crtr/Assets/EricHaines/TextureScale.cs

namespace EricHaines {
	// Only works on ARGB32, RGB24 and Alpha8 textures that are marked readable

	using System.Threading;
	using UnityEngine;

	public class TextureScale {
		public class ThreadData {
			public int start;
			public int end;
			public ThreadData(int s, int e) {
				start = s;
				end = e;
			}
		}

		private static Color[] texColors;
		private static Color[] newColors;
		private static int w;
		private static float ratioX;
		private static float ratioY;
		private static int w2;
		private static int finishCount;
		private static Mutex mutex;

		public static void Point(Texture2D tex, int newWidth, int newHeight) {
			ThreadedScale(tex, newWidth, newHeight, false);
		}

		public static void Bilinear(Texture2D tex, int newWidth, int newHeight) {
			ThreadedScale(tex, newWidth, newHeight, true);
		}

		private static void ThreadedScale(Texture2D tex, int newWidth, int newHeight, bool useBilinear) {
			texColors = tex.GetPixels();
			newColors = new Color[newWidth * newHeight];
			if (useBilinear) {
				ratioX = 1.0f / ((float)newWidth / (tex.width - 1));
				ratioY = 1.0f / ((float)newHeight / (tex.height - 1));
			}
			else {
				ratioX = (float)tex.width / newWidth;
				ratioY = (float)tex.height / newHeight;
			}
			w = tex.width;
			w2 = newWidth;
			var cores = Mathf.Min(SystemInfo.processorCount, newHeight);
			var slice = newHeight/cores;

			finishCount = 0;
			if (mutex == null) {
				mutex = new Mutex(false);
			}
			if (cores > 1) {
				int i = 0;
				ThreadData threadData;
				for (i = 0; i < cores - 1; i++) {
					threadData = new ThreadData(slice * i, slice * (i + 1));
					ParameterizedThreadStart ts = useBilinear ? new ParameterizedThreadStart(BilinearScale) : new ParameterizedThreadStart(PointScale);
					Thread thread = new Thread(ts);
					thread.Start(threadData);
				}
				threadData = new ThreadData(slice * i, newHeight);
				if (useBilinear) {
					BilinearScale(threadData);
				}
				else {
					PointScale(threadData);
				}
				while (finishCount < cores) {
					Thread.Sleep(1);
				}
			}
			else {
				ThreadData threadData = new ThreadData(0, newHeight);
				if (useBilinear) {
					BilinearScale(threadData);
				}
				else {
					PointScale(threadData);
				}
			}

#if UNITY_2021_2_OR_NEWER
			tex.Reinitialize(newWidth, newHeight);
#else
			tex.Resize(newWidth, newHeight);
#endif
			tex.SetPixels(newColors);
			tex.Apply();

			texColors = null;
			newColors = null;
		}

		public static void BilinearScale(object obj) {
			ThreadData threadData = (ThreadData) obj;
			for (var y = threadData.start; y < threadData.end; y++) {
				int yFloor = (int)Mathf.Floor(y * ratioY);
				var y1 = yFloor * w;
				var y2 = (yFloor+1) * w;
				var yw = y * w2;

				for (var x = 0; x < w2; x++) {
					int xFloor = (int)Mathf.Floor(x * ratioX);
					var xLerp = x * ratioX-xFloor;
					newColors[yw + x] = ColorLerpUnclamped(
						ColorLerpUnclamped(texColors[y1 + xFloor], texColors[y1 + xFloor + 1], xLerp),
						ColorLerpUnclamped(texColors[y2 + xFloor], texColors[y2 + xFloor + 1], xLerp),
						y * ratioY - yFloor
					);
				}
			}

			mutex.WaitOne();
			finishCount++;
			mutex.ReleaseMutex();
		}

		public static void PointScale(object obj) {
			ThreadData threadData = (ThreadData) obj;
			for (var y = threadData.start; y < threadData.end; y++) {
				var thisY = (int)(ratioY * y) * w;
				var yw = y * w2;
				for (var x = 0; x < w2; x++) {
					newColors[yw + x] = texColors[(int)(thisY + ratioX * x)];
				}
			}

			mutex.WaitOne();
			finishCount++;
			mutex.ReleaseMutex();
		}

		private static Color ColorLerpUnclamped(Color c1, Color c2, float value) {
			return new Color(
				c1.r + (c2.r - c1.r) * value,
				c1.g + (c2.g - c1.g) * value,
				c1.b + (c2.b - c1.b) * value,
				c1.a + (c2.a - c1.a) * value
			);
		}
	}
}