Add new optional command line parameter --doubleSidedMaterial to force materials to be rendered on both sides

README.md

@@ -114,6 +114,7 @@ As a convenience the PBR textures may be supplied directly to the command line.
 | `--input-up-axis`                       | Up axis of the obj.                                                                                                                                                                                                                                                                                                                                                                                                                                       | No                     |
 | `--output-up-axis`                      | Up axis of the converted glTF.                                                                                                                                                                                                                                                                                                                                                                                                                            | No                     |
 | `--triangle-winding-order-sanitization` | Apply triangle winding order sanitization.                                                                                                                                                                                                                                                                                                                                                                                                                | No                     |
+| `--doubleSidedMaterial`                 | Allow the material properties to be double-sided                                                                                                                                                                                                                                                                                                                                                                                                          | No, default `false`    |
 
 ## Build Instructions
 

bin/obj2gltf.js

@@ -160,6 +160,11 @@ const argv = yargs
       type: "boolean",
       default: defaults.triangleWindingOrderSanitization,
     },
+    doubleSidedMaterial: {
+      describe: "Allow the material properties to be double-sided",
+      type: "boolean",
+      default: defaults.doubleSidedMaterial,
+    },
   })
   .parse(args);
 
@@ -216,6 +221,7 @@ const options = {
   inputUpAxis: argv.inputUpAxis,
   outputUpAxis: argv.outputUpAxis,
   triangleWindingOrderSanitization: argv.triangleWindingOrderSanitization,
+  doubleSidedMaterial: argv.doubleSidedMaterial,
 };
 
 console.time("Total");

lib/loadMtl.js

@@ -846,7 +846,12 @@ function createSpecularGlossinessMaterial(material, options) {
   } else {
     const alpha = material.alpha;
     diffuseFactor[3] = alpha;
-    transparent = alpha < 1.0;
+
+    if (options.doubleSidedMaterial) {
+      transparent = true;
+    } else {
+      transparent = alpha < 1.0;
+    }
   }
 
   if (defined(diffuseTexture)) {
@@ -927,7 +932,12 @@ function createMetallicRoughnessMaterial(material, options) {
   } else {
     const alpha = material.alpha;
     baseColorFactor[3] = alpha;
-    transparent = alpha < 1.0;
+
+    if (options.doubleSidedMaterial) {
+      transparent = true;
+    } else {
+      transparent = alpha < 1.0;
+    }
   }
 
   if (defined(baseColorTexture)) {

lib/obj2gltf.js

@@ -40,6 +40,7 @@ module.exports = obj2gltf;
  * @param {Logger} [options.logger] A callback function for handling logged messages. Defaults to console.log.
  * @param {Writer} [options.writer] A callback function that writes files that are saved as separate resources.
  * @param {String} [options.outputDirectory] Output directory for writing separate resources when options.writer is not defined.
+ * @param {Boolean} [options.doubleSidedMaterial=false] Allows materials to be double sided.
  * @return {Promise} A promise that resolves to the glTF JSON or glb buffer.
  */
 function obj2gltf(objPath, options) {
@@ -54,6 +55,10 @@ function obj2gltf(objPath, options) {
     options.checkTransparency,
     defaults.checkTransparency
   );
+  options.doubleSidedMaterial = defaultValue(
+    options.doubleSidedMaterial,
+    defaults.doubleSidedMaterial
+  );
   options.secure = defaultValue(options.secure, defaults.secure);
   options.packOcclusion = defaultValue(
     options.packOcclusion,
@@ -179,6 +184,12 @@ obj2gltf.defaults = {
    * @default false
    */
   checkTransparency: false,
+  /**
+   * Gets and sets whether a material will be doubleSided or not
+   * @type Boolean
+   * @default false
+   */
+  doubleSidedMaterial: false,
   /**
    * Gets or sets whether the source model can reference paths outside of its directory.
    * @type Boolean