From ea464f37c07d31d534b510a7e78454ae62a46761 Mon Sep 17 00:00:00 2001
From: Tobias Haeussler <mail@tobiashaeussler.com>
Date: Sat, 25 Jul 2020 13:47:08 +0200
Subject: [PATCH 1/7] Add initial support for KHR_materials_specular and
 KHR_materials_ior.

---
 .../blender/exp/gltf2_blender_gather_image.py | 63 ++++++++----
 .../exp/gltf2_blender_gather_materials.py     | 76 +++++++++++++++
 .../exp/gltf2_blender_gather_texture.py       |  3 +-
 .../exp/gltf2_blender_gather_texture_info.py  |  9 +-
 .../blender/exp/gltf2_blender_image.py        | 96 +++++++++++++++++++
 5 files changed, 224 insertions(+), 23 deletions(-)

diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_image.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_image.py
index 7c1fa8610..82a4b7b37 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_image.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_image.py
@@ -22,7 +22,7 @@
 from io_scene_gltf2.io.exp import gltf2_io_binary_data
 from io_scene_gltf2.io.exp import gltf2_io_image_data
 from io_scene_gltf2.io.com import gltf2_io_debug
-from io_scene_gltf2.blender.exp.gltf2_blender_image import Channel, ExportImage, FillImage
+from io_scene_gltf2.blender.exp.gltf2_blender_image import Channel, SpecularColorSource, ExportImage, FillImage
 from io_scene_gltf2.blender.exp.gltf2_blender_gather_cache import cached
 from io_scene_gltf2.io.exp.gltf2_io_user_extensions import export_user_extensions
 
@@ -153,27 +153,29 @@ def __get_image_data(sockets, export_settings) -> ExportImage:
     # in a helper class. During generation of the glTF in the exporter these will then be combined to actual binary
     # resources.
     results = [__get_tex_from_socket(socket, export_settings) for socket in sockets]
+
+    is_specular_color = False
+    for socket in sockets:
+        if socket.name == 'Specular' or socket.name == 'Specular Tint':
+            is_specular_color = True
+
     composed_image = ExportImage()
     for result, socket in zip(results, sockets):
-        if result.shader_node.image.channels == 0:
-            gltf2_io_debug.print_console("WARNING",
-                                         "Image '{}' has no color channels and cannot be exported.".format(
-                                             result.shader_node.image))
-            continue
-
         # rudimentarily try follow the node tree to find the correct image data.
-        src_chan = Channel.R
-        for elem in result.path:
-            if isinstance(elem.from_node, bpy.types.ShaderNodeSeparateRGB):
-                src_chan = {
-                    'R': Channel.R,
-                    'G': Channel.G,
-                    'B': Channel.B,
-                }[elem.from_socket.name]
-            if elem.from_socket.name == 'Alpha':
-                src_chan = Channel.A
+        if result:
+            src_chan = Channel.R
+            for elem in result.path:
+                if isinstance(elem.from_node, bpy.types.ShaderNodeSeparateRGB):
+                    src_chan = {
+                        'R': Channel.R,
+                        'G': Channel.G,
+                        'B': Channel.B,
+                    }[elem.from_socket.name]
+                if elem.from_socket.name == 'Alpha':
+                    src_chan = Channel.A
 
         dst_chan = None
+        specular_color_src_type = None
 
         # some sockets need channel rewriting (gltf pbr defines fixed channels for some attributes)
         if socket.name == 'Metallic':
@@ -188,7 +190,23 @@ def __get_image_data(sockets, export_settings) -> ExportImage:
             dst_chan = Channel.R
         elif socket.name == 'Clearcoat Roughness':
             dst_chan = Channel.G
-
+        elif is_specular_color and socket.name == 'Specular':
+            specular_color_src_type = SpecularColorSource.Specular
+        elif is_specular_color and socket.name == 'Specular Tint':
+            specular_color_src_type = SpecularColorSource.SpecularTint
+        elif is_specular_color and socket.name == 'Base Color':
+            specular_color_src_type = SpecularColorSource.BaseColor
+        elif is_specular_color and socket.name == 'Transmission':
+            specular_color_src_type = SpecularColorSource.Transmission
+        elif is_specular_color and socket.name == 'IOR':
+            specular_color_src_type = SpecularColorSource.IOR
+
+        if specular_color_src_type is None and result.shader_node.image.channels == 0:
+            gltf2_io_debug.print_console("WARNING",
+                                         "Image '{}' has no color channels and cannot be exported.".format(
+                                             result.shader_node.image))
+            continue
+            
         if dst_chan is not None:
             composed_image.fill_image(result.shader_node.image, dst_chan, src_chan)
 
@@ -199,8 +217,13 @@ def __get_image_data(sockets, export_settings) -> ExportImage:
             elif socket.name == 'Roughness' and not composed_image.is_filled(Channel.B):
                 composed_image.fill_white(Channel.B)
         else:
-            # copy full image...eventually following sockets might overwrite things
-            composed_image = ExportImage.from_blender_image(result.shader_node.image)
+            if specular_color_src_type is not None:
+                # bake specular color texture
+                composed_image.fill_specular_color(result.shader_node.image if result else None, specular_color_src_type, socket.default_value)
+            else:
+                # copy full image...eventually following sockets might overwrite things
+                composed_image = ExportImage.from_blender_image(result.shader_node.image)
+
 
     return composed_image
 
diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
index ea597f90a..3294d3ef3 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
@@ -141,6 +141,13 @@ def __gather_extensions(blender_material, export_settings):
     if clearcoat_extension:
         extensions["KHR_materials_clearcoat"] = clearcoat_extension
 
+    # KHR_materials_specular and KHR_materials_ior
+    ior_extension, specular_extension = __gather_ior_and_specular_extensions(blender_material, export_settings)
+    if ior_extension:
+        extensions["KHR_materials_ior"] = ior_extension
+    if specular_extension:
+        extensions["KHR_materials_specular"] = specular_extension
+
     # TODO KHR_materials_pbrSpecularGlossiness
 
     return extensions if extensions else None
@@ -284,3 +291,72 @@ def __gather_clearcoat_extension(blender_material, export_settings):
         )
 
     return Extension('KHR_materials_clearcoat', clearcoat_extension, False)
+
+def __gather_ior_and_specular_extensions(blender_material, export_settings):
+    lerp = lambda a, b, v: (1-v)*a + v*b
+    luminance = lambda c: 0.3 * c[0] + 0.6 * c[1] + 0.1 * c[2]
+
+    specular_ext_enabled = False
+    ior_ext_enabled = False
+
+    specular_extension = {}
+    ior_extension = {}
+
+    specular_socket = gltf2_blender_get.get_socket(blender_material, 'Specular')
+    specular_tint_socket = gltf2_blender_get.get_socket(blender_material, 'Specular Tint')
+    base_color_socket = gltf2_blender_get.get_socket(blender_material, 'Base Color')
+    transmission_socket = gltf2_blender_get.get_socket(blender_material, 'Transmission')
+    ior_socket = gltf2_blender_get.get_socket(blender_material, 'IOR')
+
+    specular_not_linked = isinstance(specular_socket, bpy.types.NodeSocket) and not specular_socket.is_linked
+    specular_tint_not_linked = isinstance(specular_tint_socket, bpy.types.NodeSocket) and not specular_tint_socket.is_linked
+    base_color_not_linked = isinstance(base_color_socket, bpy.types.NodeSocket) and not base_color_socket.is_linked
+    transmission_not_linked = isinstance(transmission_socket, bpy.types.NodeSocket) and not transmission_socket.is_linked
+    ior_not_linked = isinstance(ior_socket, bpy.types.NodeSocket) and not ior_socket.is_linked
+
+    specular = specular_socket.default_value if specular_not_linked else None
+    specular_tint = specular_tint_socket.default_value if specular_tint_not_linked else None
+    base_color = base_color_socket.default_value[0:3] if base_color_not_linked else None
+    transmission = transmission_socket.default_value if transmission_not_linked else None
+    ior = ior_socket.default_value if ior_not_linked else 1.0   # textures not supported
+
+    no_texture = (specular_not_linked and specular_tint_not_linked and
+        (specular_tint == 0.0 or (specular_tint != 0.0 and base_color_not_linked)))
+
+    has_transmission = (transmission_not_linked and transmission > 0) or not transmission_not_linked
+    if has_transmission:
+        ior_ext_enabled = True
+        ior_extension['ior'] = ior
+    else:
+        # If there is no transmission/refraction, we are free to choose
+        # any value for glTF's IOR. Therefore, if specular is overshooting,
+        # we increase the IOR and adjust specular color accordingly in the
+        # next step.
+        if specular_not_linked and specular > 0.5:
+            ior_ext_enabled = True
+            ior_extension['ior'] = 1.788789
+
+    if no_texture:
+        normalized_base_color = [bc / luminance(base_color) if luminance(base_color) > 0 else 0 for bc in base_color]
+        if specular != 0.5 or specular_tint != 0.0:
+            specular_ext_enabled = True
+            specular_color = [min(lerp(1, bc, specular_tint), 1) for bc in normalized_base_color]
+
+            # The IOR dictates the maximal reflection strength, therefore we need to clamp
+            # reflection strenth of non-transmissive (aka plastic) fraction (if any)
+            plastic = [min(1/((ior - 1) / (ior + 1))**2 * 0.08 * specular * sc, 1) for sc in specular_color]
+            glass = specular_color
+            specular_extension['specularColorFactor'] = [lerp(plastic[c], glass[c], transmission) for c in range(0,3)]
+    else:
+        sockets = (specular_socket, specular_tint_socket, base_color_socket, transmission_socket, ior_socket)
+        info = gltf2_blender_gather_texture_info.gather_texture_info(sockets, export_settings)
+        if info is None:
+            return None
+
+        specular_ext_enabled = True
+        specular_extension['specularColorTexture'] = info
+
+    ior_extension = Extension('KHR_materials_ior', ior_extension, False) if ior_ext_enabled else None
+    specular_extension = Extension('KHR_materials_specular', specular_extension, False) if specular_ext_enabled else None
+        
+    return ior_extension, specular_extension
diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture.py
index 52c2e8b3d..1a7ae204a 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture.py
@@ -72,7 +72,8 @@ def __gather_name(blender_shader_sockets, export_settings):
 
 
 def __gather_sampler(blender_shader_sockets, export_settings):
-    shader_nodes = [__get_tex_from_socket(socket).shader_node for socket in blender_shader_sockets]
+    shader_nodes = [__get_tex_from_socket(socket) for socket in blender_shader_sockets]
+    shader_nodes = [tex.shader_node if tex is not None else None for tex in shader_nodes]
     if len(shader_nodes) > 1:
         gltf2_io_debug.print_console("WARNING",
                                      "More than one shader node tex image used for a texture. "
diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py
index f42ee0369..6cf2b5614 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py
@@ -27,11 +27,16 @@
 def gather_texture_info(
         blender_shader_sockets: typing.Tuple[bpy.types.NodeSocket],
         export_settings):
-    if not __filter_texture_info(blender_shader_sockets, export_settings):
+    is_specular_color = False
+    for socket in blender_shader_sockets:
+        if socket.name == 'Specular' or socket.name == 'Specular Tint':
+            is_specular_color = True
+
+    if not is_specular_color and not __filter_texture_info(blender_shader_sockets, export_settings):
         return None
 
     texture_info = gltf2_io.TextureInfo(
-        extensions=__gather_extensions(blender_shader_sockets, export_settings),
+        extensions=None if is_specular_color else __gather_extensions(blender_shader_sockets, export_settings),
         extras=__gather_extras(blender_shader_sockets, export_settings),
         index=__gather_index(blender_shader_sockets, export_settings),
         tex_coord=__gather_tex_coord(blender_shader_sockets, export_settings)
diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
index ee45784c5..09231f35c 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
@@ -18,6 +18,7 @@
 import numpy as np
 import tempfile
 import enum
+from io_scene_gltf2.io.com.gltf2_io_debug import print_console
 
 
 class Channel(enum.IntEnum):
@@ -26,6 +27,13 @@ class Channel(enum.IntEnum):
     B = 2
     A = 3
 
+class SpecularColorSource(enum.IntEnum):
+    Specular = 0
+    SpecularTint = 1
+    BaseColor = 2
+    Transmission = 3
+    IOR = 4
+
 # These describe how an ExportImage's channels should be filled.
 
 class FillImage:
@@ -38,6 +46,54 @@ class FillWhite:
     """Fills a channel with all ones (1.0)."""
     pass
 
+class FillSpecularColor:
+    """Fills a channel of the specular color from a Blender image."""
+    def __init__(self):
+        self.size = None
+        self.images = {}
+        self.src_default_values = {}  # used if image is None
+
+    def append(self, image: bpy.types.Image, src_type: SpecularColorSource, src_default_value):
+        self.images[src_type] = image
+        self.src_default_values[src_type] = src_default_value
+
+        if src_type is SpecularColorSource.IOR and image is not None:
+            # IOR textures not supported
+            self.images[SpecularColorSource.IOR] = None
+            self.src_default_values = 1.0
+
+        if image is not None:
+            if self.size is None:
+                # first image determines size
+                self.size = image.size
+            else:
+                # all other images must have the same size
+                if self.size[0] != image.size[0] or self.size[1] != image.size[1]:
+                    print_console("WARNING",
+                        "Specular, specular tint, transmission and/or base color textures have different "
+                        "sizes. Textures will be ignored.")
+                    self.images[src_type] = None
+
+    def has_image(self, src_type: SpecularColorSource):
+        return src_type in self.images and self.images[src_type] is not None
+
+    def image_size(self):
+        return (self.size[0], self.size[1])
+
+    def as_buffer(self, src_type: SpecularColorSource):
+        width, height = self.image_size()
+        if self.has_image(src_type):
+            out_buf = np.ones(height * width * 4, np.float32)
+            self.images[src_type].pixels.foreach_get(out_buf)
+            out_buf = np.reshape(out_buf, (height, width, 4))
+            if src_type == SpecularColorSource.BaseColor:
+                out_buf = out_buf[:,:,0:3]
+            else:
+                out_buf = out_buf[:,:,0]
+        else:
+            channels = 3 if src_type == SpecularColorSource.BaseColor else 1
+            out_buf = np.full((height, width, channels), self.src_default_values[src_type])
+        return out_buf
 
 class ExportImage:
     """Custom image class.
@@ -66,6 +122,7 @@ class ExportImage:
 
     def __init__(self):
         self.fills = {}
+        self.specular_color_fill = None
 
     @staticmethod
     def from_blender_image(image: bpy.types.Image):
@@ -80,6 +137,12 @@ def fill_image(self, image: bpy.types.Image, dst_chan: Channel, src_chan: Channe
     def fill_white(self, dst_chan: Channel):
         self.fills[dst_chan] = FillWhite()
 
+    def fill_specular_color(self, image: bpy.types.Image, src_type: SpecularColorSource, src_default_value):
+        self.fills[Channel.A] = FillWhite()
+        if self.specular_color_fill is None:
+            self.specular_color_fill = FillSpecularColor()
+        self.specular_color_fill.append(image, src_type, src_default_value)
+
     def is_filled(self, chan: Channel) -> bool:
         return chan in self.fills
 
@@ -110,6 +173,10 @@ def encode(self, mime_type: Optional[str]) -> bytes:
             "image/png": "PNG"
         }.get(mime_type, "PNG")
 
+        # Specular color path = we need to bake the specular color image
+        if self.specular_color_fill is not None:
+            return self.__encode_specular_color()
+
         # Happy path = we can just use an existing Blender image
         if self.__on_happy_path():
             return self.__encode_happy()
@@ -203,6 +270,35 @@ def __encode_from_image(self, image: bpy.types.Image) -> bytes:
             tmp_image = guard.image
             return _encode_temp_image(tmp_image, self.file_format)
 
+    def __encode_specular_color(self) -> bytes:
+        lerp = lambda a, b, v: (1-v)*a + v*b
+        luminance = lambda c: 0.3 * c[:,:,0] + 0.6 * c[:,:,1] + 0.1 * c[:,:,2]
+        stack3 = lambda v: np.dstack([v]*3)
+
+        ior = self.specular_color_fill.src_default_values[SpecularColorSource.IOR]
+
+        specular_buf = self.specular_color_fill.as_buffer(SpecularColorSource.Specular)
+        specular_tint_buf = self.specular_color_fill.as_buffer(SpecularColorSource.SpecularTint)
+        base_color_buf = self.specular_color_fill.as_buffer(SpecularColorSource.BaseColor)
+        transmission_buf = self.specular_color_fill.as_buffer(SpecularColorSource.Transmission)
+
+        width, height = self.specular_color_fill.image_size()
+
+        normalized_base_color_buf = base_color_buf / stack3(luminance(base_color_buf))
+
+        has_transmission = np.amax(transmission_buf) > 0
+        if not has_transmission and np.amax(specular_buf) > 0.5:
+            # material is not transmissive, extend specular range by using a high number for IOR
+            ior = 1.788789
+        
+        sc = np.minimum(lerp(1, normalized_base_color_buf, stack3(specular_tint_buf)), 1)
+        plastic = np.minimum(1/((ior - 1) / (ior + 1))**2 * 0.08 * stack3(specular_buf) * sc, 1)
+        glass = sc
+        out_buf = lerp(plastic, glass, stack3(transmission_buf))
+
+        out_buf = np.dstack((out_buf, np.ones((height, width))))
+        out_buf = np.reshape(out_buf, (width * height * 4))
+        return self.__encode_from_numpy_array(out_buf.astype(np.float32), (width, height))
 
 def _encode_temp_image(tmp_image: bpy.types.Image, file_format: str) -> bytes:
     with tempfile.TemporaryDirectory() as tmpdirname:

From 97e240c6856af2f1d70d794fff9b4702c5b03a4e Mon Sep 17 00:00:00 2001
From: Tobias Haeussler <mail@tobiashaeussler.com>
Date: Sun, 9 Aug 2020 21:48:08 +0200
Subject: [PATCH 2/7] Fix unit tests.

---
 .../blender/exp/gltf2_blender_gather_materials.py             | 4 ++--
 .../blender/exp/gltf2_blender_gather_texture_info.py          | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
index 3294d3ef3..88a7335bd 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
@@ -337,9 +337,9 @@ def __gather_ior_and_specular_extensions(blender_material, export_settings):
             ior_extension['ior'] = 1.788789
 
     if no_texture:
-        normalized_base_color = [bc / luminance(base_color) if luminance(base_color) > 0 else 0 for bc in base_color]
         if specular != 0.5 or specular_tint != 0.0:
             specular_ext_enabled = True
+            normalized_base_color = [bc / luminance(base_color) if luminance(base_color) > 0 else 0 for bc in base_color]
             specular_color = [min(lerp(1, bc, specular_tint), 1) for bc in normalized_base_color]
 
             # The IOR dictates the maximal reflection strength, therefore we need to clamp
@@ -351,7 +351,7 @@ def __gather_ior_and_specular_extensions(blender_material, export_settings):
         sockets = (specular_socket, specular_tint_socket, base_color_socket, transmission_socket, ior_socket)
         info = gltf2_blender_gather_texture_info.gather_texture_info(sockets, export_settings)
         if info is None:
-            return None
+            return None, None
 
         specular_ext_enabled = True
         specular_extension['specularColorTexture'] = info
diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py
index 6cf2b5614..c2daef17e 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py
@@ -29,7 +29,7 @@ def gather_texture_info(
         export_settings):
     is_specular_color = False
     for socket in blender_shader_sockets:
-        if socket.name == 'Specular' or socket.name == 'Specular Tint':
+        if socket and (socket.name == 'Specular' or socket.name == 'Specular Tint'):
             is_specular_color = True
 
     if not is_specular_color and not __filter_texture_info(blender_shader_sockets, export_settings):

From e4080eb086f7396ab6c3ac3f749b9b547a1ff3dd Mon Sep 17 00:00:00 2001
From: Tobias Haeussler <mail@tobiashaeussler.com>
Date: Tue, 3 Nov 2020 19:17:54 +0100
Subject: [PATCH 3/7] Replace NaNs in base color texture with 0.

---
 addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
index 09231f35c..a521c87f0 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
@@ -285,6 +285,7 @@ def __encode_specular_color(self) -> bytes:
         width, height = self.specular_color_fill.image_size()
 
         normalized_base_color_buf = base_color_buf / stack3(luminance(base_color_buf))
+        np.nan_to_num(normalized_base_color_buf, copy=False, nan=0.0)     # if luminance in a pixel was zero
 
         has_transmission = np.amax(transmission_buf) > 0
         if not has_transmission and np.amax(specular_buf) > 0.5:

From caf1c2c38791789bb4fbaadb10dc0561488a9442 Mon Sep 17 00:00:00 2001
From: Tobias Haeussler <mail@tobiashaeussler.com>
Date: Tue, 3 Nov 2020 19:19:26 +0100
Subject: [PATCH 4/7] Skip invalid texture nodes.

This issue occurs if base color is a texture and specular and specular tint are greater 0.
---
 .../blender/exp/gltf2_blender_gather_texture.py               | 4 ++--
 .../blender/exp/gltf2_blender_gather_texture_info.py          | 3 ++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture.py
index 1a7ae204a..4852e4155 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture.py
@@ -73,13 +73,13 @@ def __gather_name(blender_shader_sockets, export_settings):
 
 def __gather_sampler(blender_shader_sockets, export_settings):
     shader_nodes = [__get_tex_from_socket(socket) for socket in blender_shader_sockets]
-    shader_nodes = [tex.shader_node if tex is not None else None for tex in shader_nodes]
     if len(shader_nodes) > 1:
         gltf2_io_debug.print_console("WARNING",
                                      "More than one shader node tex image used for a texture. "
                                      "The resulting glTF sampler will behave like the first shader node tex image.")
+    first_valid_shader_node = next(filter(lambda x: x is not None, shader_nodes)).shader_node
     return gltf2_blender_gather_sampler.gather_sampler(
-        shader_nodes[0],
+        first_valid_shader_node,
         export_settings)
 
 
diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py
index c2daef17e..a834e57f2 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_texture_info.py
@@ -88,7 +88,8 @@ def __gather_index(blender_shader_sockets, export_settings):
 
 
 def __gather_tex_coord(blender_shader_sockets, export_settings):
-    blender_shader_node = __get_tex_from_socket(blender_shader_sockets[0]).shader_node
+    blender_shader_nodes = [__get_tex_from_socket(socket) for socket in blender_shader_sockets]
+    blender_shader_node = next(filter(lambda x: x is not None, blender_shader_nodes)).shader_node
     if len(blender_shader_node.inputs['Vector'].links) == 0:
         return 0
 

From 43c6ffbc080c712c88b3eaacda4a0fc862e15bc7 Mon Sep 17 00:00:00 2001
From: Tobias Haeussler <mail@tobiashaeussler.com>
Date: Tue, 3 Nov 2020 19:22:12 +0100
Subject: [PATCH 5/7] Fix base color normalization if specular tint is 0.

---
 .../blender/exp/gltf2_blender_gather_materials.py               | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
index 88a7335bd..ab6288c31 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
@@ -316,7 +316,6 @@ def __gather_ior_and_specular_extensions(blender_material, export_settings):
 
     specular = specular_socket.default_value if specular_not_linked else None
     specular_tint = specular_tint_socket.default_value if specular_tint_not_linked else None
-    base_color = base_color_socket.default_value[0:3] if base_color_not_linked else None
     transmission = transmission_socket.default_value if transmission_not_linked else None
     ior = ior_socket.default_value if ior_not_linked else 1.0   # textures not supported
 
@@ -339,6 +338,7 @@ def __gather_ior_and_specular_extensions(blender_material, export_settings):
     if no_texture:
         if specular != 0.5 or specular_tint != 0.0:
             specular_ext_enabled = True
+            base_color = base_color_socket.default_value[0:3] if base_color_not_linked else [0, 0, 0]
             normalized_base_color = [bc / luminance(base_color) if luminance(base_color) > 0 else 0 for bc in base_color]
             specular_color = [min(lerp(1, bc, specular_tint), 1) for bc in normalized_base_color]
 

From 9c97fb38dc13958fcde006267adffe284d7b1018 Mon Sep 17 00:00:00 2001
From: Tobias Haeussler <mail@tobiashaeussler.com>
Date: Sun, 28 Mar 2021 11:22:03 +0200
Subject: [PATCH 6/7] Adapt to recent changes in specular extension: specular
 color may be greater than 1.

---
 .../exp/gltf2_blender_gather_materials.py     | 21 +++++++------------
 .../blender/exp/gltf2_blender_image.py        | 10 +++------
 2 files changed, 11 insertions(+), 20 deletions(-)

diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
index ab6288c31..6ec51288c 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
@@ -317,34 +317,25 @@ def __gather_ior_and_specular_extensions(blender_material, export_settings):
     specular = specular_socket.default_value if specular_not_linked else None
     specular_tint = specular_tint_socket.default_value if specular_tint_not_linked else None
     transmission = transmission_socket.default_value if transmission_not_linked else None
-    ior = ior_socket.default_value if ior_not_linked else 1.0   # textures not supported
+    ior = ior_socket.default_value if ior_not_linked else 1.5   # textures not supported
 
     no_texture = (specular_not_linked and specular_tint_not_linked and
         (specular_tint == 0.0 or (specular_tint != 0.0 and base_color_not_linked)))
 
-    has_transmission = (transmission_not_linked and transmission > 0) or not transmission_not_linked
-    if has_transmission:
+    if ior != 1.5:
         ior_ext_enabled = True
         ior_extension['ior'] = ior
-    else:
-        # If there is no transmission/refraction, we are free to choose
-        # any value for glTF's IOR. Therefore, if specular is overshooting,
-        # we increase the IOR and adjust specular color accordingly in the
-        # next step.
-        if specular_not_linked and specular > 0.5:
-            ior_ext_enabled = True
-            ior_extension['ior'] = 1.788789
 
     if no_texture:
         if specular != 0.5 or specular_tint != 0.0:
             specular_ext_enabled = True
             base_color = base_color_socket.default_value[0:3] if base_color_not_linked else [0, 0, 0]
             normalized_base_color = [bc / luminance(base_color) if luminance(base_color) > 0 else 0 for bc in base_color]
-            specular_color = [min(lerp(1, bc, specular_tint), 1) for bc in normalized_base_color]
+            specular_color = [lerp(1, bc, specular_tint) for bc in normalized_base_color]
 
             # The IOR dictates the maximal reflection strength, therefore we need to clamp
             # reflection strenth of non-transmissive (aka plastic) fraction (if any)
-            plastic = [min(1/((ior - 1) / (ior + 1))**2 * 0.08 * specular * sc, 1) for sc in specular_color]
+            plastic = [1/((ior - 1) / (ior + 1))**2 * 0.08 * specular * sc for sc in specular_color]
             glass = specular_color
             specular_extension['specularColorFactor'] = [lerp(plastic[c], glass[c], transmission) for c in range(0,3)]
     else:
@@ -356,6 +347,10 @@ def __gather_ior_and_specular_extensions(blender_material, export_settings):
         specular_ext_enabled = True
         specular_extension['specularColorTexture'] = info
 
+        # If specular>0.5, specular color may be >1. As we cannot store values >1 in a byte texture,
+        # we use the specular color factor to rescale the value range.
+        specular_extension['specularColorFactor'] = [2, 2, 2]
+
     ior_extension = Extension('KHR_materials_ior', ior_extension, False) if ior_ext_enabled else None
     specular_extension = Extension('KHR_materials_specular', specular_extension, False) if specular_ext_enabled else None
         
diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
index a521c87f0..e9562d020 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
@@ -286,19 +286,15 @@ def __encode_specular_color(self) -> bytes:
 
         normalized_base_color_buf = base_color_buf / stack3(luminance(base_color_buf))
         np.nan_to_num(normalized_base_color_buf, copy=False, nan=0.0)     # if luminance in a pixel was zero
-
-        has_transmission = np.amax(transmission_buf) > 0
-        if not has_transmission and np.amax(specular_buf) > 0.5:
-            # material is not transmissive, extend specular range by using a high number for IOR
-            ior = 1.788789
         
-        sc = np.minimum(lerp(1, normalized_base_color_buf, stack3(specular_tint_buf)), 1)
-        plastic = np.minimum(1/((ior - 1) / (ior + 1))**2 * 0.08 * stack3(specular_buf) * sc, 1)
+        sc = lerp(1, normalized_base_color_buf, stack3(specular_tint_buf))
+        plastic = 1/((ior - 1) / (ior + 1))**2 * 0.08 * stack3(specular_buf) * sc
         glass = sc
         out_buf = lerp(plastic, glass, stack3(transmission_buf))
 
         out_buf = np.dstack((out_buf, np.ones((height, width))))
         out_buf = np.reshape(out_buf, (width * height * 4))
+        out_buf *= 0.5  # specularColorFactor is 2
         return self.__encode_from_numpy_array(out_buf.astype(np.float32), (width, height))
 
 def _encode_temp_image(tmp_image: bpy.types.Image, file_format: str) -> bytes:

From ec9eb682a622d886eb2dc19881e7783e5b9bc5b9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tobias=20H=C3=A4u=C3=9Fler?= <mail@tobiashaeussler.com>
Date: Sat, 30 Oct 2021 21:33:12 +0200
Subject: [PATCH 7/7] Fix crash when only specular and specular tint are
 textured.

---
 .../blender/exp/gltf2_blender_gather_materials.py      |  8 ++++----
 .../io_scene_gltf2/blender/exp/gltf2_blender_image.py  | 10 ++++++++--
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
index b25b82c87..5dfb25046 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py
@@ -446,10 +446,10 @@ def __gather_ior_and_specular_extensions(blender_material, export_settings):
         primary_socket = specular_socket
         if specular_not_linked:
             primary_socket = specular_tint_socket
-        if specular_tint_not_linked:
-            primary_socket = base_color_socket
-        if base_color_not_linked:
-            primary_socket = transmission_socket
+            if specular_tint_not_linked:
+                primary_socket = base_color_socket
+                if base_color_not_linked:
+                    primary_socket = transmission_socket           
         info = gltf2_blender_gather_texture_info.gather_texture_info(primary_socket, sockets, export_settings)
         if info is None:
             return None, None
diff --git a/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py b/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
index 5a38d7198..325c5ceda 100644
--- a/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
+++ b/addons/io_scene_gltf2/blender/exp/gltf2_blender_image.py
@@ -91,8 +91,14 @@ def as_buffer(self, src_type: SpecularColorSource):
             else:
                 out_buf = out_buf[:,:,0]
         else:
-            channels = 3 if src_type == SpecularColorSource.BaseColor else 1
-            out_buf = np.full((height, width, channels), self.src_default_values[src_type])
+            if src_type == SpecularColorSource.BaseColor:
+                rgb = [self.src_default_values[src_type][0],
+                       self.src_default_values[src_type][1],
+                       self.src_default_values[src_type][2]]
+                out_buf = np.full((height, width, 3), rgb)
+            else:
+                f = self.src_default_values[src_type]
+                out_buf = np.full((height, width, 1), f)
         return out_buf
 
 class ExportImage: