151 lines
4.8 KiB
C++
151 lines
4.8 KiB
C++
/* SPDX-FileCopyrightText: 2023 Blender Authors
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*
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* SPDX-License-Identifier: GPL-2.0-or-later */
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#pragma once
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/** \file
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* \ingroup fn
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*
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* A `MultiFunction` encapsulates a function that is optimized for throughput (instead of latency).
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* The throughput is optimized by always processing many elements at once, instead of each element
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* separately. This is ideal for functions that are evaluated often (e.g. for every particle).
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*
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* By processing a lot of data at once, individual functions become easier to optimize for humans
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* and for the compiler. Furthermore, performance profiles become easier to understand and show
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* better where bottlenecks are.
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*
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* Every multi-function has a name and an ordered list of parameters. Parameters are used for input
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* and output. In fact, there are three kinds of parameters: inputs, outputs and mutable (which is
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* combination of input and output).
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*
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* To call a multi-function, one has to provide three things:
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* - `Params`: This references the input and output arrays that the function works with. The
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* arrays are not owned by Params.
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* - `IndexMask`: An array of indices indicating which indices in the provided arrays should be
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* touched/processed.
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* - `Context`: Further information for the called function.
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*
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* A new multi-function is generally implemented as follows:
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* 1. Create a new subclass of MultiFunction.
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* 2. Implement a constructor that initialized the signature of the function.
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* 3. Override the `call` function.
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*/
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#include "BLI_hash.hh"
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#include "FN_multi_function_context.hh"
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#include "FN_multi_function_params.hh"
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namespace blender::fn::multi_function {
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class MultiFunction : NonCopyable, NonMovable {
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private:
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const Signature *signature_ref_ = nullptr;
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public:
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virtual ~MultiFunction() {}
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/**
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* The result is the same as using #call directly but this method has some additional features.
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* - Automatic multi-threading when possible and appropriate.
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* - Automatic index mask offsetting to avoid large temporary intermediate arrays that are mostly
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* unused.
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*/
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void call_auto(const IndexMask &mask, Params params, Context context) const;
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virtual void call(const IndexMask &mask, Params params, Context context) const = 0;
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virtual uint64_t hash() const
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{
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return get_default_hash(this);
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}
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virtual bool equals(const MultiFunction & /*other*/) const
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{
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return false;
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}
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int param_amount() const
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{
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return signature_ref_->params.size();
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}
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IndexRange param_indices() const
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{
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return signature_ref_->params.index_range();
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}
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ParamType param_type(int param_index) const
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{
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return signature_ref_->params[param_index].type;
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}
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StringRefNull param_name(int param_index) const
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{
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return signature_ref_->params[param_index].name;
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}
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StringRefNull name() const
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{
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return signature_ref_->function_name;
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}
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virtual std::string debug_name() const;
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const Signature &signature() const
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{
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BLI_assert(signature_ref_ != nullptr);
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return *signature_ref_;
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}
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/**
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* Information about how the multi-function behaves that help a caller to execute it efficiently.
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*/
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struct ExecutionHints {
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/**
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* Suggested minimum workload under which multi-threading does not really help.
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* This should be lowered when the multi-function is doing something computationally expensive.
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*/
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int64_t min_grain_size = 10000;
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/**
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* Indicates that the multi-function will allocate an array large enough to hold all indices
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* passed in as mask. This tells the caller that it would be preferable to pass in smaller
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* indices. Also maybe the full mask should be split up into smaller segments to decrease peak
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* memory usage.
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*/
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bool allocates_array = false;
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/**
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* Tells the caller that every execution takes about the same time. This helps making a more
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* educated guess about a good grain size.
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*/
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bool uniform_execution_time = true;
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};
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ExecutionHints execution_hints() const;
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protected:
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/* Make the function use the given signature. This should be called once in the constructor of
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* child classes. No copy of the signature is made, so the caller has to make sure that the
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* signature lives as long as the multi function. It is ok to embed the signature into the child
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* class. */
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void set_signature(const Signature *signature)
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{
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/* Take a pointer as argument, so that it is more obvious that no copy is created. */
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BLI_assert(signature != nullptr);
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signature_ref_ = signature;
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}
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virtual ExecutionHints get_execution_hints() const;
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};
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inline ParamsBuilder::ParamsBuilder(const MultiFunction &fn, const IndexMask *mask)
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: ParamsBuilder(fn.signature(), *mask)
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{
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}
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} // namespace blender::fn::multi_function
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namespace blender {
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namespace mf = fn::multi_function;
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}
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