Deadly border fighting breaks out between Pakistan and Afghanistan
Historic England
，更多细节参见搜狗输入法2026
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The tree is rebuilt every frame. For scenes of this scale, quadtree construction is fast enough to rebuild from scratch each frame, though larger simulations may benefit from incremental updates. Each particle queries its neighborhood for potential collisions, typically checking only 5 to 15 candidates instead of all 40. Red highlights indicate colliding pairs.