Update avatar_layers implementation, assets and documentation

tests/AvatarLayerDefinitionTests.cs

@@ -0,0 +1,26 @@
+using System.Text.Json;
+using Cthangover.Core.Mods.Testing;
+
+namespace Cthangover.Mods.AvatarLayers.Tests
+{
+    /// <summary>Layer and canvas authoring DTOs preserve every visual property through JSON.</summary>
+    public sealed class AvatarLayerDefinitionTests
+    {
+        [ModTest("avatar_layers/layer_and_canvas_json_roundtrip")]
+        public static void RoundTrip(ModTestContext ctx)
+        {
+            var layer = new AvatarLayerDefinition { Image = "sample/eyes.png", Order = -2, X = 3, Y = -4,
+                Width = 12, Height = 16, Visible = false, Opacity = 0.25f, FlipH = true, FlipV = true };
+            var copy = JsonSerializer.Deserialize<AvatarLayerDefinition>(JsonSerializer.Serialize(layer));
+            ModAssert.Equal(layer.Image, copy.Image); ModAssert.Equal(layer.Order, copy.Order);
+            ModAssert.CloseTo(layer.X, copy.X); ModAssert.CloseTo(layer.Y, copy.Y);
+            ModAssert.CloseTo(layer.Width, copy.Width); ModAssert.CloseTo(layer.Height, copy.Height);
+            ModAssert.False(copy.Visible); ModAssert.CloseTo(layer.Opacity, copy.Opacity);
+            ModAssert.True(copy.FlipH); ModAssert.True(copy.FlipV);
+            var canvas = JsonSerializer.Deserialize<AvatarCanvasDefinition>(JsonSerializer.Serialize(new AvatarCanvasDefinition { Width = 640, Height = 960 }));
+            ModAssert.CloseTo(640, canvas.Width); ModAssert.CloseTo(960, canvas.Height);
+            ModAssert.True(new AvatarLayerDefinition().Visible);
+            ModAssert.CloseTo(1, new AvatarLayerDefinition().Opacity);
+        }
+    }
+}