180 lines
5.6 KiB
C++
180 lines
5.6 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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#include <algorithm>
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#include "BLI_index_mask_fwd.hh"
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#include "BLI_index_range.hh"
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#include "BLI_span.hh"
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namespace blender::offset_indices {
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/**
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* References an array of ascending indices. A pair of consecutive indices encode an index range.
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* Another common way to store the same kind of data is to store the start and size of every range
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* separately. Using offsets instead halves the memory consumption. The downside is that the
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* array has to be one element longer than the total number of ranges. The extra element is
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* necessary to be able to get the last index range without requiring an extra branch for the case.
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*
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* This class is a thin wrapper around such an array that makes it easy to retrieve the index range
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* at a specific index.
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*/
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template<typename T> class OffsetIndices {
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private:
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static_assert(std::is_integral_v<T>);
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Span<T> offsets_;
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public:
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OffsetIndices() = default;
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OffsetIndices(const Span<T> offsets) : offsets_(offsets)
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{
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BLI_assert(offsets_.size() < 2 || std::is_sorted(offsets_.begin(), offsets_.end()));
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}
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/** Return the total number of elements in the referenced arrays. */
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T total_size() const
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{
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return offsets_.size() > 1 ? offsets_.last() : 0;
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}
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/**
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* Return the number of ranges encoded by the offsets, not including the last value used
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* internally.
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*/
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int64_t size() const
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{
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return std::max<int64_t>(offsets_.size() - 1, 0);
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}
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bool is_empty() const
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{
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return this->size() == 0;
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}
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IndexRange index_range() const
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{
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return IndexRange(this->size());
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}
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IndexRange operator[](const int64_t index) const
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{
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BLI_assert(index >= 0);
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BLI_assert(index < offsets_.size() - 1);
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const int64_t begin = offsets_[index];
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const int64_t end = offsets_[index + 1];
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return IndexRange::from_begin_end(begin, end);
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}
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IndexRange operator[](const IndexRange indices) const
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{
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const int64_t begin = offsets_[indices.start()];
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const int64_t end = offsets_[indices.one_after_last()];
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return IndexRange::from_begin_end(begin, end);
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}
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/**
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* Return a subset of the offsets describing the specified range of source elements.
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* This is a slice into the source ranges rather than the indexed elements described by the
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* offset values.
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*/
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OffsetIndices slice(const IndexRange range) const
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{
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BLI_assert(range.is_empty() || offsets_.index_range().drop_back(1).contains(range.last()));
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return OffsetIndices(offsets_.slice(range.start(), range.size() + 1));
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}
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Span<T> data() const
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{
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return offsets_;
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}
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};
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/**
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* References many separate spans in a larger contiguous array. This gives a more efficient way to
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* store many grouped arrays, without requiring many small allocations, giving the general benefits
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* of using contiguous memory.
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*
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* \note If the offsets are shared between many #GroupedSpan objects, it will still
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* be more efficient to retrieve the #IndexRange only once and slice each span.
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*/
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template<typename T> struct GroupedSpan {
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OffsetIndices<int> offsets;
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Span<T> data;
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GroupedSpan() = default;
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GroupedSpan(OffsetIndices<int> offsets, Span<T> data) : offsets(offsets), data(data)
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{
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BLI_assert(this->offsets.total_size() == this->data.size());
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}
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Span<T> operator[](const int64_t index) const
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{
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return this->data.slice(this->offsets[index]);
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}
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int64_t size() const
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{
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return this->offsets.size();
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}
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IndexRange index_range() const
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{
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return this->offsets.index_range();
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}
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bool is_empty() const
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{
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return this->data.size() == 0;
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}
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};
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/**
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* Turn an array of sizes into the offset at each index including all previous sizes.
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*/
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OffsetIndices<int> accumulate_counts_to_offsets(MutableSpan<int> counts_to_offsets,
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int start_offset = 0);
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/** Create offsets where every group has the same size. */
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void fill_constant_group_size(int size, int start_offset, MutableSpan<int> offsets);
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/** Copy the number of indices in every group in the mask to the corresponding index. */
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void copy_group_sizes(OffsetIndices<int> offsets, const IndexMask &mask, MutableSpan<int> sizes);
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/** Gather the number of indices in each indexed group to sizes. */
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void gather_group_sizes(OffsetIndices<int> offsets, const IndexMask &mask, MutableSpan<int> sizes);
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void gather_group_sizes(OffsetIndices<int> offsets, Span<int> indices, MutableSpan<int> sizes);
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/** Build new offsets that contains only the groups chosen by \a selection. */
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OffsetIndices<int> gather_selected_offsets(OffsetIndices<int> src_offsets,
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const IndexMask &selection,
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int start_offset,
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MutableSpan<int> dst_offsets);
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inline OffsetIndices<int> gather_selected_offsets(OffsetIndices<int> src_offsets,
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const IndexMask &selection,
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MutableSpan<int> dst_offsets)
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{
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return gather_selected_offsets(src_offsets, selection, 0, dst_offsets);
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}
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/**
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* Create a map from indexed elements to the source indices, in other words from the larger array
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* to the smaller array.
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*/
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void build_reverse_map(OffsetIndices<int> offsets, MutableSpan<int> r_map);
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/**
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* Build offsets to group the elements of \a indices pointing to the same index.
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*/
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void build_reverse_offsets(Span<int> indices, MutableSpan<int> offsets);
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} // namespace blender::offset_indices
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namespace blender {
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using offset_indices::GroupedSpan;
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using offset_indices::OffsetIndices;
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} // namespace blender
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