Treat alpha of 0 as 1

lib/loadMtl.js

@@ -63,10 +63,10 @@ function loadMtl(mtlPath) {
             material.specularShininess = parseFloat(value);
         } else if (/^d /i.test(line)) {
             value = line.substring(2).trim();
-            material.alpha = parseFloat(value);
+            material.alpha = correctAlpha(parseFloat(value));
         } else if (/^Tr /i.test(line)) {
             value = line.substring(3).trim();
-            material.alpha = 1.0 - parseFloat(value);
+            material.alpha = correctAlpha(1.0 - parseFloat(value));
         } else if (/^map_Ka /i.test(line)) {
             material.ambientTexture = normalizeTexturePath(line.substring(7).trim(), mtlDirectory);
         } else if (/^map_Ke /i.test(line)) {
@@ -90,6 +90,11 @@ function loadMtl(mtlPath) {
         });
 }
 
+function correctAlpha(alpha) {
+    // An alpha of 0.0 usually implies a problem in the export, change to 1.0 instead
+    return alpha === 0.0 ? 1.0 : alpha;
+}
+
 function normalizeTexturePath(texturePath, mtlDirectory) {
     // Removes texture options from texture name
     // Assumes no spaces in texture name

specs/data/box-transparent/box-transparent.mtl

@@ -0,0 +1,12 @@
+# Blender MTL File: 'None'
+# Material Count: 1
+
+newmtl Material
+Ns 96.078431
+Ka 0.100000 0.000000 0.000000
+Kd 0.640000 0.640000 0.640000
+Ks 0.500000 0.500000 0.500000
+Ke 0.000000 0.000000 0.100000
+Ni 1.000000
+d 0.000000
+illum 2

specs/data/box-transparent/box-transparent.obj

@@ -0,0 +1,46 @@
+# Blender v2.78 (sub 0) OBJ File: ''
+# www.blender.org
+mtllib box-transparent.mtl
+o Cube
+v -1.000000 -1.000000 1.000000
+v -1.000000 1.000000 1.000000
+v -1.000000 -1.000000 -1.000000
+v -1.000000 1.000000 -1.000000
+v 1.000000 -1.000000 1.000000
+v 1.000000 1.000000 1.000000
+v 1.000000 -1.000000 -1.000000
+v 1.000000 1.000000 -1.000000
+vt 0.0000 0.0000
+vt 1.0000 0.0000
+vt 1.0000 1.0000
+vt 0.0000 1.0000
+vt 0.0000 0.0000
+vt 1.0000 0.0000
+vt 1.0000 1.0000
+vt 0.0000 1.0000
+vt 0.0000 0.0000
+vt 1.0000 0.0000
+vt 1.0000 1.0000
+vt 0.0000 1.0000
+vt 0.0000 0.0000
+vt 1.0000 0.0000
+vt 1.0000 1.0000
+vt 0.0000 1.0000
+vt 1.0000 0.0000
+vt 1.0000 1.0000
+vt 0.0000 0.0000
+vt 0.0000 1.0000
+vn -1.0000 0.0000 0.0000
+vn 0.0000 0.0000 -1.0000
+vn 1.0000 0.0000 0.0000
+vn 0.0000 0.0000 1.0000
+vn 0.0000 -1.0000 0.0000
+vn 0.0000 1.0000 0.0000
+usemtl Material
+s off
+f 1/1/1 2/2/1 4/3/1 3/4/1
+f 3/5/2 4/6/2 8/7/2 7/8/2
+f 7/9/3 8/10/3 6/11/3 5/12/3
+f 5/13/4 6/14/4 2/15/4 1/16/4
+f 3/5/5 7/17/5 5/18/5 1/16/5
+f 8/19/6 4/6/6 2/15/6 6/20/6

specs/lib/loadMtlSpec.js

@@ -4,6 +4,7 @@ var loadMtl = require('../../lib/loadMtl');
 
 var complexMaterialUrl = 'specs/data/box-complex-material/box-complex-material.mtl';
 var multipleMaterialsUrl = 'specs/data/box-multiple-materials/box-multiple-materials.mtl';
+var transparentMaterialUrl = 'specs/data/box-transparent/box-transparent.mtl';
 
 function getImagePath(objPath, relativePath) {
     return path.normalize(path.join(path.dirname(objPath), relativePath));
@@ -40,4 +41,12 @@ describe('loadMtl', function() {
                 expect(materials.Blue.diffuseColor).toEqual([0.0, 0.0, 0.64, 1.0]);
             }), done).toResolve();
     });
+
+    it('alpha of 0.0 is treated as 1.0', function(done) {
+        expect(loadMtl(transparentMaterialUrl)
+            .then(function(materials) {
+                var material = materials.Material;
+                expect(material.alpha).toBe(1.0);
+            }), done).toResolve();
+    });
 });