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1 :	glk	1446	***************************************************
2 :			***************************************************
3 :			THIS TODO HAS BEEN MOVED TO THE DIDEROT WIKI:
4 :	nseltzer	1445
5 :	glk	1446	http://diderot-wiki.cs.uchicago.edu/index.php/Todo
6 :
7 :	jhr	1568	PLEASE USE THAT PAGE TO UPDATE PROBLEMS AND PROGRESS
8 :	glk	1446	***************************************************
9 :			***************************************************
10 :
11 :	glk	1162	NOTE: GLK's approximate ranking of 8 most important tagged with
12 :	jhr	1115	[GLK:1], [GLK:2], ...
13 :
14 :	glk	1156	========================
15 :			SHORT TERM ============= (*needed* for streamlines & tractography)
16 :			========================
17 :	jhr	1115
18 :	glk	1338	[GLK:2] Add sequence types (needed for evals & evecs)
19 :	jhr	1115	syntax
20 :			types: ty '{' INT '}'
21 :			value construction: '{' e1 ',' … ',' en '}'
22 :			indexing: e '{' e '}'
23 :
24 :	glk	1338	[GLK:3] evals & evecs for symmetric tensor[2,2] and
25 :	glk	1162	tensor[3,3] (requires sequences)
26 :
27 :	glk	1156	ability to emit/track/record variables into dynamically re-sized
28 :	glk	1389	runtime output buffer
29 :	jhr	1115
30 :	glk	1442	[GLK:4] tensor fields from tensor images: Initially need at least
31 :			convolution on tensor[2,2] and tensor[3,3] (the same component-wise
32 :			convolution as for vectors).
33 :	jhr	1115
34 :	glk	1156	========================
35 :	glk	1162	SHORT-ISH TERM ========= (to make using Diderot less annoying to
36 :			======================== program in, and slow to execute)
37 :	jhr	1115
38 :	glk	1167	Allow ".ddro" file extensions in addition to ".diderot"
39 :
40 :	glk	1204	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
43 :	glk	1167
44 :	glk	1338	[GLK:1] Proper handling of stabilize method
45 :	jhr	1115
46 :	glk	1442	Convolution on general tensor images (order > 2)
47 :
48 :	glk	1162	allow "*" to represent "modulate": per-component 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 :			implicit type promotion of integers to reals where reals are
54 :			required (e.g. not exponentiation "^")
55 :
56 :	glk	1442	[Nick working on this] Save Diderot output to nrrd, instead of "mip.txt"
57 :	jhr	1115	For grid of strands, save to similarly-shaped array
58 :			For list of strands, save to long 1-D (or 2-D for non-scalar output) list
59 :			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
61 :			to index into complete list
62 :
63 :	glk	1442	[GLK:6] ability to declare a field so that probe positions are
64 :	glk	1120	*always* "inside"; with various ways of mapping the known image values
65 :			to non-existant index locations. One possible syntax emphasizes that
66 :			there is a index mapping function that logically precedes convolution:
67 :	glk	1162	F = bspln3 ⊛ (img ◦ clamp)
68 :	glk	1120	F = bspln3 ⊛ (img ◦ repeat)
69 :			F = bspln3 ⊛ (img ◦ mirror)
70 :			where "◦" or "∘" is used to indicate function composition
71 :	jhr	1115
72 :	glk	1162	Level of differentiability in field type should be statement about how
73 :			much differentiation the program *needs*, rather than what the kernel
74 :			*provides*. The needed differentiability can be less than or equal to
75 :			the provided differentiability.
76 :
77 :	glk	1156	Use ∇⊗ etc. syntax
78 :			syntax [DONE]
79 :			typechecking
80 :			IL and codegen
81 :	jhr	1115
82 :	glk	1156	Add type aliases for color types
83 :			rgb = real{3}
84 :			rgba = real{4}
85 :	jhr	1115
86 :	glk	1389	Revisit how images are created within the language.
87 :	jhr	1568	The "load" operator should probably go away, and its strange
88 :	glk	1389	that strings are there only as a way to refer to nrrd filenames
89 :
90 :	jhr	1115	==============================
91 :	glk	1156	MEDIUM TERM ================== (*needed* for particles)
92 :	jhr	1115	==============================
93 :
94 :	glk	1442	[Lamont working on this] run-time birth of strands
95 :	jhr	1115
96 :			"initially" supports lists
97 :
98 :	glk	1254	"initially" supports lists of positions output from different
99 :			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 :			to another invocation of the same program)
102 :	jhr	1115
103 :	glk	1442	[Lamont working on this] Communication between strands: they have to
104 :			be able to learn each other's state (at the previous iteration).
105 :			Early version of this can have the network of neighbors be completely
106 :			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 :	jhr	1115
110 :	glk	1156	============================
111 :			MEDIUM-ISH TERM ============ (to make Diderot more useful/effective)
112 :			============================
113 :	jhr	1115
114 :	glk	1442	[GLK:5] Want code-generation 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 :	glk	1156	Python/ctypes interface to run-time
121 :	jhr	1115
122 :	glk	1156	support for Python interop and GUI
123 :	jhr	1115
124 :	glk	1162	Allow integer exponentiation ("^2") to apply to square matrices,
125 :			to represent repeated matrix multiplication
126 :
127 :	glk	1156	Put small 1-D and 2-D fields, when reconstructed specifically by tent
128 :			and when differentiation is not needed, into faster texture buffers.
129 :			test/illust-vr.diderot is good example of program that uses multiple
130 :			such 1-D fields basically as lookup-table-based function evaluation
131 :
132 :			extend norm (|exp|) to all tensor types [DONE for vectors and matrices]
133 :
134 :			determinant ("det") for tensor[3,3]
135 :
136 :	jhr	1115	add ":" for tensor dot product (contracts out two indices
137 :			instead of one like •), valid for all pairs of tensors with
138 :			at least two indices
139 :
140 :	glk	1156	test/uninit.diderot:
141 :			documents need for better compiler error messages when output variables
142 :			are not initialized; the current messages are very cryptic
143 :	jhr	1115
144 :			want: warnings when "D" (reserved for differentiation) is declared as
145 :			a variable name (get confusing error messages now)
146 :
147 :	glk	1156	==============================
148 :			LONG TERM ==================== (make Diderot more interesting/attractive from
149 :			============================== a research standpoint)
150 :	jhr	1115
151 :	glk	1156	IL support for higher-order tensor values (matrices, etc).
152 :			tensor construction [DONE]
153 :			tensor indexing [DONE]
154 :			tensor slicing
155 :	jhr	1115
156 :	glk	1156	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,
158 :			for example, we should lift strand-invariant variables to global
159 :			scope. Also prune out useless variables, which should include field
160 :			variables after the translation to mid-il.
161 :
162 :			test/vr-kcomp2.diderot: Add support for code like
163 :			(F1 if x else F2)@pos
164 :			This will require duplication of the continuation of the conditional
165 :			(but we should only duplicate over the live-range of the result of the
166 :			conditional.
167 :
168 :	glk	1338	[GLK:7] Want: non-trivial field expressions & functions.
169 :	glk	1162	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 :	glk	1156	image(2)[2] Vimg = load(...);
174 :			field#0(2)[] Vlen = |Vimg ⊛ bspln3|;
175 :	glk	1162	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 :	glk	1156	field#2(2)[] F = Fimg ⊛ bspln3;
180 :			field#0(2)[] Gmag = |∇F|;
181 :	glk	1162	scalar field of squared gradient magnitude (simpler to differentiate):
182 :	glk	1156	field#2(2)[] F = Fimg ⊛ bspln3;
183 :			field#0(2)[] Gmsq = ∇F•∇F;
184 :	glk	1162	There is value in having these, even if the differentiation of them is
185 :			not supported (hence the indication of "field#0" for these above)
186 :	glk	1156
187 :	jhr	1195	Introduce region types (syntax region(d), where d is the dimension of the
188 :			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 :	glk	1162	co- vs contra- index distinction
197 :	glk	1156
198 :	glk	1162	Permit field composition:
199 :	glk	1156	field#2(3)[3] warp = bspln3 ⊛ warpData;
200 :			field#2(3)[] F = bspln3 ⊛ img;
201 :			field#2(3)[] Fwarp = F ◦ warp;
202 :	glk	1162	So Fwarp(x) = F(warp(X)). Chain rule can be used for differentation.
203 :			This will be instrumental for expressing non-rigid registration
204 :			methods (but those will require co-vs-contra index distinction)
205 :	glk	1156
206 :	glk	1155	Allow the convolution to be specified either as a single 1D kernel
207 :			(as we have it now):
208 :			field#2(3)[] F = bspln3 ⊛ img;
209 :			or, as a tensor product of kernels, one for each axis, e.g.
210 :			field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img;
211 :	glk	1212	This is especially important for things like time-varying fields
212 :			and the use of scale-space in field visualization: one axis of the
213 :			must be convolved with a different kernel during probing.
214 :			What is very unclear is how, in such cases, we should notate the
215 :			gradient, when we only want to differentiate with respect to some
216 :			subset of the axes. One ambitious idea would be:
217 :	glk	1162	field#0(3)[] Ft = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; // 2D time-varying field
218 :	glk	1204	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 :	glk	1155
221 :	glk	1162	representation of tensor symmetry
222 :	jhr	1115	(have to identify the group of index permutations that are symmetries)
223 :
224 :			dot works on all tensors
225 :
226 :			outer works on all tensors
227 :
228 :	glk	1204	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 :	jhr	1115	Einstein summation notation
245 :
246 :			"tensor comprehension" (like list comprehension)
247 :
248 :	glk	1204	Fields coming from different sources of data:
249 :			* triangular or tetrahedral meshes over 2D or 3D domains (of the
250 :			source produced by finite-element 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 :	jhr	1115	======================
258 :			BUGS =================
259 :			======================
260 :
261 :			test/zslice2.diderot:
262 :			// HEY (bug) bspln5 leads to problems ...
263 :			// uncaught exception Size [size]
264 :			// raised at c-target/c-target.sml:47.15-47.19
265 :			//field#4(3)[] F = img ⊛ bspln5;
266 :	glk	1336

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