Fix glTF material alpha mode when alpha is defined without an alpha texture

Exporters/3ds Max/BabylonExport.Entities/BabylonPBRMetallicRoughnessMaterial.cs

@@ -5,6 +5,14 @@ namespace BabylonExport.Entities
     [DataContract]
     public class BabylonPBRMetallicRoughnessMaterial : BabylonMaterial
     {
+        public enum TransparencyMode
+        {
+            OPAQUE = 0,
+            ALPHATEST = 1,
+            ALPHABLEND = 2,
+            ALPHATESTANDBLEND = 3
+        }
+
         [DataMember]
         public string customType { get; private set; }
 
@@ -70,7 +78,7 @@ namespace BabylonExport.Entities
             emissiveColor = new[] { 0f, 0f, 0f };
             occlusionStrength = 1.0f;
             alphaCutOff = 0.4f;
-            transparencyMode = 0;
+            transparencyMode = (int)TransparencyMode.OPAQUE;
         }
     }
 }

Exporters/3ds Max/Max2Babylon/Exporter/BabylonExporter.GLTFExporter.Material.cs

@@ -375,33 +375,44 @@ namespace Max2Babylon
 
         private void getAlphaMode(BabylonStandardMaterial babylonMaterial, out string alphaMode, out float? alphaCutoff)
         {
-            if ((babylonMaterial.diffuseTexture != null && babylonMaterial.diffuseTexture.hasAlpha) ||
+            if (babylonMaterial.alpha != 1.0f ||
+                (babylonMaterial.diffuseTexture != null && babylonMaterial.diffuseTexture.hasAlpha) ||
                  babylonMaterial.opacityTexture != null)
             {
-                // TODO - Babylon standard material is assumed to useAlphaFromDiffuseTexture. If not, the alpha mode is a mask.
+                // Babylon standard material is assumed to useAlphaFromDiffuseTexture. If not, the alpha mode is a mask.
                 alphaMode = GLTFMaterial.AlphaMode.BLEND.ToString();
             }
             else
             {
-                // glTF alpha mode default value is "OPAQUE"
-                alphaMode = null; // GLTFMaterial.AlphaMode.OPAQUE.ToString();
+                alphaMode = null;  // glTF alpha mode default value is "OPAQUE"
             }
             alphaCutoff = null;
         }
 
         private void getAlphaMode(BabylonPBRMetallicRoughnessMaterial babylonMaterial, out string alphaMode, out float? alphaCutoff)
         {
-            if (babylonMaterial.baseTexture != null && babylonMaterial.baseTexture.hasAlpha)
-            {
-                // TODO - Babylon standard material is assumed to useAlphaFromDiffuseTexture. If not, the alpha mode is a mask.
-                alphaMode = GLTFMaterial.AlphaMode.BLEND.ToString();
-            }
-            else
+            alphaMode = null;
+            alphaCutoff = null;
+            switch (babylonMaterial.transparencyMode)
             {
-                // glTF alpha mode default value is "OPAQUE"
-                alphaMode = null; // GLTFMaterial.AlphaMode.OPAQUE.ToString();
+                case (int)BabylonPBRMetallicRoughnessMaterial.TransparencyMode.OPAQUE:
+                    alphaMode = null; // glTF alpha mode default value is "OPAQUE"
+                    break;
+                case (int)BabylonPBRMetallicRoughnessMaterial.TransparencyMode.ALPHABLEND:
+                    alphaMode = GLTFMaterial.AlphaMode.BLEND.ToString();
+                    break;
+                case (int)BabylonPBRMetallicRoughnessMaterial.TransparencyMode.ALPHATEST:
+                    alphaCutoff = babylonMaterial.alphaCutOff;
+                    alphaMode = GLTFMaterial.AlphaMode.MASK.ToString();
+                    break;
+                case (int)BabylonPBRMetallicRoughnessMaterial.TransparencyMode.ALPHATESTANDBLEND:
+                    RaiseWarning("GLTFExporter.Material | Alpha test and blend mode is not supported in glTF. Alpha blend is used instead.", 3);
+                    alphaMode = GLTFMaterial.AlphaMode.BLEND.ToString();
+                    break;
+                default:
+                    RaiseWarning("GLTFExporter.Material | Unsupported transparency mode: " + babylonMaterial.transparencyMode, 3);
+                    break;
             }
-            alphaCutoff = null;
         }
 
         BabylonColor3 dielectricSpecular = new BabylonColor3(0.04f, 0.04f, 0.04f);