glTF exporter: fix export when texture is used only for alpha

io_scene_gltf2/__init__.py

@@ -15,7 +15,7 @@
 bl_info = {
     'name': 'glTF 2.0 format',
     'author': 'Julien Duroure, Scurest, Norbert Nopper, Urs Hanselmann, Moritz Becher, Benjamin Schmithüsen, Jim Eckerlein, and many external contributors',
-    "version": (1, 5, 2),
+    "version": (1, 5, 3),
     'blender': (2, 91, 0),
     'location': 'File > Import-Export',
     'description': 'Import-Export as glTF 2.0',

io_scene_gltf2/blender/exp/gltf2_blender_gather_image.py

@@ -182,7 +182,7 @@ def __get_image_data(sockets, export_settings) -> ExportImage:
             dst_chan = Channel.G
         elif socket.name == 'Occlusion':
             dst_chan = Channel.R
-        elif socket.name == 'Alpha' and len(sockets) > 1 and sockets[1] is not None:
+        elif socket.name == 'Alpha':
             dst_chan = Channel.A
         elif socket.name == 'Clearcoat':
             dst_chan = Channel.R

io_scene_gltf2/blender/exp/gltf2_blender_gather_materials_pbr_metallic_roughness.py

@@ -81,12 +81,16 @@ def __gather_base_color_texture(blender_material, export_settings):
         base_color_socket = gltf2_blender_get.get_socket_old(blender_material, "BaseColor")
 
     alpha_socket = gltf2_blender_get.get_socket(blender_material, "Alpha")
-    if alpha_socket is not None and alpha_socket.is_linked:
-        inputs = (base_color_socket, alpha_socket, )
-    else:
-        inputs = (base_color_socket,)
 
-    return gltf2_blender_gather_texture_info.gather_texture_info(base_color_socket, inputs, export_settings)
+    # keep sockets that have some texture : color and/or alpha
+    inputs = tuple(
+        socket for socket in [base_color_socket, alpha_socket]
+        if socket is not None and __has_image_node_from_socket(socket)
+    )
+    if not inputs:
+        return None
+
+    return gltf2_blender_gather_texture_info.gather_texture_info(inputs[0], inputs, export_settings)
 
 
 def __gather_extensions(blender_material, export_settings):