ニアレストネイバー法

20180206_Bitmap.cs

using System;
using System.Collections.Generic;
using System.Threading;
using UnityEngine;
using UnityEngine.Assertions;

public partial class Bitmap
{
	public uint width { get { return _width; } }
	public uint height { get { return _height; } }

	public uint count { get { return _width * _height; } }

	public Color[] pixels { get { return _pixels; } }

	public Color this[int x, int y]
	{
		get { return _pixels[_width * y + x]; }
		set { _pixels[_width * y + x] = value; }
	}

	public Color this[int index]
	{
		get { return _pixels[index]; }
		set { _pixels[index] = value; }
	}

	public Bitmap(Texture2D texture)
		: this(texture.GetPixels(), (uint)texture.width, (uint)texture.height)
	{
	}

	public Bitmap(uint width, uint height)
		: this(new Color[width * height], width, height)
	{
	}

	public Bitmap(Color[] pixels, uint width, uint height)
	{
		Assert.IsTrue(pixels.Length == width * height);

		_width = width;
		_height = height;
		_pixels = pixels;
	}

	public Bitmap copy()
	{
		var bitmap = new Bitmap(_width, _height);
		_pixels.CopyTo(bitmap._pixels, 0);
		return bitmap;
	}

	public Texture2D createTexture()
	{
		var texture = new Texture2D((int)_width, (int)_height, TextureFormat.RGBA32, false);
		texture.SetPixels(_pixels);
		texture.Apply();
		return texture;
	}

	public Color get(int x, int y)
	{
		x = clamp(x, 0, (int)_width - 1);
		y = clamp(y, 0, (int)_height - 1);
		return this[x, y];
	}

	private Bitmap resizeNearestNeighbor(uint width, uint height)
	{
		var bitmap = new Bitmap(width, height);

		// スケール
		var scaleX = (float)width / _width;
		var scaleY = (float)height / _height;

		// 単位を原画像の座標系に変換
		var unitX = 1.0f / scaleX;
		var unitY = 1.0f / scaleY;

		// 1ピクセル幅を考慮した座標の補正
		var correctionX = unitX * 0.5f;
		var correctionY = unitY * 0.5f;

		parallelFor(0, (int)bitmap._height, y => {
			for(int x = 0; x < bitmap._width; ++x) {
				// 原画像の座標系に変換
				var srcX = unitX * x + correctionX;
				var srcY = unitY * y + correctionY;

				bitmap[x, y] = get((int)srcX, (int)srcY);
			}
		});

		return bitmap;
	}

	private static int clamp(int value, int min, int max)
	{
		if(value > max) return max;
		if(value < min) return min;
		return value;
	}

	private static void parallelFor(int start, int end, Action<int> action)
	{
		var length = Math.Abs(end - start);
		if(length == 0) return;

		// start <= endを保証する
		if(start > end) {
			var tmp = start;
			start = end;
			end = tmp;
		}

		extendHandlePoolCapacity(length);

		// 並列タスクの生成と同期オブジェクトの取得
		var index = 0;
		var handles = new ManualResetEvent[length];
		for(int i = start; i < end; ++i) {
			var arg = i;
			var handle = popHandle();
			ThreadPool.QueueUserWorkItem(state => {
				action(arg);
				handle.Set();
			});

			handles[index++] = handle;
		}

		// 並列タスクの終了待ち
		foreach(var handle in handles) {
			handle.WaitOne();
			pushHandle(handle);
		}
	}

	private static void extendHandlePoolCapacity(int capacity)
	{
		if(_handlePool.Capacity < capacity) {
			_handlePool.Capacity = capacity;
		}
	}

	private static void pushHandle(ManualResetEvent handle)
	{
		_handlePool.Add(handle);
	}

	private static ManualResetEvent popHandle()
	{
		if(_handlePool.Count <= 0) {
			return new ManualResetEvent(false);
		}

		var lastIndex = _handlePool.Count - 1;
		var handle = _handlePool[lastIndex];
		_handlePool.RemoveAt(lastIndex);
		handle.Reset();
		return handle;
	}

	private static readonly List<ManualResetEvent> _handlePool = new List<ManualResetEvent>();

	private uint _width = 0u;
	private uint _height = 0u;

	private Color[] _pixels = null;
}