Add principle texture colorspace tests.

Assets/VRMShaders/GLTF/IO/Tests/4x4_gray_import_as_linear.png.meta

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Assets/VRMShaders/GLTF/IO/Tests/4x4_gray_import_as_srgb.png.meta

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Assets/VRMShaders/GLTF/IO/Tests/TextureColorSpaceSpecificationTests.cs

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+using System;
+using NUnit.Framework;
+using UnityEditor;
+using UnityEngine;
+
+namespace VRMShaders
+{
+    public sealed class TextureColorSpaceSpecificationTests
+    {
+        private static readonly string AssetPath = "Assets/VRMShaders/GLTF/IO/Tests";
+        private static readonly Texture2D SrgbGrayTex = AssetDatabase.LoadAssetAtPath<Texture2D>($"{AssetPath}/4x4_gray_import_as_srgb.png");
+        private static readonly Texture2D LinearGrayTex = AssetDatabase.LoadAssetAtPath<Texture2D>($"{AssetPath}/4x4_gray_import_as_linear.png");
+        private static readonly Color32 JustGray = new Color32(127, 127, 127, 255);
+        private static readonly Color32 SrgbGrayInSrgb = JustGray;
+        private static readonly Color32 SrgbGrayInLinear = ((Color) SrgbGrayInSrgb).linear;
+        private static readonly Color32 LinearGrayInLinear = JustGray;
+        private static readonly Color32 LinearGrayInSrgb = ((Color) LinearGrayInLinear).gamma;
+
+        [Test]
+        public void InputAssetsRawImage()
+        {
+            Assert.AreEqual(SrgbGrayInSrgb, GetFirstPixelInTexture2D(SrgbGrayTex));
+
+            // Image color space is sRGB even through Texture color space was Linear.
+            Assert.AreEqual(SrgbGrayInSrgb, GetFirstPixelInTexture2D(LinearGrayTex));
+        }
+
+        [Test]
+        public void CopyToSrgbRenderTexture()
+        {
+            var srgbRt = RenderTexture.GetTemporary(4, 4, 0, RenderTextureFormat.ARGB32, RenderTextureReadWrite.sRGB);
+
+            Graphics.Blit(SrgbGrayTex, srgbRt);
+            Assert.AreEqual(SrgbGrayInSrgb, GetFirstPixelInRenderTexture(srgbRt));
+
+            Graphics.Blit(LinearGrayTex, srgbRt);
+            Assert.AreEqual(LinearGrayInSrgb, GetFirstPixelInRenderTexture(srgbRt));
+
+            RenderTexture.ReleaseTemporary(srgbRt);
+        }
+
+        [Test]
+        public void CopyToLinearRenderTexture()
+        {
+            var linearRt = RenderTexture.GetTemporary(4, 4, 0, RenderTextureFormat.ARGB32, RenderTextureReadWrite.Linear);
+
+            Graphics.Blit(SrgbGrayTex, linearRt);
+            Assert.AreEqual(SrgbGrayInLinear, GetFirstPixelInRenderTexture(linearRt));
+
+            Graphics.Blit(LinearGrayTex, linearRt);
+            Assert.AreEqual(LinearGrayInLinear, GetFirstPixelInRenderTexture(linearRt));
+
+            RenderTexture.ReleaseTemporary(linearRt);
+        }
+
+        private Color32 GetFirstPixelInTexture2D(Texture2D tex)
+        {
+            return tex.GetPixels32()[0];
+        }
+
+        private Color32 GetFirstPixelInRenderTexture(RenderTexture rt)
+        {
+            // This function copies memory values and just read, so Texture2D's color space is not important.
+            var srgbTex = new Texture2D(rt.width, rt.height, TextureFormat.ARGB32, mipChain: false, linear: false);
+            RenderTexture.active = rt;
+            srgbTex.ReadPixels(new Rect(0, 0, rt.width, rt.height), 0, 0);
+            srgbTex.Apply();
+            RenderTexture.active = null;
+            var pixel = GetFirstPixelInTexture2D(srgbTex);
+            UnityEngine.Object.DestroyImmediate(srgbTex);
+            return pixel;
+        }
+    }
+}

Assets/VRMShaders/GLTF/IO/Tests/TextureColorSpaceSpecificationTests.cs.meta

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+guid: 19082be49cd24881a2f53c13de83ac70
+timeCreated: 1621413009