example of program that uses multiple 


such 1D fields basically as lookuptablebased function evaluation 




95 
runtime birth of strands 
runtime birth of strands 
96 


97 
"initially" supports lists 
"initially" supports lists 
98 


99 
"initially" supports lists of positions output from 
"initially" supports lists of positions output from different 
100 
different initalization Diderot program 
initalization Diderot program (or output from the same program; 
101 

e.g. using output of iso2d.diderot for one isovalue to seed the input 
102 

to another invocation of the same program) 
103 


104 

Communication between strands: they have to be able to learn each 
105 

other's state (at the previous iteration). Early version of this can 
106 

have the network of neighbors be completely static (for running one 
107 

strand/pixel image computations). Later version with strands moving 
108 

through the domain will require some spatial data structure to 
109 

optimize discovery of neighbors. 
110 


111 

============================ 
112 

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

============================ 
114 


115 
spatial data structure that permits strands' queries of neighbors 
Python/ctypes interface to runtime 
116 


117 
proper handling of stabilize method 
support for Python interop and GUI 
118 


119 
test/vrkcomp2.diderot: Add support for code like 
Allow integer exponentiation ("^2") to apply to square matrices, 
120 

to represent repeated matrix multiplication 
121 


122 
(F1 if x else F2)@pos 
Alow X *= Y, X /= Y, X += Y, X = Y to mean what they do in C, 
123 

provided that X*Y, X/Y, X+Y, XY are already supported. 
124 

Nearly every Diderot program would be simplified by this. 
125 


126 
This will require duplication of the continuation of the conditional 
Put small 1D and 2D fields, when reconstructed specifically by tent 
127 
(but we should only duplicate over the liverange of the result of the 
and when differentiation is not needed, into faster texture buffers. 
128 
conditional. 
test/illustvr.diderot is good example of program that uses multiple 
129 

such 1D fields basically as lookuptablebased function evaluation 
130 


131 

expand trace in mid to low translation 
132 


133 

extend norm (exp) to all tensor types [DONE for vectors and matrices] 
134 


135 

determinant ("det") for tensor[3,3] 
136 


137 
add ":" for tensor dot product (contracts out two indices 
add ":" for tensor dot product (contracts out two indices 
138 
instead of one like •), valid for all pairs of tensors with 
instead of one like •), valid for all pairs of tensors with 
139 
at least two indices 
at least two indices 
140 


141 
============================== 
test/uninit.diderot: 
142 
other MEDIUM TERM ============ 
documents need for better compiler error messages when output variables 
143 
============================== 
are not initialized; the current messages are very cryptic 
144 


145 
want: warnings when "D" (reserved for differentiation) is declared as 
want: warnings when "D" (reserved for differentiation) is declared as 
146 
a variable name (get confusing error messages now) 
a variable name (get confusing error messages now) 
147 



support for Python interop and GUI 





Python/ctypes interface to runtime 





============================== 


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

148 
============================== 
============================== 
149 

LONG TERM ==================== (make Diderot more interesting/attractive from 
150 

============================== a research standpoint) 
151 


152 

IL support for higherorder tensor values (matrices, etc). 
153 

tensor construction [DONE] 
154 

tensor indexing [DONE] 
155 

tensor slicing 
156 

verify that hessians work correctly [DONE] 
157 


158 
Better handling of variables that determines the scope of a variable 
Better handling of variables that determines the scope of a variable 
159 
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, 
161 
scope. Also prune out useless variables, which should include field 
scope. Also prune out useless variables, which should include field 
162 
variables after the translation to midil. 
variables after the translation to midil. 
163 


164 

test/vrkcomp2.diderot: Add support for code like 
165 

(F1 if x else F2)@pos 
166 

This will require duplication of the continuation of the conditional 
167 

(but we should only duplicate over the liverange of the result of the 
168 

conditional. 
169 


170 

[GLK:8] Want: nontrivial field expressions & functions. 
171 

scalar fields from scalar fields F and G: 
172 

field#0(2)[] X = (sin(F) + 1.0)/2; 
173 

field#0(2)[] X = F*G; 
174 

scalar field of vector field magnitude: 
175 

image(2)[2] Vimg = load(...); 
176 

field#0(2)[] Vlen = Vimg ⊛ bspln3; 
177 

field of normalized vectors (for LIC and vector field feature extraction) 
178 

field#2(2)[2] F = ... 
179 

field#0(2)[2] V = normalize(F); 
180 

scalar field of gradient magnitude (for edge detection)) 
181 

field#2(2)[] F = Fimg ⊛ bspln3; 
182 

field#0(2)[] Gmag = ∇F; 
183 

scalar field of squared gradient magnitude (simpler to differentiate): 
184 

field#2(2)[] F = Fimg ⊛ bspln3; 
185 

field#0(2)[] Gmsq = ∇F•∇F; 
186 

There is value in having these, even if the differentiation of them is 
187 

not supported (hence the indication of "field#0" for these above) 
188 


189 

Introduce region types (syntax region(d), where d is the dimension of the 
190 

region. One useful operator would be 
191 

dom : field#k(d)[s] > region(d) 
192 

Then the inside test could be written as 
193 

pos ∈ dom(F) 
194 

We could further extend this approach to allow geometric definitions of 
195 

regions. It might also be useful to do inside tests in world space, 
196 

instead of image space. 
197 


198 
co vs contra index distinction 
co vs contra index distinction 
199 


200 
some indication of tensor symmetry 
Permit field composition: 
201 

field#2(3)[3] warp = bspln3 ⊛ warpData; 
202 

field#2(3)[] F = bspln3 ⊛ img; 
203 

field#2(3)[] Fwarp = F ◦ warp; 
204 

So Fwarp(x) = F(warp(X)). Chain rule can be used for differentation. 
205 

This will be instrumental for expressing nonrigid registration 
206 

methods (but those will require covscontra index distinction) 
207 


208 

Allow the convolution to be specified either as a single 1D kernel 
209 

(as we have it now): 
210 

field#2(3)[] F = bspln3 ⊛ img; 
211 

or, as a tensor product of kernels, one for each axis, e.g. 
212 

field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; 
213 

This is especially important for things like timevarying fields 
214 

and the use of scalespace in field visualization: one axis of the 
215 

must be convolved with a different kernel during probing. 
216 

What is very unclear is how, in such cases, we should notate the 
217 

gradient, when we only want to differentiate with respect to some 
218 

subset of the axes. One ambitious idea would be: 
219 

field#0(3)[] Ft = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; // 2D timevarying field 
220 

field#0(2)[] F = lambda([x,y], Ft([x,y,42.0])) // restriction to time=42.0 
221 

vec2 grad = ∇F([x,y]); // 2D gradient 
222 


223 

Tensors of order 3 (e.g. gradients of diffusion tensor fields, or 
224 

hessians of vector fields) and order 4 (e.g. Hessians of diffusion 
225 

tensor fields). 
226 


227 

representation of tensor symmetry 
228 
(have to identify the group of index permutations that are symmetries) 
(have to identify the group of index permutations that are symmetries) 
229 


230 
dot works on all tensors 
dot works on all tensors 
231 


232 
outer works on all tensors 
outer works on all tensors 
233 


234 

Help for debugging Diderot programs: need to be able to uniquely 
235 

identify strands, and for particular strands that are known to behave 
236 

badly, do something like printf or other logging of their computations 
237 

and updates. 
238 


239 

Permit writing dimensionally general code: Have some statement of the 
240 

dimension of the world "W" (or have it be learned from one particular 
241 

field of interest), and then able to write "vec" instead of 
242 

"vec2/vec3", and perhaps "tensor[W,W]" instead of 
243 

"tensor[2,2]/tensor[3,3]" 
244 


245 

Traits: all things things that have boilerplate code (especially 
246 

volume rendering) should be expressed in terms of the unique 
247 

computational core. Different kinds of streamline/tractography 
248 

computation will be another example, as well as particle systems. 
249 


250 
Einstein summation notation 
Einstein summation notation 
251 


252 
"tensor comprehension" (like list comprehension) 
"tensor comprehension" (like list comprehension) 
253 


254 

Fields coming from different sources of data: 
255 

* triangular or tetrahedral meshes over 2D or 3D domains (of the 
256 

source produced by finiteelement codes; these will come with their 
257 

own specialized kinds of reconstruction kernels, called "basis 
258 

functions" in this context) 
259 

* Large point clouds, with some radial basis function around each point, 
260 

which will be tuned by parameters of the point (at least one parameter 
261 

giving some notion of radius) 
262 


263 
====================== 
====================== 
264 
BUGS ================= 
BUGS ================= 
265 
====================== 
====================== 