Diff of /branches/pure-cfg/TODO

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	revision 1303, Fri Jun 10 21:39:54 2011 UTC	revision 1304, Fri Jun 10 21:44:33 2011 UTC
#	Line 1	Line 1
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).
	Level of differentiability in field type should be statement about how
	much differentiation the program *needs*, rather than what the kernel
	*provides*.  The needed differentiability can be less than or equal to
	the provided differentiability.
9
10	[GLK:1] Add sequence types (needed for evals & evecs)	[GLK:3] 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 higher-order 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 re-sized
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		SHORT-ISH TERM ========= (to make using Diderot less annoying to
26		========================  program in, and slow to execute)
27
28	expand trace in mid to low translation	value-numbering optimization [DONE]
29
30	value-numbering 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": per-component 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 similarly-shaped array	For grid of strands, save to similarly-shaped array
60	For list of strands, save to long 1-D (or 2-D for non-scalar output) list	For list of strands, save to long 1-D (or 2-D for non-scalar 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" command-line parser for getting	[GLK:6] Use of Teem's "hest" command-line 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 non-existant index locations.  One possible syntax emphasizes that	to non-existant 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:
#	Line 76	Line 74
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 re-sized	*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, X-Y are already supported.
	Nearly every Diderot program would be simplified by this.
81
82	Want: non-trivial field expressions & functions:	Introduce "∇•" and "∇×" operators
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 1-D and 2-D fields, when reconstructed specifically by tent
	and when differentiation is not needed, into faster texture buffers.
	test/illust-vr.diderot is good example of program that uses multiple
	such 1-D fields basically as lookup-table-based function evaluation
95	run-time birth of strands	run-time 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		MEDIUM-ISH TERM ============ (to make Diderot more useful/effective)
113		============================
114
115	spatial data structure that permits strands' queries of neighbors	Python/ctypes interface to run-time
116
117	proper handling of stabilize method	support for Python interop and GUI
118
119	test/vr-kcomp2.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, X-Y are already supported.
124		Nearly every Diderot program would be simplified by this.
125		[DONE]
126
127	This will require duplication of the continuation of the conditional	Put small 1-D and 2-D fields, when reconstructed specifically by tent
128	(but we should only duplicate over the live-range of the result of the	and when differentiation is not needed, into faster texture buffers.
129	conditional.	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		expand trace in mid to low translation [DONE]
133
134		extend norm (|exp|) to all tensor types [DONE for vectors and matrices]
135
136		determinant ("det") for tensor[3,3]
137
138	add ":" for tensor dot product (contracts out two indices	add ":" for tensor dot product (contracts out two indices
139	instead of one like •), valid for all pairs of tensors with	instead of one like •), valid for all pairs of tensors with
140	at least two indices	at least two indices
141
142	==============================	test/uninit.diderot:
143	other MEDIUM TERM ============	documents need for better compiler error messages when output variables
144	==============================	are not initialized; the current messages are very cryptic
145
146	want: warnings when "D" (reserved for differentiation) is declared as	want: warnings when "D" (reserved for differentiation) is declared as
147	a variable name (get confusing error messages now)	a variable name (get confusing error messages now)
148
	support for Python interop and GUI
	Python/ctypes interface to run-time
	==============================
	LONG TERM ====================
149	==============================	==============================
150		LONG TERM ==================== (make Diderot more interesting/attractive from
151		==============================  a research standpoint)
152
153		IL support for higher-order tensor values (matrices, etc).
154		tensor construction [DONE]
155		tensor indexing [DONE]
156		tensor slicing
157		verify that hessians work correctly [DONE]
158
159	Better handling of variables that determines the scope of a variable	Better handling of variables that determines the scope of a variable
160	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,
#	Line 161	Line 162
162	scope.  Also prune out useless variables, which should include field	scope.  Also prune out useless variables, which should include field
163	variables after the translation to mid-il.	variables after the translation to mid-il.
164
165		test/vr-kcomp2.diderot: Add support for code like
166		(F1 if x else F2)@pos
167		This will require duplication of the continuation of the conditional
168		(but we should only duplicate over the live-range of the result of the
169		conditional.
170
171		[GLK:8] Want: non-trivial field expressions & functions.
172		scalar fields from scalar fields F and G:
173		field#0(2)[] X = (sin(F) + 1.0)/2;
174		field#0(2)[] X = F*G;
175		scalar field of vector field magnitude:
176		image(2)[2] Vimg = load(...);
177		field#0(2)[] Vlen = |Vimg ⊛ bspln3|;
178		field of normalized vectors (for LIC and vector field feature extraction)
179		field#2(2)[2] F = ...
180		field#0(2)[2] V = normalize(F);
181		scalar field of gradient magnitude (for edge detection))
182		field#2(2)[] F = Fimg ⊛ bspln3;
183		field#0(2)[] Gmag = |∇F|;
184		scalar field of squared gradient magnitude (simpler to differentiate):
185		field#2(2)[] F = Fimg ⊛ bspln3;
186		field#0(2)[] Gmsq = ∇F•∇F;
187		There is value in having these, even if the differentiation of them is
188		not supported (hence the indication of "field#0" for these above)
189
190		Introduce region types (syntax region(d), where d is the dimension of the
191		region.  One useful operator would be
192		dom : field#k(d)[s] -> region(d)
193		Then the inside test could be written as
194		pos ∈ dom(F)
195		We could further extend this approach to allow geometric definitions of
196		regions.  It might also be useful to do inside tests in world space,
197		instead of image space.
198
199	co- vs contra- index distinction	co- vs contra- index distinction
200
201	some indication of tensor symmetry	Permit field composition:
202		field#2(3)[3] warp = bspln3 ⊛ warpData;
203		field#2(3)[] F = bspln3 ⊛ img;
204		field#2(3)[] Fwarp = F ◦ warp;
205		So Fwarp(x) = F(warp(X)).  Chain rule can be used for differentation.
206		This will be instrumental for expressing non-rigid registration
207		methods (but those will require co-vs-contra index distinction)
208
209		Allow the convolution to be specified either as a single 1D kernel
210		(as we have it now):
211		field#2(3)[] F = bspln3 ⊛ img;
212		or, as a tensor product of kernels, one for each axis, e.g.
213		field#0(3)[] F = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img;
214		This is especially important for things like time-varying fields
215		and the use of scale-space in field visualization: one axis of the
216		must be convolved with a different kernel during probing.
217		What is very unclear is how, in such cases, we should notate the
218		gradient, when we only want to differentiate with respect to some
219		subset of the axes.  One ambitious idea would be:
220		field#0(3)[] Ft = (bspln3 ⊗ bspln3 ⊗ tent) ⊛ img; // 2D time-varying field
221		field#0(2)[] F = lambda([x,y], Ft([x,y,42.0]))     // restriction to time=42.0
222		vec2 grad = ∇F([x,y]);                             // 2D gradient
223
224		Tensors of order 3 (e.g. gradients of diffusion tensor fields, or
225		hessians of vector fields) and order 4 (e.g. Hessians of diffusion
226		tensor fields).
227
228		representation of tensor symmetry
229	(have to identify the group of index permutations that are symmetries)	(have to identify the group of index permutations that are symmetries)
230
231	dot works on all tensors	dot works on all tensors
232
233	outer works on all tensors	outer works on all tensors
234
235		Help for debugging Diderot programs: need to be able to uniquely
236		identify strands, and for particular strands that are known to behave
237		badly, do something like printf or other logging of their computations
238		and updates.
239
240		Permit writing dimensionally general code: Have some statement of the
241		dimension of the world "W" (or have it be learned from one particular
242		field of interest), and then able to write "vec" instead of
243		"vec2/vec3", and perhaps "tensor[W,W]" instead of
244		"tensor[2,2]/tensor[3,3]"
245
246		Traits: all things things that have boilerplate code (especially
247		volume rendering) should be expressed in terms of the unique
248		computational core.  Different kinds of streamline/tractography
249		computation will be another example, as well as particle systems.
250
251	Einstein summation notation	Einstein summation notation
252
253	"tensor comprehension" (like list comprehension)	"tensor comprehension" (like list comprehension)
254
255		Fields coming from different sources of data:
256		* triangular or tetrahedral meshes over 2D or 3D domains (of the
257		source produced by finite-element codes; these will come with their
258		own specialized kinds of reconstruction kernels, called "basis
259		functions" in this context)
260		* Large point clouds, with some radial basis function around each point,
261		which will be tuned by parameters of the point (at least one parameter
262		giving some notion of radius)
263
264	======================	======================
265	BUGS =================	BUGS =================
266	======================	======================

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