From fba3cdf4e99d255efad6dd303edcb747d69a0a17 Mon Sep 17 00:00:00 2001
From: Chetan <chetan.rogbeer@screeningeagle.com>
Date: Mon, 2 Oct 2023 16:45:36 +0800
Subject: [PATCH] Add new optional command line parameter --doubleSidedMaterial
 to force materials to be rendered on both sides

---
 README.md       |  1 +
 bin/obj2gltf.js |  6 ++++++
 lib/loadMtl.js  | 14 ++++++++++++--
 lib/obj2gltf.js | 11 +++++++++++
 4 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 3403b4d..574c61a 100644
--- a/README.md
+++ b/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
 
diff --git a/bin/obj2gltf.js b/bin/obj2gltf.js
index e1d1abe..6e3da08 100755
--- a/bin/obj2gltf.js
+++ b/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");
diff --git a/lib/loadMtl.js b/lib/loadMtl.js
index da80de7..a9953bf 100644
--- a/lib/loadMtl.js
+++ b/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)) {
diff --git a/lib/obj2gltf.js b/lib/obj2gltf.js
index 0916df9..811ea71 100644
--- a/lib/obj2gltf.js
+++ b/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