This completes a deep and very challenging series of refactorings
with the goal to introduce support for **Parameters** into the Render invocation code.
A secondary goal was to re-assess the prototype code written thus far
and thereby to establish a standard processing scheme.
With these rearrangements, the `FeedManifold` is poised to act as **central link**
between the Render-Node invocation code and the actual Media-Processing code in a Library Plug-in
Up to this point, the existing code from the Prototype is still compilable, yet broken.
The __next step__ will be to harness the possible simplifications and enable
the actual invocation to work on arbitrary combinations of buffers and parameters,
enabled by the **compile-time use-case classification** now provided by `FeedManifold`
While basically the `FeedPrototype` could be created directly,
passing both the processing- and the parameter-functor, in practice
a two-step configuration can be expected, since the processing-functor
is built by the Library-Plug-in, while the parameter-functor is then
later added as decoration by the builder.
Thus we need the ability to ''collect configuration'' within the Level-2 builder,
which can be achieved by a ''cross-builder'' mechanic, where we create an adapted builder
from the augmented configuration. A similar approach is also used to add
the configuration of the custom allocator.
Added an extensive demo in the test, playing with several instances
to highlight the point where the parameter-functor is actually invoked.
Some further tweaks to the logic to allow using the `FeedPrototype` in the default setup,
where ''nothing shall be done with parameters...''
Provide the basic constructors and a type constructor in FeedManifold,
so that it is possible to install a ''processing functor'' into the prototype
and then drop off a copy into each new `FeedManifold`
With this additions, can now **demonstrate simple usage**
__Remark__: using the `DiagnosticBufferProvider` developed several years ago;
Seems to work well; however, when creating a new instance in the next test case,
we get a hard failure when the previous test case did not discard all buffers.
Not sure what to think about that
* for one, it is good to get an alarm, since actually there should not be any leak
* but on the other hand, `reset()` does imply IMHO „I want a clean slate“
Adding some code thus to clean out memory blocks marked as used.
When a test wants to check that all memory was released, there are tools to do so.
This basically completes the reworked implementation of the `FeedManifold`
An important aspect however is now separated out and still remains to be solved:
''how to configure and invoke a Parameter-Functor?''
This is one remaining tricky detail to be solved.
The underlying difficulty is architectural:
- the processing functor will be supplied by the Media-Lib-Plug-in
- while a functor to set parameters and automation will be added from another context
Yet both have to work together, and both together will determine the effective type of the ''Weaving Pattern''
Thus we'll have to get both functors somehow integrated into the Level-2-Builder,
yet we must be able first to pass this builder instance to the Library-Plug-in and then,
in a second step, another part of the Lumiera Builder logic will have to add the Parameter wiring.
The solution I'm proposing is to exploit the observation that in fact the processing functor
is stored as a kind of »Prototype« within the ''Weaving Pattern'' and will be ''copied'' from there
for each individual Render Node invocation. The reasons for this is, we want the optimiser
to see the full instantiation of the library function and thus get maximum leverage;
thus the code doing the actual call must see the functor or lambda to be able to inline it.
This leads to the idea to ''separate'' this »prototype« from the `FeedManifold`;
the latter thereby becomes mostly agnostic of parameter processing.
However, `FeedManifold` must then accept a copy of the parameter values
as constructor argument and pass it into its internal storage.
This forces yet another reorganisation of the class structure.
Basically the storage modules for `FeedManifold` are now prepared within a configuratiton class,
which actually helps to simplify the metaprogramming definitions and keeps the enclosing namespace clean.
Can now invoke the FeedManifold with
- either only one output buffer pointer
- or an input and output buffer pointer
With the new support tooling developed yesterday,
the decision logic is now stright-forward to express
__NOTE__ there is a known problem with type-handler registration in the `BufferProvider`;
basically all functors with the same signature are treated as ''identical type'',
which does not account for the fact that functors may hold captured data:
in the example here the second buffer is created with the constructor arguments
given to the first one, ignoring all further sets of similar arguments
Tuples and the ''C++ tuple protocol'' build upon variadic arguments
and are thus rather tedious to handle, especially in this situation here,
where the argument can ''sometimes be a tuple...''
Several years ago I made the observation that processing by explicit ''type sequences''
(Loki-style) is much simpler to handle and easier to lift to a generic level of processing.
Thus I'll attempt now to extract the ''iteration and extraction part'' of the logic into a new helper.
`lib::meta::ElmTypes<TUP>` allows to process all ''tuple-like types'' and generic ''type sequences'' uniformely
and enables to use both styles interchangably (btw, it is quite common to ''abuse'' `std::tuple` as a type sequence).
With this helper, we can now
- build a ''type sequence'' from any ''tuple-like'' object (and vice-versa)
- re-bind (i.e. transfer the template parameters to another template)
- apply some wrapper
- create AND / OR evaluations over the types
This changeset is a sketch how to switch the entire implementation of the ''Invocation Adatper''
over to a generic argument usage scheme. This requires the ability to
- detect if some argument is actually a ''structured type''
- investigate components of such a structured type to draw a distinction between »Buffer« and »Parameter«
- ''lift'' the implementation of simple values to work on tuples
- provide a way to ''bridge'' from ''tuple-style'' programming to ''array access''
As a building block, we use a new iteration-over-index construct,
based on an idea discussed in https://stackoverflow.com/q/53522781/444796
The trick is to pass a `std::integer_constant` to a λ-generic
This is a possible extension which frequently comes up again during the design of the Engine.
Basically, the `TypeHandler` in the metadata-descriptor used by the `BufferProvder` could capture
additional context-arguments, which are then later passed to an object instance embedded into the buffer.
Yesterday I attempted to use this feature for a simple demonstration in `NodeBasic_test`,
just to find out that passing additional constructor arguments to the capture fails with
a confusing compilation error message. This failure could be traced down to the function binder;
and what at first sight seemed to be a compiler error, turned out to be a quite logical limitation:
When we »close« some objects of the constructor, but delay the construction itself, we'll have to
store a copy in the constructor-λ. And this implies, that we'll have to change the types
used for instantiation of the compiler, so that the construction-function can be invoked
by passing references from the captured copy of the additional arguments.
When naively passing those forwarded arguments into the std::bind()-call,
the resulting functor will fail at instantiation, when the compiler attempts
to generate the function-call `operator()`
see: https://stackoverflow.com/q/30968573/444796
We have now a roughly complete classification of possible use cases.
The invocation can only produce output, process input to output,
and can optionally also accept parameters.
Moreover, each of these cases can require an arbitrary number of actual arguments.
To support all these drastically different case by a common scheme,
`FeedManifold` now uses a »storage slice« for output, input and parameters,
which can be configured at compile time.
TODO: there is an unresolved bug in the test-helper code for the `DiagnosticHeapBlockProvider`,
which prevents us to embed constructor arguments into a buffer descriptor
This is an attempt to rework gradually while keeping the existing code valid.
For the simple reason that the existing code is quite elaborate and difficult to re-orient.
Thus using a ''second branch,'' and sharing the traits template while expanding its capabilities
What I'm about to do amounts to a massive generalisation, which is tricky.
Instead of having a fixed array-style layout, we want to accept arbitrary and mixed arguments.
Notably, we want to give the ''actual Library Plug-in'' a lot of leeway for binding:
- optionally, the library might want to require **Parameters** (which is the reason for this change)
- moreover, accepting input-buffers shall now be optional, since many generation functions do not need them
- and on top of all this, we want to accept an arbitrary mix of types for each kind.
So conceptually we are switching from C-style arrays to tuples with full type safety
''this going to become quite nasty and technical, I'm afraid...''
Starting from a prototypical implementation,
where each »slot« in the function is directly connected to the corresponding lead / port,
the implementation of the `SimpleWeavingPattern` (as it was called previously) could be
augmented and adapted gradually — and seems well suited to cover most standard cases of ''media processing''
So a name change is mandated, and the code is also extracted and relocated, possibly even
to be combined with the code of the `InvocationAdapter`, thereby hopefully making the implementation more accessible
Generally speaking, ''weaving patterns'' take on the role of the prime extension point regarding `Port` implementation.
During Render Node invocation, automation parameter data must be maintained.
For the simple standard path, this just implies to store the ''absolute nominal Time''
directly in the invoking stack frame and let some parameter adaptors do the translation.
However, it is conceivable to have much more elaborate translation functions,
and thus we must be prepared to handle an arbitrary number of parameter slots,
where each slot has arbitrary storage requirements.
The conclusion is to start with an intrusive linked list of overflow buckets.
This is an attempt to take aim at the next step,
which is to fill in the missing part for an actual node invocation...
''...still fighting to get ahead, due to complexity of involced concerns...''
This was an extended digression into architecture planning,
which became necessary in order to suitably map out the role
for the `TurnoutSystem` — which can now be defined as ''mediator''
to connect and forward control- and parameter data while specific
render invocation proceeds through the render node network.
After the actual processing functions are defined,
the "next level" of test framework building is to find a way
how these bare bone operations can be used easily from a test
with the goal to ''build and invoke a Render-Node''
* we need some descriptor
* the bare bone operation must be packaged into an ''Invocation-Adapter''
* we need some means to configure variants of the setup
The overall goal is eventually to arrive at something akin to a ''»Dummy Media-processing Library«''
* this will offer some „Functionality“
* it will work on different ''kinds'' or ''flavours'' of data
* it should provide operations that can be packaged into ''Nodes''
However — at the moment I have no clue how to get there...
And thus I'll start out with some rather obvious basic data manipulation functions,
and then try to give them meaningful names and descriptors. This in turn
will allow to build some multi-step processing netwaorks — which actually
is the near-term goal for the ''main effort'' (which is after all, to get
the Render Node code into some sufficient state of completion)...
Bugfix: should use the full bit-range for randomised data in `TestFrame`
Bugfix: prevent division by zero for approximate floatingpoint equality
...and use the new zip()-itertor to simplify the loops
* based on reproducible data in `TestFrame`
* using Murmur64A hash-chaining to »mark« with a parameter
This emulates the simplest case of 1:1 processing and can also be applied ''in-place''
For simplified tests there is a helper function to attain a reference to some `TestFrame` data, created on-demand and maintained in a repository in heap memory.
This storage has now be switched to `std::deque`
* provided addresses are stable
* less memory waste
__note__: `TestFrame::reseed()` will discard this repository, and draw a new (reproducible) seed.
Since each `TestFrame` now has a metadata header,
we can store an additional data checksum there,
so that it is now possible both to detect if data
is in pristine state, or if it matches a changed state
recorded in the additional checksum.
So we have now three different levels of verification
isSane:: consistent metadata header found
isValid:: metadata header found and checksum there matches data
isPristine:: in addition, the data is exactly as generated from the `(frameNr,family)`
Change data layout to place a metadata record ''behind the'' payload data,
and add a checksum to allow for validating dummy calculations and also
detect data corruption on data modified after initial generation.
By virtue of a marker data word, the presence of a valid metadata record can be confirmed.
Based on the recent work it is now possible to generate reproducible yet randomly distributed data content.
A new `TestFrame::reseed()` operation is introduced, which attaches to the `lib::defaultGen`
Using the linear-congruential engine for the actual data generation.
* Lumiera source code always was copyrighted by individual contributors
* there is no entity "Lumiera.org" which holds any copyrights
* Lumiera source code is provided under the GPL Version 2+
== Explanations ==
Lumiera as a whole is distributed under Copyleft, GNU General Public License Version 2 or above.
For this to become legally effective, the ''File COPYING in the root directory is sufficient.''
The licensing header in each file is not strictly necessary, yet considered good practice;
attaching a licence notice increases the likeliness that this information is retained
in case someone extracts individual code files. However, it is not by the presence of some
text, that legally binding licensing terms become effective; rather the fact matters that a
given piece of code was provably copyrighted and published under a license. Even reformatting
the code, renaming some variables or deleting parts of the code will not alter this legal
situation, but rather creates a derivative work, which is likewise covered by the GPL!
The most relevant information in the file header is the notice regarding the
time of the first individual copyright claim. By virtue of this initial copyright,
the first author is entitled to choose the terms of licensing. All further
modifications are permitted and covered by the License. The specific wording
or format of the copyright header is not legally relevant, as long as the
intention to publish under the GPL remains clear. The extended wording was
based on a recommendation by the FSF. It can be shortened, because the full terms
of the license are provided alongside the distribution, in the file COPYING.
⚠ __This is a problematic decision__
It temporarily **breaks compatibility with 32bit** until this issue is resolved.
== Explanation ==
Lumiera relies on a mix of the Standard library and Lib-Boost for calculation of hash values.
Before C++11, the Standard did not support and hashtable implementation; meanwhile, we
got several hash based containers in the STL and a framework for hashes,
which unfortunately is incomplete and cumbersome to use.
The C++ Committee has spend endless discussions and was not able to settle
on a convincing solution without major drawbacks regarding one aspect or the other.
This situation is problematic, since Lumiera relies heavily on the technique
of building stable systematic identifiers based on chained hash values.
It is thus essential to use a strong, reliable and portable hash function.
But unfortunately...
* the standard-fallback solution is known to be weak.
* Lib-Boost automatically uses stronger implementations for 64bit systems
* this implies that Hash-Values **are non-portable**
As the Lumiera project currently has no developer time to expend on such a
difficult and deep topic of fundamental research, today I decided to go down
the path of least resistance and **effectively abandon any system
that can not compile and use the 64bit `hash_combine` implementation.
This changeset extracts code from Lib-Boost 1.67 and adds a static assertion
to **break compilation** on non-64bit-platforms (whatever this means)
* most usages are drop-in replacements
* occasionally the other convenience functions can be used
* verify call-paths from core code to identify usages
* ensure reseeding for all tests involving some kind of randomness...
__Note__: some tests were not yet converted,
since their usage of randomness is actually not thread-safe.
This problem existed previously, since also `rand()` is not thread safe,
albeit in most cases it is possible to ignore this problem, as
''garbled internal state'' is also somehow „random“
...to the base-class of all tests
* `seedRand()` shall be invoked by every test using randomisation
* it will draw a new seed for the implicit default-PRNG
* it will document this seed value
* but when a seed was given via cmdline, it will inject that instead
* `makeRandGen()` will create a new dedicated generator instance,
attached (by seeding) to the current default-PRNG
It is not clear yet how to pass the actual `SeedNucleus`, which
for obvious reasons must be maintained by the `test::Suite`
This is the first step towards a »Test Domain Ongology« #1372,
which is a systematic arrangement of test-dummy functionality assumed
to mirror the actual media processing functionality present in external libs.
Each media-processing library not only provides functions to crunch data,
but also establishes a framework of entities and classification to determine
what »media« is an how it is structured and can be generated, transformed
and qualified. Since a essential goal for Lumiera is to be **library agnostic,**
it is important to avoid naïvely to take some popular library's choices
as universal truth regarding structure and nature of »media« as such.
Rather, the architecture of the Lumiera Render Engine must be kept
sufficiently open to accommodate the working style of various libraries,
even ones not known today.
To validate this architectural openness, we use a set of test functions
unrelated to any existing library to validate access to and usage of
rendering functionality — followed by further steps to adopt existing
popular libraries like **FFmpeg** or **Gstreamer**, without tilting
the basic structure of the Render Engine one way or the other.
showing the Node-symbol and a reduced rendering of
either the predecessor or a collection of source nodes.
For this we need functionality to traverse the node graph depth-first
and collect all leaf nodes (which are the source nodes without predecessor);
such can be implemented with the help of the expandAll() functionality
of `lib::IterExplorer`. In addition we need to collect, sort and deduplicate
all the source-node specs; since this is a common requirement, a new
convenience builder was added to `lib::IterExplorer`
...taking into account the prospecive usage context
where the builder expressions will be invoked from within
a media-library plug-in, using std::string_view to pass
the symbolic information seems like a good fit, because
the given spec will typically be assembled from some
building blocks, and thus in itself not be literal data.
Building a precise Frame Cache is a tough job, and is doomed to fail
when attempting to tie cache invalidation to state changes. The only
viable path is to create a system of systematic tagging of processing
steps, and use this as foundation for chained hash values, linked
in accordance to the actual processing structure.
This is complicated by the secondary concern of maintaining memory efficacy
for the render node model, which can be expected to grow to massive scale.
And even while this invocation can not be fully devised right now,
an attempt can be made to build a foundation that is not outright
wasteful, by detaching the logical information from the specific
weaving pattern used for implementation, and by minimising the
representation in memory and computing the compound information
on-demand....
The immediate next goal is to verify properties of render nodes
generated by the builder framework; two kinds of validations
can be distinguished
* structural aspects of the wiring
* the fact that processing functionality is invoked in proper order
Looking into the structural aspects brings about the necessity
to identify the actual processing function bound into some functor.
Some recapitulation of goals and requirements revealed, that this
can not be a merely technical identity record — because the intention
is to base the ''cache key'' on chained processing node identities,
so that the key is stable as long as the user-visible results will be
equivalent. And while structural data can be aggregated, at the
core this information must be provided by the scheme embedded
into the domain ontology, which is tasked with invoking the
builder in order to implement a ''specific processing-asset''
Review the achievements from the last days and map out the further path
for test-driven build-up of a render-node network and invocation.
Notably ''several layers of prototyping'' are in the works now;
it is important to understand the purpose of each such round of
prototyping and to draw the necessary conclusions after closing out.
The next topic to investigate relates to the ''identity'' of nodes and
ports within nodes; this entails to generate a ''symbolic spec'' that
can be verified and used as base for a systematic hash-ID and cache-key...
Since it would in fact be possible to access and write beyond the configured storage,
simply by using the builder API without considering consistency,
it seems advisable to use explicit runtime checks here, instead of
only assertions, and to throw an exception when violating bounds.
Moreover, unsuccessfully attempted to better arrange the functionality
between PortBuilder and WeavingBuilder; seemingly we have an rather tight
coupling here, and also the expectations regarding the processing function
seem to be too tight (but that's the reason why it's an prototype...)
- the chaining constructor is picked reliably when the
slicing is done by a direct static_cast
- the function definition can be passed reliably in all cases
after it has been ''decayed,'' which is done here simply by
taking it by-value. This is adequate, since the function
definition must be copied / inlined for each invocation.
With these fixes, the simplest test case now for the first time
**runs through without failure**
This change allows to disentangle the usages of `lib::SeveralBuilder`,
so that at any time during the build process only a single instance is
actively populated, all in one row — and thus the required storage can
either be pre-allocated, or dynamically extended and shrinked (when
filling elements into the last `SeveralBuilder` currently activated)
By packaging into a λ-closure, the building of the actual `Port`
implementation objects (≙ `Turnout` instances) is delayed until the
very end of the build process, and then unloaded into yet another
`lib::Several` in one strike. Temporarily, those building functor
objects are „hidden“ in the current stack frame, as a new `NodeBuilder`
instance is dropped off with an adapted type parameter (embedding the
λ-type produced by the last nested `PortBuilder` invocation, while
inheriting from previous ones.
However, defining a special constructor to cause this »chaining«
poses some challenge (regarding overload resolution). Moreover,
since the actual processing function shall be embedded directly
(as opposed to wrapping it into a `std::function`), further problems
can arise when this function is given as a ''function reference''
...and as expected, this turns up quite some inconsistencies,
especially regarding usage of the »buffer types«.
Basically, the `PortBuilder` is responsible for the high-level functionality
and thus must ensure the nested `WiringBuilder` is addressed and parameterised
properly to connect all »slots« of the processing function.
- can use a helper function in the WiringBuilder to fill in connections
- but the actual buffer types passed over these connectinos are totally
unchecked at that level, and can not see yet how this danger can be
mitigated one level above, where the PortBuilder is used.
- it is still unclear what a »buffer type« actually means; it could
be the pointer type, but it could also imply a class or struct type
to be emplaced into the buffer, which is a special extension to the
`BufferProvider` protocol, yet seems to be used here rather to transport
specific data types required by the actual media handling library (e.g. FFmpeg)
__Analysis__: what kind of verifications are sensible to employ
to cover building, wiring and invocation of render nodes?
Notably, a test should cover requirements and observable functionality,
while ''avoiding direct hard coupling to implementation internals...''
__Draft__: the most simple node builder invocation conceivable...
Code clean-up: mark all buffers with a dedicated tagging type
The point in question is: if we work the LocalTag into the type-hash,
could it be possible to miss an existing entry in the metadata registry?
This could cause two entries to be locked for a single buffer address,
leading to data corruption.
As far as I can see, in the current usage this would not happen,
but unfortunately this problem can not be ruled out, since the BufferProvider
API and protocol is designed to be open for various usage patterns.
However, the same potentially disastrous pattern could also materialise
when registering two different buffer types, and then locking each
for the same buffer location.
...this is a surprisingly tricky issue, since it undercuts the
generic and recursive implementation of buffer handling;
fortunately I've foreseen such demands may arise down the road
and I've reserved an »Local Key« (now renamed into `LocalTag`),
whose meaning is implementation defined and interpreted by
the specific `BufferProvider`
It became clear that a secondary system of connections must be added,
running top-down from a global model context, and thus contrary to the
regular orientation of the node network, which connects upwards from
predecessor to successor, in accordance with the pull principle.
If we accept this wiring as part of the primary structure, it can be
established immediately while building the nodes, thus adding a preconfigured
''pattern of Buffer Descriptors'' to each node, since there is no further
''moving part'' — beyond the wiring to the `BufferProvider`, which thus
becomes part of a global `ModelContext`
As an immediate consequence, the storage for this configuraion should
also be switched to `lib::Several` and handled similar to the primary
node wiring in the Builder...
...especially what is necessary to represent at this level and what information
is implicit; notably there will be an implicit default wiring, but we allow
for case-by-case deviations
To escape a possible deadlock in analysis, I resort to developing
some kind of free-wheeling presupposition how the **Builder** could
be implemented — a centrepiece of the Lumiera architecture envisioned
thus far — which ''unfortunately'' can only be planned and developed
in a more solid way ''after'' the current »Vertical Slice« is completed.
Thus I find myself in the uncomfortable situation of having to work towards
a core piece, which can not yet be built, since it relies heavily on
the very structures to be built...
