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Most modules find themselves wanting some kind of "t" value increasing
with time or frames rendered. It's common for them to create and
maintain this variable locally, incrementing it with every frame
rendered.
It may be interesting to introduce a global notion of ticks since
rototiller started, and have all modules derive their "t" value from
this instead of having their own private versions of it.
In future modules and general innovations it seems likely that playing
with time, like jumping it forwards and backwards to achieve some
visual effects, will be desirable. This isn't applicable to all
modules, but for many their entire visible state is derived from their
"t" value, making them entirely reversible.
This commit doesn't change any modules functionally, it only adds the
plumbing to pull a ticks value down to the modules from the core.
A ticks offset has also been introduced in preparation for supporting
dynamic shifting of the ticks value, though no API is added for doing
so yet.
It also seems likely an API will be needed for disabling the
time-based ticks advancement, with functions for explicitly setting
its value. If modules are created for incorporating external
sequencers and music coordination, they will almost certainly need to
manage the ticks value explicitly. When a sequencer jumps
forwards/backwards in the creative process, the module glue
responsible will need to keep ticks synchronized with the
sequencer/editor tool.
Before any of this can happen, we need ticks as a first-class core
thing shared by all modules.
Future commits will have to modify existing modules to use the ticks
appropriately, replacing their bespoke variants.
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Mechanical change removing abbreviation for consistency
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Mostly mechanical change, though threads.c needed some jiggering to
make the logical cpu id available to the worker threads.
Now render_fragment() can easily addresss per-cpu data created by
create_context().
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Back in the day, there was no {create,destroy}_context(), so passing
num_cpus to just prepare_frame made sense. Modules then would
implicitly initialize themselves on the first prepare_frame() call
using a static initialized variable.
Since then things have been decomposed a bit for more sophisticated
(and cleaner) modules. It can be necessary to allocate per-cpu data
structures and the natural place to do that is @ create_context(). So
this commit wires that up.
A later commit will probably have to plumb a "current cpu" identifier
into the render_fragment() function. Because a per-cpu data structure
isn't particularly useful if you can't easily address it from within
your execution context.
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Viscosity and diffusion are supported, it'd be neat to add a
configurable size (the ROOT define) for the flow field in the
future.
I didn't go crazy here, it's just a list of orders of magnitude you
choose from for each. It'd probably be more interesting to change
this into a single knob with descriptive names like "smoke" "goop"
"water" mapping to a LUT.
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s/Joe/Jos/, I should wear my glasses more.
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This implements near verbatim the code found in the paper titled:
Real-Time Fluid Dynamics for Games
By Jos Stam
It sometimes has the filename GDC03.PDF, or Stam_fluids_GDC03.pdf
The density field is rendered using simple linear interpolation of
the samples, in a grayscale palette. No gamma correction is being
performed.
There are three configurable defines of interest:
VISCOSITY, DIFFUSION, and ROOT.
This module is only threaded in the drawing stage, so basically the
linear interpolation uses multiple cores. The simulation itself is
not threaded, the implementation from the paper made no such
considerations.
It would be nice to reimplement this in a threaded fashion with a
good generalized API, then move it into libs. Something where a unit
square can be sampled for interpolated densities would be nice.
Then extend it into 3 dimensions for volumetric effects...
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