99 lines
2.5 KiB
Go
99 lines
2.5 KiB
Go
// Copyright 2014, 2015, 2017 by Sascha L. Teichmann
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// Use of this source code is governed by the MIT license
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// that can be found in the LICENSE file.
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package common
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import "container/heap"
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// YOrder is a "streaming" Y sorter. The blocks comming from the
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// database are not sorted in Y order. To unpack only the
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// relevant blocks (the one at the surface) it would be nice
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// to have them sorted in inverse Y order so that blocks with
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// lower Y value are shadowed by ones wither higher value.
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//
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// Sorting all blocks correctly would leadind to load all blocks
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// before rendering. But a perfect order is not strictly necessary
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// because the problem is (expensively) solved at per node level.
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//
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// The YOrder defines a "windowed" data structure in which all blocks
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// are sorted correctly. So for small amounts of blocks the
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// sorting is perfect. For larger amounts it is possible to
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// have partial incorrect sortings but as stated above it doesn't
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// matter. The window allows not to preload all blocks.
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type YOrder struct {
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RenderFn func(*Block) error
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blocks []*Block
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capacity int
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}
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func NewYOrder(renderFn func(*Block) error, capacity int) *YOrder {
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return &YOrder{
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RenderFn: renderFn,
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blocks: make([]*Block, 0, capacity),
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capacity: capacity}
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}
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func (yo *YOrder) Reset() {
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blocks := yo.blocks
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for i := range blocks {
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blocks[i] = nil
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}
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yo.blocks = blocks[:0]
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}
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func (yo *YOrder) RenderBlock(block *Block) (*Block, error) {
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if len(yo.blocks) == yo.capacity {
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oblock := yo.blocks[0]
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if oblock.Coord.Y < block.Coord.Y {
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// New one is above highest old. Directly render new.
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err := yo.RenderFn(block)
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return block, err
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}
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// Render old one. Store copy of new in heap.
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heap.Pop(yo)
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heap.Push(yo, block)
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err := yo.RenderFn(oblock)
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return oblock, err
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}
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heap.Push(yo, block)
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return nil, nil
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}
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func (yo *YOrder) Drain() error {
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for len(yo.blocks) > 0 {
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if err := yo.RenderFn(heap.Pop(yo).(*Block)); err != nil {
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return err
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}
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}
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return nil
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}
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func (yo *YOrder) Len() int {
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return len(yo.blocks)
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}
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func (yo *YOrder) Swap(i, j int) {
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yo.blocks[i], yo.blocks[j] = yo.blocks[j], yo.blocks[i]
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}
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func (yo *YOrder) Less(i, j int) bool {
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// Reverse order intented.
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return yo.blocks[i].Coord.Y > yo.blocks[j].Coord.Y
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}
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func (yo *YOrder) Push(x interface{}) {
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yo.blocks = append(yo.blocks, x.(*Block))
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}
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func (yo *YOrder) Pop() interface{} {
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blocks := yo.blocks
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l := len(blocks)
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x := blocks[l-1]
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blocks[l-1] = nil
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yo.blocks = blocks[:l-1]
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return x
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}
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