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




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). 

7 


8 
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) 

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 


14 
IL support for higherorder tensor values (matrices, etc). 
[GLK:4] evals & evecs for symmetric tensor[2,2] and 
15 
tensor construction [DONE] 
tensor[3,3] (requires sequences) 

tensor indexing [DONE] 


tensor slicing 


verify that hessians work correctly [DONE] 





Use ∇⊗ etc. syntax 


syntax [DONE] 


typechecking 


IL and codegen 

16 


17 
test/uninit.diderot: 
ability to emit/track/record variables into dynamically resized 
18 
documents need for better compiler error messages when output variables 
runtime buffer 

are not initialized; the current messages are very cryptic 

19 


20 
determinant ("det") for tensor[3,3] 
tensor fields: convolution on general tensor images 
21 


22 
expand trace in mid to low translation 
======================== 
23 

SHORTISH TERM ========= (to make using Diderot less annoying to 
24 

======================== program in, and slow to execute) 
25 


26 
valuenumbering optimization 
valuenumbering optimization 
27 


28 
Add type aliases for color types 
[GLK:1] Add a clamp function, which takes three arguments; either 
29 
rgb = real{3} 
three scalars: 
30 
rgba = real{4} 
clamp(lo, hi, x) = max(lo, min(hi, x)) 
31 

or three vectors of the same size: 
32 

clamp(lo, hi, [x,y]) = [max(lo[0], min(hi[0], x)), 
33 

max(lo[1], min(hi[1], y))] 
34 

This would be useful in many current Diderot programs. 
35 

One question: clamp(x, lo, hi) is the argument order used in OpenCL 
36 

and other places, but clamp(lo, hi, x) is much more consistent with 
37 

lerp(lo, hi, x), hence GLK's preference 
38 


39 
============================== 
[GLK:2] Proper handling of stabilize method 
40 
MEDIUM TERM ================== (including needed for streamlines & tractography) 

41 
============================== 
allow "*" to represent "modulate": percomponent multiplication of 
42 

vectors, and vectors only (not tensors of order 2 or higher). Once 
43 

sequences are implemented this should be removed: the operation is not 
44 

invariant WRT basis so it is not a legit vector computation. 
45 


46 
[GLK:1] evals & evecs for symmetric tensor[3,3] (requires sequences) 
implicit type promotion of integers to reals where reals are 
47 

required (e.g. not exponentiation "^") 
48 


49 
[GLK:2] Save Diderot output to nrrd, instead of "mip.txt" 
[GLK:5] Save Diderot output to nrrd, instead of "mip.txt" 
50 
For grid of strands, save to similarlyshaped array 
For grid of strands, save to similarlyshaped array 
51 
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 
52 
For ragged things (like tractography output), will need to save both 
For ragged things (like tractography output), will need to save both 
53 
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 
54 
to index into complete list 
to index into complete list 
55 


56 
[GLK:3] Use of Teem's "hest" commandline parser for getting 
[GLK:6] Use of Teem's "hest" commandline parser for getting 
57 
any input variables that are not defined in the source file 
any input variables that are not defined in the source file 
58 


59 
[GLK:4] ability to declare a field so that probe positions are 
[GLK:7] ability to declare a field so that probe positions are 
60 
*always* "inside"; with various ways of mapping the known image values 
*always* "inside"; with various ways of mapping the known image values 
61 
to nonexistant index locations. One possible syntax emphasizes that 
to nonexistant index locations. One possible syntax emphasizes that 
62 
there is a index mapping function that logically precedes convolution: 
there is a index mapping function that logically precedes convolution: 
65 
F = bspln3 ⊛ (img ◦ mirror) 
F = bspln3 ⊛ (img ◦ mirror) 
66 
where "◦" or "∘" is used to indicate function composition 
where "◦" or "∘" is used to indicate function composition 
67 


68 
extend norm (exp) to all tensor types [DONE for vectors and matrices] 
Level of differentiability in field type should be statement about how 
69 

much differentiation the program *needs*, rather than what the kernel 
70 
ability to emit/track/record variables into dynamically resized 
*provides*. The needed differentiability can be less than or equal to 
71 
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. 

72 


73 
[GLK:5] Want: nontrivial field expressions & functions: 
Use ∇⊗ etc. syntax 
74 
image(2)[2] Vimg = load(...); 
syntax [DONE] 
75 
field#0(2)[] Vlen = Vimg ⊛ bspln3; 
typechecking 
76 
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. 

77 


78 
tensor fields: convolution on general tensor images 
Add type aliases for color types 
79 

rgb = real{3} 
80 

rgba = real{4} 
81 


82 
============================== 
============================== 
83 
other MEDIUM TERM ============ (needed for particles) 
MEDIUM TERM ================== (*needed* for particles) 
84 
============================== 
============================== 
85 



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 




86 
runtime birth of strands 
runtime birth of strands 
87 


88 
"initially" supports lists 
"initially" supports lists 
90 
"initially" supports lists of positions output from 
"initially" supports lists of positions output from 
91 
different initalization Diderot program 
different initalization Diderot program 
92 


93 
spatial data structure that permits strands' queries of neighbors 
Communication between strands: they have to be able to learn each 
94 

other's state (at the previous iteration). Early version of this can 
95 

have the network of neighbors be completely static (for running one 
96 

strand/pixel image computations). Later version with strands moving 
97 

through the domain will require some spatial data structure to 
98 

optimize discovery of neighbors. 
99 


100 

============================ 
101 

MEDIUMISH TERM ============ (to make Diderot more useful/effective) 
102 

============================ 
103 


104 
proper handling of stabilize method 
Python/ctypes interface to runtime 
105 


106 
test/vrkcomp2.diderot: Add support for code like 
support for Python interop and GUI 
107 


108 
(F1 if x else F2)@pos 
Allow integer exponentiation ("^2") to apply to square matrices, 
109 

to represent repeated matrix multiplication 
110 


111 
This will require duplication of the continuation of the conditional 
Alow X *= Y, X /= Y, X += Y, X = Y to mean what they do in C, 
112 
(but we should only duplicate over the liverange of the result of the 
provided that X*Y, X/Y, X+Y, XY are already supported. 
113 
conditional. 
Nearly every Diderot program would be simplified by this. 
114 


115 

Put small 1D and 2D fields, when reconstructed specifically by tent 
116 

and when differentiation is not needed, into faster texture buffers. 
117 

test/illustvr.diderot is good example of program that uses multiple 
118 

such 1D fields basically as lookuptablebased function evaluation 
119 


120 

expand trace in mid to low translation 
121 


122 

extend norm (exp) to all tensor types [DONE for vectors and matrices] 
123 


124 

determinant ("det") for tensor[3,3] 
125 


126 
add ":" for tensor dot product (contracts out two indices 
add ":" for tensor dot product (contracts out two indices 
127 
instead of one like •), valid for all pairs of tensors with 
instead of one like •), valid for all pairs of tensors with 
128 
at least two indices 
at least two indices 
129 


130 
============================== 
test/uninit.diderot: 
131 
other MEDIUM TERM ============ 
documents need for better compiler error messages when output variables 
132 
============================== 
are not initialized; the current messages are very cryptic 
133 


134 
want: warnings when "D" (reserved for differentiation) is declared as 
want: warnings when "D" (reserved for differentiation) is declared as 
135 
a variable name (get confusing error messages now) 
a variable name (get confusing error messages now) 
136 


137 
support for Python interop and GUI 
============================== 
138 

LONG TERM ==================== (make Diderot more interesting/attractive from 
139 

============================== a research standpoint) 
140 


141 
Python/ctypes interface to runtime 
IL support for higherorder tensor values (matrices, etc). 
142 

tensor construction [DONE] 
143 

tensor indexing [DONE] 
144 

tensor slicing 
145 

verify that hessians work correctly [DONE] 
146 


147 

Better handling of variables that determines the scope of a variable 
148 

based on its actual use, instead of where the user defined it. So, 
149 

for example, we should lift strandinvariant variables to global 
150 

scope. Also prune out useless variables, which should include field 
151 

variables after the translation to midil. 
152 


153 

test/vrkcomp2.diderot: Add support for code like 
154 

(F1 if x else F2)@pos 
155 

This will require duplication of the continuation of the conditional 
156 

(but we should only duplicate over the liverange of the result of the 
157 

conditional. 
158 


159 

[GLK:8] Want: nontrivial field expressions & functions. 
160 

scalar fields from scalar fields F and G: 
161 

field#0(2)[] X = (sin(F) + 1.0)/2; 
162 

field#0(2)[] X = F*G; 
163 

scalar field of vector field magnitude: 
164 

image(2)[2] Vimg = load(...); 
165 

field#0(2)[] Vlen = Vimg ⊛ bspln3; 
166 

field of normalized vectors (for LIC and vector field feature extraction) 
167 

field#2(2)[2] F = ... 
168 

field#0(2)[2] V = normalize(F); 
169 

scalar field of gradient magnitude (for edge detection)) 
170 

field#2(2)[] F = Fimg ⊛ bspln3; 
171 

field#0(2)[] Gmag = ∇F; 
172 

scalar field of squared gradient magnitude (simpler to differentiate): 
173 

field#2(2)[] F = Fimg ⊛ bspln3; 
174 

field#0(2)[] Gmsq = ∇F•∇F; 
175 

There is value in having these, even if the differentiation of them is 
176 

not supported (hence the indication of "field#0" for these above) 
177 


178 

co vs contra index distinction 
179 


180 

Permit field composition: 
181 

field#2(3)[3] warp = bspln3 ⊛ warpData; 
182 

field#2(3)[] F = bspln3 ⊛ img; 
183 

field#2(3)[] Fwarp = F ◦ warp; 
184 

So Fwarp(x) = F(warp(X)). Chain rule can be used for differentation. 
185 

This will be instrumental for expressing nonrigid registration 
186 

methods (but those will require covscontra index distinction) 
187 


188 
Allow the convolution to be specified either as a single 1D kernel 
Allow the convolution to be specified either as a single 1D kernel 
189 
(as we have it now): 
(as we have it now): 
192 
field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; 
field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; 
193 
This is especially important for things like timevarying data, or 
This is especially important for things like timevarying data, or 
194 
other multidimensional fields where one axis of the domain is very 
other multidimensional fields where one axis of the domain is very 
195 
different from the rest. What is very unclear is how, in such cases, 
different from the rest, and hence must be treated separately when 
196 

it comes to convolution. What is very unclear is how, in such cases, 
197 
we should notate the gradient, when we only want to differentiate with 
we should notate the gradient, when we only want to differentiate with 
198 
respect to some of the axes. 
respect to some subset of the axes. One ambitious idea would be: 
199 

field#0(3)[] Ft = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; // 2D timevarying field 
200 
============================== 
field#0(2)[] F = lambda([x,y], Ft([x,y,42.0])) // restriction to time=42.0 
201 
LONG TERM ==================== 
vec2 grad = ∇F([x,y]); // 2D gradient 

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





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 strandinvariant variables to global 


scope. Also prune out useless variables, which should include field 


variables after the translation to midil. 





co vs contra index distinction 

202 


203 
some indication of tensor symmetry 
representation of tensor symmetry 
204 
(have to identify the group of index permutations that are symmetries) 
(have to identify the group of index permutations that are symmetries) 
205 


206 
dot works on all tensors 
dot works on all tensors 