Preserve material opacity when parsing RGB colors

pywavefront/material.py

@@ -181,19 +181,27 @@ def parse_newmtl(self):
 
     @auto_consume
     def parse_Kd(self):
-        self.this_material.set_diffuse(self.values[1:])
+        self._parse_color(self.this_material.set_diffuse)
 
     @auto_consume
     def parse_Ka(self):
-        self.this_material.set_ambient(self.values[1:])
+        self._parse_color(self.this_material.set_ambient)
 
     @auto_consume
     def parse_Ks(self):
-        self.this_material.set_specular(self.values[1:])
+        self._parse_color(self.this_material.set_specular)
 
     @auto_consume
     def parse_Ke(self):
-        self.this_material.set_emissive(self.values[1:])
+        self._parse_color(self.this_material.set_emissive)
+
+    def _parse_color(self, setter):
+        """Preserve material opacity when a color statement omits alpha."""
+        values = self.values[1:]
+        if len(values) < 4:
+            values = self.this_material.pad_light(values)
+            values[3] = self.this_material.transparency
+        setter(values)
 
     @auto_consume
     def parse_Ns(self):

tests/test_material_opacity.py

@@ -0,0 +1,68 @@
+import gzip
+
+import pytest
+
+import pywavefront
+from pywavefront.material import MaterialParser
+
+
+COLORS = [('Ka', 'ambient'), ('Kd', 'diffuse'),
+          ('Ks', 'specular'), ('Ke', 'emissive')]
+
+
+@pytest.mark.parametrize('statement,attribute', COLORS)
+@pytest.mark.parametrize(
+    'opacity,expected', [('d 0.25', 0.25), ('Tr 0.75', 0.25), ('d 0', 0.0), ('Tr 0', 1.0)])
+@pytest.mark.parametrize('before', [False, True])
+def test_color_preserves_opacity(tmp_path, statement, attribute, opacity, expected, before):
+    color = statement + ' 0.2 0.3 0.4'
+    lines = [opacity, color] if before else [color, opacity]
+    path = tmp_path / 'material.mtl'
+    path.write_text('newmtl paint\n' + '\n'.join(lines) + '\n')
+    material = MaterialParser(str(path), strict=True).materials['paint']
+    assert material.transparency == expected
+    assert getattr(material, attribute) == [0.2, 0.3, 0.4, expected]
+
+
+@pytest.mark.parametrize('statement,attribute', COLORS)
+def test_default_opaque_color(tmp_path, statement, attribute):
+    path = tmp_path / 'material.mtl'
+    path.write_text('newmtl paint\n' + statement + ' 0.2 0.3 0.4\n')
+    material = MaterialParser(str(path), strict=True).materials['paint']
+    assert getattr(material, attribute) == [0.2, 0.3, 0.4, 1.0]
+
+
+@pytest.mark.parametrize('statement,attribute', COLORS)
+def test_abbreviated_color_preserves_opacity(tmp_path, statement, attribute):
+    path = tmp_path / 'material.mtl'
+    path.write_text('newmtl paint\nd 0.25\n' + statement + ' 0.2\n')
+    material = MaterialParser(str(path), strict=True).materials['paint']
+    assert getattr(material, attribute)[3] == 0.25
+
+
+@pytest.mark.parametrize('statement,attribute', COLORS)
+def test_explicit_alpha_keeps_existing_behavior(tmp_path, statement, attribute):
+    path = tmp_path / 'material.mtl'
+    path.write_text('newmtl paint\nd 0.25\n' + statement + ' 0.2 0.3 0.4 0.8\n')
+    material = MaterialParser(str(path), strict=True).materials['paint']
+    assert getattr(material, attribute) == [0.2, 0.3, 0.4, 0.8]
+
+
+@pytest.mark.parametrize('compressed', [False, True])
+def test_opacity_is_per_material_in_loaded_scene(tmp_path, compressed):
+    colors = ''.join(statement + ' 0.2 0.3 0.4\n' for statement, _ in COLORS)
+    mtl = 'newmtl glass\nd 0.25\n' + colors + 'newmtl solid\n' + colors
+    mtl_path = tmp_path / ('material.mtl.gz' if compressed else 'material.mtl')
+    opener = gzip.open if compressed else open
+    with opener(str(mtl_path), 'wb') as stream:
+        stream.write(mtl.encode('ascii'))
+    obj_path = tmp_path / 'triangle.obj'
+    obj_path.write_text('mtllib ' + mtl_path.name + '\nv 0 0 0\nv 1 0 0\nv 0 1 0\n'
+                        'usemtl glass\nf 1 2 3\nusemtl solid\nf 1 2 3\n')
+    scene = pywavefront.Wavefront(str(obj_path), strict=True)
+    for name, alpha in [('glass', 0.25), ('solid', 1.0)]:
+        material = scene.materials[name]
+        assert material.transparency == alpha
+        assert len(material.vertices) == 9
+        for _, attribute in COLORS:
+            assert getattr(material, attribute) == [0.2, 0.3, 0.4, alpha]