glTF exporter: correctly convert UV texture transforms

2 files changed, 23 insertions, 1 deletions

diff --git a/io_scene_gltf2/blender/com/gltf2_blender_conversion.py b/io_scene_gltf2/blender/com/gltf2_blender_conversion.py
index adc797ee..7adb3c9b 100755
--- a/io_scene_gltf2/blender/com/gltf2_blender_conversion.py
+++ b/io_scene_gltf2/blender/com/gltf2_blender_conversion.py
@@ -13,7 +13,7 @@
 # limitations under the License.
 
 from mathutils import Matrix, Quaternion
-from math import sqrt
+from math import sqrt, sin, cos
 
 def matrix_gltf_to_blender(mat_input):
     """Matrix from glTF format to Blender format."""
@@ -47,3 +47,22 @@ def correction_rotation():
     # and lamps has no vertices :)
     return Quaternion((sqrt(2)/2, -sqrt(2)/2, 0.0, 0.0)).to_matrix().to_4x4()
 
+def convert_texture_transform(texture_transform):
+    """
+    Converts a KHR_texture_transform object in one UV space (glTF or Blender)
+    into the equivalent in the other UV space. The returned transform is the
+    same as switching UV spaces (with u,v -> u,1-v), applying texture_transform,
+    then switching back.
+    """
+    offset = texture_transform.get('offset', [0, 0])
+    rotation = texture_transform.get('rotation', 0)
+    scale = texture_transform.get('scale', [1, 1])
+    return {
+        'offset': [
+            offset[0] - scale[1] * sin(rotation),
+            1 - offset[1] - scale[1] * cos(rotation),
+        ],
+        'rotation': -rotation,
+        'scale': [scale[0], scale[1]],
+    }
+
diff --git a/io_scene_gltf2/blender/exp/gltf2_blender_get.py b/io_scene_gltf2/blender/exp/gltf2_blender_get.py
index d3c7d148..3e604bb7 100755
--- a/io_scene_gltf2/blender/exp/gltf2_blender_get.py
+++ b/io_scene_gltf2/blender/exp/gltf2_blender_get.py
@@ -20,6 +20,7 @@ import bpy
 
 from . import gltf2_blender_export_keys
 from ...io.exp import gltf2_io_get
+from ...blender.com.gltf2_blender_conversion import convert_texture_transform
 from io_scene_gltf2.io.com import gltf2_io_debug
 #
 # Globals
@@ -365,6 +366,8 @@ def get_texture_transform_from_texture_node(texture_node):
         texture_transform["rotation"] = mapping_node.rotation[2]
         texture_transform["scale"] = [mapping_node.scale[0], mapping_node.scale[1]]
 
+    texture_transform = convert_texture_transform(texture_transform)
+
     if all([component == 0 for component in texture_transform["offset"]]):
         del(texture_transform["offset"])
     if all([component == 1 for component in texture_transform["scale"]]):