Note: the actual root cause, why this re-entrance happens,
is due to another obvious numerics bug not yet solved.
Here, the canvas width was suddenly set to zero, causing
the scrollbar position to change and thus the ZoomWindow
to re-fire the structure change signal.
However, such invalidation of previously established baseline
values can never be totally excluded in advanced layout calculations,
and thus the evaluation mechanism must be prepared and re-triggered
to start over, until a stable layout is achieved.
- rearrange cell content and disable auto-expand to prevent
the content area from becoming oversized initially
- fix autocompletion error in signal binding,
causing segfault when moving the scrollbar
attempting to get the vertical space allocation in header and content area
synchronised; previously we conflated the content size and additional
padding, but even after distinguishing both, we still get a cyclic
dependency, leading to progressive increasing of allocated size...
After quite some tinkering, instead of extending the DisplayManager interface,
I now prefer to treat this connection rather as an intricate implementation detail:
The TimelineLayout implementatino now provides two translation functions,
which are directly wired as slots from the Signals emitted by moving the
hand of the scrollbar; the idea is that these functions mutate the ZoomWindow,
which then triggers a DisplayEvaltuation, which in turn causes the
drawing code to pick up and translate back the new metric and position.
Results look promising, insofar the DisplayEvaluation is now triggered
repeatedly, and the actual window width in pixel is propagated;
however, the response of the layout code is seemingly random at times,
the allocated height grows monontonously and the code Segfaults when
moving the scrollbar...
this makes the arrangement more symmetric and natural
and also makes the overview ruler scroll alongside the content pane,
thereby creating the (intended) impression of one uniform layout space
As it turns out, this happens as side-effect from the workaround 2019-08-22
fc5eaf857c
Obviously, just set_size() on the canvas is not sufficient for
GTK actually to establish a size-request (seemingly the canvas counts
as /empty/ and only real widgets would make a difference).
However, since the ruler canvas is directly placed into the box,
and not adapted by a ScrolledWindow, explicitly set_size_request()
also causes the enclosing Box to "inherit" this minimal required size,
thereby also spreading out the BodyCanvasWidget beyond the size
actually available. GTK handles this situation by hard-clipping
on the right side, which causes the vertical scrollbar to disappear
and keeps the horizontal scrollbar disabled (since nominally it still
spans the whole size available, even while this size is then clipped
subsequently).
This changeset adds a lot of debug printing and demonstrates this
behaviour by setting only a minimal horizontal size_request, so that
the window is no longer expanded and clipped.
This does not really change the logic of the DisplayEvaluation mechanism,
but makes it much more flexible: instead of having two hard wired components,
the DisplayEvaluation visitor now holds a collection of LayoutElement pointers.
This way, the Layout manager itself (on behalf of the ZoomWindow) can
participate in the process, and on activation will now establish the
window width in pixel.
This works now insofar the drawing on the canvas is adapted coherently;
however something with the setup of the Scrollbar is still not quite right;
some time ago I recall the scrollbar worked, but now it is blocked
and the canvas just clips to the right side.
It is now tied to the start of ZoomWindow::overallSpan(),
thereby defining the (technical) pixel coordinates within the window
and for drawing on the canvas to be always positive. Whenever ZoomWindow
re-calibrates, it's change signal will trigger, causing the
TimelineLayout to perform a new DisplayEvaluationPass,
which in turn prompts all embedded widgets to readjust
their positions accordingly.
Note: changing behaviour of TimeSpan to possibly flip start and end,
and also to use Offset as Offset and then re-orient,
since this seems the least surprising behaviour.
These changes carry over into changed default and limiting
on ZoomWindow constructor and various mutators, and most
notably shifting the time span always into allowed domain.
...the implementation was way too naive; in some cases we could go
into an infinite loop. In the end, using Newton approximation was not
necessary (and thus there is no loop anymore), but it helped me get
at a much better solution with very small error margin on average case.
All these corner cases are obviously "academic" to some degree,
but it turns out there is no clear-cut point where you'd be able
just so set a limit and be sure that fractional integer arithmetic
works flawless in all cases.
Thus the choice is
- give up (fractional) integers and work with floats and have to
deal with error accumulation
- or do something as chosen here, namely add a boundary zone, where
fractional integer arithmetic can be kept under control, while admitting
small errors, and in turn get the absolutely precise integers in all
everyday standard cases
The value used previously was too conservative, and prevented ZommWindow
from zooming out to the complete Time domain. This was due to missing the
Time::SCALE denominator, which increaded the limit by factor 1e6
In fact the code is able to handle even this extremely reduced limit,
but doing so seems over the top, since now detox() kicks in on several
calculations, leading to rather coarse grained errors.
Thus I decided to use a compromise: lower the limit only by factor 1000;
with typical screen pixel widths, we can reach the full time domain,
while most scaling and zoom calculations can be performed precisely,
without detox() kicking in. Obviously this change requires adjusting
a lot of the test case expectations, since we can now zoom out maximally.
As it turns out, the calculation path initially choosen for the mutateScale(Rat)
was needlessly indirect, and also duplicated several of the safeguards,
meanwhile implemented way better in conformWindowToMetric(Rat)
Thus, instead of relatively re-scaling the window, now we just
limit the given zoomFactor and pass it to conformWindowToMetric()
There is a built-in limitation, which now is even
lowered to 100000 pixels horizontally.
With the techniques introduced in this changeset, it seems possible
to support more -- yet this would be a case of unnecessary genricity;
handling such large numbers will drive more computations into the
danger zone, and doing so incurs cost in terms of testing and debugging.
Placing that into context, contemporary displays are not even 4K on
average, and it does not look likely even for cinema display to go
way beyond 8k -- so yes, I want display hardware with 100000 pixels!!
The key takeaway of this changeset:
- can calculate px = trunc(zoomFactor * duration) step wise,
even when the direct calculation would lead to wrap-around
- can safely adjust and fix the zoomFactor using Newton approximation
...even zooming out to span the complete time domain (~19000 years).
But only under the condition that the display window is sufficiently
large in terms of pixels, so we can handle the computation without
glitches.
This should not be a relevant limitation in practice, since a window
size of some 100 pixels is enough to handle Duration::MAX. Needless to add
that it's hard to imagine a media timeline of such tremendous size...
building on these Library changes, plus the safe-add function
developed some days ago, it is now possible to mark a large displacement
as `time::Offset`, and apply this to yield any valid time position,
even extreme negative values
...building on these Library changes, plus the safe-add function
developed some days ago, it is now possible to mark a large displacement
as `time::Offset`, and apply this to yield any valid time position,
even extreme negative values
The APIs for time quantisation were drafted in an early stage of the project
and then never followed-up. Especially Grid::gridAlign has no
real-world usage yet, and is only massaged in some tests.
When looking at QuantiserBasics_test, I was puzzled and led astray,
since this function suggests to materialise a continuous time into
a quantised time -- which it doesn't (there is another dedicated
function Quantiser::materialise() to that end); so, without engaging
into the discussion if this function is of any use, I'll hereby
choose a name better reflecting what it does.
This is a deep refactoring to allow to represent the distance
between all valid time points as a time::Offset or time::Duration.
By design this is possible, since Time::MAX was defined as 1/30 of
the maximum value technically representable as int64_t. However,
introducing a different limiter for offsets and durations turns
out difficult, due to the inconsistencies in the exiting hierarchy
of temporal entities. Which in turn seems to stem from the unfortunate
decision to make time entities immutable, see #1261
Since the limiter is hard wired into the `time::TimeValue` constructor,
we are forced to create a "backdoor" of sorts, to pass up values
with different limiting from child classes. This would not be so
much of a problem if calculations weren't forced to go through `TimeVar`,
which does not distinguish between time points and time durations.
This solution rearranges all checks to be performed now by time::Offset,
while time::Duration will only take the absolute value at construction,
based on the fact that there is no valid construction path to yield
a duration which does not go through an offset first.
Later, when we're ready to sort out the implementation base of time values
(see #1258), this design issue should be revisited
- either we'll allow derived classes explicitly to invoke the limiter functions
- or we may be able to have an automatic conversion path from clearly
marked base implementation types, in which case we wouldn't use the
buildRaw_() and _raw() "backdoor" functions any more...
While the calculation was already basically under control, I just was not content
with the achieved numeric precision -- and the fact that the test case in fact
misses the bar, making it difficult do demonstrate that the calculation
is not derailed. I just had the gut feeling that it must be somehow possible
to achieve an absolute error level, not just a relative error level of 1e-6
Thus I reworked this part into a generic helper function, see #1262
The end result is:
* partial failure. we can only ''guarantee'' the relative error margin of 1e-6
* but in most cases not out to the most extreme numbers, the sophisticated
solution achieves much better results way below the absolute error level of 1µ-Tick
Thus with using rational numbers, we have now a solution that is absolutely precise
in the regular case, and gradually introduces errors at the domain bound
but with an guaranteed relative error margin of 1e-6 (== Time::SCALE)
...now able to achieve the expected error bound of 1e-6
...this seems to be the worst-case for ZoomWindow::setVisiblePos(factor)
for extremely large timeline; seemingly not possible to achieve the
goal set for this special test case
...in a similar vein as done for the product calculation.
In this case, we need to check the dimensions carefully and pick
the best calculation path, but as long as the overall result can
be represented, it should be possible to carry out the calculation
with fractional values, albeit introducing a small error.
As a follow-up, I have now also refactored the re-quantisation
functions, to be usable for general requantisation to another grid,
and I used these to replace the *naive* implementation of the
conversion FSecs -> µ-Grid, which caused a lot of integer-wrap-around
However, while the test now works basically without glitch or wrap,
the window position is still numerically of by 1e-6, which becomes
quite noticeably here due to the large overall span used for the test.
...using a requantisation trick to cancel out some factors in the
product of two rational numbers, allowing to calculate the product
without actual multiplication of (dangerously large) numbers.
with these additional safeguards, the anchorWindowAtPosition()
succeeds without Integer-wrap, but the result is not fully correct
(some further calculation error hidden somewhere??)
- detailed documentation of known problematic behaviour
when working with rational fractions
- demonstrate the heuristic predicate to detect dangerous numbers
- add extensive coverage and microbenchmarks for the integer-logarithm
implementation, based on an example on Stackoverflow. Surprising result:
The std::ilog(double) function is of comparable speed, at least for
GCC-8 on Debian-Buster.
Especially rational numbers with large denominator can be insidious,
since they might cause numeric overflow on seemingly harmless operations,
like adding a small number.
A solution might be to *requantise* the number into a different,
way smaller denominator. Obviously this is a lossy operation;
yet a small and controlled numeric error is always better than
an uncontrolled numeric wrap-around.
- protection against negative numbers seems adequate
- a possible concern are handling of very large time spans
- definitively have to guard against "poisonous" fractions
(e.g. n / INT_MAX)
- some test definitions were simply numerically wrong
- changed some aspects of the specified behaviour, to be more consistent
+ scrolling is more liberal and always allows to extend canvas
+ setting window to a given duration expands around anchor point
This function allows to move the visible range such that it contains
a given time position; the relative location of this point within
the visible range however is in turn determined by relating it to
the current overall canvas: if we are close to the beginning, the
position is also located rather to the left side, and if we're
approaching the canvas end, the position tends to the right side...
(and yes, I am aware that the variant taking a rational number
can be derailed by causing internal numeric overflow, when passing
a maliciously crafted rational number, like INT_MAX-1 / INT_MAX )
Rearrange the internal mutator functions to follow a common scheme,
so that most of the setters can be implemented by simple forwarding.
Move the change-listener triggering up into the actual setters.
This makes further test cases pass
- verify_setup
- verify_calibration
...implying that the pixel width is now retained
and basic behaviour matches expectations
Since conformWindowToMetric() is always called prior to performing
the complete invariant-reestablishment sequence, we can even integrate
the rule for relative scaling into this central function, which
simplifies the mutation implementation significantly. Should
relative positioning go south, the following sanity checks
will push the window back into bounds.
With these changes, the verify_simpleUsage() test passes!
Extensive tests with corner cases soon highlighted this problem
inherent to integer calculations with fractional numbers: it is
possible to derail the calculation by numeric overflow with values
not excessively large, but using large numbers as denominator.
This problem is typically triggered by addition and subtraction,
where you'd naively not expect any problems.
Thus changed the approach in the normalisation function, relying
on an explicitly coded test rather, and performing the adjustment
only after conversion back to simple integral micro-tick scale.
Getting all those requirements translated into code turns out to be a challenging task;
and the usual ascent to handle such a situation is to define **Invariants**
in conjunction with a normalisation scheme; each manipulation will then be
translated into invocation of one of the three fundamental mutators,
and these in turn always lead into the common normalisation sequence.
__Invariants__
- oriented and non-empty windows
- never alter given pxWidth
- zoom metric factor < max zoom
- visibleWindow ⊂ Canvas
Writing this specification unveiled a limitation of our internal
time base implementation, which is a 64bit microsecond grid.
As it turns out, any grid based time representation will always
be not precise enough to handle some relevant time specifications,
which are defined by a divisor. Most notably this affects the precise
display of frame duration in the GUI, and even more relevant,
the sample accurate editing of sound in the timeline.
Thus I decided to perform the internal computation in ZoomWindow
as rational numbers, based on boost::rational
Note: implementation stubbed only, test fails
This ZoomWindow_test highlights again the question about the intended usage
of the Lumiera time entities. In which way do we want to perform time calculations,
and under which circumstances is it adequate to perform arithmetic on
raw time values?
These questions made me think about rather far reaching concerns regarding
subsidiarity and implicit or explicit usage context. Basically I could
reconfirm the design choices taken some years ago -- while I must admit
that the project is headed towards a way larger scale and more loose
coupling of the parts, than I could imagine several years ago, at the
time when the design started...
As a side note: we can not avoid that some knowledge about the time implementation
leaks out from the support lib; time codes themselves are tightly coupled
to the usage scenario within the session and can not be used as means
for implementing UI concerns. And the more generic time frameworks,
like std::chrono (as much as it is desirable to have some integration here)
will not be of any help for most of our specific usage patterns.
The reason is, for film editing we do not have a global time scale,
rather the truth is when the film starts....
implement the first test case: nudge the zoom factor
⟹ scale factor doubled
⟹ visible window reduced to half size
⟹ visible window placed in the middle of the overall range
The solution is to provide a standard implementation in the form of a mix-in,
which directly houses a `ZoomWindow` instance. Moreover, the latter
is deemed a prominent use case for the time::Control, allowing other
components to attach and push changes of the zoom state or register
as listeners to react to state changes.
Actually, the `TimelineLayout`, which hosts all the actual visible
widgets forming the timeline-UI, now integrates this mix-in; and since
`TimelineLayout` is passed to `TimelineController` and used there as
reference-`CanvasHook` for the root track, this implementation of
the `DisplayMetric` interface will ''effectively be used by all
widgets'' attached to the timeline canvas.
Reading my work notes from two years ago, the concept can be validated.
Clarify the relation of the interfaces involved, and the role foreseen
for the upcoming `ZoomWindow` abstraction. This solution approach
will lead to multiple-stage indirect calls, which however are deemed
not to be overly concerning and will be investigated later, to avoid
premature optimisation (see #1254)
- `DisplayMetric` is a focused special purpose abstraction
- it belongs into the general abstraction of the `DisplayManager`
- it is rather linked by use to the other abstraction, the `CanvasHook`
- while the `RelativeCanvasHook` is not an interface, but an implementation mix-in
- and the actual `DisplayMetric` implementation can likewise be provided
as mix-in, since it will typically be implemented in terms of a `ZoomWindow`
Using this scheme, it will be possible to avoid some of the indirect cally
by making this mix-in visible higher up the call graph -- in case the
actual need for optimisation can be confirmed in practice.
* restructure the widgets used to implement ElementBox
* inject a Gtk::EventBox top-level base type to capture all Gdk-Events
* push the Gtk::Frame one level down (TODO: API for managing children)
With these changes
* dragging of Clips in the timeline works as expected
* size constraints are observed precisely
* all warnings and assertion failures from GTK disappeared
Thus we can conclude that the solution approach for size constrained widgets
was successful and this challenging problem is solved.
